The Sunshine Year

So, we’re here at last. One year (and, if I’m being pedantic, a little bit) since we had the solar panels fitted to the west-facing roof of our house in Charfield, in the west of England. The roof was actually fitted at the start of December 2013, but I don’t think I’m going to worry about the tiny additional amount of generation that we managed in that commissioning period, and anyway it’s still the 30th December as I write this up.  I’ll just go read the tariff meter, which says 3545.98 kWh.

In comparison with the technical forecast from the IET Joint Research Centre we’ve done well, beating the estimate of 2980 kWh by a reasonable amount. One year can be better than another of course, but while 2014 beat a lot of weather records they weren’t all about the amount of sunshine! Let’s assume it was an average year for solar.

Screen Shot 2014-12-30 at 22.20.19Every month I’ve put up the generation graph, and here’s the graph for December.

One thing that pops out from the monthly graph above is how chaotic it is – the colder weather doesn’t mean a lack of blue sunny skies, and the panels are renown for working more efficiently in the cold. But the Sun hangs low in the sky and the solar energy doesn’t hit the panels at a good angle… Much of the energy is lost for the same reason winter is colder than summer.

But what you want to see is the year overall, which looks pretty much as you’d expect, peaking in the summer and dropping to almost nothing in the winter.

Generaytor 2014

Ok, let’s talk about the money then…

The solar installation cost £6250 last December, including the additional cost of the solar diverter. Ignoring inflation that’s the cost we need to recoup. The amount generated over the last year, 3545.98 kWh, brings in a cash sum which is a combination of the Feed In Tariff and the Export Payment. This is calculated below.

  • Feed In Tariff of £0.153 per kWh = £542.53
  • Export Payment of £0.0477 per kWh /2 = £84.57
  • Total cash payment for 2014 = £627.10

At the same time we have to estimate the reduction in our energy import from the electricity and gas utilities; the gas reduction being the direct effect of the solar diverter heating our water in the summer, instead of using the gas boiler.  At the start of this project I calculated our annual use for 2013 as

  • Electricity – 6300 kWh
  • Gas – 15000 * kWh
    ( * note: this is calculated kWh equivalent, not the units on the gas meter)

Checking the meters and calculating the use for 2014 we have imported

  • Electricity – 4490 kWh
  • Gas – 6300 kWh

And running a quick guestimate of the costs we have reduced our energy import costs by £586.40
Therefore it’s clear that the panel has paid off £1213.50 of that £6250 outlay, meaning it will be paid for in a little over five years. Since the FIT contract runs for twenty years linked to RPI, I think the project has worked pretty well!  Hypothesis proved, student passes with distinction, tosses hat into air.

On the way we saved a bit of greenhouse gas too. Or did we???

The consumption of the gas and electricity we didn’t use because of the solar panels amounted to about 2400kgCO2e, which sounds great.  But the solar installation had a production cost in carbon terms as well as financial, and there are ongoing debates about the carbon footprints of various methods of generation.

A 2011 parliamentary paper suggests that solar generation has a relatively high carbon footprint in comparison with other “low carbon” technologies such as wind, geothermal and even nuclear.  And given that my panels were constructed in China, one can reliably assume they were built using electricity from very dirty coal fired power stations.  Nothing is as green as it at first appears…

None of the currently available studies are conclusive of course, but perhaps in the end the financial gain was better than the environmental, who knows… best to simply use less energy per person, hey.

I’m going to stop boring you with the monthly updates now. Oh, if you weren’t actually bored senseless, please do say so in the comments. Ask questions too if you like. I’m no expert, but I kind of learned some bits along the way. The solar page will still be updated month on month though, so you can see how next year and those to follow turn out.

Happy and Hopefully Sunny New Year.

3 thoughts on “The Sunshine Year

Add yours

  1. Looking good- I assume your system is 4kw. Mine’s a south to south west facing 4kW PV system in North Wales; it’s been running for just over 3 years. First year generation was hampered as the inverter failed and needed replacing, so a week or so generation lost in a “peak”summer month. But the system nevertheless produced 3800kWhrs in that year. In each of years 2 and 3, outputs of 4200kW for each year. Very pleased, as the original certified annual output was estimated at 3100kWhrs, although the more accurate PVGIS anticipates 3450kWhrs. But still better in reality by just over 20%. The savings on electricity bill is not as good as anticipated, maybe 25% saving at best, but I do use electrical heaters, particularly on cold sunny days in autumn and spring (sometimes mid winter)from late morning to early afternoon – extended as days become longer. And using an electric immersion heater rather than gas (except in winter) has impacted on my gas bill – definitely lower but can’t say by how much. Oh! of course not forgetting the FIT which is on the highest rate, which will help pay back my initial capital cost of £12k just within 6 years – already 1/2 way there!


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