Does our forum expertise and knowledge on solar and batteries inform domestic solar applications

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pcatterall

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Working on solar on the boat but not moving from lead acid just yet although the various articles are very interesting.
looking at my household energy at this time, perhaps my investigations will inform decisions for the boat.
Most of the info I find for housing applications seem to be from companies trying to sell their wares.
My dilemma is that I can mount a solar array providing lots of energy for 5 hours on a summer day but I cant use it and fitting batteries adds more complexity and cost.
I guess that other ways to store that surplus would be .... to heat my domestic water cylinder (( rather than use cheaper( still) gas)) to charge my electric car ( when I can afford one)
to create hydrogen to power my hydrogen boiler ( when I get one), to store heat in the bricks of my space heater etc etc. ( yes I have a fertile but strange imagination!)
selling back to the grid seems a common option but buying electricity from them at 29 pence and selling back at 5 pence a unit doesn't seem a good deal.
Any more ideas please sensible ones will be great but all welcome!
 
Batteries all the way, and cost/benefit wise, probably lead acid. Conventionally you’d have a smart inverter, to prioritise the use of the leccy you generate. Something like, solar goes 1st to the houe, 2nd to battery, 3rd to immersion, then to the grid. With no sun, your house runs on batteries, though you might also want an economy 7 type tariff, so on dull weeks you can recharge the batteries off peak. Such devices exist now, btw. The trick is big enough batteries. Maybe ones with wheels on, in future;)
 
Look at the Tesla powerwall. Although Mr Musk is as irritating as they come, the product sets the standard that others fail to meet.

I’ve been looking at domestic solar for a while, and have recently ordered an 11 kWp system plus Tesla Powerwall. Payback is 8 years or so, but that’s in the specific circumstances of our very high - 35kw a year - energy use.

Its needed some spreadsheet modelling to see how it will all work.
 
girlofwight said:
Look at the Tesla powerwall. Although Mr Musk is as irritating as they come, the product sets the standard that others fail to meet.

I’ve been looking at domestic solar for a while, and have recently ordered an 11 kWp system plus Tesla Powerwall. Payback is 8 years or so, but that’s in the specific circumstances of our very high - 35kw a year - energy use.

Its needed some spreadsheet modelling to see how it will all work.
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A friend has gone down that route. I did some calculations a few years ago for solar and he said they've been pretty spot-on. He has 7kW solar and a Tesla powerwall. His next step might be another 3kW solar or a wind-gen. I managed to persuade him that a small wind-gen was a waste of money and a large one would very expensive and stick out a bit. I think he is considering buying into a large commercial wind-gen. and getting some cheap electricity from that route via some sort of rebate based on level of investment. A second Tesla powerwall is probably on the cards.

He's a real Musk fan with 2 Tesla cars, a powerwall, shares and internet via Starlink. He gave me a figure for kW/mile recently and a rough mental calc. seemed to put that in the 300 mpg range with current fuel prices. That will change a bit when his fixed price deal runs out.:D

He pays 5p/kWh at night to charge cars and battery. The battery provides power in the morning and then solar kicks in with enough to run the house and re-charge the battery a bit. He only uses full price electricity for part of the evening but that's still quite expensive. I think extra solar and another battery might be enough to solve that issue. He doesn't have dedicated solar hot water but using excess PV capacity via his heat pump is probable a good solution.

I haven't done the sums but he seems happy. Cars will be through the business and his office is also at home. I think virtually everything is on 0% interest loans with the cash he'd spend invested to make a decent return.
 
Around here something like 20% of all homes and businesses have solar PV systems. Judging by advertisements batteries are becoming, or likely to become more popular.
I think solar PV to electric hot water is a very useful approach. Although again around here many hoses have solar hot water systems. (solar collector to tank) Unfortunately solar hot water tends to be too hot in summer with boiling off water and too cold in winter so need electric booster. I think the best approach is solar PV to electric hot water tank. With some sort of control to only heat water when solar PV power is surplus. Yes we also have a very poor buy back price for solar generated power.
We do not have off peak power costing but my guess is that off peak would actually be during the day when solar PV is pumping in lots of power. UK obviously different.
So yes to OP solar PV battery and electric hot water. My system is a mere 1500 w but is 10 years old well and truly paid for by a short term generous buy back price. Typical domestic PV seems to be 6kw or more. Individual panels seem to be able to produce near twice the power of old style panels. Ourt yacht club has 40kw which presumably pays for itself easily providing power for fridges airconditioning, cookers and about 50 boats. But then I reckon we would get twice the solar energy in a year to UK. ol'will
 
girlofwight said:
Look at the Tesla powerwall. Although Mr Musk is as irritating as they come, the product sets the standard that others fail to meet.

