Navitron Renewable Energy and Sustainability Forum

SOLAR PHOTOVOLTAIC => Solar Photovoltaic Systems => Topic started by: jonboy on June 24, 2011, 08:13:46 PM



Title: excess power from pv
Post by: jonboy on June 24, 2011, 08:13:46 PM
I have just had a pv system installed. (18 x 220 sharp panels, sunny boy 4000TL).
I am very happy with the performance and output. (145kwh in a week)
I know it is early days but i seem to have excess of power not being used by myself, and obviously being given back to the grid at a low return.
I would like to try and use this power to heat up my hot water tank.
I have done some searches on the net, and this has already been looked at an implemented using a microprocessor to ensure that that you are only using the excess power.
Does anybody have any thoughts or ideas?

thanks
jonboy


Title: Re: excess power from pv
Post by: BruceB on June 24, 2011, 08:31:17 PM
As a very simple way of controlling an immersion or similar there is a relay built into the 4000TL that can be programmed to switch on at any particular value of generation.  Use it to power a contactor.  A bit clumsy/rough, but you might want to use it until you have designed programmed your all singing/dancing plc and bank of contactors.
Regards
Bruce


Title: Re: excess power from pv
Post by: marshman on June 24, 2011, 08:39:46 PM
In my opinion it is difficult to match a large load such as an immersion heater - a typical domestic immersion is around 3kW - to a moderate PV installation. Your peak output is around 4kW, but this full output - depending on inclination, direction and area of the country - will only be present for a smallish proportion of the time - and you pretty much need the full output to guarantee that you have the capacity to supply the entire load from the PV output. You can install various power moinitors and controllers as well as a variable load controller - all at some expense as discussed on earlier threads - but it is a lot of hassle for little gain. (in my opinion). You only need to exceed the output for a small time to lose any benefit you may have gained. You can get lower power heaters but then these cost money and there is a long pay back time. My opinion is that it is better to do as much as you can when you are generating - such as washing and cooking (assuming you are electric cooking) - and leave the immersion on economy 7. Also don't bother with an export meter. Benefit from 50% deemed export but try to ensure you use more during the day yourself. This is much easier if the house is occupied during the day. If it is not then you will have to become skilled in the art of a) setting devices to work on timers and b) weather forcasting (i.e how sunny will it be, how much cloud, temperature and wind (affects cooling of panels and hence output)).

Remember deemed export is  50% of the generation at 3.1p per unit. I guess you pay around 11p per peak unit import and 4 to 5p import for economy 7 units.

Roger


Title: Re: excess power from pv
Post by: billt on June 24, 2011, 10:18:20 PM

I know it is early days but i seem to have excess of power not being used by myself, and obviously being given back to the grid at a low return.

Does anybody have any thoughts or ideas?

thanks
jonboy


You are getting paid 43.3p per unit, that is a b***** good rate of return!


Title: Re: excess power from pv
Post by: rhodie on June 25, 2011, 12:42:39 PM
In my opinion it is difficult to match a large load such as an immersion heater - a typical domestic immersion is around 3kW - to a moderate PV installation.

Roger
Then reduce the Immersion load. There's a simple and inexpensive way of doing this without changing the immersion heater elements. If you have two immersion heater elements fitted to your tank all you have to do is wire them up in series. A simple Ohm's Law calculation will tell us that  two immersion heaters both rated at 3 kw when connected in series across the original voltage will use a total of 1.5 kw.  All you need to achieve this is a short piece of twin and earth cable run between the heaters and a single pole connector.

A secondary consideration is that perhaps your immersion heater is rated at 240 volts whilst the mains voltage is now 230 volts. If this is the case then using the above details the total power consumption would be 1.38 kw.

A 4kwp PV installation would have no problem coping with this on a sunny day.

How you connect and set the individual thermostats of the immersion heaters brings up some interesting possibilities.



Title: Re: excess power from pv
Post by: marshman on June 25, 2011, 09:21:13 PM
In my opinion it is difficult to match a large load such as an immersion heater - a typical domestic immersion is around 3kW - to a moderate PV installation.

Roger
Then reduce the Immersion load. There's a simple and inexpensive way of doing this without changing the immersion heater elements. If you have two immersion heater elements fitted to your tank all you have to do is wire them up in series. A simple Ohm's Law calculation will tell us that  two immersion heaters both rated at 3 kw when connected in series across the original voltage will use a total of 1.5 kw.  All you need to achieve this is a short piece of twin and earth cable run between the heaters and a single pole connector.

A secondary consideration is that perhaps your immersion heater is rated at 240 volts whilst the mains voltage is now 230 volts. If this is the case then using the above details the total power consumption would be 1.38 kw.

A 4kwp PV installation would have no problem coping with this on a sunny day.

How you connect and set the individual thermostats of the immersion heaters brings up some interesting possibilities.



Hi Rhodie welcome to the forum.

I did say that a typical immersion is around 3kW and also there is not a simple way to match this to the available output - you will probably be using a few 100 watts or so for the rest of the house so won't know exactly how much spare you have.  I'm also not sure how many houses have twin immersion heaters.

It is also very wrong to assume that UK mains voltage is now "230V" instead of 240V. The change was a paperwork excercise to "harmonise us with Europe. In reality nothing changed. The UK mains supply is now 230V +10% -6% (I think) but in reality it is still 240V +/- 5%.  Mine sits at around 250V the majority of the time and even higher when I'm generating lots.

Roger


Title: Re: excess power from pv
Post by: JamesE on June 27, 2011, 02:18:09 PM
A simple answer to cut an immersion heater from 3KW to half that is to wire a rectifier diode in series. Something like a 1N5406. I did this with my boat in The Netherlands as many electricity points at marinas/harbours were only 6 Amps. As I have now re-programmed my hot water (for which I use the immersion heater for the summer quarter with no gas used at all to in effect remove the "standing charge" caused by the first lot of units at a higher price) to come on 10:30 to 13:30 thus being able to offset much of its usage by the PV, when the spirit moves me I'm going to do the same at home.


Title: Re: excess power from pv
Post by: Andy_WSM on June 27, 2011, 03:15:40 PM
A simple answer to cut an immersion heater from 3KW to half that is to wire a rectifier diode in series. Something like a 1N5406.

That's only a 3A device, how does that work?


Title: Re: excess power from pv
Post by: EccentricAnomaly on June 27, 2011, 05:56:10 PM
A simple answer to cut an immersion heater from 3KW to half that is to wire a rectifier diode in series.

However, during the 50% of the time that the diode is conducting you'll still be importing. I imagine the meter will register this otherwise we'd all be putting in diodes to get free hot water.


Title: Re: excess power from pv
Post by: Justme on June 27, 2011, 05:58:22 PM
Er wont that still draw 3kw but have a 50 hertz pulse width modulation?

The total energy drawn per hour will be less as its only on for 50% of the time but the peak draw will stay the same.


Title: Re: excess power from pv
Post by: Baz on June 27, 2011, 06:31:07 PM
yes, the reason it wroked for the boat is the reduced average load stopped the fuse getting hot enough to blow!.

We don't seem to have mentioned 110v dropping transformets yet - gives 1/4 the power. But if you get a transformer core and rewind it yourself you could get the right voltage for whatever power you decide you want, or put in tappings for a whole series of outputs. Or (shudder) go 240 >120, then 120 > 60, then add the 60 to another 120 (in phase) and you get 180 which would give you about 1.5kW  svengo


Title: Re: excess power from pv
Post by: Other-Power on June 27, 2011, 08:05:05 PM
Could have a look at EMMA?

http://www.coolpowerproducts.com/uk/project-scotland-uk.html (http://www.coolpowerproducts.com/uk/project-scotland-uk.html)

Jon


Title: Re: excess power from pv
Post by: john999boy on June 27, 2011, 08:39:46 PM
Anyone else (or even just anyone) got EMMA? What are the costs involved and thoughts of the installation so far?

