It's been quite cold recently barely managing to keep above freezing but yesterday the sun came out and it hit 50 degrees C in my Greenhouse at some point.
Thats not good either is it. It's a plastic greenhouse around 8 foot by 16 foot by around 6 ft 6 so while it has vents there is no way to automate the opening and closing.
I read somewhere about using milk cartons painted black to store a little heat, I did it with the black inside of a compost bag sellotaped to milk cartons and they do end up full of warm water
Theres also a suggestion of having a water barrel in the greenhouse to help absorb some of the daytime heat.
I do have a domestic thermostat which can easily be wired into a battery operated fan. this has a common and 2 outputs normally open and normally closed so can be used as a heat / cool activated switch. it'd also be relatively simple to hook up a solar powered battery charger (not a huge output but it was good enough for a radio when i was fishing).
what temperature range should I be aiming for in my greenhouse ? I don't think my seedlings will appreciate going from 3 to 50 degrees C in a day.