The Greening of Hedgerley Wood

Please find us on our new site here:
http://www.hedgerleywood.org/category/greening/

Our first attempt at growing more of our own vegetables got off to a great start when Anuradha organised four raised beds in the sunniest part of the garden. But although planting happened in the Spring and the rabbits were kept off with netting, we were defeated by the weeds. Now Franny and Adam have come to the rescue and cleared the beds, adding a thick layer of our plentiful leafmold to try and hold back the weeds.

So now it’s up to us to make the best plan for planting in the Spring and then keeping our crops weed free.

Time to do the calculations again after almost 2 years of operation of the solar PV.

We’ve written to our suppliers to ask why last year’s output (1.5Mw from the top 16 panels) is 20% down on what they projected/promised.

What’s also puzzling, as you can see from this reading, is that even at noon on a day of full sun in August, the best panel is only producing 148w, rather than the specified output of 180.

Of course, maintaining our pool at all (originally a water tank) is hardly green. But given that mixture of indulgence and health rationalisations, has the enclosure we’ve now put up made it greener or not?

The enclosure came directly from the Czech Repubic in a giant Ikea-style flatpack. Phil put it together with a little help from me over a few days and it’s been in operation since February. I’ve been able to swim since the beginning of March, which will almost double the length of the old swimming season.

So what are the arguments on both sides?

Less Green:
1. We are putting heat into the pool for longer. The comes from the ground source heat pump and uses electricity from the PV panels and Good energy, which sort of counts as carbon free.
2. The enclosure had to be manufactured and driven from the Czech Republic.

More Green:
1. The heating going to the pool would otherwise be going to the house, so perhaps we can manage without that or use the wood-burning stove more.
2. We will need less heating in the old swimming months because of heat retention and solar gain.
3. We definitely save water because the pool is protected from debris. It was previously emptied every winter and sometimes in the summer as well.
4. We save on electricity associated with pumping and filtering to keep water clean.
5. Phil is now adding extra insulation around the pool which should further conserve heat.

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.