Solar installation feasible?

[spon88]

I'm keen to investigate solar panels and Powerwall. However I think we may be snookered as our house points pretty much W/E (actually 255 deg) and I'd always considered that this would not really be feasible. However, I'm seeing the "newer" tech actually might be OK with only around 15% power drop versus true S/N positioning. We get a lot of sun on the back roof in the morning and then through until late afternoon on the front.

We don't have any chimmneys or other shadowing obstructions.

Non-starter or worth a more detailed check please? Decent payback would be good but not absolutely critical.

What's a typical installation cost for "good" basic gear these days please - I'm aware that will vary but just to get an idea of budget.

Cheers

 

[HKP_Tom]

following (as we are due W/E!)

 

[MrBadger]

True south facing is a bit of a mis understood thing. Whilst it is potentially best orientation (slope makes a huge difference) for peak power, a dual aspect E/W positioning potentially gives a better peak energy install, especially if you can over install or give an asymmetric install in favour of the end of day where you are likely to have more usage. A battery install will help reduce that bias, but its not essential.

Most installs will use multiple strings, normally 2, so if running multi aspect, you need to make sure that all panels on an aspect are on the same string. Unless using optimisers or micro inverters, Solar PV output will be heavily influenced by the poorest performing panel, so if you have one panel partially shaded (even partial shading from a TV aerial or overhead wire is enough), or on a less favourable aspect, it will severely drag down the performance of others.

I've made my views on Powerwalls very clear in the past, and I know that many will disagree, but unless you have a very large non typical array, a Powerwall will never get close to paying for itself. I believe that in the future, battery installs will be subject to a mis selling investigation. Its very easy to highlight the cost benefits of a solar + battery install, when the reality is that most of that benefit comes from the PV install alone. I battery install must be looked at with how much energy it is likely to be able store/discharge over its lifespan, work out savings from that, then treat that as absolute maximum that you may never get close to achieving. A few decent (and some to avoid) alternatives to powerwalls also exist, look on non Tesla forums. Don't be taken in to thinking that bigger = better. A 4kWh battery is likely to achieve a significant amount of what a larger install will give, at a fraction of the price. And some will be modular so can be cheaply expanded.

imho

 

[spon88]

Very useful, thanks for that. So looks like it's worth investigating. I was considering a phased installation - so PV and then evaluate battery. Most of our electricity usage is during the day as we have a big home office with multiple PCs, 4K screens, UPS, NAS etc running. We do relatively little mileage and so charge the car maybe twice a week max. So simple white meter rate is OK for that.

I need to do the numbers but was thinking the PV might make sense to help cover some of the office daily load. Plus environmentally friendly, albeit our current mains supply is supposed to be 100% green.

I'll make some enquiries once we start to get some idea of when lockdown might be relaxed. Any recommendations for reputable installers would also be great please. Cheers!

 

[Dilly]

I have 33 south facing and 8 west facing panels (11.9 Kw total)
I have two Powerwalls with backup gateway.
The Powerwalls won’t payback in my lifetime but:
I can draw 10KWh from them and I don’t notice power cuts.
It allows what I generate to be stored and used Virtually without any draw on The grid between Feb and Oct.
I could if needed, even charge the M3 with at least 20Kwh from the Powerwalls

 

[spon88]

I have 33 south facing and 8 west facing panels (11.9 Kw total)
I have two Powerwalls with backup gateway.
The Powerwalls won’t payback in my lifetime but:
I can draw 10KWh from them and I don’t notice power cuts.
It allows what I generate to be stored and used Virtually without any draw on The grid between Feb and Oct.
I could if needed, even charge the M3 with at least 20Kwh from the Powerwalls

Very comprehensive. I don't think I'll be going to those lengths just yet but I'm keen to make a start

 

[MorrisonHiker]

You can use a site such as https://pvwatts.nrel.gov/ to estimate solar production. It's a pretty simple calculator that allows you to enter array sizes, orientation, angle, etc. and it even takes weather into account.

Our house faces southeast but we have arrays facing multiple locations, including northwest, so that we have all-day production. Of our 63 panels, 6 of them face east, 36 face southeast, 9 face west and 12 face northwest. The ROI on the panels facing northwest will definitely take longer than the panels facing southeast but they still help with our daily production numbers. We have multiple Powerwalls thanks to the Tesla referral program. They help greatly with our utility bills since we can send all solar production back to the grid during peak periods. Also, they are great for keeping everything running during power outages. We did an off-grid test and went over 200 hours (8 days) off-grid.

