Thinking about solar cells and powerwall.

[MrBadger]

I'll have a read through at some point. But some initial thoughts.

Can I suggest that you run the solar figures for your location through PVGIS - it is updated from time to time but looks like the latest version is here JRC Photovoltaic Geographical Information System (PVGIS) - European Commission (europa.eu) - you need to be as exact as you can with orientation, pitch and as much as you can, potential shadows - even slightest shadows.

On a quick skim, I would be wary of the SolarEdge claims. I have had SE for 6+ years so have the data to know how well its works. Its a great system if its needed, but the financial gains may not match what the headlines imply. I actually ended up on the Solar Edge installers list for a while so have a bit of knowledge on how their systems may be pushed.

As for high efficiency panels, they are only of real benefit if you are size limited for standard panels. I went with some high efficiency smaller panels for our setup. My first quote from another company, our roof was size limited (because their panels were very inefficient) and when they came to survey, they were only prepared to put approx 2.6kWp of panels on there - you can only get to close to the edges of the roof. I could have gone for a more standard efficiency panel and got (in those days the max optimal financially) 4kWp on it but I would have had a section of roof full of panels. In the end I went higher efficiency panels, smaller panels but an extra one, and still had loads of roof space.

Also on figures, bear in mind that the bulk of your financial savings will come from the PV. The battery will actually drag down the overall ROI figures.

Easy to work out potential savings on water heater diverters. Look at your summer gas (don't include your standing charge) usage (assuming your dhw is currently gas) for a month and think of 6-7 months of that will be your max saving that would be down to the HW diverter.

And finally, I see you highlighted guarantee. Looks to be only the panels - tbh they should pretty much have an indefinite lifetime. The items likely to fail will be connectors (if incorrectly fitted) and anything that contains electrolytic capacitors, ie the inverter. I ended up extending our SolarEdge warranty (with SolarEdge) from 5(?) to 20 years for a nominal charge.

 

[Glan gluaisne]

We're also looking at solar/battery options for our passive house design.

For those of us who are at home during the day, diverting excess solar to cars or hot water looks far more sensible and cheaper option than powerwall. Anyone doing this with 3-phase solar and ZAPPI/EDDI products?

What about micro-inverters?

Our passive house has a bit over 6kWp of PV. We can't hope to use much of this for around 6 to 8 months of the year, although we do run things like the dishwasher, washing machine and car charging when the sun's shining if we can. We also divert excess PV generation into heating our hot water, but at most that only uses around 9 to 10 kWh per day, most of the time maybe half that, so it doesn't really make a dent in the generation on a sunny day (we can generate well over 30 kWh on a good day).

Similarly, a battery system doesn't do much in summer, as the house just doesn't use enough electricity overnight at that time of year for there to be more than a few pounds a year saving. PV generation pretty much falls off a cliff at the end of October each year and doesn't really recover until about March, as shown on this PVGIS plot for our installation:

 

[sliyk]

I have gotten a few quotes and here is my (amateur) breakdown of what they offer;

Quote #1 Stratford energy

Sunpower MAX 3 400w (there is also the 325w but I would rather go for the most powerful one if I am going for a solar pv anyways so did not put that into consideration)
Cost of installing 12 panels and all the auxiliaries =£8006 (includes vat 5%)

Powerwall 2
Installation and all auxiliaries = £8995 (includes Vat 20 percent)

EDDI hot water warmer= £500

Grand total if going with this installer (minimum) £17501

Quote #2 Eco sunpower

Hanwha Q Cells Q Peak Duo G9 385W £1,486.99
Mounting System K2 On-Roof mounting for Tiled Roofs £780.00
Inverter SolarEdge 3680W Single Phase Inverter HD-Wave £804.00
Optimisers SolarEdge P405 Optimisers £547.20
Battery Tesla Powerwall 2 w/Backup Gateway £6,828.00
Electrical Circuit RCD, DC & AC ancillaries, Generation meter etc. 1 £240.00
Other Products: as specified 0 £0.00
product total £10,686.19


Services Design, Supply, Installation & Commissioning £2,065.00
Scaffolding /Netting & Access (assumed) £650.00
Other Services – as specified HIES Insurance Backed Warranty £75.00

services total £2,790.00

subtotal £13,476.19 VAT VAT @ 5% £673.81

GRAND TOTAL £14,150.00

 

[26ct2143]

I'm lucky enough to live on a farm and have 30kw of solar (7 yrs old) and 56kw (3.5 yrs old) combined heat and power unit (CHP).
I'm fairly convinced from a financial point of view that solar doesn't work out very well for house install.
The greatest consumption of power is in the winter, especially around 5pm, when solar does nothing.
Also with daylength short and sun low and raining all the time, solar does little from Oct - Mar.
I attach here my daily output for a 30kw system on spreadsheet, if your looking at 3kw or whatever, then just add a column next to mine and divide by the correct factor, 10 for 3 etc.
My panels are south facing (perfectly) and have no shading of any kind, but slightly flatter than optimal, this makes output (vvv slightly) higher in summer and lower in winter. (but vvv slight). They are washed every other year.