I’ve been looking at domestic solar for a while, and have recently ordered an 11 kWp system plus Tesla Powerwall. Payback is 8 years or so, but that’s in the specific circumstances of our very high - 35kw a year - energy use.

Its needed some spreadsheet modelling to see how it will all work.
Click to expand...
35kw/Yr is tiny consumption?
 
William_H said:
Around here something like 20% of all homes and businesses have solar PV systems. Judging by advertisements batteries are becoming, or likely to become more popular.
I think solar PV to electric hot water is a very useful approach. Although again around here many hoses have solar hot water systems. (solar collector to tank) Unfortunately solar hot water tends to be too hot in summer with boiling off water and too cold in winter so need electric booster. I think the best approach is solar PV to electric hot water tank. With some sort of control to only heat water when solar PV power is surplus. Yes we also have a very poor buy back price for solar generated power.
We do not have off peak power costing but my guess is that off peak would actually be during the day when solar PV is pumping in lots of power. UK obviously different.
So yes to OP solar PV battery and electric hot water. My system is a mere 1500 w but is 10 years old well and truly paid for by a short term generous buy back price. Typical domestic PV seems to be 6kw or more. Individual panels seem to be able to produce near twice the power of old style panels. Ourt yacht club has 40kw which presumably pays for itself easily providing power for fridges airconditioning, cookers and about 50 boats. But then I reckon we would get twice the solar energy in a year to UK. ol'will
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I also assumed that electricity would be cheap in the afternoons when surplus solar power was being generated, but my provider offers it from 2am to 6am at 8.8p KWh which is higher than I haves seen, never the less
it did set me thinking that it would be a good way/time to charge the house batteries on the cheap. The penalty was a higher unit rate for the rest of the day (33P) but then most of that would be on solar?
 
Thanks all for some interesting answers, not sure of the boat relevance yet though! I have found that, contrary to the solar salesman's pitch, just generating masses of energy is less important than targeting the energy to meet the individual household needs.
If anyone can point me to material ( spreadsheet sounds good) where more of these issues are explained that would be much appreciated.
 
I have a device called Solar IBoost. It detects when we are exporting to the grid and diverts excess power to the immersion heater.

We generate approx 3,600kwh p.a. of which about 1,200 go to hot water. It provides all our hot water for 6 months of the year.
 
Perhaps the relevance of boat systems is in the way the problem is approached. Not many people will ever have done an energy audit to calculate and/or observe what energy they need at different times of the day and year. With that info you could plan which system supported which area of usage best. While batteries are important and difficult to replicate at a house level for heating, you could run house lights and appliances off solar and batteries, and find another solution for heating (heat pumps, biomass etc). Perhaps 240V is not necessary for everything? Personally I find the idea of an energy self sufficient house really appeals. Just might have to happen in stages, and in different ways in different climates. Hard to do in a flat....
 
Supertramp said:
Perhaps the relevance of boat systems is in the way the problem is approached. Not many people will ever have done an energy audit to calculate and/or observe what energy they need at different times of the day and year. With that info you could plan which system supported which area of usage best. While batteries are important and difficult to replicate at a house level for heating, you could run house lights and appliances off solar and batteries, and find another solution for heating (heat pumps, biomass etc). Perhaps 240V is not necessary for everything? Personally I find the idea of an energy self sufficient house really appeals. Just might have to happen in stages, and in different ways in different climates. Hard to do in a flat....
Click to expand...
Yes, heating is quite another matter. my current understanding is that a ground source pump requires a kw of electricity for every 4kw of heat produced. My current gas usage is 17000kwh /year so 4000kw of electricity to
find from somewhere. That's about my current electricity usage so a 'simple' doubling up exercise!
 
pcatterall said:
Yes, heating is quite another matter. my current understanding is that a ground source pump requires a kw of electricity for every 4kw of heat produced. My current gas usage is 17000kwh /year so 4000kw of electricity to
find from somewhere. That's about my current electricity usage so a 'simple' doubling up exercise!
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And electric kwh are much more expensive than gas kwh. But I think the idea of multiple generation methods and tackling each problem as a separate system is useful. It also depends what the overall goal is, or the relative balance between goals such as cost, simplicity, CO2 emissions and so on.
 
