Solar Panels

I'm still very interested in this, but the Govt's goal-post-changing has put us off so far.

Hi FB
I've had solar panels for 2 years. I don't have the sophisticated measuring system that you have however, mine is a pen and paper job at the end of the day. I've averaged out my output each month and can compare month by month. December is the worst month, followed by January & November; February and October are roughly equal and the other months are much improved.
For a 2.38 Kw system, I generate about 1670 kwh pa, which is more than I use during the year.
I'm happy but I agree, the winter output is insufficient for our needs. As a nation, we still need some form of generator other than solar or wind as these are too variable to be relied upon.

Yes, I had mine installed after the early-December cutoff, so I don't know what subsidy rate I would receive. The government has lost twice in the courts after its moving of the goalposts, so it looks like installations completed before 03rd March will probably receive the older (higher) Feed-in-Tariff (FiT).

The old FiT rate was pitched at quite a high level to get the industry on its feet. Since then, prices have come down, performance of components has increased - and so has the skill of the installers.
This now means that the older subsidy rate of 43p does look very generous and that the proposed FiT rate is actually a fairer rate, given that the FiT is only intended to help get the industry up on its own feet.

The 43p FiT was probably appropriate when it cost £15000-20000 for a big 4kW installation a couple of years ago, but now that a 4kW installation can be had for £9000-£13000 kind of price range, it is only fair that the over-generous subsidy is reduced.

The subsidy is paid out of other bill payers' bills, so we all want to see that subsidy come down as fast as possible, but not so fast that it stifles a budding industry before it is established.

There's a "return on investment" calculator here:
> Link <

The default price estimates are, in my experience, at the upper end of actual prices and reflect the cost of the highest quality systems with components made by companies such as Panasonic/Sanyo.

You can use the following link to get estimates of performance. I suggest considering using the PVGIS-CMSAF option from the two database options at the top, and even that may underestimate actual solar radiation by as much as 20%, according to a number of other solar panel results that I've seen (my panels are already at 117% of February quota with a couple of days to go - and others who I have spoken to agree).

> Link here <


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I paid £12,500 - but had a £2500 grant towards it. So net cost £10,000 for a 2.38 system. As you say, FB prices have dropped significantly in the last 2 years - I would have had more panels but couldn't afford them then.

What would I gain from estimates of performance when I can record daily output on the generation meter?
I know that my panels are not due south facing and that there is a bank and trees behind the panels which affects output during the winter months when the sun is lower. I don't know how these factors could be taken into account on these charts.

veggiechicken

If your panels are a couple of years old, it may be that their performance is not comparable with the more efficient modern panels. That's technological progress. That's what the FiT was intended to do; to keep the industry going long enough to promote advancements in technology, advancements in installation techniques and reductions in prices.

In a few years time my panels will also be dinosaurs, just like the computer that I'm using to write this reply!

The original government methodology for estimating performance was:

Roof pitch and facing of roof:
30' South = 1100
30' SE/SW = 1000
30' E/W = 900
45' South = 1050
45' SE/SW = 1000
45' E/W = 850

Shading:
None/negligible = 1.0
Modest = 0.8
Significant = 0.65
Heavy = 0.5

So my system would come closest to 45' SE = 1000
and no shading = 1.0

Multiply the two
= 1000

This is multiplied by the maximum output potential of the system (in my case 3.75kW)
= 3750

and this is multiplied by a constant value of 0.8 to give the annual generation in kWh
= 3000kWh

This is the estimate for my system, according to government methodology which is now two years out of date.

In fact, my system - and many other modern ones - appear to be about 20% above this.

So I would suggest that your system:

1000 for its pitch and facing.
0.8 for modest shading.
Multiply the two
= 800

Multiplied by your system capacity (2.38kW)
=1904

Multiplied by the 0.8 constant
= 1523kWh per year.