For info our farm house uses 25-30kwh a day currently (excluding power for the car), (less probably in summer)

For a house setup before going down the solar route, I'd look at a CHP unit, if your lucky enough to be on mains gas, you can make electricity from that and recover the heat to your housing heating. It definitely won't suit a lot of people, but should always consider options.

The farm CHP (bigger scale I know) is a 7 litre turbo gas engine running on wood chip(gas). It turns a generator making 56kw of electric continuously, the exhaust gases go through a heat exchanger and that makes 85kw of heat. Which is consumed by the house and sheds etc onsite.

There are available house scale CHP units using mains gas. Since you probably have a boiler anyway, consider a small CHP to generate electric and the heat is the by product used to heat the house. Could have the powerwall there to soak up excess for use later.
Downside will be changing boiler and possible lack of use in summer meaning not much electrical output.

I think unfortunately for solar to work well, you need a big setup to cover you for those crappy weather days/winter.
Also at farm scale it is very common to overpanel solar installs, so perhaps 40kw of panels on a 30kw inverter. This is because the inverters are expensive and panels not so much, but there are only a few days that 30kw of panels would output 30kw. Once the inverter reaches 30kw, if the panels send more power, it just ignores its and stays at 30kw.

Also some of you have the octupus low power price in the night. Maybe a powerwall (or 2) and charge at night and run on the electric from the powerwall in the day might work out better than money on solar?

Just my take on things, see spreadsheet below. had to zip as the forum doesn't allow xlsx files

 

[Gatsojon]

Here's my 2020 summary from a 5 kWp system installed at the end of January. 16 320 kW panels, 10 SE and 6 SW at 40 degrees incline in Manchester. I think 2020 was a good year generally for solar. Total Generation was 4,008 kWh for the year against a predicted 3,700 from the installers.

 

[Dilly]

View attachment 626635
Here's my 2020 summary from a 5 kWp system installed at the end of January. 16 320 kW panels, 10 SE and 6 SW at 40 degrees incline in Manchester. I think 2020 was a good year generally for solar. Total Generation was 4,008 kWh for the year against a predicted 3,700 from the installers.

Your graph is pretty similar. I have 10.9Kw PV mostly south facing with 20% west facing.
January is missing from my graph but adds 158Kwh to the total.
A good year but 2019 was better.

 

[sliyk]

There is apparently a 4 month wait for a powerwall

 

[PDB33]

Your graph is pretty similar. I have 10.9Kw PV mostly south facing with 20% west facing.
January is missing from my graph but adds 158Kwh to the total.
A good year but 2019 was better.
View attachment 626642

Does anyone have experience/expertise/advice on suboptimal roof orientations? I have a 50 m2 tiled roof orientated NE with slope 15 degrees (at this orientation better than 40 degrees, at least in summer). My objective would be to make some electricity, not ROI. Is it a non-starter?

PVGIS shows rather better summer output than I had expected but the reduction Oct to March is severe.

 

[sliyk]

I have hit a bit of a snag and wanted to get some general advice. Can you install solar panels on a property you bought using help to buy equity loan (not paid off yet).

Their website says the following.

Decorating, kitchen/bathroom re-fitting, solar panel installation or window replacements are not considered home improvements and are permitted without our approval.

But the above is under the heading
Conduct Home Improvements

Adapting your home for a disability.


All of it is really confusing. Who would install solar panels for a disability?

Are they allowed? I have spoken to two people in the HTB helpline one has said yes the other has said no. So confusing.

 

[tsh2]

On valuations, I bought a house with a 2013? PV system installed (paying £2000 per year in FIT), and disregarded this in the value calculation on the basis that I don't really know how long it will last before it needs maintenance. Plus its east facing and part shaded, so not really optimal. All the properties I looked at were different, but there didn't seem to be any premium for having panels (and I think this was the only one out of the ones we looked at that did).

 

[Obliter8]

I have been told that Tesla no longer handles the Powerwall process, they just handed off enquiries to the nearest installer. This is crap, as I'm part way through the process, and the installer they choose for me is useless at communicating. Seems like I'm done

 

[ACarneiro]

I had my Powerwalls installed by the people who installed my solar panels. I never spoke to Tesla, thank God, otherwise I’d still be waiting for a call back.
You could approach other installers directly?

 

[SpareHeadOne]

Whatever you decide to go for I'd definitely add an optimiser into the system because when just one or several panels in a string of panels is shaded, their output is diminished to the “lowest common denominator” of that string.