 

[spon88]

You can use a site such as https://pvwatts.nrel.gov/ to estimate solar production. It's a pretty simple calculator that allows you to enter array sizes, orientation, angle, etc. and it even takes weather into account.

Our house faces southeast but we have arrays facing multiple locations, including northwest, so that we have all-day production. Of our 63 panels, 6 of them face east, 36 face southeast, 9 face west and 12 face northwest. The ROI on the panels facing northwest will definitely take longer than the panels facing southeast but they still help with our daily production numbers. We have multiple Powerwalls thanks to the Tesla referral program. They help greatly with our utility bills since we can send all solar production back to the grid during peak periods. Also, they are great for keeping everything running during power outages. We did an off-grid test and went over 200 hours (8 days) off-grid.

Impressive! We are UK based but that site seems to recognise our location so I'll have a play. Thanks!

 

[MrBadger]

I need to do the numbers but was thinking the PV might make sense to help cover some of the office daily load. Plus environmentally friendly, albeit our current mains supply is supposed to be 100% green.

If you want numbers, there is a reasonable selection of monthly generation figures here Electricity Generation/Consumption Data Logs Also, worth a look at PV Ladder which will hopefully default you to UK systems where you can then start looking for more relevant sites to you.

We have a 4kWp install, we average 8-9kWh daily across the year (see below). PV systems, like batteries, will degrade, get dirty (doesn't make a huge difference) and (inverters) fail over time.

Our winter output is dire, we have a nice woody area of trees at bottom of garden, we also drop off earlier in the evening, as we are on a hill, so get a bit of late afternoon shading from the west. We are probably annual 10-15% efficiency down on what a peak system would do, but that seasonal, so winter 100% down (f-all of f-all is still f-all), high summer not too much. Worth pointing out, this April is exceptional PV wise and may go on to beat our all time April generation record.

Install wise, FiT scheme no longer plays a major part as it once did, but when it did, an average domestic PV install use to top out at 4kWp (there was a hard financial cutoff at 4kW) - typically 16 panels if you go counting panels on roofs - often 2 strings of 8 panels (the bit about split orientation I mentioned). Now FiT plays negligible part, the 4kW bit is no longer so critical, but the 16A export limit is. To exceed that, you need DNO permission and its by far a foregone conclusion that you will get it granted on single phase without very expensive kit to limit. The much cheaper solution seems to be sticking with a 16A inverter, but slightly overcooking the PV - maybe 5kW or a bit more. That flattens the curve and provides a small (20% or so) power benefit outside the peak window.

Putting @Dilly system into perspective, its 3 x a typical size that most mere mortals achieve. There are different rules for systems that size that simply do not work for smaller systems. Lets play fit a 10A charge under a (normally) rare generation curve. This one was 9% in 3 hours. Obviously a Powerwall will give a potential longer period, but so will a much smaller capacity battery. Again, worth reiterating, this April is exceptional, near perfect insolation curves such as this are a rarity over the course of a year. Don't go buying PV if you think performance like this is typical, it is not.

Finally! This graph below shows the potential for storing and using excess/exported energy. The numbers equate to around £250/year at 13.8p/unit or £100/year at 5p/unit. If you could store every one of these kWh, which due to storage and usage limits you will not be able to, this represents the maximum saving that can be made by storing free PV energy. On top of that, saving can be made at less sunny times, you can make additional savings by time shifting, say saving 9p/unit, but I'm yet to see that being any more significant when a significant amount of charge time can be achieved at 5p/unit without doing anything other than scheduling a charge. If you look at the battery at having a 10 year lifespan, hopefully a bit more, the numbers really do fall short on a typical Powerwall install. Something that some less scrupulous installers will mention.

PV and batteries is a seriously large rabbit hole. Once you go down, you may not return for a very long time.

 

[spon88]

If you want numbers, there is a reasonable selection of monthly generation figures here Electricity Generation/Consumption Data Logs Also, worth a look at PV Ladder which will hopefully default you to UK systems where you can then start looking for more relevant sites to you.

