"Solar" Greenhouse: frost free in winter?

[BertieFox]

I thought I would share some details of my new 'solar' greenhouse, which I am just completing (see photo). It is based on a design I found on the Internet.
It faces south and uses twin wall polycarb panels steeply inclined to catch the winter sun. Ideally I should have used triple wall sheets but these were beyond my budget!
The back wall is built into a steep bank which gives it protection from the cold northerly winds, while the rear roof is metal panels but insulated with fibreglass and lined inside with wooden panelling. The ends are floorboard panels on the outside and more wood panels on the inside, filled with fibreglass for insulation.
There will be a 'heat sink' consisting of a line of old 20 litre plastic containers which will be filled with water, painted black, and stacked along the inside of the rear wall. I will put a shelf above these for the really tender small things.
There will be small electric fans above the two doorways (where there will be solid wood doors) to ventilate and let out any excess heat.
The main aim is to have somewhere where my tender shrubs and trees, like the guava, avocado and other sub tropical things can survive the winter. They make it through in another building which has walls on three sides and a polycarb roof but that is too dark and I needed something with more light. If the temperatures drop too far, and here we do often get minus 19 and 20 C, I will see if I can afford to run a small electric fan heater set to switch on if temperatures get towards 3 or 4C. I'm hoping as the place will be well insulated it shouldn't be needed much, but winter always brings those dull grey days where the sun won't get a chance to heat the place up.
I hope others are inspired to do something similar. I am going to keep the max/min thermometer readings to see how much heat it loses on the first cold nights.
Even if doesn't work, I will have a very nice melon house for next summer!

[redser]

That looks great Bertie. I've been scouring the net for free/cheap ways to heat my greenhouse so I'm interested to see how you get on.
I guess you could add another layer to the poly carbonate by taping on bubble wrap for triple glazing. And try get your hands on thick polystyrene boards for added insulation. On those really cold nights, chuck a tarp or large blankets over the polycarbonate panels, I've read of people doing that.
You can make hobo stoves and rocket stoves too which run for free if you can scavenge the fuel/wood or make newspaper bricks with one of those brick makers. Lots of videos on youtube.

[BertieFox]

Thanks for those suggestions. I'd thought about throwing a blanket over the panels on really cold nights but bubble wrap might be an easier option and is much lighter and easier to join into larger sheets (the total panel area is 15 sq m.

[Alison]

I always use polystrene boards on the bottom half of the vertical section of my greenhouse and bubble wrap above and it really does help

[Lazy Gardener]

I did wonder if a small compost heap would offer some heat, Maybe in a steel barrel so it can be
easily removed when the weather warms?

Would it work? Do they call them hotbeds where they have a compost heap under or around a plant?

[Olorin2001]

A larger thermal mass heat store would increase your chances of keeping the frost out without a heater. I use 1000 litre IBC's with a solar powered pump to circulate water through an external solar collector plate.

[Capsid]

A larger thermal mass heat store would increase your chances of keeping the frost out without a heater. I use 1000 litre IBC's with a solar powered pump to circulate water through an external solar collector plate.

That sounds really neat. Care to show some photos and where you get the parts from?

[Olorin2001]

Found the parts through eBay - 840L/H 1.1A 3M 12V DC 2Phase Brushless Water Pump F Car CPU Cooling SYS Aquarium - 16mm 25m LDPE poly pipe black, Garden irrigation, Hozelock compatible - I bought individual PV cells and soldered them together but you could source a ready made panel if your not fussy about a specific size and shape. Try youtube for details of how if you don't know how.

[Olorin2001]

Ibc

Just been out to try and get photos, it's raining, but I think you can see the basics. Had I been clever I would have thought of solar power and sunk the tanks into the ground while building the greenhouse, rather than cutting them down to fit under the central propagating bench. And I am in the process of replacing the HDPE tanks with ones cut to the same height as the cut down frames (that comes from accepting help from someone who thought he knew better than to follow my plan)
Get these tanks locally for £25 each, delivered free, but you can pay a lot more.

[BertieFox]

Wow! Those are impressive. My stack of 'bidons' look insignificant in comparison. Using a home made solar panel of some kind to warm the water is a great idea.

[rhonsal]

Really interested in the posts in this thread as i posted a similar at the beginning of the year and didn't get any responses

http://www.growfruitandveg.co.uk/gra...t=#post1084747

As i live in central Scotland i want to get heat in the greenhouse to as early in the spring as possible to get things going, but as i work away from home sometimes i need something that basically takes care of itself and cheap to run in the longer term!

[Olorin2001]

I didn't join until recently, but this subject has come up three times in the last few months, if you check back on my posts I seem to have comented on all occasions.
You might like to take a look at the only blog I have found time to write.
Solar power for a greenhouse is possible and works, but you have to do your maths about hours of sunshine etc. and you need a backup to the system for those days of extreme weather. A wood burner recycling scrap wood is cheap but involves regular filling up, Gas, either mains or propane involves less time and with thermostatic controls the costs are reasonable. Electric is only for those lottery winners.
If your good with DIY and prepared to do your research then a multiple input system works fine.
On youtube there are examples of what others have done, some even tell you about the mistakes they made along the way. One guy who impressed me did a whole series of videos showing the build from day one, if you have a few hours to spare on cold winter nights you might like to see just how involved the design can become. Geodesic Dome Greenhouse - Part 10 - ROCKET MASS HEATER - YouTube - this is one of the videos at the end of the series but from there you can find the first.

[Nicos]

Any updates on this Bertie?

[Bigmallly]

I thought I had seen an update Nic but you know how my mind works, I could be making it up.........

[BertieFox]

Coming up to a year since I started building my solar greenhouse. It worked wonderfully during the winter and never dropped below 4C, keeping my guavas and other tender plants frost free. Of course, this last winter was hardly typical so we will have to wait for some prolonged cold period to see how effective it really is going to be.

As for summer use, the steeply inclined panels seem to cut down on overheating in the summer even though the only ventilation is a door at either end. The light levels are perhaps less than I hoped though I am using it for melons at the back on a trellis and aubergines in front.

Not quite sure why but I am getting fewer pollinating insects getting through the doors and inside than I hoped, certainly compared to the polytunnel, which is probably why there is a bad set on the aubergines and fewer melons than I hoped.

It has been very sturdy in the high winds we have had, though it is against a north facing hedge and slope so quite well protected. I need to remake the doors as I skimped on the wood and used cheap pine which has warped. I will make some new doors out of planks or maybe pieces of polycarbonate panel with a wooden surround as I have done successfully on the polytunnel.