Warm season crops will grow much better if you can maintain a minimum of 60F soil temperature. But you don't need to do it all courtesy of your electric bill. A black soil surface, black plastic or weed barrier alone or combined with clear poly over black will also heat the soil.

In your locale I think it may be possible. You will need a good air moving system to cut down the chances of disease due to moisture droplets just sitting on the plants and to vent out the heat. Lots of plants do better with moving air without the above considerations.If you look at local commercial growers you will see many of them with plastic houses set them up so the sides can be rolled up to allow heat and air exchange. In the summer your biggest challenge will be to vent the heat and a fan and open door may not do it, opening the sides might. You didn't say how long you wish to extend the season therefore if you wish to heat the house.You can find lots of info on four season gardening through books like Elliot Colemans where he uses hoops inside the GH over his plants to protect from the cold and extend the season.This might be an alternative to heating. You can also learn a lot of tricks by going to computer sites in the UK, maybe in Canada and Alaska,where the climate will not allow for warm weather crops to be grown outdoors with great success. Other then the heat issue they face similar challenges when it comes to bugs, disease, pollination etc as we do when working inside a structure. I'd encourage you to keep researching and give this idea a shot, sounds doable to me. Good luck, PQ

I find this very interesting. I am a novice at both gardening and the art of season extension. I had never even read the packaging on a solar panel until last summer so I am floundering with this technology - but it is so much fun. This is like tinker toys for adults! I have a small 6 x 8 palram polycarbonate greenhouse. It sits on a deck. I created a trough inside the greenhouse using 2 x 6's, a rubber liner and then topped it with leftover ceramic tiles that I had so that this square footage was still usable for plant placement. I then made myself a solar water heater with pop cans, paint, pvc, plastic, wood and which originally worked using thermosyphoning but I considered that too slow a movement so I added a small water fountain pumps run by a solar panel. It is direct connected - no sun, no heat, no movement. Sun out, the water circulates to heat up the trough. It is not a huge gain, but I don't pay for any energy to run this spring throughout the fall. I have bought a deep cell battery and have additional solar panels set up in preparation to store energy for after sundown use - not to operate the pump, but for lighting or to run an ozone generator from time to time. I did try to insulate some for the later fall season using Johnny seeds bubble stuff but there wasn't much use to this. I do have a natural gas heater but shut it down for February and most of March because my GH is too leaky and I see no reason to pay to heat the outdoors. I will take you advice and do a better job of sealing the GH this year. I am also building a cold frame and will be making bases for two small pre-fab cold frames. I plan to have these completed by the end of next week. Our ground is still frozen so I won't be able to properly prepare the area for these to fit over for maybe another few weeks. I am champing at the bit. Come on thaw! Thanks for sharing your ideas with us. I will be looking forward to your posts.

I got the full sized dome one on sale last year for ~$100 off regular price. Took me/us a little while to get it assembled (DH & I aren't so swift in the handy-ness category), but it seems quite sturdy and the plastic seems strong. One down-side is that because the shelving is secured together, it would take more than I'd like to do (and I'm not sure it's advisable anyway) to remove one shelf for taller plants. Some of the mini-greenhouses allow for shelves to be simply removed since they just lift off. Re how wide the shelves are, hmmm.... if I can remember tomorrow I can go measure them. But the big one is 5.5' across, whereas the half one is 3.5' across - I think I read that on a tear off sheet that Cdn Tire had for several of their models. Maybe 1.5'? More than a foot I'd say. The windows are manually zip-operated of course, and are sizable with screens when open. I didn't have it up early in the season last year, and have it located in a shady spot, so it's not really functioning as a "hothouse". I actually liked it very much as a "workhouse" for less than ideal weather. I don't seem to tolerate really hot (for us out here, lol) weather, so it provided a nice area to do some potting up or even sitting to read or eat lunch or drink tea! I have a rolling seat and a wee table at the end, and bring out a bag of books sometimes.... so pleasant (if no mosquitoes - can close the door though if so) under cover when it's raining or too hot/sunny, &/or listening to the birds. It didn't work to overwinter tender items like pelargoniums and begonias of course, and they got moldy since it's damp here. I forgot a favorite hat out there for a while and it got moldy too, dang. I need to experiment to see what will thrive in it... might be a good place to start/grow greens or cuttings that don't want the hotter sunnier part of the yard in summer. I had planned to move it to a sunnier part of the yard for the winter, but didn't end up doing that. Will see this winter. I think it might have said a 3 season greenhouse.... I'm not sure what season is supposed to be left out, but I presume winter for colder areas??? Or summer if too hot??? Didn't have any problems with wind, but we do have some protection with fences and tall trees and sheds. There are stakes to hold the plastic to the ground. I realize we're in different parts of the country and climates, but I think that on sale it's a very decent buy. Full price seems high but I haven't done a LOT of shopping around. They are much sturdier than many of the mini-greenhouses, but I do wish the shelving were more flexible (maybe there's a way I don't know). Hope this helps a bit; sorry for the long and meandering post but I'm sleepy now. Btw, re seedling protection from squirrels - have you tried sowing in 2- or 4-litre milk jugs (as often described on the Winter Sowing forum which I haven't found time to peruse much this year)? I love those (except for the appearance to others), especially as I'm not always quick to plant things out.