We have a 4kWp install, we average 8-9kWh daily across the year (see below). PV systems, like batteries, will degrade, get dirty (doesn't make a huge difference) and (inverters) fail over time.

Our winter output is dire, we have a nice woody area of trees at bottom of garden, we also drop off earlier in the evening, as we are on a hill, so get a bit of late afternoon shading from the west. We are probably annual 10-15% efficiency down on what a peak system would do, but that seasonal, so winter 100% down (f-all of f-all is still f-all), high summer not too much. Worth pointing out, this April is exceptional PV wise and may go on to beat our all time April generation record.

View attachment 535381
View attachment 535375

Install wise, FiT scheme no longer plays a major part as it once did, but when it did, an average domestic PV install use to top out at 4kWp (there was a hard financial cutoff at 4kW) - typically 16 panels if you go counting panels on roofs - often 2 strings of 8 panels (the bit about split orientation I mentioned). Now FiT plays negligible part, the 4kW bit is no longer so critical, but the 16A export limit is. To exceed that, you need DNO permission and its by far a foregone conclusion that you will get it granted on single phase without very expensive kit to limit. The much cheaper solution seems to be sticking with a 16A inverter, but slightly overcooking the PV - maybe 5kW or a bit more. That flattens the curve and provides a small (20% or so) power benefit outside the peak window.

Putting @Dilly system into perspective, its 3 x a typical size that most mere mortals achieve. There are different rules for systems that size that simply do not work for smaller systems. Lets play fit a 10A charge under a (normally) rare generation curve. This one was 9% in 3 hours. Obviously a Powerwall will give a potential longer period, but so will a much smaller capacity battery. Again, worth reiterating, this April is exceptional, near perfect insolation curves such as this are a rarity over the course of a year. Don't go buying PV if you think performance like this is typical, it is not.

View attachment 535383

Finally! This graph below shows the potential for storing and using excess/exported energy. The numbers equate to around £250/year at 13.8p/unit or £100/year at 5p/unit. If you could store every one of these kWh, which due to storage and usage limits you will not be able to, this represents the maximum saving that can be made by storing free PV energy. On top of that, saving can be made at less sunny times, you can make additional savings by time shifting, say saving 9p/unit, but I'm yet to see that being any more significant when a significant amount of charge time can be achieved at 5p/unit without doing anything other than scheduling a charge. If you look at the battery at having a 10 year lifespan, hopefully a bit more, the numbers really do fall short on a typical Powerwall install. Something that some less scrupulous installers will mention.
View attachment 535385


PV and batteries is a seriously large rabbit hole. Once you go down, you may not return for a very long time.

This is very comprehensive and quite eye opening, thanks. I need to do a lot more work on it but gut feel and initial inspection suggests 10+ years payback rather than 4 or 5. Food for thought and may not be worthwhile purely from a financial perspective. But I'll certainly look closer

 

[gangzoom]

Install wise, FiT scheme no longer plays a major part as it once did

Removal of the FIT scheme has really changed the financial numbers for solar PV. We are very very lucky our current house came with fully owned solar PV panels that were installed in 2015 which I didn't even think about till the solicitors were sorting out paper work, than add to that our PowerWall was a referral award from Tesla so our financial layout for solar + battery has been pretty much £0 - excluding buying the house and Tesla in the first place .

Looking at our solar PV which is split SW/SE we are getting about 3000kWh a year.

So 3,000×£0.14 for FIT generation payment than 1,500×£0.055 for 50% assumed export = £503 a year just from FIT, I have no idea how much the original panels cost.

Now our PW + EV pretty much means every kWh of electricity generated by our solar PV is been used, so if we didn't have either that would mean paying an extra £400/year electricity bill- assuming 15p per kWh and 10% losses.

So with FIT solar PV + PW we are 'saving' about £900/year in electricity bill. Given a PW install isnt far off £10k that's 11 year pay back just on the PW, not including cost of solar PV AND assuming FIT solar PV payments.

I suspect by the time you add in the cost of solar PV install, take away the guaranteed inflation linked FIT payment, the chance of making the numbers balance on a solar PV + battery setup = zero .

But there is something nice about seeing your total grid reliance been sub 1kWh for the week......I would say it's a priceless feeling, but sadly there is a very real price associated with it, we are just lucky enough not to have paid for it directly .