Looks like it could be promising.


Title: Re: excess power from pv
Post by: Justme on June 27, 2011, 10:08:41 PM
Arnt they about £2k ish?

Would take a long time to recover that.


Title: Re: excess power from pv
Post by: ecogeorge on June 27, 2011, 11:06:13 PM
Rather than just applying a variable load to the emersion heater (which is what I assume it does) I'd like to see it developed further and control a variable speed drive to a heat pump - how useful would that be!!!
Surely it couldn't be that hard to link the output to a frequency drive input?
I'll get my coat - surrender:


Title: Re: excess power from pv
Post by: JamesE on June 28, 2011, 10:38:02 AM
That's only a 3A device, how does that work?
Er, you're right! It must have been some other one. Though I have strong recollection that that that is what I used, but I also had some fat ones at the time which were good for 10A+ which I used on the battery float charger. However the principle is right and it worked.


Title: Re: excess power from pv
Post by: michaelwr on June 28, 2011, 08:37:59 PM
Looks like another buyer for Alan's Gizmoid, http://www.navitron.org.uk/forum/index.php/topic,9072.15.html

Makes me smile whenever I read it, looks completely dangerous but does a job.

Bodge-a-tastic!


Title: Re: excess power from pv
Post by: SnaxMuppet on June 28, 2011, 09:19:41 PM
The good thing about EMMA is that it only sends power to the immersion if there is more power generated than is being used. BUT it is rediculously expensive and simply not worth the money.

We just decided to accept that we would export at 3p/kWh. It is only going to be less than £200 per year so we switched to Econ7 and use the immersion at night. It then only costs us 5p/kWh overnight and we get 3p back by exporting so our immersion only costs us 2p/kWh and I am happy with that instead of haing the cost of EMMA or complication of something home-built. 


Title: Re: excess power from pv
Post by: brackwell on June 29, 2011, 08:52:36 AM
When I enquired about EMMA i now believe that for eg when you have say 1 Kw of unused elec the emma will allow the import of 2Kw grid elec to "drive" the 3Kw immersion heater for eg.

I am not sure this is what people are really wanting.  I am not good at elec but again when asking a heating element manufacturer i now believe you could put the say 1Kw excess into the "3Kw". It will of course take longer to heat the water and perhaps not to the same high temp if that is what is required ?  The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken


Title: Re: excess power from pv
Post by: MikeD on June 29, 2011, 09:03:56 AM
The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken

As long as you keep to the normal voltage, ie 240v or so, you're never going to persuade a 3KW element to suck up more than 3KW. The resistance of the element limits the current and thus the power.

But I agree with the other bit - if I'd got a spare 1KW, I'd much rather use it to heat water slowly than either

a) export it at 3p (assuming export meter fitted) or
b) pay for the other 2KW so I can run the immersion heater at the full 3KW

So we need a suitable gizmo. I'll give it some thought....  :onpatrol


Title: Re: excess power from pv
Post by: Jober on June 29, 2011, 10:58:10 AM
So, all you EMMA sellers/installers - you will have to come up with a better price if you want it to sell like hot cakes!


Title: Re: excess power from pv
Post by: Justme on June 29, 2011, 11:45:10 AM
So, all you EMMA sellers/installers - you will have to come up with a better price if you want it to sell like hot cakes!

They also need to make it work better than was explained in a post above.


People want to STOP importing day time elec & use the "spare" PV not use the grid to top up the PV.

That is just stupid. They would be better off loosing the PV's 1kw export & using the 3kw E7 than buying in 2kw of day time power.


Title: Re: excess power from pv
Post by: Jonathan on June 29, 2011, 12:00:45 PM

People want to STOP importing day time elec & use the "spare" PV not use the grid to top up the PV.

That is just stupid. They would be better off loosing the PV's 1kw export & using the 3kw E7 than buying in 2kw of day time power.

Not everyone has an E7 supply at home.


Title: Re: excess power from pv
Post by: Justme on June 29, 2011, 12:21:38 PM
True, but then not everyone has PV either.

Either way using night time elec is still better as its going to get "lost" any way if not used.

Plus it would still be better to have the heater running at 1kw using the spare for 3 hours than having the PV topped up to 3kw via the grid for 1 hour. Assuming the tank get to cut off heat in one / three hours.


Title: Re: excess power from pv
Post by: Jonathan on June 29, 2011, 12:34:47 PM
Justme,

I feel I must be missing something here. The subject of the thread means we are only talking about those with PV, so what does your first comment mean "True, but then not everyone has PV either."

Also what do you mean by "Either way using night time elec is still better as its going to get "lost" any way if not used." PV doesn't produce anything at night???

regards Jonathan


Title: Re: excess power from pv
Post by: Baz on June 29, 2011, 01:20:43 PM
Not everyone has an E7 supply at home.
but everyone can get it if it makes ecenomic sense for them.
It should be possible to run on pv much of the day and E7 at night. The problem is the evening with neither and a lifestyle that maximises use in precisely that time slot.
So it comes back to needing a way of storing the excess pv for use in the evening. The grid provides such a solution but at what is seen as a huge premium. Batteries are just as expensive.
For some a change in lifestyle would help a lot.

Back to EMMA. The technical requirement is simple but the ecenomics relative to demand is still unfavourable, but should be improving with more pv installations. In effect it needs someone to come up with a design tht the far east can rip off and sell on ebay.


Title: Re: excess power from pv
Post by: Countrypaul on June 29, 2011, 01:29:36 PM
When I enquired about EMMA i now believe that for eg when you have say 1 Kw of unused elec the emma will allow the import of 2Kw grid elec to "drive" the 3Kw immersion heater for eg.

I am not sure this is what people are really wanting.  I am not good at elec but again when asking a heating element manufacturer i now believe you could put the say 1Kw excess into the "3Kw". It will of course take longer to heat the water and perhaps not to the same high temp if that is what is required ?  The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken

Based on this I can't see what EMMA does other than cost a lot of money. If you just use a 3kW immersion heater and are generating 1kw of PV, then you would import 2kw anyway no EMMA needed. Maybe I'm missing something?

Paul


Title: Re: excess power from pv
Post by: Other-Power on June 29, 2011, 01:33:39 PM
When I enquired about EMMA i now believe that for eg when you have say 1 Kw of unused elec the emma will allow the import of 2Kw grid elec to "drive" the 3Kw immersion heater for eg.

I am not sure this is what people are really wanting.  I am not good at elec but again when asking a heating element manufacturer i now believe you could put the say 1Kw excess into the "3Kw". It will of course take longer to heat the water and perhaps not to the same high temp if that is what is required ?  The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken

This is not how EMMA works!.
Please refer to the following PDF:

http://www.coolpowerproducts.com/documents/How-EMMA-Works-CoolPowerProducts-v1106a.pdf (http://www.coolpowerproducts.com/documents/How-EMMA-Works-CoolPowerProducts-v1106a.pdf)

Cheers

Jon


Title: Re: excess power from pv
Post by: Other-Power on June 29, 2011, 01:37:29 PM
So, all you EMMA sellers/installers - you will have to come up with a better price if you want it to sell like hot cakes!

Coolpower know this and are working on this, I would say £2,500 would cover a 15 amp EMMA instillation, cheaper then solar thermal!

