solar panel power generation 22 February 2022 at 1:46AM in Green & ethical MoneySaving 44 replies 1K views

Happy_Sloth

Hey all we've been pricing up a solar panel array. 

We've been given a quote this evening and i'll be honest i'm not sure the numbers tally up so id like a second opinion, mostly because ive seen a fair few people posting larger arrays that seem to generate less than it's been suggested we'd be able to get.  I totally understand that no-one can really know what we'd get power wise, but we'd be using the last of my husband inheritance to pay for it at a time we don't have tons of cash laying about, so im looking to figure out if this would be a good use of that money? As we've identified our energy usage is very high and only getting higher. 

• We have a large south facing roof, with no obstructions in the north west of England. 
• We use about 25 KWH per day which is about 9125 per year. 
• We use energy all day, we work from home and have the highest usage during the day. 

It's been suggested that we get an array containing 12 X 410 watt panels making a total of 4.92 KWH system and a 3.3KW battery. 

We've been told this should generate 7.183 KWH  of our 9125 KWH usage? At a price of around £11k? 

Firstly, does the expected power generation seem sensible? is that battery a good size and finally how's the price? 

Hexane

Happy_Sloth said:

but we'd be using the last of my husband inheritance to pay for it at a time we don't have tons of cash laying about, so im looking to figure out if this would be a good use of that money? 

No it would not. Start by establishing an emergency fund, perhaps 6 or 12 months' outgoings, put that somewhere sensible like Premium bonds.

Then work out how your state pension and other pension funds are doing.

If all of that is looking peachy, then you could maybe consider investing in solar panels as a long term hedge against rising energy prices. I have!

Happy_Sloth said:

It's been suggested that we get an array containing 12 X 410 watt panels making a total of 4.92 KWH system and a 3.3KW battery. 

What was the reason given for not buying a larger array? For example, 16 x 410 watt panels with a larger inverter? Just to give an idea, I have 23 x 315W panels.

Happy_Sloth said:

We've been told this should generate 7.183 KWH  of our 9125 KWH usage? At a price of around £11k? 

Firstly, does the expected power generation seem sensible? is that battery a good size and finally how's the price? 

I am no expert on batteries, I didn't buy one. Every time I see someone promise that you will generate a certain percentage of your existing usage, I feel suspicious.

You could ask your installer what the cost would be without the battery?

You could ask two other independent installers, perhaps local ones, to quote with and without a battery?

hosay299

Hexane said:

Happy_Sloth said:

but we'd be using the last of my husband inheritance to pay for it at a time we don't have tons of cash laying about, so im looking to figure out if this would be a good use of that money? 

No it would not. Start by establishing an emergency fund, perhaps 6 or 12 months' outgoings, put that somewhere sensible like Premium bonds.

Then work out how your state pension and other pension funds are doing.

If all of that is looking peachy, then you could maybe consider investing in solar panels as a long term hedge against rising energy prices. I have!

Happy_Sloth said:

It's been suggested that we get an array containing 12 X 410 watt panels making a total of 4.92 KWH system and a 3.3KW battery. 

What was the reason given for not buying a larger array? For example, 16 x 410 watt panels with a larger inverter? Just to give an idea, I have 23 x 315W panels.

Happy_Sloth said:

We've been told this should generate 7.183 KWH  of our 9125 KWH usage? At a price of around £11k? 

Firstly, does the expected power generation seem sensible? is that battery a good size and finally how's the price? 

I am no expert on batteries, I didn't buy one. Every time I see someone promise that you will generate a certain percentage of your existing usage, I feel suspicious.

You could ask your installer what the cost would be without the battery?

You could ask two other independent installers, perhaps local ones, to quote with and without a battery?

i would get some other people to give u a quote and see if u local council has any one as some do have 

QrizB

Hi Happy_Sloth, good to see you again.

Happy_Sloth said:

We have a large south facing roof, with no obstructions in the north west of England

It's been suggested that we get an array containing 12 X 410 watt panels making a total of 4.92 KWH system and a 3.3KW battery. 
We've been told this should generate 7.183 KWH  of our 9125 KWH usage? At a price of around £11k? 
Firstly, does the expected power generation seem sensible? is that battery a good size and finally how's the price?

That power generation number seems unlikely. The best you're likely to see in a perfect location in the sunny South of England is 1kWh of electricity from each watt of panel. The further north you go, the lower that number becomes.

There's a useful EU-run solar modelling website called PVGIS here. I don't know exactly where in the north-west you are but if I drop a pin in central Carlisle and model a 4.92kWp array, it predicts an annual output of 4360kWh.

That's an awful lot less than the 7183kWh your installer has predicted which makes me think there's a gross error somewhere.

Of those 4360kWh, even with a battery you are only likely to use 60-65% yourself. Call it 2800kWh used (in place of electricity from the grid) and 1560kWh exported (and paid under SEG).

