Solar,
Thanks for the photos. Could you give some details on the exhaust fan set up, and the intake vents please. My high temp. this summer was an equal 112 F. so I appreciate the challenges. Also, what does the solar electric panel attach to? CR

My exhaust fan is really a mastercool wall unit that I intend to exchange the 120 v motors for 12 volt ones. The front vents are from Home depot and open outward as the cooler creates a higher air pressure inside. The solar panels when installed will connect to a controller and batteries to provide power.I have a patio roof handy just behind the GH to mount panels on and expect to run 4 100 watt panels, pricey but that will make the GH off-grid and low cost to operate I hope.

Solar,
What climate zone are you in? Mine is USDA 8, and the much more useful, Sunset zone 7. I currently use about 1500 watts to heat my 10 X16 gh in the winter, and would like to consider solar electric. Your 400 watt panels would help, but do you plan to also have grid electric or are you in a much warmer area? CR

Guess I am in 9??? I am in the Phoenix area. I am going to play with 12 v heat but don't have a feel for the total need yet. With a good battery bank, I should be able to handle all but the worst nights but that experiment has yet to happen. I just got the house up this month so don't have any history yet. I do know that some of my tropicals don't like it below low to mid 50s.

Solar,
By my probably inaccurate calculations, you are in USDA zone 9 (as you guessed), sunset zone 13. Not too far off my zone 8. One more question - what is the size of your GH? Based on my 10X 16 in USDA zone 8, I know from several years experience I need at least 1500 watts to keep the GH to 50 F. Based on my calculations, that much solar electric - panels, controllers, batteries, etc, would take about 40 years to pay for themselves. Since I will probably not be around in 40 years, I decided to so far go for grid. Have you done any similar calculations, or better yet, have any less expensive options?
Finally, if you supply the size of your greenhouse, the glazing material, the expected nightime lowest temp', and the desired inside temp. (50?), it is fairly easy to calculate how much heat you will need. CR

A 10 by 12 with a pool cover protected location so wind isn't much of a factor, standard HF twinwall glazing. My goal is more toward making solar the primary with grid backup. We take long weekends for now and I want the house to be self sufficient in the spring/summer/fall so we don't have to rely on neighbors. All our neighbors are snowbirds. I will spend money prior to retirement (9 months) to keep the rising cost of electricity down afterwards. I expect to have about 3K in greenhouse and solar but we know what a money pit they can be! :-)

You can find heating calculators on this site.
http://www.littlegreenhouse.com/heat-calc.shtml

Here is a link that might be useful: also cooling calculator

Has anyone got a value for pool cover insulating efficiency? I looked at the cooling calculator but that doesn't take the cooling effect of a swamp cooler into account. This counting in electricity thing could get a bit pricey!!! Time to add more panels and batteries but that cost lots also. Oh well, gas is too high to go anywhere anyways! :-)

Swamp cooling information below.
The solar cover is hard to say, At least a factor of 2 to 3. Depends on how much sun you get during the day and what kind of heat storage you have. Ex. -water barrels, rock, gravel or brick floor. Double or triple panels or single layer glass as I have.
If you read my page you will see I use very little heat and I am in a colder zone. I have bananas and elephant ears and lots of different gingers (which needs to go dormant to bloom).
I had kept my temps between 45-47 but it got to 35 a few times with no harm.
I have lowered my temps to below 45. Zone 9 should be no problem to heat to keep above freezing. Things still grow and my callas love the cool temps and bloom in Jan. MY blue sky vine also blooms in the winter.
Cooling is your biggest concern. A smaller greenhouse is harder to cool than a larger one. But easier to heat.
I can only keep my summer temp 10 degrees above outside temps with what I have now. So a few days it hit close to 110* in between misting times. Our humidity stays between 80-90 most days. That makes it harder to cool.
I am 10 miles from Lake Lanier, our main watershed. If you have heard the news this is the worst drought ever for Georgia. So I cut back on watering as much as possible.

Here is a link that might be useful: Swamp cooler

Cooling is a lot easier here where the humidity is often below 15%. The Mastercool I installed is very efficient and can cool the outside air as much as 30 degrees. The air exchange rate is the key here. Daughter lives in Woodstock?? Georgia so I hear about the drought. We are in the 8th year here and our average rain is about 7 inches per year. Somewhere in my distant memory when I had the retail tropical foliage house, I remember some tropicals that went permanently dormant below 55 degrees.
We see an occasional freeze but usually middle 30s is the low average with 28-29 once in a while. Guess I need to look into min temps for what is in there now instead of trying to maintain 55.