 

[markharro]

We have plans for a 12-14kw PV array and this is probably only going to be affordable if my ideas on sourcing cheap panels are realistic. For example, 2 pallets of these - 8.1Kw pallet of 30 x 270W JA Solar 270W 5BB Cypress - Polycrystalline - MCS approved - Cheapest New Pallet Option - come in around £5500. I have also been looking at SecondSol - Your marketplace for new & used PV products for used panels and some of their used panels are at very keen prices eg Solar Panel - CSG Solar AG - CSG 250 M2-35-1956x992 - 250Wp - Poly - Secondsol - 60 panels for around £3500 before delivery.
Has anyone got any comments on sourcing budget panels as it would be good to know I am not overlooking something?

 

[nightowl]

I have 4kW of panels split across both sides of the roof (facing E/W). I don't think I've ever reached 3kW peak power, but I gather I generate for more of the day as there's more coverage? For the past couple of weeks I've been generating almost 20kWh per day.

I've toyed repeatedly with getting a Powerwall. I love the idea of them, but several factors sway me away from them at the moment (mainly the price!) For now I'm sticking with an immersion water heater diverter and just charging my car when it's sunny enough that I'm not drawing anything (or very little) from the grid.

 

[im85288]

Without wanting to go into mega fine detail as others have already covered, my system is a 7.8kW split across east, south and west facing. From what I can tell this split gives the most “pull” time from the sun that is possible. The east facing gets the early mor ing sun, south the majority and finally west has the later afternoon/early evening sun.

What I’ve noticed (this is my first year of having solar) is my powerwall is usually full by around 11am. The hot water is then heated (using an Eddi) which completes by around 1pm. After that (given that it’s lockdown and the cars always fully charged!) the rest is exported to the grid, This continues until around 7pm...where the powerwall takes over and keeps everything going until the next day..where the pattern starts again.

I missed the FIT scheme but use Octopus Agile Export..as a rough guide between 3.30 pm and 6.30pm they pay roughly 8p/kWH the rest of the time it’s around 2-3p/kWH. Not much but I seem to be averaging about 20 kWh exported per day..which means that my export will cover the standard daily charge of 21p per day for electricity and leave a bit more to play with.

People who do the maths will most likely advise against a powerwall. I think it’s a necessity if your going for a PV array beyond the normal 4kWh...especially if you do not work from home to use the power it’ll generate.

 

[spon88]

Thanks for all the useful feedback. Having done a few more sums, I think I'll hold off for a while as the payback appears to be relatively poor. I love the idea of it but 10 years (possibly more) isn't great. Technology could improve and maybe incentives will return, so I'll certainly keep an eye on it. Cheers

 

[im85288]

Thanks for all the useful feedback. Having done a few more sums, I think I'll hold off for a while as the payback appears to be relatively poor. I love the idea of it but 10 years (possibly more) isn't great. Technology could improve and maybe incentives will return, so I'll certainly keep an eye on it. Cheers

Yeah makes sense, not something to get into if your goal is payback. Personally as a software developer I just had to have the powerwall/solar once I’d seen the app...and as anyone who has it will confirm..the tech is awesome!

 

[Dilly]

Without wanting to go into mega fine detail as others have already covered, my system is a 7.8kW split across east, south and west facing. From what I can tell this split gives the most “pull” time from the sun that is possible. The east facing gets the early mor ing sun, south the majority and finally west has the later afternoon/early evening sun.

What I’ve noticed (this is my first year of having solar) is my powerwall is usually full by around 11am. The hot water is then heated (using an Eddi) which completes by around 1pm. After that (given that it’s lockdown and the cars always fully charged!) the rest is exported to the grid, This continues until around 7pm...where the powerwall takes over and keeps everything going until the next day..where the pattern starts again.

I missed the FIT scheme but use Octopus Agile Export..as a rough guide between 3.30 pm and 6.30pm they pay roughly 8p/kWH the rest of the time it’s around 2-3p/kWH. Not much but I seem to be averaging about 20 kWh exported per day..which means that my export will cover the standard daily charge of 21p per day for electricity and leave a bit more to play with.

People who do the maths will most likely advise against a powerwall. I think it’s a necessity if your going for a PV array beyond the normal 4kWh...especially if you do not work from home to use the power it’ll generate.

