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Author Topic: excess power from pv  (Read 33256 times)
brackwell
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« Reply #30 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
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marshman
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« Reply #31 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 Smiley

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
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Other-Power
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« Reply #32 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

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Baz
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« Reply #33 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.
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Other-Power
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« Reply #34 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
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Justme
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« Reply #35 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.
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hawkie
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« Reply #36 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,

 Grin Grin Hawkie Grin Grin
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billi
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« Reply #37 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
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tange179
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« Reply #38 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  Wink

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

John
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EccentricAnomaly
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« Reply #39 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.
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Philip R
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« Reply #40 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
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ecogeorge
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« Reply #41 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?
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Philip R
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« Reply #42 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
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billi
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« Reply #43 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

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MikeD
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« Reply #44 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.
« Last Edit: July 04, 2011, 12:21:23 PM by MikeD » Logged
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