Archive for the ‘PV’ Category

pllWith the election looming, it’s time to nail your colours to the mast. Ain’t no purdah round here, so here’s my contribution…

If I were Secretary of State for Energy and Climate Change, my mission would be to put us firmly on the path to zero carbon heat and electricity. Only by doing this will we meet our legally binding promise to decarbonise the UK economy and mitigate the worst effects of climate change.

As you’ll see, I also wouldn’t get too hung up on where my remit officially stopped.

To get back on the path, we’ll need to radically improve energy efficiency, develop our ability to shift electricity demand, enable renewables to meet the bulk of our electricity requirements, and rapidly develop our district heating market.

First: ramp up energy efficiency


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Here’s the promo video for the Sol-evo PV carport we’ve developed over the last 3 years or so. One of several reasons why this blog has suffered! I try and console myself that at least there’s a good reason.

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It’s taken longer than I’d hoped, but here we go:


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The feed in tariff has arrived and my inbox is filling up fast with emails from companies selling PV systems making wild claims about payback periods and rates of return. Some of them are clearly from cowboys. Some of them are from reputable companies that (unless I’ve missed something or they’re temporarily insane) should know better. In this febrile flurry of market positioning,  PV may rapidly become the new double glazing.

I have to admit that I love PV. As soon as I got to know PV properly through some projects we’re doing in Italy, I fell in love.  PV is the business and I have absolutely no doubt that it’s a key solution to our long term energy needs.

But you’ve got to be realistic about costs and output. The UK isn’t Italy. As a result of years of domination by very few players, the UK PV market remains immature and install costs are high. In addition, (obviously) there’s less solar radiation so outputs are lower.

So what sort of IRR is realistic? I’ll go do some graphs now.

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As currently proposed, the feed-in-tariffs are likely to be the exclusive domain of the middle class with lower income households shut out from participating.

To prevent the FiT being accessible only to the middle classes, it needs to be set at a level that allows banks and private equity providers to step in and cover the capital costs of PV while sharing some of the benefit with householders.

In order to be attractive, the return needs to be between 7.5% and 8.5% (ungeared) depending on interest rate and how the FiT revenues are taxed. Some institutional investors say it needs to be higher, but if we stick to this figure we stay on the conservative side.

Taking PV as an example, the FiT as currently proposed would generate a 3-4% return in a mature market (e.g. £4700/kWp installed for a household system as we’re seeing in Italy). In a less mature market (e.g. £5.5k/kWp) the return would be 1.9%.

Looking at it another way, in order to achieve a 7.5% return in the real world based on the proposed FiT, the installed price of PV would need to be £3350/kWp! The other £1.35k is value shortfall (i.e. the difference between £3.35k and £4.7), which might be covered by an eco-minded middle income household but will certainly not be attractive to a low income household.

Bottom line: the proposed FiT for PV is too low. In order to provide an 8% return in a mature market (£4.7k/kWp installed for a small system), the FiT needs to be set at around 55p/kWh. For the largest schemes (>100kW), this would step down to 37p.

Sorry I’ve departed from my usual policy of putting all the underlying numbers up. The calculations are pretty straightforward but they require a spreadsheet and I don’t have a public facing version yet.

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homespun PV at Alex’s house

I spent yesterday at Alex Moody’s house (ex-colleague at XCO2) eating barbequed pizza (awesome) and wiring up a home-made PV panel from single cells (even better). Equipped with an almost-hot-enough soldering iron, I was a one man tabbing line while Alex put the wooden box together. When I left in the late afternoon, Alex took over and finished the lot.


This panel will one day power Alex’s LED-based garden lighting. Next steps are to get the string working with the charge controller and battery.

At Fontenergy, we’re doing some industrial PV installations in Italy. I’m really looking forward to seeing them up and running but I can’t help feeling that building a single 60W panel from scratch might be more satisfying (if in a slightly different way) than seeing a rooftop covered with someone else’s panels.

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Following on from discussion about planning reports last week, here’s a chart I put together showing roughly how much PV you can fit on a flat roof. It’s based on the formulas described by Volker Quaschning, the German Godfather of Sol (Thank you! I’ll be here all week. Try the crab).


The shading angle is the angle from the bottom of the panel behind to the top of the panel in front. As a rule of thumb, you can use the height of the sun at noon on the winter solstice – for London, this is about 15°. Utilisation factor is the ratio of panel area to roof area.


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