Coolpower also make a GVS or grid voltage stabilizing version that can be used to limit export where the export limit is less than that of the PV/Wind turbine can produce.

The EMMA only makes sense currently, due to cost, if you have 4kW of PV or a 6kW wind turbine and the demand for heat either hot water or space heating via thermal store.

I do love the idea of getting an EMMA unit that will drive a heat pump!

Cheers

Jon


Title: Re: excess power from pv
Post by: mellifera on June 29, 2011, 02:09:05 PM
Trawling around the information super highway I came across 3 phase 3kW immersion heaters, they've got three 1kW elements. You could perhaps measure (with a clamp on current transformers) how much you're generating, and how much you are consuming. Subtract one from the other, add a bit of hysteresis and use the result to switch in 1, 2 or 3kW of water heating. You could even have an "open loop" design and just switch in the three 1kW elements depending on just how much you're generating - not as good but probably satisfies the old 80/20 rule. Just an idea.

Cheers, Mike.

http://www.tpfay.co.uk/OurProducts/immersion_heaters.aspx (http://www.tpfay.co.uk/OurProducts/immersion_heaters.aspx)

http://www.cicn.co.uk/Merchant2/merchant.mvc?Screen=PROD&Product_Code=IIH3000-275&Category_Code=003 (http://www.cicn.co.uk/Merchant2/merchant.mvc?Screen=PROD&Product_Code=IIH3000-275&Category_Code=003)


Title: Re: excess power from pv
Post by: brackwell on June 29, 2011, 02:54:09 PM
Other-Power,

Do you work for the EMMA company?  I have read the pdf you quote but that does not preclude the situation i have exampled. When personally I asked the Irish Co. direct i got the answer as i have indicated. I could not care less but it probably does need clarification if you are thinking otherwise.

Ken


Title: Re: excess power from pv
Post by: marshman on June 29, 2011, 03:32:32 PM
Other-Power,

Do you work for the EMMA company?  I have read the pdf you quote but that does not preclude the situation i have exampled. When personally I asked the Irish Co. direct i got the answer as i have indicated. I could not care less but it probably does need clarification if you are thinking otherwise.

Ken

Hi Ken,

1. I'm nothing to do with EMMA or coolpower :)

2. I'm certain that Otherpower is correct. If you have the time read this patent - this is the US version but the E.U. version will be similar.

http://www.google.com/patents?id=s8zWAAAAEBAJ&printsec=frontcover&dq=12/596,048&hl=en&ei=wDILTrynC4Wh8QPc8Jxt&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCkQ6AEwAA

or search for US Patent   2010/0235010     (use Google patents as its free and lets you download a complete PDF copy)

The patent refers to Thyristor control of the power diverted to the thermal store and ensures that only the "spare" renewable power goes there. The patent covers a lot of other stuff as well to do with smartmetering etc. and controlling when certain appliances are used - essentially to smooth out consumption. In essence the patent covers everything "we" as PV people could want.

I am sure most of the ideas described in the patent are implemented in the EMMA unit - there would be no reason not to - so in the scenario where you only have 1kW of "spare" PV power this is all it would send to the immersion heater regardless of the actual rating of the immersion heater.

Roger


Title: Re: excess power from pv
Post by: Other-Power on June 29, 2011, 03:37:32 PM
Other-Power,

Do you work for the EMMA company?  I have read the pdf you quote but that does not preclude the situation i have exampled. When personally I asked the Irish Co. direct i got the answer as i have indicated. I could not care less but it probably does need clarification if you are thinking otherwise.

Ken

Ken, I work for a company that installs EMMA devices and I find them to be very good in situations exampled in my last post, they do however need to be much cheaper for this simple load balance operation.  The GVS version is very good and offers advantages that no other product on the market can.  The important thing to note with EMMA is the fact it has infinite modulation were as other load 'balancing' devices tend to be stepped or pulsed DC which limits the effectiveness and range of device the power can be diverted to.  

The situation you have indicated is possible with the EMMA device if you have an additional boost button which turns the immersion on to 100%, however in day to day operation the EMMA modulates it output between 0% and 100% to equal that of the amounted being generated minus that which is being used in the house, with the outcome being an almost 0 watt export.

Cheers

Jon



Title: Re: excess power from pv
Post by: Baz on June 29, 2011, 04:44:30 PM
Having waded through part of the above mentioned patent I think it is trying to cover domestic level load shedding / engagement in response to variable supply (eg due to tarrifs) rather than precision load matching.

The emma pdf is interesting in what it leaves out rather than the long winded way it presents minimal information. Pointedly ommited is an indication of how it adjusts the dump load power which could just be crude unsmoothed phase angle which relies on your inverter doing the real work of current smoothing necessary for efficiency or the more expensive but proper way by incorporating a variable output voltage inverter.


Title: Re: excess power from pv
Post by: Other-Power on June 29, 2011, 05:05:59 PM
Having waded through part of the above mentioned patent I think it is trying to cover domestic level load shedding / engagement in response to variable supply (eg due to tarrifs) rather than precision load matching.

The emma pdf is interesting in what it leaves out rather than the long winded way it presents minimal information. Pointedly ommited is an indication of how it adjusts the dump load power which could just be crude unsmoothed phase angle which relies on your inverter doing the real work of current smoothing necessary for efficiency or the more expensive but proper way by incorporating a variable output voltage inverter.

The patent is for application and not technology specifically, the best ones all ways are.
 
As mentioned above the EMMA use phase angle and a thyristor as a retro fit solution rather than variable output voltage, I assume you mean PWM?

Cheers

Jon


Title: Re: excess power from pv
Post by: Justme on June 29, 2011, 07:46:06 PM
Justme,

I feel I must be missing something here. The subject of the thread means we are only talking about those with PV, so what does your first comment mean "True, but then not everyone has PV either."

Also what do you mean by "Either way using night time elec is still better as its going to get "lost" any way if not used." PV doesn't produce anything at night???

regards Jonathan

It was a light hearted reply to your E7 comment. It is available just like PV is. If you want it you can have it (in most cases). As you will be using less of the costly day time units it should be a good match with PV. Yes the times outside of PV generation & E7 really need to have the loads reduced as much as possible.

Using night time (grid) power is better than using day time (grid) power as you are helping to balance the load over the full day. Its well known that at night much more power is made than is used as they cant turn off the power stations as they will need them the next day.


Title: Re: excess power from pv
Post by: hawkie on July 03, 2011, 10:41:11 AM
Hi jonboy

Good to see you're up and running, How about posting some figures and photos for us all to look at,

 ;D ;D Hawkie ;D ;D


Title: Re: excess power from pv
Post by: billi on July 03, 2011, 11:22:01 AM
Quote
I do love the idea of getting an EMMA unit that will drive a heat pump!

Cheers

Jon

How will this work then ?  A heatpump cannot switched on and off fast and often   like an immersion element  , or is the missing power from PV then provided by the grid  to allow a more stable operation ?

Thanks Billi


Title: Re: excess power from pv
Post by: tange179 on July 03, 2011, 12:01:06 PM
......time to think outside the box...

I heat my water via an immersion heater on econ7 at 6.00 am while 8.30 am then at midday for 1hr and again at 6.30pm for 1/2 an hour to cover evening shower time.  The cost of this in conjuction with my 3kW PV system is minimal.

Manual diversion of excess leccy to Lithium Ion/Lead Acid batteries can be achieved now with an existing Grid Tied PV system but this is obviously not ideal.  The designers of this device need to focus their energy on making this an automatic solution i.e. it would be very nice to use the excess power when the sun has gone down. The device would be akin to UPS power supplies  ;)

Then a price point of around £1 to 1.5k installed for such technology may be tempting......