Now for the man-maths:

• 2800kWh used @ 21p/kWh = £588
  
• 1560kWh exported @ 7.5p/kWh = £117

so:

• Total annual return = £705
• Payback period = 15.6 years, 25-year ROI = 1.9%

A 1.9% ROI is pretty poor. You would be considerably better off investing the money elsewhere.

ABrass

Happy_Sloth said:

Hey all we've been pricing up a solar panel array. 

We've been given a quote this evening and i'll be honest i'm not sure the numbers tally up so id like a second opinion, mostly because ive seen a fair few people posting larger arrays that seem to generate less than it's been suggested we'd be able to get.  I totally understand that no-one can really know what we'd get power wise, but we'd be using the last of my husband inheritance to pay for it at a time we don't have tons of cash laying about, so im looking to figure out if this would be a good use of that money? As we've identified our energy usage is very high and only getting higher. 

• We have a large south facing roof, with no obstructions in the north west of England. 
• We use about 25 KWH per day which is about 9125 per year. 
• We use energy all day, we work from home and have the highest usage during the day. 

It's been suggested that we get an array containing 12 X 410 watt panels making a total of 4.92 KWH system and a 3.3KW battery. 

We've been told this should generate 7.183 KWH  of our 9125 KWH usage? At a price of around £11k? 

Firstly, does the expected power generation seem sensible? is that battery a good size and finally how's the price? 

No. It doesn't seem right.
The battery is small, how much power do you use between say 8pm and 8am? I'd want a battery that can at least manage that.

In the UK one Watt of panels produces roughly one KWh of power a year. Your 4.92kW system will probably generate around 4700 KWh in total. You should check with PVGIS

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#PVP

It also seems expensive and that they quoted you the amount of power with no reference (apparently) to the amount you'd be using of that mythical 7kWh is suspect.

Get more quotes.

Edit: Ninjas by QrizB.

Merlin139

The figures quoted for production are to put it bluntly, F***ing Impossible!

First thing I would ask the installer is to get them to show you a similar installation giving that level of production!

Those levels of returns would require your system to be in Spain!

I get returns above 1kWh of Electricity from each panel and I am 300 miles north of the South Coast but I put that down to having Micro Inverters on each panel so when I get shading it only effects that panel and not the whole string.

You need other quotes and each one you get comeback with all the details. You will get lots of good, free advice from the people on these boards.

Exiled_Tyke

Merlin139 said:

The figures quoted for production are to put it bluntly, F***ing Impossible!

First thing I would ask the installer is to get them to show you a similar installation giving that level of production!

Those levels of returns would require your system to be in Spain!

I get returns above 1kWh of Electricity from each panel and I am 300 miles north of the South Coast but I put that down to having Micro Inverters on each panel so when I get shading it only effects that panel and not the whole string.

You need other quotes and each one you get comeback with all the details. You will get lots of good, free advice from the people on these boards.

For me, once a company has made one spurious claim then the trust is gone.  Run a mile and find someone who will tell it like it is!

1961Nick

It may be wise to discount that installer & look elsewhere because they've grossly exaggerated the generation, the likely consumption, & clearly can't be trusted. The price is also too high unless it's a particularly complicated installation.

For a typical property, £10K should buy a 5kWp array & around 10kWh of storage.

QrizB

QrizB said:

Now for the man-maths:

• 2800kWh used @ 21p/kWh = £588
  
• 1560kWh exported @ 7.5p/kWh = £117

so:

• Total annual return = £705
• Payback period = 15.6 years, 25-year ROI = 1.9%

A 1.9% ROI is pretty poor. You would be considerably better off investing the money elsewhere.

Sorry to quote myself, it's a bit narcissistic.

Energy prices are currently higher than the long-term average. Whether they'll stay that way is anyone's guess but I wouldn't want to plan a 25-year investment on that basis.

If we run those numbers using last spring's (more typical) prices:

• 2800kWh used @ 15p/kWh = £420
  
• 1560kWh exported @ 5p/kWh = £78

so:

• Total annual return = £498
• Payback period = 22 years, 25-year ROI = 0.5%

Effician

Happy_Sloth said:

Hey all we've been pricing up a solar panel array. 

 we'd be using the last of my husband inheritance to pay for it at a time we don't have tons of cash laying about, so im looking to figure out if this would be a good use of that money?

At a price of around £11k? 

Maybe a good time to go back to your debt free wannabe thread as i'm sure the experts on there could find far better ways of making use of the £11k you've just found.

QrizB

Effician said:

Happy_Sloth said:

Hey all we've been pricing up a solar panel array. 

 we'd be using the last of my husband inheritance to pay for it at a time we don't have tons of cash laying about, so im looking to figure out if this would be a good use of that money?

At a price of around £11k?

Maybe a good time to go back to your debt free wannabe thread as i'm sure the experts on there could find far better ways of making use of the £11k you've just found.

Good point.

Clearing the kitechen loan (5.2%) and car loan (4.5%) would be a much better ROI than solar, and would reduce the OP's outgoings by £325/month.