The Greening of Hedgerley Wood

If you’ve been keeping up, you’ll know that Ardenham Energy have generously agreed to replace our original solar inverter, since the shaded panels were pulling down the performance of the whole array of 16. So in the pouring rain the scaffolding was put up again - amazingly in only about 3 hours.

Then the installers brought in the new magic boxes. They are micro-inverters made by enecsys. They’ve just been developed by the Cambridge-based firm and are being put into the first few houses in the UK on an experimental basis. The are mounted behind each individual solar panel and do their thing individually, so that the whole array will now work in parallel rather than in series. In time the idea is to build them into the panels themselves.

Being so new for the Ardenham Energy installers, they started by laying out all 16 and working out how the wiring should be done.

Then it was just a question of removing the panels, securing and wiring each micro-inverter and putting the panels back.

And while we had the scaffolding up, we installed a further four panels (using an old inverter), to take it up to the maximum of 20 allowed without a further licence of some kind.

Then the other magic box was put in place connected to our BT internet router.

This enecsys gateway reads the output of each micro-inverter wirelessly and then sends the readings to our dedicated web interface.

This was a really excellent bonus. The main display (which of course we can check from anywhere in the world) gives a real-time picture of the output of the array. In the first few hours of only patchy sunlight it recorded 2 kWh generated. And nice to see this expressed in all sorts of other ways - enough to power 22 light bulbs or 28 fridge freezers, or representing the same carbon savings as planting one tree or driving 5 miles. The money earned is wrong at the moment, but will actually have been close to £1 taking together the feed-in tariff and the money not paid to the electricity provider.

Then you can drill down and see the performance of each of the 16 panels. This is where the shading factor is so striking, with the output varying from 89 W for the best panel down to 9 for the worst, which was only lightly shaded. This was in weak sunlight, so it will be interesting to see how close the panels get to their stated output of 180 W.

Even more importantly we can now compare the performance of the new system to the previous one. Exciting day - and always a rush from being one of first kids on the block.

We received an invitation from the energy company Segen to visit a wind turbine that has been installed near us. I was particularly interested to see it and get some practical information, with the idea that perhaps we could have a turbine in the clearing at the top of our wood, if it were on a high enough tower.

This is a Gaia 133 11kW Small Wind Turbine of which has generated 23,600kWh within its first year with the NOABL windspeed of 5.1ms measured at 10m.

However, after just a few questions it became obvious that it was a non-starter for us. The engineer reckoned that to avoid turbulence (which would reduce the performance and the life of the turbine) it would have to be at least 200 meters away from any trees. Impossible for us.

It was, though, a chance to learn things I didn’t know. Like the fact that the turbine always rotates at the same speed, with stronger winds generating more power through increased torque. And that it includes an electric motor to kick it into this speed at lower wind speeds. I was also amazed at the complexity of the electronics needed in the control box at the base of the 18 meter tower.

We were so moved to come across this tiny piece of evidence that greening has its own power - in spite of everything. And reminded of the lines from Yeats:

While I stand on the roadway,

I hear it in the deep heart’s core.

As well as waiting for the new inverters, it’s clear that we can prevent a lot of shading by trimming a few of the trees.

So our friendly tree surgeons came in and cutting a few laterals opened up a surprising amount of sky.

We’ll start measuring the impact in conjunction with the new inverters in August.

To be sure that we are saving our 10% as part of the 10:10 campaign, we will have to factor in our total electricity use which is in any case too high. It looks as though the new PV will save us about 20%, but only for the second half of the year. And to reduce our emissions overall we will have to keeping looking at our other energy uses like the mileage on the Prius.

The first 3 days have been very sunny and have produced a total of 26 kWh. This seems disappointing and doesn’t suggest the system will achieve the promised results over the year.

Clearly shading from the trees is a major factor. The attached montage shows the shadowing against the output (on the main inverter only since the smaller one does not have a display) for each hour, plus 10.30 as the point where the output suddenly improves.

These results then sent me back to the original documentation from Ardenham Energy. The output they promised in their proposal letter was 2,448 kWh/annum. Whereas in the document sent after the commissioning this has gone down to 2,004 kWh/annum. Why such a significant change? This would seem to be a reduction of about a fifth in what we were expecting for the quoted price.

Ardenham’s reaction was very helpful. They looked into it and found that their original quotation had omitted consideration of the shading factor. Since we were not getting what we had paid for, they made a really good offer - to change the inverters to the newly developed ones when they become available. These prevent the shading of one panel pulling down the output of the rest, so should restore our promised annual output to 2,448. These new inverters will be available in August, so we shall see.