John


Title: Re: excess power from pv
Post by: EccentricAnomaly on July 03, 2011, 04:46:30 PM
tange179, it's worth doing the arithmetic on the depreciation of the batteries, per cycle, vs the cost of just exporting at 3p per kWh in the day and importing at 13p or whatever in the evening. It depends on your assumptions how it comes out but the saving by using batteries is not likely to be very large and may well be negative.


Title: Re: excess power from pv
Post by: Philip R on July 03, 2011, 11:18:42 PM
Quote from Justme, "Its well known that at night much more power is made than is used as they cant turn off the power stations as they will need them the next day."  Hmm an erroneous comment, and lacking in fact.

They can be turned off. Trouble is, doing so shortens the time between overhauls drastically and increases operating costs.
Electricity generated by thermal power stations has to balance the load, or the grid frequency will rapidly deviate beyond its nomimal tolerance level.
The only power stations that are inflexible to load changes are the nukes which were designed to run at base load, as were the 500MW and 660MW coal fired generating units. However, the latter coal units do two shift and load follow with a small loss of efficiency compared to their full load design points. At night, some of these units are shut down as the load drops off, then the gas turbine CCGT units are sequentially deloaded/ shut down. Although the gas stations are relatively quick to start up/ shut down, the fuel supply in the gas pipe is not. You cannot easily shut down a gas field without affecting oil flows from the field.
The pump storage plants provide response reserve capability, but with a limited power and energy capability, nonetheless, extremely important as they can generate/ absorb large power swings very quickly.
PVs contribute to reducing peak generation during the day (peak time). As PV generation increases, Pumped storage and Flow battery storage will be required, Philip R


Title: Re: excess power from pv
Post by: ecogeorge on July 03, 2011, 11:20:12 PM
Quote
I do love the idea of getting an EMMA unit that will drive a heat pump!

Cheers

Jon

How will this work then ?  A heatpump cannot switched on and off fast and often   like an immersion element  , or is the missing power from PV then provided by the grid  to allow a more stable operation ?

Thanks Billi



I don't know but , what about using the emma  variable output as an input  reference for a variable speed drive inverter driving the heatpump ?
Starting to use variable speed drives at work on vacuum pumps and with  little or no vacuum demand motor speed can go as low as 3 or 4% with output hz of 7hz.
Surely an heat pump running at say 10% of max speed will still produce  more heat than an element at 10% ?
or am I being too simplistic?


Title: Re: excess power from pv
Post by: Philip R on July 03, 2011, 11:32:48 PM
Following on from ecogeorge

If we are going to use invertor driven loads, i.e. heatpumps. Then we need to look in the longerterm to using the dc link supply from before the PV DC/AC invertor to source the power, rather than invert to AC then to rectify back to DC in the load before feeding the variable speed drive invertor stage, generating a whole load of waste heat and harmonics to boot. Alas, this will all take a long time to materialise.

Nothing wrong in principle with modulating heat pump using variable speed drive, just need to ensure that the motors cooling air is required when its fan is producing next to cooling draft. Same idea now being used in modern domestic circulator pumps.

Philip R


Title: Re: excess power from pv
Post by: billi on July 04, 2011, 12:21:29 AM
.... there is a lot going on in Europe to try to achieve more  usage  /self consumption  of PV on the roof

I personally do not like the Emma  cause it seems it is designed for immersion only ( i asume it is just a fast switching relay  to switch the immersion on and off  in relation to powerproduction and usage )


I hope there will be other regulations or FIT schemes coming  to make it easier to self-consume  and feed the grid   more balanced

One Idea could be a battery in every house  ,  and  do not use Grid tie Inverters , but charge controllers  and only a small GTI that constantly (24 hours) can feed into the Grid  and can be used in windy times  to take on some windpower units to pass that on into the grid later ....

But sure one problem has to be solved in any-case , that people do not exploit the supported schemes to dump electricity   and get bigger consumers of electricity than they have been before FIT

Billi



Title: Re: excess power from pv
Post by: MikeD on July 04, 2011, 12:16:20 PM
I reckon that 3-phase immersion heater has got to be the best way to soak up the excess energy.

The Emma thing looks like a fantastic bit of kit, but it canna change the laws of physics captain. If it's feeding a 3KW immersion heater and it's only got (say) 1KW of excess energy to play with, it's either got to draw the other 2KW from the grid or reduce the output voltage to get the current and thus the power to stay at the 1KW level.

It's not easy to vary the output voltage in a seamless manner, and it doesn't lend itself to cheap electronics either. Which is probably why the Emma is so expensive. Plus there's a lot of things you can't drive at all if you start dropping the voltage, eg fridges and freezers.

So if you're going to stick to just driving an immersion heater, it's a lot easier to have that 3-phase element and use a nice cheap bit of dedicated kit to switch the elements in series and/or parallel, to provide a load which is roughly balanced to the power available. It won't be as good as an Emma, but it could be done by a gizmo costing maybe a couple of hundred quid instead of the thousands of pounds (?) for an Emma.

My company does some bespoke hardware, they might even be interested in making the electronics if anyone reckons it's a good idea.


Title: Re: excess power from pv
Post by: Other-Power on July 04, 2011, 01:28:14 PM
I reckon that 3-phase immersion heater has got to be the best way to soak up the excess energy.

The Emma thing looks like a fantastic bit of kit, but it canna change the laws of physics captain. If it's feeding a 3KW immersion heater and it's only got (say) 1KW of excess energy to play with, it's either got to draw the other 2KW from the grid or reduce the output voltage to get the current and thus the power to stay at the 1KW level.


The EMMA unit modulates its output, it dose not work as you have explained.

Cheers

Jon


Title: Re: excess power from pv
Post by: MikeD on July 04, 2011, 05:52:40 PM
Modulates it how ?

We talking PWM here or what ?

The spec suggests a current limiting device, in which case it effectively drops the output voltage to achieve the desired current. I'm not saying that's a bad thing BTW, quite the opposite. It's a very elegant solution.


Title: Re: excess power from pv
Post by: hernibles on July 04, 2011, 09:06:19 PM
I have just had a pv system installed. (18 x 220 sharp panels, sunny boy 4000TL).
I am very happy with the performance and output. (145kwh in a week)
I know it is early days but i seem to have excess of power not being used by myself, and obviously being given back to the grid at a low return.
I would like to try and use this power to heat up my hot water tank.
I have done some searches on the net, and this has already been looked at an implemented using a microprocessor to ensure that that you are only using the excess power.
Does anybody have any thoughts or ideas?

thanks
jonboy


You really don't need to look further than the Navitron forums for an elegant solution.

Check out http://tinyurl.com/6dwps8e .  I made one inspired by that thread and it works. 

THE key component is the Unted Automation load controller.




Title: Re: excess power from pv
Post by: billi on July 04, 2011, 09:52:16 PM
come one   people , what is  excellent about a device that burns all the power  (one get FIT payment for)  into hot water ?  Feed the grid as well !


Billi


Title: Re: excess power from pv
Post by: Alan on July 04, 2011, 10:48:09 PM
Quote from Billi. “ come one   people , what is  excellent about a device that burns all the power  (one get FIT payment for)  into hot water ?  Feed the grid as well !  “

Basic sums Billi. What you produce you use. Like off grid. Very efficient way of using energy.
100 % ( Battery losses not included. )   exhappy:

If you use the grid to power your immersion.

Power from a coal fired power station. Typical efficiency 31 – 38%   facepalm

Power lost in the grid typically 7%   facepalm

Here power also goes to a heat pump with variable speed drive. Only thing to be careful about is keeping the speed fast enough to splash lubricate the crankcase bearings.


