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Posted by on Nov 10, 2015 in Articles, Energy, Environment, Others | 0 comments

15 in 15 Commitment 2: Solar so good

15 in 15 Commitment 2: Solar so good

Jaya Chakrabarti

Jaya Chakrabarti MBE

Vice President – Bristol Chamber of Commerce & Initiative

Just in case you missed part 1 of my commitments take a look at my first commitment.

We had intentionally borrowed extra on our mortgage so we could invest in solar panels for the new house. However, we were nervous about when to invest given the uncertainty in tariffs, efficiencies, brands and the number of solar panel companies bombarding our mail boxes with solar spam. It can be quite overwhelming and doesn’t help when making such a serious investment in your home…

So we were really happy when the council scheme folks were able to coordinate getting us an extra quote beyond the two we’d independently asked for from local suppliers. The scheme comes with additional supplier guarantees which de-risked the investment further and we were finally able to select a supplier to spend our cash with. There was minimal upheaval, the scaffolding went up in a weekend and the job was completed within a day. There’s something really lovely about knowing that we’re reducing our impact and making money at the same time. The returns are said to be between 8% and 10%, and our own (not typical) set up with the number of panels we commissioned (a 4KW system) would enable us to break even by year 7. It was relatively painless to see the money leave the account, and our house was looking shiny.

And because I’m a geek girl, I even have an app that connects to the data being transmitted by wifi to our network from our inverter, so I can tell you exactly how much cash we’ve generated overall, the CO2 savings and the power (0.89 kW in case you were wondering – it’s cloudy..). The app usability needs a bit of work but it can only get better, and the main thing is that I know when our peak is so I can set up our dishwasher to start at the best time.


Ok now for some figures. The average household uses between 3200kWh and 4600kWh per year. I think in our case, based on tech use, we would be at the upper end of that scale.

We spent just under £12k (inc VAT) for 32 panels (two sets of 4KW systems as we have an annexe for my parents on a separate meter so we did both at the same time). For the sake of providing estimates on a more normal situation (16 panels for a 4KW system) I’ll stick to figures for just our own house.

In the two (Summer) months we generated 980kWh on a 4KW system. Now of course we only use a fraction of the amount that our panel has generated thanks to the day jobs, but the rest does feed into the local grid and is already being used by local neighbours and businesses (effectively what we get paid the feed in tariff for).

In the quote we were promised a minimum of £889.29 income per year for a 4KW system, including the amount we save in usage. £511 of this will be (according to the estimates) what we get for our annual generation. According to our app, we’ve generated £120 of that in two months excluding the additional amount we get for just generating it (FITs mean you get paid first for how much you sell back into the grid at a decent price, and then again for the whole of the amount you generate at a much lower price). Whilst you’d think that summer months would generate the peak values, it turns out that panels are actually more efficient in winter if it’s not cloudy (hot days lower the efficiency of panels so actually we might in some cases be better off in the UK – imagine that!!).

Jaya Chakrabarti01

The picture above is courtesy of Bristol City Council with me looking happy and smiley thanks to a make-electricity-when-the-sun-shines sort of day. You can see our annexe panels in the distance on the left.

If you’re wondering about the future of the feed-in tariffs, then it will almost certainly be a blip until home batteries (check out Tesla’s powerwall and others!) kick into the UK market (they’re already on sale in the US). However, there are already exciting developments being tested at my old summer holiday employer (back when I was knee-high to a scientist), the Building Research Establishment in Watford, using special solar panels to pre-heat domestic hot water so that both electricity and heating are powered with the help of heat pipes just under the panels. I might just get in touch with them to see if we can spread some of that solar water heating love at our end of the M4…




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