Installed 13 panels and a 8kw battery last October coupled with an iboost to switch on the Immersion Heater.

Over the winter we often, but not always refilled the battery during the day. The battery lasts overnight except when we’ve had family round and have done a lot of cooking ( we are all electric ).
Since mid March we haven’t used any grid electricity And the Gas boiler is only heating the radiators. During the day when the solar is generating, it supplies the house first, then fills the battery, then switches the immersion on, then exports any left over. Most days in April we are exporting at least 5 kw and it has been as high as 12kw

i haven’t yet costed it out since the energy prices went up, but the logic behind getting it was to be a little independent of the grid supply and obviously to save money. Since prices have gone up, lots of my neighbours are now very interested

The game changer is the battery, as it allows you to use the solar generated energy when you want.

For info the Inverter and Battery are from GivEnergy. Their app to control the system is excellent.
 
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We have both solar water and solar PV down here in Nth Devon
4.3kw of PV panels with a Solax 3.6kWHybrid inverter and a 5.8kwh lithium battery.
Our grid usage has dropped from 241kWh in January to 47kwh in March with a 250kWh export.
In April we are now averaging less than 0.5kWh usage a day with an export of between 5 and 19kWh.
The battery although small tides us over the hours of darkness and its now a rare morning when there is not enough to keep us powered up until the sun starts to do its job. However we restrict the usage of any high power items apart from the oven to daylight hours, also we only use one at a time as once our demand goes over 3.6kW it starts to draw from the grid.
At this time of year the solar water panels give us enough hot water, however I have the gas boiler topping it up at 7am for half an hour just to make sure we have hot showers in the morning.

Couple of things to note is that the PV system has to be installed by an MCS installer if you want to export to the grid and the DNO notified.
If you want to go over 3.6kw you have to apply to the DNO rather than just informing them that you are doing it.
 
Kevin and Loddon.
Many thanks for these practical examples. I just focussed on the battery bank and the recommendations about the Tesla Power Wall 2 system.
£10 k fitted made me think and consider that unlike our boaty issues weight and bulk are less of a problem.
A lead acid set up would seem to be a lot cheaper even accepting the issue to limit the discharge. Under good working conditions their life expectancy should not be too bad.
 
pcatterall said:
Kevin and Loddon.
Many thanks for these practical examples. I just focussed on the battery bank and the recommendations about the Tesla Power Wall 2 system.
£10 k fitted made me think and consider that unlike our boaty issues weight and bulk are less of a problem.
A lead acid set up would seem to be a lot cheaper even accepting the issue to limit the discharge. Under good working conditions their life expectancy should not be too bad.
Click to expand...
The 5.8kWh Solax are about £2100 each and you can link three giving 17kWh.
I am thinking of adding a second one before the winter so the system can charge from the grid overnight to make up for the lack of sun however its going to take a while before it pays for itself. :(
 
KevinT1 said:
The Tesla Powerwall is way more expensive than you need - think the price differential for their cars. My GivEnergy 8kw battery, that links beautifully into the Inverter, was around £2,500 And it comes with a 10 year warranty.

Midsummer Wholesale
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I did think the Tesla version was over-priced but at least it worked in a power cut. I think my friend mentioned getting an extra part free to allow that feature. I saw cheaper ones without that facility and also some cheaper models using 2nd hand EV packs. I haven't looked recently but see that the GivEnergy does work in a power-cut and the price looks good.

I might consider it in October when I return home, thanks for pointing it out. Of course things might have moved on by then and could be better and cheapr or more expensive (development and scale vs. inflation).:D

Solar makes no sense for me just now.
  1. I'm away from home for 6 months in summer (plus the odd week in winter)
  2. I'm looking for a new property

A house battery could work as it will lower existing costs and can be moved to a new home fairly easily.
 
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