It seems all solar installation firms are very busy, and it was mid-May before Ardenham could find a slot. On day one scaffolding was erected on the whole length of the south side of the house. The plan was to put the 16 panels on the highest part of the mansard roof. The following day installation began.

Rails were fixed through the slates and the panels came with a clip-fixing system that make them pretty simple to secure to the rails.

The panels themselves are made in China and sold by Amerisolar. They have a capacity of 180Wp each.

It took until late on the third day before the last of the 16 panels were in place.

The electrical work had been progressing in parallel and we were all set for the moment of switch-on.

But it was too late in the evening and very little power was produced until the following days. Then the calculations could begin.

We’ve been thinking about the economics of putting PV panels on the roof, particularly to offset the power requirments of the ground source heat pump, which takes 2.8 kW when it’s running. Although we are getting this electricity from Green Energy who use only renewable sources, it still costs a lot and anyway the capacity isn’t currently there for the whole country to use renewables. So, a good idea but a pity it’s so expensive since it could help our commitment to saving 10% of our emissions as part of the amazing 10:10 campaign. We were also worried about the degree of shading by trees - more on that later.

What has suddenly changed the cost equation is the Labour government’s introduction of the Feed-in Tariff. This pays 41.3p for every kW we generate. What’s so amazing is that they pay this much (around 3 times the cost we buy it at) whether we use it or export it. So we have a double saving. It’s a no-brainer for middle class families that have the space and capital to invest in it.

So I looked around for a reputable installer, having heard there were a lot of pirates out there. I came up with Ardenham Energy of Aylesbury, who have turned out to be excellent. Following a site survey, they quoted £11,316 to install 16 panels with a total output of 2.88kW. This included the scaffolding and the rather complex electrical installation, since 2 inverters to be needed for this capacity.

Very important at this stage is their expert prediction of the likely annual output in practice. They estimated this at 2,448 kWhours. This would provide a feed-in tariff of £1,011, a saving of £147 and an export return of £37, making a total each year of £1,195. So the system would pay for itself in 10 years and provide this much income and savings thereafter. And of course it would be mean that a proportion of our electricity use would be entirely emission free.

The only snag that arose was the discovery that the current generation of inverters have the strange property that if even one of the 16 panels is in shade, the output of all of them is reduced. There is a new generation of inverters to avoid this but they were not available at the time.

So we accepted the quotation.

To the new Prius we’ve added excellent bike racks at only £65 each. They hold the bikes really well, so now we’ve been able to get beyond the impossible local hills to find some really nice cycle tracks. Feeling much better and a little fitter after this week’s eco holiday.

We’ve been keen for a long time to install a wood-burning stove to replace the old aga. The problem was always going to be the solid concrete chimney breast built in the 1930s. In the event it took two very persistent workmen from the Czech Republic most of a day the hammer through a big enough opening to the pull through the chimney lining.

It wasn’t until the second day that they managed to get it all installed.

Since then we’ve been only moderately pleased with this Clearview model. It’s heats this side of the house pretty well, but it uses more logs than we expected and it doesn’t seem to stay alight as it should when the vents are closed down. Maybe our chestnut, beech and oak logs are not ideal. Or maybe we have to learn more about the optimum settings. We’d been looking forward to coming down to a warm kitchen in the morning.

However, the ground source heat pump has performed heroically throughout this very cold winter and has kept the whole house really warm.

It’s a long story but at last we have gone for a Prius.

Ideally we would have liked an electric car and my researches at the motor show turned up a few possibilities:

But then I went to a really interesting lunch at the World Economic Forum in Davos, where the leading manufacturers were discussing their plans for launching electric cars in the next few years. What I picked up was the very strong advice that this was not the right time to buy electric - at least for a family car. The reason is that battery technology is evolving rapidly, so the plan for the future is to sell the car and battery separately - like a torch. That way batteries can be upgraded and even exchanged at future electric filling stations. But buying a car with a fixed battery now would render it unsalable in a few years. And it will be, by all accounts, at least three years before the new electric cars will be available in Europe.

So the best option for the next few years seemed to be the Prius, not only for the low emissions but also because I’d really enjoyed driving them in the States. Plus Andrew has one and is very fond of it. Second-hand prices turned out to be reasonable. And so far we are really delighted with it.