Velutina

Pauly, you should be able to keep a greenhouse cool enough in full sun, even if it is 115 degrees outside. You will need to use shade cloths and some sort of misting/fogging system. Yes, this would be a little extra work in the hottest summer months, but the winter is when the real benefit comes in.

Lighting: Place the greenhouse where it will recieve the most light during winter months. This will prevent you from needing any supplemental lighting which are expensive to buy and run.

Heating: There are lots of ways to collect solar energy during the day and slowly release it at night. Probably the best way would be to have a large water tank that is connected to a solar water heater (the kind you see on roofs all over Vegas). At night, the hot water could be used to heat the greenhouse. A backup heating source should always be on stand-by.

You may even get a tax credit if you use the greenhouse to help heat your home.

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Adam