What's needed for small greenhouse power?

[Tweac-It]

Howdy folks

It's my first post here after many nights of skulking-around in the background, so please be gentle at my lack of full knowledge.

I am planning to build a small greenhouse (8'x12'x9'H) for growing veggies hydroponically. I know that I will be using a 5watt pump for my plants, running approx 8 to 10 hours per day. I am still trying to find an appropriate ventilation fan that is sufficient and, yet, low power consumption. Can anyone help me to understand how to plan PV needs vs greenhouse equipment? I was planning on building an 80 watt PV using 2w 6x6 cells and 2 12v deep-cycle batteries (am thinking about the LiFePo cells).

I hope to build something that can keep the greenhouse off-grid as much as possible, but if need be I can run an extension cord to keep my tomatoes alive.

Cheers,
Tweac-It

[Mike90250]

If you have grid power, that is the least expensive way you can run things.

Vent fans, generally only need to run while sun is out, so, batteries would not be needed.

If your hydroponics can last 18 hours overnight, you could simply run your pump from the PV too.

When you add batteries, you also need a charge controller, and your efficiency goes from about 75% to about 50%

If you must add solar power, follow the general outline I use here under Sizing and Recommendations:

http://www.solarpaneltalk.com/showthread.php?p=6604#post6604

to determine your loads, run time, battery size, and then solar. Add all the prices up, then price a 200' extension cord.

[Tweac-It]

Thanks for the quick reply

My "want" to build a PV is mostly to keep me busy (sorta like A.D.D. therapy for me..well...more like schizophrenic therapy LOL ). I don't really "need" to build one, and if you are suggesting that regular grid power is the cheaper option, then I would totally agree, but then it's just a greenhouse and not a "Green" greenhouse (male ego thing).

I also agree that the pumps/fans are basically going to be needed during daylight hours only. If I build a system that is devoid of batteries, I assume (and I hate assuming) that I will need my pump and fans to be 12V dc? Is there something that I can use to automatically switch to grid power when the sun doesn't shine on this dog's @ss, and vice versa?

[Mike90250]

I pressed the "quick reply" button, but a quickie is just not coming to me.

Most small 12V fans will start to spin around 8 or 9 volts, and a simple zener diode can clamp the voltage at 12 or 13V. But getting it all to switch to the grid on a cloudy day, is the tougher problem. Relays, zener diodes, all come to mind, but it would be a real messy thing. Maybe someone else has thoughts?