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Green Energy in the Greenhouse

By: Dr Gareth Evans - Updated: 4 Oct 2020 | comments*Discuss
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“Well, if you can’t be green in the greenhouse, what hope is there?” laughs Clare Miles – and she should know; that’s exactly what she and her husband David have started to do in their recently built, eco-friendly plant house in Scotland. As a keen gardener, a greenhouse was high on Clare’s wish list, but when they moved to their new house, it was instantly clear that it wasn’t going to be a simple case of down to the local garden centre and buying an off the shelf-kit.

“I had a greenhouse where I used to live, and I really wanted to get back to being able to grow things like that again, but our garden is a bit of a challenge.”

As she would be the first to acknowledge, that’s something of an understatement. Their garden lies across the road from their house, and for the most part it is on a slope so steep that the lower 30 degree section is the area they describe as the “flat bit”! The only truly level patch is a small area of patio behind a large wooden shed – and so that’s where they built their greenhouse.

An Unusual Design

It’s an unusual design. A lean-to, tucked against the sheltered wall of the shed, it has been laboriously constructed by the pair of them from scratch, from timber, glazed with horticultural-grade polycarbonate and then roofed with UV-stable corrugated plastic sheets. The shape of the existing patio constrained the width to a little under 5 feet, but by cleverly matching the slope of the roof to the pent of the shed, they’ve created a huge canopy that grabs all the light available and makes the inside feel incredibly roomy.

Power and Water

Without mains services, managing a greenhouse is a bit of a daunting prospect, but the Miles solved the problem; making sure they have enough water for their plants with a pretty smart arrangement of interlocking gutters which channel rainwater into a butt, with a second one to act as an overflow. Having no electricity, however, presented more of a problem, as Clare explains.

“I’d been used to setting my fan heater to frost-guard and pretty much letting it get on with things in my old greenhouse – and of course I used lights and timers too. We got a quote from the suppliers to bring power over, but it would have cost us about ten times what we spent on the greenhouse, so that was a complete non-starter! Then one of our friends – a bit of an old hippie, actually, bless him – suggested we went green.” They did, and despite a few minor setbacks, they’ve never really looked back.

Going Green

“We’ve heard all the jokes about trying to use solar this far north, but actually it can be amazingly sunny up here in the summer,” David explains “and there’s more than enough free wind energy come the winter, too!” The greenhouse now has solar lighting and solar powered fans to help stop things getting too hot – one of Clare’s favourite green gizmos. “It’s such a brilliant idea; they work hardest when the sun shines at it strongest, which is just exactly when you want the most ventilation. No batteries, no storage, just straight PV panel to fan and away they go!”

Perhaps the biggest green energy gain, however, came by simple accident; by building their greenhouse against a dark painted shed and over its traditional dark felt roof, they’ve inadvertently created a massive storage heater/radiator. The net result is that as the night cools down outside, the stored energy gently keeps the greenhouse warm overnight and the system begins to warm up again as soon as the sun rises. It’s meant that in spring the inside temperatures get warmer sooner, and they stay warmer later in autumn allowing them to lengthen their growing period, which is a major consideration this far north, where summers are noticeably shorter. It has also allowed them to grow some seemingly unlikely plants. Lemon trees, kiwi fruit and grape vines in Northern Scotland? Oh yes.

Future Plans

The project isn’t over, and the pair of them have some new ideas to try. “At the moment, if we need to heat the greenhouse in the winter, even just to keep off frost, it’s a case of burning paraffin. It’s our only option, but David’s been developing a way of turning wind energy straight into heat – same idea as the fans; when the wind blows strongest is when you really need the heat. No storage, nothing complicated, just wind to electricity to heat. He’s fairly hopeful it’ll do the business; to tell the truth, I think it’s the first time I’ve ever known him looking forward to the weather turning windy, just so he can try it out!”

They’re also working on an idea to humidify, irrigate and water-cool the greenhouse using solar power. David describes this idea as “top secret” at the moment – and he’s not giving anything else away about his plan – but if the rest of their green greenhouse is anything to go by, when he does eventually unveil it it’ll certainly be something worth seeing.

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As an addition to my previous comment I should mention that I also live in the north of Scotland and we have recently built a greenhouse out of recycled 15 pane glass doors - we built a frame from 4x4 which we sunk into the ground (because the wind gets very strong in that part of the garden) and it has a polycarbonate roof. I have all my compost heaps round there too so I am wondering if I can use the heat generated by those to warm the greenhouse. It regularly reached 30° on a sunny day (I have three windows at the front top which I open and a reclaimed sash window at the back for ventilation too) - I am in the process of painting the inside green to match the outside but am now thinking the back wall should be black to absorb the heat - I am looking into solar and wind powered options because I really want the greenhouse to be off grid. We have recycled guttering to attach to the back which will feed via a chain into an oak barrel - any help and advice on how I can heat this in the winter preferably using wind power (which we have a lot of) would be amazing!
Emma - 4-Oct-20 @ 10:54 AM
This article is brilliant and just what I am looking for - are Clare and David Miles still working on their wind powered heating project? I can’t believe it can’t be done and would really love to hear more about it - if you are out there Clare and David please please can you get in touch! ??
Emma - 4-Oct-20 @ 10:44 AM
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