Regards

Alan


Title: Re: excess power from pv
Post by: john999boy on July 05, 2011, 02:03:27 AM
come one   people , what is  excellent about a device that burns all the power  (one get FIT payment for)  into hot water ?  Feed the grid as well !
I agree with Alan billi.
I'd rather had something keeping my water up to temperature than have to pay to do the same via importing. After all, the immersion will also cut off at the required temperature so EMMA will then feed back to the grid anyway.


Title: Re: excess power from pv
Post by: billi on July 05, 2011, 07:42:17 AM
Sure ,

But if FIT payments result in an increase (wasteful) of personal consumption  , than the system is wrong ....

Using an immersion as the heating idea for hot water  is wasteful  in my eyes  at the current situation

Where is the space in my garden for a swimming pool to dump my units  :hysteria


Quote
If you use the grid to power your immersion.

Power from a coal fired power station. Typical efficiency 31 – 38%   facepalm

But if you export your unit into the grid  another person in the country uses  your unit with a heatpump  .... what is that efficiency than ?  200-400 %   ?

To buy a thing like Emma for  a couple of thousand euro to  increase my immersion heater runtime , buys me other things more usefull   for example a 1-2 kw off grid PV with Inverter and battery  and spread my grid independency  more towards 24 hours a day  whistle


Billi


Title: Re: excess power from pv
Post by: brackwell on July 05, 2011, 08:42:00 AM
If this immersion heater is displacing gas heating then perhaps Billi is correct but otherwise the others are.

 Using a heat pump is perhaps a good idea but in my book the best is charging the electric car - no export,no petrol and pollution,use the batteries to run the house when the sun goes down, use night elec as/if necessary . This way the return on your few pence has become perhaps 10X

Ken


Title: Re: excess power from pv
Post by: billt on July 05, 2011, 08:49:30 AM
I agree with you Billi. Changing the time that you do your washing to a time when your PV is producing is one thing, as that energy would be used anyway. Gaming the system for what seem to be totally selfish reasons (not giving power away to anyone else, basically; power that has already been paid for handsomely) is not very edifying.


Title: Re: excess power from pv
Post by: Alan on July 05, 2011, 09:10:06 AM

Reality check needed.

Quote “ Where is the space in my garden for a swimming pool to dump my units    :hysteria “

Quote “ Gaming the system for what seem to be totally selfish reasons (not giving power away to anyone else, basically; power that has already been paid for handsomely) is not very edifying.  :hysteria

Don't Do swimming pools.
Water tank has a thermostat on the immersion.
Tank gets hot.
Thermostat turns power off. Excess above house load gets exported to the grid.

Regards

Alan


Title: Re: excess power from pv
Post by: MikeD on July 05, 2011, 09:56:31 AM
Given that you are going to heat the water anyway, it makes good sense to use your locally generated electricity to do it. As Alan says, once the water is hot any further excess power goes back to the grid anyway, all you're doing is avoiding a pointless and expensive export/import cycle.

Having said that, the idea of spending thousands of pounds on a bit of kit to make it happen looks distinctly iffy to me. The trick is to do it cheaply.


Title: Re: excess power from pv
Post by: billi on July 05, 2011, 10:44:54 AM
I just got a quote for a heatpump  similar like the ecocent but 300 l stainless steel  boiler tank with heatexchanger for solar or wood   delivered to my door from Germany to Ireland  for 1600 Euro  uses uses 0.7 kw   

Just put that on a timer and let it run during the day    and you still have  some money left compared to the EMMA  to buy 1 kw more PV   :hysteria


Title: Re: excess power from pv
Post by: Richard Owen on July 05, 2011, 12:36:13 PM
I just got a quote for a heatpump  similar like the ecocent but 300 l stainless steel  boiler tank with heatexchanger for solar or wood   delivered to my door from Germany to Ireland  for 1600 Euro  uses uses 0.7 kw   


Details please


Title: Re: excess power from pv
Post by: billi on July 05, 2011, 12:45:57 PM
http://www.wm-feinwerk.de/water/

1620 Euro  excl.vat


Title: Re: excess power from pv
Post by: Richard Owen on July 05, 2011, 12:59:54 PM
Thank you.


Title: Re: excess power from pv
Post by: echase on July 13, 2011, 06:44:33 PM
come one   people , what is  excellent about a device that burns all the power  (one get FIT payment for)  into hot water ?  Feed the grid as well !


Billi

In summer my gas Rayburn with its long pipes is a very inefficient way to heat hot water so I use the immersion. Rather than sell PV to the grid in daytime and buy it back at 3 times the price in evening I’d like to use my PV directly. Not to mention grid losses.


Title: Re: excess power from pv
Post by: billi on July 13, 2011, 07:03:38 PM
Sure .... sad that you have an inefficient  hot water system


Title: Re: excess power from pv
Post by: greentangerine on July 13, 2011, 07:18:10 PM
come one   people , what is  excellent about a device that burns all the power  (one get FIT payment for)  into hot water ?  Feed the grid as well !


Billi

In summer my gas Rayburn with its long pipes is a very inefficient way to heat hot water so I use the immersion. Rather than sell PV to the grid in daytime and buy it back at 3 times the price in evening I’d like to use my PV directly. Not to mention grid losses.

If you're going to be using the immersion heater anyway since that's the only method you are using to heat the DHW during the summer then just have it switched on during the day instead of the evening.  You don't need any fancy controls and you'll be sure not to export to the grid. 

(The only reason not to do this is if you have Economy 7 of course)


Title: Re: excess power from pv
Post by: billi on July 13, 2011, 07:23:47 PM
every PV unit fed into the grid helps to reduce coal and gas nuclear


Title: Re: excess power from pv
Post by: Andy_WSM on July 16, 2011, 08:20:43 PM
Directly related to this subject, for a project I want to try, does anyone have any links to sites selling lower wattage immersion heaters to fit a standard UK tank?


Title: Re: excess power from pv
Post by: Richard Owen on July 16, 2011, 08:51:04 PM
Directly related to this subject, for a project I want to try, does anyone have any links to sites selling lower wattage immersion heaters to fit a standard UK tank?

Try a ship's chandlers. I've seen a 500W immersion in a boat.


Title: Re: excess power from pv
Post by: cj on July 16, 2011, 09:08:03 PM
Failing that, perhaps a 3kw dimmer thus limiting it to 500W. May play havoc with the waveform though.


Title: Re: excess power from pv
Post by: Justme on July 16, 2011, 10:36:06 PM
Would be a hell of a dimmer to handle 3000watts


Title: Re: excess power from pv
Post by: MikeD on July 16, 2011, 11:00:27 PM
I'm interested in this subject. The obvious way to do it is to use a triac to chop the AC (basically the same as a dimmer), thereby allowing precise control of the power that goes to the heating element. The triac can be turned on for a short period as the mains AC voltage goes through zero, and is turned off before the voltage has gone through the entire cycle. Leave it on for longer the more power you have available.

But if you do this, then you may be drawing in excess of the available PV power while the triac is on (ie, importing), and then exporting again for the part of the cycle when it is off.

So if you're doing this import and export 50 times a second, I guess the question is, will the average electricity meter notice or will it just take an average and show zero in and zero out ?


Title: Re: excess power from pv
Post by: cj on July 16, 2011, 11:58:56 PM
Would be a hell of a dimmer to handle 3000watts

Most only go to 1000W but www.hedcom.fi/files/hedcom/RVE/rve_high_power_dimmers_04.pdf does 5.5kw - 11kw

I think the DNO may be concerned at high power dimmers.

