Looking at real world examples it seems that the main problem (apart from the difficulties in construction) is the large swing in day/night temps. http://www-unix.oit.umass.edu/~caffery/greenhouse/performance.html They modified the structure and now ""We are very happy with how are greenhouse is performing. The longer term results: we've moderated the temps so that we the greenhouse doesn't get so hot (mostly because we added hens, and they don't like it hot). We still haven't lost any plants--including tomatoes--due to low temps."" http://www.ibiblio.org/london/renewable-energy/solar/Nick.Pine/msg00002.html A very good article on the progression from passive to active to agressive solar heating. Note again the problem with excessive temperature swings. http://www.ibiblio.org/london/renewable-energy/solar/Nick.Pine/msg00028.html ""I've rethought the problem you mentioned, that there may be a daily air temperature variation (delta T) larger than most growers can tolerate, in this solar-heated greenhouse design."" As for SHCS then that system is using the thermal mass of wet dirt. It could just as easily be pipes through water. However, if the SHCS greenhouse also used above ground water storage as well, a hybrid system would have kept the structure at 32F on the times when ""The gross response was such that we could have a 90 deg house when it was 95 outside and a 28 degree house when it was 30 deg below outside with the wind howling away."" That magical 32F. In a "phase change" type of system you would think they would have spotted that important point. The SHCS system emphasises latent heat of vaporisation, not solidification. And, from the world's expert in raising plants in an unheated greenhouse a realisation of the problems that have to be faced I present! http://forums2.gardenweb.com/forums/load/strucs/msg1108354418631.html "" * Posted by: Chris_in_Iowa 4b (My Page) on Thu, Nov 10, 05 at 21:43 I am all for starting seeds and growing them on to transplant size in a minimally heated structure in the spring. If you have minimal or no supplimental heating the biggest problem is it is TOO hot in there during the DAY. I say that because the temptation is to run the greenhouse as hot as you can during the day so as to store up enough energy in there to make it through the sub freezing night. This causes me to have major problems with "leggy" plants, too hot but not the corresponding intensity of light "" The "world's expert" comment was a joke.... :)

ok, if the 6 buck 30 gallon trash cans with lids are good, would they be any better with some type of material wrapped around them? Yes, I plan to recycle the water into the garden as dry periods dictate. Experiments? ok, I'll try it as soon as I can find enough wax for the right price. I guess a block of it could go into a 10 gallon glass aquarium that I have. That would be easy to move about into the right places with light. I'll put a thermometer on top and measure it at different times. The thickness would come to bear so if I can find the right supply place, I'll test different sizes and shapes. Anybody have more ideas for this unscientific experiment? thanks, ~Tom

SalmanBah- In a climate like yours, the main issue is killing the plants from too much heat. I live in a climate where the summer, outdoor temperatures only get to about 25C, but, even with venting, the greenhouse can easily get to 45C...which is a threat to many plants. In your country, you could get to much higher temperatures if the greenhouse was not well-designed. I don't have firsthand knowledge of greenhouses in Bahrain, but any greenhouse you would build there should have: 1) automatic roof vent openers, 2) one or more large volume fans operating on a thermostat, 3) a misting system on an automatic timer; and 4) shade cloth on the roof. What size greenhouse are you talking about, and what would you want to grow in it?

Thanks for your response Robert. I'm not looking for quantity in my GH, just quality and economy. Heating a GH with fossil fuels or electricity costs too much in my opinion. I only have 2 mouths to feed! I want to grow some lettuce and stuff for fresh salads, without worrying about salmonella. Use it for starting tomatoes, peppers, ETC. Extending some tender veggies later in the fall. When I was younger, and had my really great greenhouse, I had tomatoes almost year round. I had a tomato that lived for 3 years! It might have lived longer, but I had to move. I drove by about 6 months after I sold the house and the new owner had tore it down!!!!!! I felt really sad!