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Author Topic: excess power from pv  (Read 34078 times)
echase
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« Reply #90 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.
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tony.
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« Reply #91 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
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echase
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« Reply #92 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.
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john999boy
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« Reply #93 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?
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8.46kWp solar PV - 169° - 40° slope - 53°N. Immersun fuelled DHW.
echase
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« Reply #94 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.
« Last Edit: August 01, 2011, 10:22:29 PM by echase » Logged
billi
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« Reply #95 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  Grin 

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

Thats my opinion

Billi

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
cj
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« Reply #96 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.
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billi
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« Reply #97 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  Roll Eyes


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

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
cj
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« Reply #98 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  Roll Eyes


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?
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EccentricAnomaly
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« Reply #99 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.
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cj
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« Reply #100 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.
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brackwell
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« Reply #101 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
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echase
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« Reply #102 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.
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echase
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« Reply #103 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.
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climber
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« Reply #104 on: August 11, 2011, 08:20:20 PM »

echase,

Any further info on these units? Cost/Availability?

Thanks!
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