From Consumer to Producer

Phew! After months of thought and planning, our home Solar Electricity (PV) Panels are finally up and running – just days before the government halves the FIT (Feed-In Tariff) subsidy.

Choosing what to fit… and who to fit it

There are plenty of good online guides about choosing and siting your solar panels. To receive the maximum subsidy you can fit up to 4kWp of panels (about 20) – enough to fill the roof of a largish house. Obviously they have to be largely south-facing and unshaded for much of the day!

When I started to explore solar electricity, since it was a relatively new market I decided there was no substitute for learning from those with real-world experience. So this summer I attended an Open Eco Homes day organised by Cambridge Carbon Footprint which allowed me to go poking around several local homes whose owners have installed a variety of sustainable technologies including solar electric and solar thermal panels, super-efficient insulation, solar heat stores etc.  Not only did their generous sharing of knowledge teach me a lot about the practicalities of installing and living with solar, it also gave me some excellent pointers for trusted local installers and as a result I chose local Cambridge solar provider Midsummer Energy.

There are really just two more choices to make: your panels and your inverter which converts the panel electricity into 240VAC mains. Panels by known brands such as Sanyo are significantly more expensive, but might be more reliable, or at least you might have a better chance of come-back if they have a quality problem. After deliberation and consultation we decided they were not worth the premium – other less well-known brands have built a good reputation with installers. Because of some shading challenges, our panels were to be installed across two roofs, and on our main house roof we chose very black Sunrise panels which blend well into our black slate tiles, and on a less prominent roof we chose cheaper EGing panels with aluminium frames.


Sunrise panels with black frames

EGing panels with aluminium frames

The choice of inverter was more interesting, as we faced the common problem that our roof – although generally south-facing – is partly shaded during early morning and late afternoon. The trouble with this is that in a conventional installation all the panels are electrically wired in series, so shading of just a single panel significantly reduces the output of the whole array. It is also not widely known that inverters typically don’t last very long – 5 years is not unusual. I happen to know some of the people involved in Enecsys, a fellow Cambridge company who make micro-inverters which are placed behind every panel, and therefore don’t suffer from these problems, and was delighted to find that they are now in full production so we were able to use them.

A big side-benefit of the Enecsys solution is that the inverters all speak ZigBee to each other, and connect via a hub gateway to the internet. Sound familiar?! So you can see a live view of all your panels’ production at any time.


Enecsys inverters mounted per panel

Enecsys online interface

The day of installation

Thanks to excellent planning on the part of the installers, the installation process went smoothly. It started with the rather alarming (and loud!) process of hacking under the existing slates with a slater’s tool to cut the nails to get the first tiles out, after which others could be lifted. Then brackets were installed under the slates, then horizontal tracks put on the brackets, and finally the inverters and panels are bolted onto the tracks. This is then all wired back inside the roof to the generation meter and thence to the main house consumer unit (“fusebox” to you and me!). Useful tip: The very helpful electrician made sure we had access to separate meter “tails” for generation and consumption separately, so we can clip-on a current clamp (like the AlertMe one) to each one, and thus measure our net import/export status, to see when we are a net producer to the grid (a good feeling!).

Do solar panels really make sense in the UK?

Opinions are divided. On the one hand, thanks to the government’s feed-in tariff subsidy you receive a guaranteed, index-linked return of about 10%, which looks pretty attractive in the current dismal investment climate. But it’s a long-term proposition: it takes about 9 years to get your money back, then you should make a return for the remainder of the 25-or-so year lifetime of the panels. And of course that subsidy is about to halve, then in April things get more complicated as we move into Green Deal territory. If you can’t afford the capital outlay (about £3500/kWp today) then you could go for a “rent-a-roof” scheme, where you at least get cheaper home electricity.

On the other hand, if you’re seeking to use your cash to make the world a better place, then there are alternatives which have a higher “amount of sustainability per pound spent” than solar panels. In Mike Berners Lee’s excellent book “How Bad are Bananas” he calculates that every £1 spent on solar panels saves about 3kg of CO2 equivalent … compared with a whopping 330kgCOe saved for each £1 spent on a well-managed rainforest preservation program. But the verifiability of solar panels is perhaps higher. Also, in either financial or eco terms you’re probably better-off spending money first on really good insulation, and then on solar thermal hot water heating. In purely environmental terms, PV panels take 2-3 years to pay back their production cost to the environment.

But at least solar panels are a positive financial investment with a negative environmental cost, and there’s not a lot else like that about. And there’s a feeling that you’re a part of the future, and that by taking part you are actively helping to increase adoption and therefore decrease prices, and move the world faster into a future where they are commonplace.

Maximising your return

So you’ve installed your panels. Is that it? Increasingly no. The cost of panels is falling, as is government subsidy. But the cost of electricity imported from the grid is likely to continue to rise. There are three key numbers to consider:

  • Electricity imported from the grid costs about 13p per unit (kWh).
  • A solar PV home exporting to the grid only receives around 3p per unit exported (the grid costs a lot to run).
  • The Feed-in Tariff works by paying you for every unit generated by your panels, regardless of what happens to it after that, i.e. whether you use it, or it is exported to the grid. This payment is currently at 43.3p per unit, and is about to halve to 21p per unit.

Against a generation rate of 43.3p, the 3p you get paid to export electricity is almost insignificant.

But the generation subsidy is now halving to 21p per unit. And if you can use that electricity you’ve generated, you are also saving the 13p it would have cost you to import it. So the net effect of using your own electricity is 13p on top of that 21p subsidy. Quite a difference. The seesaw is starting to tip…

As solar subsidies fall and grid prices rise, the incentive to use-up every drop of your precious sun-juice grows and grows. Which means using electricity when the sun shines, which is of course during the day, when you’re probably out. Where can you put it? The best use of it is in things like running the washing-machine or dishwasher, or charging your car – things that only electricity can do.  A less good use is to heat things, including your home and your hot water. Heat is a much lower grade of energy than electricity though, so if you do much of that you’d be better off installing a dedicated solar thermal solution. Perhaps you can see some ways that AlertMe might be able to help you manage all of this!

The future

Solar panel technology is undergoing a renaissance: Triple-junction cells can now harvest almost twice as much electricity. CPV arrays use concentrating mirrors or lenses to capture more power. Innovators have even managed to print panels onto flexible surfaces at much lower cost. Several analysts believe that solar will achieve “parity” in 5-10 years, meaning that electricity generated in this way will cost the same as that generated by large coal-fired power stations. And of course that is the tipping-point to a sustainable world.

If you’re considering helping the world along by installing solar PV, a good independent overview of the Feed In Tariff can be found on the Energy Saving Trust website.