They would need to operate on BOTH halves of the cycle (otherwise you would get a high DC component), so that is 100 times per second, and the meter may respond 'differently', but I doubt it would act as an import and export 100 times per second.


Title: Re: excess power from pv
Post by: Andy_WSM on July 17, 2011, 08:44:55 AM
Directly related to this subject, for a project I want to try, does anyone have any links to sites selling lower wattage immersion heaters to fit a standard UK tank?

Try a ship's chandlers. I've seen a 500W immersion in a boat.

Thanks - that gave me the inspiration to search for the right thing on Google and found a 750W heater for about £40 via eBay in the end - couldn't find it on eBay's search originally - typical!


Title: Re: excess power from pv
Post by: echase on July 25, 2011, 01:05:16 PM
In doing experiments on this I tried pulsing a 3kW immersion with a cycle of 1 second on and 0.1 sec off. The element failed after 10 minutes.  I am assuming that whilst 50Hz is OK, as the thermal time constant is presumably >> 50Hz, when I use a 1 second cycle (1Hz) the element just fatigues rapidly due to it heating up and cooling down too much/quickly. Anyone else had this problem?

I am not suggesting that such a low pulse rate is a good way to do this control of export, It was just a by-product of other experiments.


Title: Re: excess power from pv
Post by: cj on July 25, 2011, 07:35:49 PM
The DNO may have rules about waveform distorting controllers used on hi power items? I would be amazed if thermal changes at that rate caused shock to make it fail. I would firstly suspect it was 'one of those things', or a dud batch, or possibly if the waveform distorts differently on the + and - cycles you end up with a DC element, that could cause vibration(?) If that resonates it might shake itself to bits.


Title: Re: excess power from pv
Post by: echase on July 27, 2011, 02:13:50 PM
Looking at failed one I suspect it was heavily corroded and so pretty much on its last legs anyway. The pulsing could be heard so it just shook itself to bits I think.


Title: Re: excess power from pv
Post by: echase on July 27, 2011, 02:18:38 PM
For some time, since before coming across this thread, I have been designing an immersion controller for my 4kW PV system. I now have it finished and have built a few for family and friends. Seeing as the professionals have not come up with a sensible product that is affordable send me a private message if anyone wants to buy one. It is available as a kit or ready built. I am a Chartered Engineer so the design is hopefully quite professional but ultimately the risk is yours if you want to fit one.


It functions similar to the ones mentioned on some threads here, i.e. it controls the power into the immersion to ensure that export power is reduced to near zero (as long as the hot water is not up to temperature already). But it uses simpler components to reduce the cost and size, e.g. instead of an expensive PLC (Programmable Logic Controller) it has a small PCB that I make; this does not reduce its performance. It is designed for a 3kW or less immersion but would probably work up 10kW, although I have not tested that and your utility company might object at more than 6kW. Two 3kW immersions in parallel should be OK.  It does not rely on an always on external PC either, which would burn lots of watts. No need to purchase an expensive <1kW immersion.


Title: Re: excess power from pv
Post by: Richard Owen on July 27, 2011, 02:44:31 PM
For some time, since before coming across this thread, I have been designing an immersion controller for my 4kW PV system. I now have it finished and have built as few for family and friends. Seeing as the professionals have not come up with a sensible product that is affordable send me a private message if anyone wants to buy one. It is available as a kit or ready built. I am a Chartered Engineer so the design is hopefully quite professional but ultimately the risk is yours if you want to fit one.


It functions similar to the ones mentioned on some threads here, i.e. it controls the power into the immersion to ensure that export power is reduced to near zero (as long as the hot water is not up the temperature already). But it uses simpler components to reduce the cost and size, e.g. instead of an expensive PLC (Programmable Logic Controller) it has a small PCB that I make; this does not reduce its performance. It is designed for a 3kW or less immersion but would probably work up 10kW, although I have not tested that and your utility company might object at more than 6kW. Two 3kW immersions in parallel should be OK.  It does not rely on an always on external PC either, which would burn lots of watts. No need to purchase an expensive <1kW immersion.



Would it work with my 300W Hydro Scheme?


Title: Re: excess power from pv
Post by: echase on July 27, 2011, 03:16:09 PM
Don’t know much about hydro but I don't see why not. But I suspect to get really fine control a lower than 3kW immersion element is desirable, as many controllers designed to work as 3kW are going to give quite coarse control when trying to reduce the 3kW to 300W, tending to turn it on fully or off altogether rather then fine controlling it over 0-300W.

In my house the minimum base load of freezers, etc. is 300W so I would have nothing to export if I only had a 300W hydro.


Title: Re: excess power from pv
Post by: Richard Owen on July 27, 2011, 04:40:03 PM
My Hydro isn't grid tied. It's stand alone. I have a spare immersion slot in a tank so it would be convenient if I could use them together.

I also happen to have a 500W immersion heater I just happened on by chance.


Title: Re: excess power from pv
Post by: cj on July 27, 2011, 11:23:26 PM
Richard, is there a description of your hydro on a thread? And is it high head or low head?  I have run of the river possibilities, but at about £900 for 100w is not cheap.  http://www.ecoresorts.net/hydro/jackrabbit-prod.htm


Title: Re: excess power from pv
Post by: Justme on July 27, 2011, 11:27:37 PM
I have run of the river possibilities, but at about £900 for 100w is not cheap. 

But that £900 100watt turbine will give you nearly the same as a 1kwp £3k array over a full year.


Title: Re: excess power from pv
Post by: cj on July 27, 2011, 11:49:25 PM
I have run of the river possibilities, but at about £900 for 100w is not cheap. 

But that £900 100watt turbine will give you nearly the same as a 1kwp £3k array over a full year.

If only. That is with 6m/sec flow, that may not be all the time, there are losses of getting the 12v to the house, and approved for export, and the cost of licenses to extract water, and all the infrastructure to channel the water, and the water comes up from 30 cms deep to 3m deep in a few hours after torrential rain ie every couple of years or so. It has to withstand  1 tonne + logs floating down fast when in spate.

Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?


Title: Re: excess power from pv
Post by: ecogeorge on July 27, 2011, 11:59:08 PM
I have run of the river possibilities, but at about £900 for 100w is not cheap. 

But that £900 100watt turbine will give you nearly the same as a 1kwp £3k array over a full year.

If only. That is with 6m/sec flow, that may not be all the time, there are losses of getting the 12v to the house, and approved for export, and the cost of licenses to extract water, and all the infrastructure to channel the water, and the water comes up from 30 cms deep to 3m deep in a few hours after torrential rain ie every couple of years or so. It has to withstand  1 tonne + logs floating down fast when in spate.

Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?
If you can get 3Kw of pv for £900 please let me know :hysteria :hysteria
I've obviously just made a hugh mistake tonight in sending £7200 for ..
20 BP4175 PV panels
Inverter Power-One Aurora PVI-3.6 Outdoors
DC isolator x 2
Generation meter

I may be able to stop the payment :genuflect.


Title: Re: excess power from pv
Post by: cj on July 28, 2011, 05:46:56 AM
Does not compute.

The Jack Rabbit is hydro and to get 1/10 of the power costs for more than 1/10 of the cost of PV. I suggest you do not cancel your pv and but a water turbine on you roof  :hysteria  :hysteria


Title: Re: excess power from pv
Post by: Richard Owen on July 28, 2011, 08:45:44 AM
Richard, is there a description of your hydro on a thread? And is it high head or low head?  I have run of the river possibilities, but at about £900 for 100w is not cheap.  http://www.ecoresorts.net/hydro/jackrabbit-prod.htm

I've got a high head (18m) system. I live on a hill.

