Solar Panels for Dummies

wiggers

Screwdriva said:

These days, £7K gets you 6500-7000kWh per annum, depending on the roof. And that's including optimizers! At a blended .18p per kWh via Octopus Flux, you're looking ~£1200 per annum return on that £7K.

My roof faces ESE so not optimal. I used the calculator provided by Energy Saving Trust. We use very little during the day.

Screwdriva

Martyn1981 said:

Thanks Srewdriva. Just playing Devil's Advocate, assuming not the best deal, and not ideal generation (maybe off south or some shading), do you think ~5,000kWh's is reasonable?

5500kWh is quite conservative, assuming an E/W aspect. I just haven't seen annual performance lower than this in recent years, otherwise I would share it. 

Regarding degradation, any thoughts on UK levels? As I mentioned, I haven't seen any, and seem to get the same answer from other PV'ers on here and several RE forums. I'd be happy with 1%pa, so I'm very surprised to see pretty much nothing after more than a decade. [Another bonus is that my early panels had a -5%/+5% of nameplate rating, whereas now they typically seem to come with 0/+5%, but of course that wouldn't alter comparisons over time of the same panels. Just nice to get a few more Wp's on your roof than you thought.]

Appreciate your concerns about Chinese panels, and of course we can open up a can of worms regarding warranties, but these are often now around 10% to 15% total over 30yrs. I think an old NREL study had pre-2000 panels at ~0.8%pa and post 2000 ~0.4% - certainly looks like things are improving steadily this century.

The NREL study I shared was based in Colorado in 2021, using panels from the latter half the previous decade. This is the closest you will get to UK conditions sadly. For the panels I help others install, I have seen next to nothing (Eurener, Sharp, Sunpower, Solarwatt, Hyundai, REC, REA, Meyer Burger etc.) in terms of degradation. (Certainly zero measured degradation for my own LG bifacial panels). 

On the flip side, I've seen Trina/ Jinko etc. panels with burnt out or corroded inter-connectors that have substantially degraded. If you really want to be pessimistic, I'd use 0.33% p.a. Note that this will increase as Chinese panel brand penetration increases. 

Alnat1

The calculations show the price of a unit of electricity going up over the years but how would it look if the price remained fairly stable for the next 20 years?

With more renewables going live every year, isn't that what has been predicted to happen?

gefnew

This is the sheet i was presented with my quote.

wiggers

Alnat1 said:

The calculations show the price of a unit of electricity going up over the years but how would it look if the price remained fairly stable for the next 20 years?

Here's the calculation with zero price inflation:

Martyn1981

wiggers said:

Screwdriva said:

These days, £7K gets you 6500-7000kWh per annum, depending on the roof. And that's including optimizers! At a blended .18p per kWh via Octopus Flux, you're looking ~£1200 per annum return on that £7K.

My roof faces ESE so not optimal. I used the calculator provided by Energy Saving Trust. We use very little during the day.

Yep, ESE here too. I've been using PVGIS for estimates for over a decade, very accurate, but perhaps a bit pessimistic with the default 14% losses. Since 2011, our system has generated between 99% and 110% of target*. [ESE is about 86% of due South, about 80% for E or W.]

But a nice bonus for E/W roof setups is that they aren't as proportionately expensive as a smaller single South roof install. So you might get only ~80% of the generation, but can install twice as much PV, for perhaps 160% of the cost. Assuming of course you have the money available. Also gives nice generation through the day, but poor in the winter.

*But this year could be low 90%'s due to abnormally poor weather, and recent system upgrades that always seem to fall on sunny days and straddle weekends. 

wiggers

gefnew said:

This is the sheet i was presented with my quote.

There's a generous FIT, which makes it difficult to enter in the NPV spreadsheet. Also assumes 9% inflation in energy prices and RPI of 3.6%.

But their calculation ignores any interest you would earn on either the initial capital or if you invested the amount you saved.

Martyn1981

Alnat1 said:

The calculations show the price of a unit of electricity going up over the years but how would it look if the price remained fairly stable for the next 20 years?

With more renewables going live every year, isn't that what has been predicted to happen?

Same thoughts here. Hopefully the variable rate will fall back to about 19/20p as it was before the invasion of Ukraine, then just rise in line with general inflation, perhaps 1% or 2%?

Of course that will also mean that savings rates will come back down, with easy access perhaps 1% or 2% too.

I'd hope PV install costs will fall further, but the panels themselves are no so incredibly cheap, that even further cost reductions won't impact residential install costs too much.

However, great progress is finally being made on Perovskite PV. This is potentially dirt cheap, so even with the added complexity of combining with Silicon for a Silicon/Perovskite panel, the cost will hopefully not rise per Wp.* So we could see something like a 50% increase in panel efficiency from around 22% to low 30's with high 30's potentially possible.

That would mean ~50% more generation from the same roof area, for a 50% increase in the panel cost, but the rest of the costs which make up the majority of the install, not being affected, or only marginally.

*For instance a 440Wp Silicon panel of ~£80 may become a 660Wp Silicon/Perovskite panel for £120.

wiggers

Martyn1981 said:

Yep, ESE here too. I've been using PVGIS for estimates for over a decade, very accurate, but perhaps a bit pessimistic with the default 14% losses. Since 2011, our system has generated between 99% and 110% of target*. [ESE is about 86% of due South, about 80% for E or W.]

PVGIS gives a much lower generation than Energy Saving Trust! (2800kWh vs 3900kWh) Makes things much worse for me.

Martyn1981

wiggers said:

Martyn1981 said:

Yep, ESE here too. I've been using PVGIS for estimates for over a decade, very accurate, but perhaps a bit pessimistic with the default 14% losses. Since 2011, our system has generated between 99% and 110% of target*. [ESE is about 86% of due South, about 80% for E or W.]

PVGIS gives a much lower generation than Energy Saving Trust! (2800kWh vs 3900kWh) Makes things much worse for me.

That's weird, everyone I know (especially on the generation thread) use PVGIS and find it extremely accurate.

Did you perhaps enter the wrong orientation? ESE has an azimuth of about -70.

But as I said, should be about 86% of due south, for comparison.