The fan I am insterested in requires a 20 watt solar panel. The fan runs directly off this panel and as the sun increases the fan increases speed. It would be hooked up to a thermostat so that it wouldn't start running untill the greenhouse is a certain temperature. The fan is .7 amps when 12vdc is used.
A light would be like 130 watts 2.1 amps 12vdc
This is just a normal light, so I can work in the evening. It is not for the plants. I am sure I can find suitable lighting elsewhere because the greenhouse place only offers this light.
I would like the battery to store power for the lights and maybe something else like a small fan.
I understand that the solar panels are NOT cheap however I just think that buying them from a company that specializes in solar products, rather than greenhouse products, would be smarter. Then I can buy the fan and other special stuff from the greenhouse place. I really only want a simple setup and right now my main concern is ventilation so starting with the simple battery-less system is fine with me. I can always upgrade later. Ventilation is a necessity as other things, like lighting, are not right now.
I have always wanted a greenhouse however I don't want to use more power for it. I am trying to build a greenhouse so I can get rid of some of my light stands and save energy.
I think that also building the greenhouse with a smaller projection from the house would also save money (less air space to heat by the sun)
I haven't fully determined what to do for winter heating yet though. We use a pellot stove mainly and will be buying a second one this summer hopefully. Our current one doesn't have a battery backup. I think the heating situation really depends on how much it does actually cost to heat. The "greenhouse heating cost" calculators don't predict it will cost too much to heat but I really don't believe them that much.