I put this think together this summer
in hopes that I could extend the summer just enough to get some figs this Year but I've noticed that it gets hot in the day time but at night its just like outside, same temp.
I even made this solar water heater to see if it helps
but the panel may be a little to small
I have insulated the North wall and I'm going to double wrap with poly
any ideas how I can keep this think above freezing in the winter
without having to run some sort of heater

Some pictures for you

that's the killer, where you are.  looks like you've done a nice job though.  i think you'll need a heater of some sort, unfortunately.  but i have no experience with greenhouses in areas that get genuinely cold.   i'm sure there are others here who can help.

in may area, i only need to get 15 - 20 degrees on the worst nights.  you've got to do a lot more than that.

Marjo, the solar heater is a good idea but you also need to store that heat so it can be released slowly at night. Lining the north wall with 55 gal black barrels filled with water would absorb and hold a lot of heat and release it slowly. If you fill them with stones and then water they would hold the heat longer. You could hook up a solar heater to each one and voila. Just my ideas. Good luck.

"gene"

Gene, if that is makeshift, I can't wait the pix of your "real" greenhouse when it comes along. My idea of makeshift was a plastic storage tub and a 25watt bulb. I found with mine, that overheating was an issue for all but a few nights, here in paradse. So mine quickly (day 2) got a shade cloth, and then a solid cover and shade cloth sides. They are great for humidity control (we have something less than 10% today), and mine has a single patio mister that takes care of the for me.

that's the dilemma i'm faced with.  when it's 70 during the day, and the sun is beating down, it will quickly bake everything unless you're there to open things up.  then the same night it will get to the 20's and freeze things to death.  so greenhousing is tricky, especially when you're not there to tend it.

i have found cylinders that will open and shut with the temp, they're hydraulic and need no electric.  that's what i'm going to try when i build a greenhouse/shadehouse next year.  or i guess i should call it a shadehouse/greenhouse.  i'll only have plastic on the sides for a few months during the year.  otherwise, it's just shadecloth.

Marjo,
very nice !
Here is a site that explains solar heating and how to do's with pictures.
I know didily squat about all this but it does look useful for someone that needs information, has pictures too. Table of contents is good place to start
.

Solar Greenhouse Resources

Best Luck.

Jon, ain't you lucky to live in almost paradise. I've been to your neighborhood a few years ago as I have a son that was living La Jolla but now lives in La Mesa right around the corner from you. We are suppose to visit there before the year is out. Hopefully we can hook up for some fig talk. When I build my dream greenhouse it will be to control moisture, like perhaps a clear plastic top and shade cloth. It will have open sides with trees planted on a hill to keep their feet dry. That way I maybe can stop splitting and souring my biggest problem aside from hurricanes.

There are doublewall plastic sheets (many different kinds and brands) that are sort of like corrogated cardboard, but translucent. They have a R value of about 2ish, which isn't huge, but makes quite a difference, and if you add some black plastic on top, in the winter, you get a lot of heating. Controlling heat loss through really tight construction  and elimination of drafts/leaks in important.