A power optimiser is a combination of both a string and micro inverter, it's a module-level power electronic device that increases the solar panel system’s energy output by constantly measuring the maximum power point tracking of each individual solar panel and adjusts DC characteristics to maximise energy output, so you get a greater energy yield even in cloudy conditions or when your panels aren't at the optimum alignment to the sun - such as early morning or late afternoon.

 

[ACarneiro]

Whatever you decide to go for I'd definitely add an optimiser into the system because when just one or several panels in a string of panels is shaded, their output is diminished to the “lowest common denominator” of that string.

A power optimiser is a combination of both a string and micro inverter, it's a module-level power electronic device that increases the solar panel system’s energy output by constantly measuring the maximum power point tracking of each individual solar panel and adjusts DC characteristics to maximise energy output, so you get a greater energy yield even in cloudy conditions or when your panels aren't at the optimum alignment to the sun - such as early morning or late afternoon.

That would very much depend on your setup and whether you are likely to have partially shaded panels throughout the day. It's not ALWAYS economically sensible to have optimisers (although I did have them installed in mine)

 

[SpareHeadOne]

That would very much depend on your setup and whether you are likely to have partially shaded panels throughout the day. It's not ALWAYS economically sensible to have optimisers (although I did have them installed in mine)

That's true, maybe I should have said that I would seriously consider an optimiser. I made an assumption that one would be suitable because it's listed on the first quote, which I also assume is based on a site survey.

That said, in my installation you can see the panels generating different amounts across the roof as the sun comes round during the day, so from April to September my yield is better before around 10am to 4pm than it otherwise would be - enough to run the house from about 7.30 in the morning until around 16.30 on good days.

Looking at my panel data, my lower generating panels at the edge of the system did 5.3-6.3 kWh each over the last year and my others did 8.9-9.4 kWh, without the optimiser they would all be at the lower end - my shade comes from nearby buildings and is limited to winter months when the sun is low, so I don't think it makes that much difference overall.

In reality I think it's safe to say that there isn't a one side fits all option, just a bunch of best guesses.

 

[ACarneiro]

In reality I think it's safe to say that there isn't a one side fits all option, just a bunch of best guesses.

Absolutely. Best option is to commission a couple of well regarded companies to make a proper assessment of the situation and propose a solution.

 

[MrBadger]

I somehow ended up on the Solar Edge installers list so got an insight into their target audience. Solar Edge is pretty good kit, I have it on my install, so I was rather disapointed to find that it was being pushed to installers as an alternative/upsell to a well designed installation.

Don't get me wrong, per panel optimisation (I'm not a fan of micro inverters on the basis of thinking that a dozen or so largely inaccessible inverters on a hot roof is really not a good idea) is great for tricky shading or orientation issues, but it was being suggested for situations where a decent installer could design the problem out to within a few % of optimal generation. The other disappointment was how the numbers for % savings were rather likely to be misleadingly used to give the impression that they were genuine boost in overall system performance rather than a % of losses recovered, ie different between optimal performance with no shading and the calculations with shading. Even more eye opening was how Solar Edge pushed their tie up with gen 1 (DC coupled) Powerwall.

tl;dr Make sure you get several quotes and if you have shading issues, confirm with the system designer how they are going to deal with the issues - many shading issues are mitigated against without needing additional cost of per panel optimisation.

 

[Glan gluaisne]

Same here, we had numpties pushing us to have optimisers on our 45 deg pitch, south-facing, roof, with no shading at all. The idea of having electronics under the panels, running at temperatures of 60 deg plus in hot weather, seemed bonkers to me. I took great care to install our inverter outside, on a sheltered north-facing wall, specifically so that it would run as cool as possible. The relationship between component failure and temperature is non-linear, particularly for capacitors, and dropping the operating temperature of an inverter by just 10 deg can double its service life.

I know that some of the optimisers have been specifically designed to deal with high temperatures, by using capacitors that have a higher temperature rating, but the warranty only covers the cost of the replacement units, I believe. The major cost will be scaffolding and labour, that will probably be several times the cost of a failed optimiser.

There is a case for them where there are shading issues, but a compromise that has to be accepted for an installation like this is probably a shorter life. Our inverter is now coming up for 7 years old, and probably has about another three years of life, in all probability. Changing it for a new one is maybe an hour's work, though, and requires no scaffolding, so would probably cost less overall than changing a single failed optimiser under a roof mounted panel.

 

[Dilly]

My original 28 panels don’t have optimisers though because of tree shading they would benefit. 4 strings of 7 isn’t the best arrangement.
The newer set of 13 are optimised and do work better.
Being on a bungalow roof, changes aren’t a big issue, when the time comes