I’d agree with that
Adding west facing panels to my south facing originals captures the last of the sun just as we start cooking and maintains what power is already stored
Adding a second Powerwall gives greater flexibility to the amount of power that can be drawn at any one time.
We’re retired, so we always using power in one way or another.

 

[Battpower]

this April is exceptional PV wise and may go on to beat our all time April generation record.

Yes! But then it makes you more depressed when the 'summer' months that you'd think should be good, are not!

I would like to challenge the benefits of battery storage though, as on the system I installed (not powerwall) I recon the money I spent on batteries is almost as worthwhile as what I spent on panels. I went with Solar Century tiles several years ago. Expensive but I was building new at the time and wanted that look. Roofs all face southerly so that was a benefit.

In total I have 9kwp now. 6kwp in 2 strings on a 5 kW (g83 for export on fit) lead acid battery storage inverter and 3kwp on a smaller 3.6kw zero export battery storage inverter with 4kwh lithium. Finally, I have a separate 5kw inverter, also non-exporting with 9kwh lithium which allows me to power-shift for running a 8kw heat pump or sometimes charge a car at 7.5kw. 2 years ago I had a year on Ebico Zero with 50p standing charge but free nighttime electricity, so having the non-solar storage made sense for those 12 months.

My system is not capable of running without a little tweaking to suit domestic use and weather, but for a large bungalow our total combined energy bill including 13k miles of driving is £600 for electric, £6-700 for heating oil and £200 for solid fuel less £900 FIT payment.

My big problem with having multiple batteries is making sure one battery system does start transferring energy from another, which tends to happen when there are sudden load transients.

But, this graph (which is from one part of the system) shows the benefit of the lead acid batteries. The batteries added about £5k to the system cost, but are allowing me to avoid exporting almost a third of the generated PV so are directly earning their keep, just like solar panels. Simply, for my system, spending up to a third of the system cost on batteries made the same sense as spending elsewhere on the system.

You can see how little I export (blue) and my whole design focus was based on using as much energy my self as possible.

The green is energy captured in batteries and used in evenings that would otherwise have gone to the grid. The batteries were installed in 2013 and are still giving virtually the same benefit as when new.

It is true that my system likely has more losses because of the inverters but overall it is making good sense. The really important time for me regarding battery cost was year 5 onwards, because then the batteries have already paid for themselves.

 

[Battpower]

Thanks for all the useful feedback. Having done a few more sums, I think I'll hold off for a while as the payback appears to be relatively poor. I love the idea of it but 10 years (possibly more) isn't great. Technology could improve and maybe incentives will return, so I'll certainly keep an eye on it. Cheers

There are always different factors for each installation, and it sounds as though for you, needing to have panels on two roofs is obviously an extra cost. As others posted, that potentially gives you a bigger potential benefit though. Since the price of the panels themselves has dropped so much, at least that mitigates the cost for you covering two different roof aspects.

If your car is available for charging during daylight hours, then having additional battery storage may be pointless as long as you can charge the car and use most of your PV energy directly. Finding a decent, trustworthy installer (I am NOT in the trade but did install my own system!) is the hardest thing.

My approach was to design the highest power system I could at the lowest cost, then look at how much value I could extract from it. I treated my roof area as my 'real estate' that I had to extract highest return from. Any costs I could directly transfer (petrol, heating oil, electricity) were all potential 'revenue' for my solar PV system.

I don't know if it's been mentioned in this thread yet, but 'diverters' are devices that avoid your exporting energy by turning on devices like immersion heaters. I would have probably gone with Zappi had it been available when I designed the system, which allows your EV charge rate to adjust automatically to exactly match your surplus PV generation. Some Tesla owners reported Zappi not working too smoothly for them, but I think software updates have largely sorted any problems.

 

[Tony Hoyle]

The more you can get the faster your payback is. Due to roof size we were limited to 2.5Kw and with FIT that's about £300 a year in a good year. Summer there's quite a bit over but spring/autumn/winter we're mostly importing (cloud cover will easily cause the solar panel output to drop 90%, and 250w generation is only about 1/3 of what the house needs).

Since that was an £8k system (you can obviously get them much cheaper now) it'll take 20-25 years to pay back.

If we'd been able to get 4kw (the average in the UK I believe) the payback time would have halved for not much more money - the cost of the panels is a fraction of the installation cost. At the silly numbers of panels I sometimes see quoted people are getting payback in 5 years or less.