I am overdue documenting it. I shall get round to it one day.


Title: Re: excess power from pv
Post by: echase on July 28, 2011, 09:52:02 AM
My Hydro isn't grid tied. It's stand alone. I have a spare immersion slot in a tank so it would be convenient if I could use them together.

I also happen to have a 500W immersion heater I just happened on by chance.

With a 500W element my system will give adequately fine control with 300W input. I used a 400W electric fire as a dummy immersion when testing it and it seemed fine.


Title: Re: excess power from pv
Post by: Justme on July 28, 2011, 01:40:32 PM

Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?


I think you mis read what I put. I compared it to ONE kwp costing £3k not THREE kwp. Also going on one days PV out put is also not what I said. You average what 1kwp can do per day over a year. Its less than a 100w constant power source can provide.

Water is just more reliable that solar or wind.

So even if all your other costs increase the £900 to £3k your still going to get more energy from the water. You might get more £ from the PV FIT's that from the water FIT's I dont know.

If I had a water power source I would use it rather than any other method. Install problems can be worked, not getting any sun / wind cant.


Title: Re: excess power from pv
Post by: brackwell on July 28, 2011, 02:27:08 PM
echase,

Can you just spell out what your box achieves please,

1)What happens when the pv is less than/ and greater than the rated watts of the immersion element.

2) what happens if the PV is not sufficient and you want to use the grid as well

3) what is fail mode and does it fail safe. Could it catch fire.

4) What might be the life span if used 24/7

Sent PM

Ken


Title: Re: excess power from pv
Post by: echase on July 28, 2011, 04:44:54 PM

1)What happens when the pv is less than/ and greater than the rated watts of the immersion element.

Power into immersion is reduced if PV not enough. If PV more than full on immersion plus the house load you will export excess to grid as normal, but excess will be 3kW less, which is good. 

2) what happens if the PV is not sufficient and you want to use the grid as well

Just drawn grid power as normal, it does not go through this box.

3) what is fail mode and does it fail safe. Could it catch fire.

It is a smallish metal box with full fuse protection and earthing. Worst case scenario is failed output so immersion does not get a feed but rest of house will be normal. Box can't catch fire even if the internals were to self destruct due to component failure (unlikely as fuses protect from this), but I can't be responsible for the way in which it's connected to the house and so for any damage due to failure to comply with relevant regulations or user error, e.g. if you use too thin connecting wire to immersion the house could catch fire but not my box. Caveat emptor.

4) What might be the life span if used 24/7

I'd say >10 years at 24/7 and > 20 years at a typical PV output, which is only large for <20% of a year. But that is not a tested claim. Immersion element life will be lowered by the extra use it will get compared with say using gas for heating the water. But reduction is small because it will be running at low power most of the time. Life increased relative to a full on element on Economy 7. Also element is not difficult to change, unlike repairing a gas boiler. I offer a 1 year warranty; once it's run OK for 1 year to prove there are no niggling defects it is difficult to see why it would fail in the 2 - 10 year period as there are no moving parts apart from one irregularly used switch.


Title: Re: excess power from pv
Post by: brackwell on July 28, 2011, 05:17:43 PM
Thanks,
Thats all good and its good to see you have considered the safety issue and covered your backside.  However i dont think there are any H&S types on here -its not in the spirit.

Ken


Title: Re: excess power from pv
Post by: cj on July 28, 2011, 05:46:35 PM

Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?


I think you mis read what I put. I compared it to ONE kwp costing £3k not THREE kwp. Also going on one days PV out put is also not what I said. You average what 1kwp can do per day over a year. Its less than a 100w constant power source can provide.

Water is just more reliable that solar or wind.

So even if all your other costs increase the £900 to £3k your still going to get more energy from the water. You might get more £ from the PV FIT's that from the water FIT's I dont know.

If I had a water power source I would use it rather than any other method. Install problems can be worked, not getting any sun / wind cant.

OK. The problem with Hydro is the infrastructure costs are so high, and for a low output system, the water 'extraction' licence route is not really viable. Dip the Jack Rabbit in the river (perhaps on a tethered floating pontoon might be, but no FiTs, make all the environmental improvements and the cost would soon be £6k - £20k, but not for 100w even 24/7.


Title: Re: excess power from pv
Post by: echase on July 28, 2011, 06:11:39 PM
Thanks,
Thats all good and its good to see you have considered the safety issue and covered your backside.  However i dont think there are any H&S types on here -its not in the spirit.

Ken

I am an engineer who assesses the safety of electronic systems for a living, but not an H&S one. So I have thought about safety carefully. But even despite that I can’t offer a 100% guarantee that the unit will never fail or cause a problem. You get what you get at a price that is a lot less than some other similar products, so you accept a small risk in return for the cheap price.


Title: Re: excess power from pv
Post by: tony. on July 29, 2011, 11:16:46 PM
Echase,

How much are the units.

Canyou post a photo of the completed unit.

Good work by the way

Tony


Title: Re: excess power from pv
Post by: echase on July 31, 2011, 11:48:58 PM
Echase,

How much are the units.

Canyou post a photo of the completed unit.

Good work by the way

Tony

Send me a private message and I will reply.


Title: Re: excess power from pv
Post by: john999boy on August 01, 2011, 04:49:14 PM
@echase
This may have been explained before but I'd just like to confirm.....

I've just been explaining the benefits of your 'gadget' to my wife and she asked what would happen during the time when there was no excess power being generated and no immersion heated water required - ie. during the night when it is dark with no hot water requirements?

Would I be correct in thinking that the immersion (apart from using your override switch) would only work if there was an excess of solar generation and therefore it would lose it's potential to work after dark? In other words, it wouldn't be taking 3kW when no sun was shining unless I'd chosen to use the override switch?


Title: Re: excess power from pv
Post by: echase on August 01, 2011, 08:11:34 PM
No, your immersion works just like today if you override it. So 3kW is sourced from PV and grid with no “dimming” function active whilst override in use. But if no PV it’s all grid. I can supply a pair of wires to connect to volt free contacts on your override timer if needed so you can top up the water on days of little sun or high hot water usage.

But in the normal automatic mode the immersion will not come on at night or at other times when there is no sun.

With my unit in place any gas boiler, etc. that currently heats the water should be off all day, but can still use it for top up in evenings.  Many such boilers are pretty inefficient methods of summer water heating due to large losses in interconnecting pipes. Personally I only use electricty in summer.


Title: Re: excess power from pv
Post by: billi on August 01, 2011, 09:40:42 PM
Quote
Any gas boiler, etc. that currently heats the water should be off all day, but can still use it for top up in evenings.  Many such boilers are pretty inefficient methods of summer water heating due to large losses in interconnecting pipes. Personally I only use electricty in summer.

Is this so ?

Every PV unit you export does more benefit   to the whole Idea at the moment  , than simply burn it in an electric heating element  in your house

So just get  an additional  non FIT registered 1000 Watt PV  for 1000 GBP  a DC water heating element   and forget about FIT  ;D 

Or   find a better way to self-use the precious PV units under the FIT scheme 

Thats my opinion

Billi



Title: Re: excess power from pv
Post by: cj on August 01, 2011, 11:00:58 PM
Depends if you are being mercenary.  If you do not work out which is the most efficient cost-wise for you, it is quite difficult to balance the Eco credentials against your bill.  If this is distorted by subsidies, it is time the subsidies were re-evaluated.  It is hard enough to do the maths without such arbitrary factors.

