DIY solar heater - night heat?

[Naga]

I may get a small polytunnel or plastic GH at the end of the summer and wanted to heat it through the winter and saw some guides online using some plexiglass and painted black fizzy cans which seemed to work pretty well. The GH would probably be around 6ft sq.

Even though day time heating with this DIY solar doesn't seem to be much of a problem, my main issues would be with night time heating and also collecting enough sun on a cloudy day.

[john9159]

Whilst black objects will absorb heat from sunlight I also think the same objects will waste most of the heat into thin air and not benefit your plants.
Try getting an indoor camping heater for around £15. I got one the other day from B&M reduced to £9.99 as they are end of line items at this time of year.

[Olorin2001]

A while ago someone asked about photovoltaic's for greenhouse heating, here is the thread where you can read my responses. Thermal mass heating works but you need large storage and for such a small greenhouse, personally I don't think it would work, the surface area to volume ratio is too small.
http://www.growfruitandveg.co.uk/gra...ble_72173.html

[Naga]

Both interesting posts, thanks.

I might look into the indoor camping heater, was it gas powered?

[bazzaboy]

Naga, you might glean some relevant ideas from an earlier discussion which is at

http://www.growfruitandveg.co.uk/gra...use_30067.html

I think the key thing is to keep it as simple as possible. I can vouch that both the water-butt heat-sink and the black beer cans mentioned in that link do work in a somewhat uncontrolled hit and miss manner, even if there are disadvantages (e.g. a water butt or heat bricks etc inside a small greenhouse take up rather a lot of space, testimony to it being very slightly warmer might be indicated by an increased number of insects! ) In trying to be inventive rather than installing a costly all singing and dancing computer controlled thermostat heater/hydration system (which professional nurseries are likely to have) you inevitably remain at the mercy of extreme weather such as the minus 20C of a few years back, not much survived that onslaught. But given more reasonable variations with some advance planning you can at least keep some winter salad crops in a usable state.