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A month-by-month breakdown, as percentages of the annual total listed above, would be, for my roof pitch and facing (and probably yours too)
January: 3%
February: 5%
March: 8%
April: 11%
May: 13%
June: 14%
July: 13%
August: 10%
September: 9%
October: 7%
November: 4%
December: 3%

So you might expect from your system, something like:

January: 3% of 1523 = 46kWh in the month (1.5kWh per day).
February: 5% = 76kWh (2.75kWh/day)
March: 8% = 122kWh (4kWh/day)
April: 11% = 168kWh (5.5kWh/day)
May: 13% = 198kWh (6.5kWh/day)
June: 14% of 1523 = 213kWh (7kWh per day).
July: 13% = 198kWh(6.5kWh/day)
August: 10% = 152kWh (5kWh/day)
September: 9% = 137kWh (4.5kWh/day)
October: 7% = 107kWh (3.5kWh/day)
November: 4% = 61kWh (2kWh/day)
December: 3%= 46kWh (1.5kWh/day)

Thanks FB. I have some projections from the installation company. I'll dig them out and see if I can compare them with these.
Comparing my actual output, the best months each year have been April, May & June with averages of 7-8kwh/day.
Its very satisfying to know that you are operating on home generated electricity on the good days!

...oh and the daily estimates are just averages, which are prone to considerable variation depending on the weather. The data showing from my panels demonstrates the wide daily variation in generation.
Bright sunny days can easily be double the expected generation figure, while rainy days can be less than half the expected generation figure.

I should be generating about 5.5kWh per day during February (closer to 6.5kWh as the days get longer at the end of the month), yet in the last week I have had rainy days as low as 1.8kWh and others as high as 13kWh when there wasn't too much cloud cover.

Panels are also especially affected by the amount of sun which shines directly on them; output can be about five times greater when the sun is in front of the panels compared to when the sun goes behind the panels. My panels, being SouthEast-facing, hit peak output around 10-11am, then steadily decline until about 2.30pm as the sun moves round the side of them, after which their output drops sharply to just a trickle by about 3pm.

Mine are SE facing too, at their best about 11-12am - so that's when the washing machine is turned on!

The projections will probably have been calculated using the same methodology.

It is quite nice to have power for free - so long as the weather is reasonable as so long as you don't turn on every appliance all at once!
However, there is the high initial installation cost (unless you have a "rent-a-roof" scheme, but that can be problematic if you have a mortgage or try to sell the house).

The bit I like most is that I am assisting a "green" industry to get off the ground (even though I have doubts that solar or wind are ideal solutions).
Although there is no obligation to provide performance feedback, I am keen to be part of an experiment on solar; I am happy to put my data for others to see and learn from because that's the way forward.

I believe there are others on here who have solar PV - it has been discussed before. I wanted to do my bit for the planet, so, while having my house extended and reroofed, I had the panels installed. Since then I've also had solar thermal for the hot water and an underground rainwater harvesting system for the toilets. Now I just try to be economical with my other resources.

Thanks for posting this FB. I was going to get solar installed, but my wife had just popped another markslet out, so we decided to hold off (and subsequently, as TS says the lower FiT put me off a bit). Now, I'm thinking of getting them leased [I'll be starting a new job with a green energy company shortly - which could help sway my decision]. For me, our usage is mostly during the day as we've two young children and my wife at home during the day - the washing machine for example is on constantly (re-usable nappies). My only concern is if we moved before the leased period is up, it may put people off from buying the house, if they'd have to be tied into the remaining lease period (and they either didn't want solar panels, or wanted to fit their own).

For me, £10k wouldn't be worth the outlay right now, especially as if we're moving (in what I hope is within 10 years). A few companies have said to us that you can triple the amount of money that you outlay in terms of putting value on your house (spend 10k, the house price can be put up by 30k) but to me, that's just sales guff.

I'd just want the free (or majority of) electricity during the day... whilst also doing a small part for the environment.

If I had the land (if my "life plan" goes to plan in other words ) then I'd have a small array of panels setup on the ground too.

my current neighbour wants us to put a wind turbine in a front garden that we share, but I'm not sure how the power would be split etc - not that I've looked into that yet.

We had them installed last October and are very pleased with them. Have rediscovered timers on various electrical items round the house so now run our washing machine / dish washer in the middle of the day when generation tends to be highest. Have had our first payback from our leccy company too which was very nice, not that high a sum over winter but still nice to get money back that route