Before the last swinging price rises, SSE quoted 3.15p unit (kWh) for gas heating, oil and bottled gas would be far more. The exported power is bought from pv generators for 3.1p/unit. The imersion is 100% efficient, (ignoring cable losses after the meter), my gas / central heating boiler has long pipe runs, and has to heat up the boiler first. And that is after the boiler inefficiency rating.  So I would assume an emersion heater is more cost effective if using PV, OR Night Rate (economy 7).

If the export is being deemed at 50%, the actual power used by the emerson heater is effectively free, whilst generating at least that much.


Title: Re: excess power from pv
Post by: billi on August 01, 2011, 11:38:44 PM
too late for me to do maths , but if FIT would not be  available not many would have PV and those that go for PV without FIT , would not just burn it in an immersion element  (but perhaps these days are close  , and PV gets so cheap that it is just burnt)

About half the  FIT payments in Germany compared to the UK and people over there still install  ::)


Quote
he imersion is 100% efficient, (ignoring cable losses after the meter), my gas / central heating boiler has long pipe runs, and has to heat up the boiler first. And that is after the boiler inefficiency rating.  So I would assume an emersion heater is more cost effective if using PV, OR Night Rate (economy 7).

And what dirty pig power-station is supplying your electricity with an efficiency below 40 %  , while you burn the PV power in your tank  and not having a solar thermal Idea or a heatpump ?

Billi



Title: Re: excess power from pv
Post by: cj on August 02, 2011, 08:59:45 AM
too late for me to do maths , but if FIT would not be  available not many would have PV and those that go for PV without FIT , would not just burn it in an immersion element  (but perhaps these days are close  , and PV gets so cheap that it is just burnt)

About half the  FIT payments in Germany compared to the UK and people over there still install  ::)


Quote
he imersion is 100% efficient, (ignoring cable losses after the meter), my gas / central heating boiler has long pipe runs, and has to heat up the boiler first. And that is after the boiler inefficiency rating.  So I would assume an emersion heater is more cost effective if using PV, OR Night Rate (economy 7).

And what dirty pig power-station is supplying your electricity with an efficiency below 40 %  , while you burn the PV power in your tank  and not having a solar thermal Idea or a heatpump ?

Billi



PV cost MIGHT come down so that, without subsidies, the power can be used to heat water, like a light tube. But that is some way off. Power stations may be 40% efficiency and 30% may be lost on the transmission, but I refer to mercenary, or a 'capitalist' point of view, a 'market' view, you do the maths, if it is more expensive to use method A rather than B, as Governments use tax to persuade change of practice, (large cars = high road tax), then so it is reasonable for the individual to comply.

Therefore I referred to after MY meter, emersion IS 100% efficient. But not the boiler sadly!

I could not justify PV on 1/2 the FIT level, as would most others as you say. In 5 years I expect the installation cost to be down and the energy costs up, to make the unit cost comparable.

So for a direct cost comparison, it IS worth my while FINANCIALLY using my PV for DHW, during the summer. So is that wrong?

I just had a new efficient boiler, and wood burning stove in place of an open fire. (No subsidy available for either). I do it for the efficiency. I considered solar thermal carefully, but there is no way it would ever pay for itself at present or imminent fuel price. For a new build of course I would.

What I would like to do is have an additional multifuel (wood chip, WVO, Log and Brush burning) stove, such as the Rocket stove.  Perhaps I can connect it in series (on the boiler return pipe), built outside the garage wall where the new boiler is, to provide low level heat during moderate heat demand?


Title: Re: excess power from pv
Post by: EccentricAnomaly on August 02, 2011, 09:32:27 AM
The house I'm staying in now has the choice of a central LPG "boiler" or an immersion for water heating. In the summer I'm using the immersion. It's very difficult to work out the costs for the LPG as the only instrumentation is a % full gauge on the large LPG tank (there's no flow meter). The pipes from the boiler to the DHW tank are medium length but I wouldn't be overly bothered about the losses in them as with this solid stone house the downstairs is pretty cool even in summer and a bit of incidental heating wouldn't go amiss.

However, what decided me was that the boiler has a pilot light and it would be too much faff to light it and remember to switch it off every day for an hour or two's water heating. I'd forget. I remember from my previous mains-gas house that the pilot light can be quite a significant proportion of gas use when only a little bit, relatively, of heating is being done.

The argument might be reversed with a more modern boiler with electronic ignition. I don't know.


Title: Re: excess power from pv
Post by: cj on August 02, 2011, 10:11:05 AM
Absolutely. I am puzzled by all of the useless information Gov give out, yet fail to give guidance on such fundamentals that affect everyone. Do you leave the heating on (in winter) 24 hours or as required, do you use an immersion heater or boiler, which is the cheapest way to heat for various costs of fuel, etc.  With advice of all the arguments that individuals need to consider for their site. You are not too concerned about pipe losses, I am, as much of the (lagged) pipe run is across a triple garage and is wasted heat. But with deemed 50% export, it is clearly most financially beneficial to use it myself, IF it is usefully employed.


Title: Re: excess power from pv
Post by: brackwell on August 02, 2011, 10:51:17 AM
I have done my best attempt to measure gas use in v USED hot water out and come to the conclusion that it is around 30% efficient. Therefore when not needing a full tank of hot water (ie no baths or visitors but 2 showers etc ) the immersion wins hands down. In Winter when the boiler is central heating then the opposite must be true.

I have now moved on and concluded just in time heating is what is required and of course you now think Combi Boiler.  With the combi i guess you could use 10mm pipe ( in a continuous run) in areas of high pressure thus further reducing losses.However i have solar thermal and conclude that this will work best if coupled to a inline programable electric heater for most of the year.
Ken


Title: Re: excess power from pv
Post by: echase on August 02, 2011, 12:51:52 PM

However, what decided me was that the boiler has a pilot light and it would be too much faff to light it and remember to switch it off every day for an hour or two's water heating. I'd forget. I remember from my previous mains-gas house that the pilot light can be quite a significant proportion of gas use when only a little bit, relatively, of heating is being done.

The argument might be reversed with a more modern boiler with electronic ignition. I don't know.

I agree; my Rayburn has a pilot light, one for cooker side and one for boiler side. These 2 keep the whole unit surprisingly warm which is a waste. So I turn off the boiler side pilot for summer and use electric water heating. And mostly use electric cooking in summer.

I would not choose a Rayburn or AGA as they are energy inefficient even in winter, but it came with the house.


Title: Re: excess power from pv
Post by: echase on August 02, 2011, 01:03:00 PM
I am puzzled by all of the useless information Gov give out, yet fail to give guidance on such fundamentals that affect everyone. Do you leave the heating on (in winter) 24 hours or as required, do you use an immersion heater or boiler, which is the cheapest way to heat for various costs of fuel, etc.  With advice of all the arguments that individuals need to consider for their site.

2 years ago one of these Gov websites kept sending me very general advice like turn down my stat by 1C. So I challenged them to give more specific advice, e.g. on timeclock setting, like you say, and they did nothing.

Incidentally Isaac Newton had it worked out. Due to Newton’s Law of Cooling I say never leave anything on permanently and turn it off 30-60mins before you actually go to bed or go out as it takes that long to cool down noticeably. The hotter the average temperature difference between the inside and outside of your house the more heat you loose, so turning it off when out/in bed reduces the average temperature.


Title: Re: excess power from pv
Post by: climber on August 11, 2011, 08:20:20 PM
echase,

Any further info on these units? Cost/Availability?

Thanks!


Title: Re: excess power from pv
Post by: fje-iptelenet on August 11, 2011, 09:44:11 PM
Just send Edward a personal message and you'll get a response - quickly!