Unrewarding small-scale solar installation

InvertedVee

All of the new-build houses on our small development came with a small 1kW solar installation.

We moved in over a year ago and I've enough data to see that it's benefited us to the tune of a princely £135/year. That's £54 of earnings and £82 worth of reduced grid consumption.

The panels generated 900kWh over the year. We don't know how much we paid for them as that cost was hidden in the total purchase price. My hunch is that their lifespan might be shorter than the payback period. Still, we've avoided a small amount of carbon emissions I suppose.

It's a good lesson in the economics of small-scale solar PV, which aren't favourable in homes which have low energy needs like ours.

The sad thing is the roof could have probably accommodated a 4kW system that would have earned us another £400/year.

I receive 15p/kWh with the Octopus SEG, which is comparable with the rate for daytime import on Agile.

QrizB

InvertedVee said:

All of the new-build houses on our small development came with a small 1kW solar installation.

We moved in over a year ago and I've enough data to see that it's benefited us to the tune of a princely £135/year. That's £54 of earnings and £82 worth of reduced grid consumption.

The panels generated 900kWh over the year. We don't know how much we paid for them as that cost was hidden in the total purchase price. My hunch is that their lifespan might be shorter than the payback period. .

1000w of solar PV, as a retrofit, would cost maybe £1500. For a new build it should be cheaper as the scaffolding will be in place already and the electrician on-site, plus the installation will be part of the initial fit-out so no need to modify anything.

The lifespan of the system should be in excess of 20 years, although the inverter might need replacing once a decade or so. (Or it might not.)

At £135 a year, it will pay back in 11 years. Over 20 years it will earn £2700, equivalent to (if my maths are right) a compound investment return of 3%.

InvertedVee said:

The sad thing is the roof could have probably accommodated a 4kW system that would have earned us another £400/year.

Did you ask the builder if that was a possibility? It wouldn't have changed the economics much (payback might have been 9 or 10 years, adding 1% or so to the return) but if it was something you valued, it would probably have been possible.

Petriix

It's mind blowing that they don't just cover every new build roof with solar panels. As I understand it, the in-roof system are close to cost-neutral because you save on the cost of the tiles. 

Krakkkers

6 panels for 1kw ? only 166 kwp each.
Anyway its better than nothing and you can add more panels.

QrizB

Krakkkers said:

6 panels for 1kw ? only 166 kwp each.

I was wondering about that.

Zooming into the picture, the split across the middle is bright not dark (doesn't have a shadow) and there are only two mounting rails, not the four you would need for two rows of three panels.

I think it is more likely to be three half-cell panels, so 330 watts each.

Example here (so you can see what they look like):

https://www.solarelectricsupply.com/rec330np-330w-n-peak-solar-panel-wholesale-price

springswood

What I'm impressed by is that you got 900kWh over the year. That's about my total electricity use. 

InvertedVee

Did you ask the builder if that was a possibility? It wouldn't have changed the economics much (payback might have been 9 or 10 years, adding 1% or so to the return) but if it was something you valued, it would probably have been possible.

Yes, but were told that the construction was nearly completed so no further changes were possible.

InvertedVee

Krakkkers said:

6 panels for 1kw ? only 166 kwp each.
Anyway its better than nothing and you can add more panels.

It's an array of 3 Trinasolar 335W panels.

tim_p

Petriix said:

It's mind blowing that they don't just cover every new build roof with solar panels. As I understand it, the in-roof system are close to cost-neutral because you save on the cost of the tiles. 

It should be part of the planning permission (assuming local grid infrastructure supports it) along with rainwater harvesting. Same applies to all commercial development, retail parks, industrial estates etc. Max out the panels. 

[Deleted User]

When I raised the issue with my local developer his response was ‘buyers do not want to pay extra for solar, and mortgage lenders are not interested in financing large arrays on new builds’.

Robin9

Locally the mixed development has Solar on the Social Housing but not on the other properties.