Solar Power Novice

I'm planning a Solar Powered system for a metal building in Tx. It's fully insulated, 40x50x12 with a 3/12 roof pitch. My initial task is to vent the heat out, now about 90 degrees inside.
I know about the solar vent fans. I think a 110 fan on an inverter will do a better job for slightly less money. I have on order a 15 watt panel and a chage controller. I have a 400 watt inverter with 10 volt shut down protection (alarm @ 10.6v.)
Im planning on starting with my good used truck battery (4 years old and 750 cca) and a new deep cycle battery from Wal-Mart also 750 cca.
The fan has a thermostat control. I also plan to use a simple wall timer to shut it off at night, and possibly intermittently during the day (if the batteries need a rest). I'm assuming the inverter can be continuous duty. I can grow the system by adding panels, (the controller can handle 105 watts).
I don't know how to figure battery life, and time to recharge.
Any information or advice is greatly appreciated!
William Utz
[email protected]


  • System2System2 Posts: 6,290 admin
    Re: Solar Power Novice

    I suggest that before you spend any money, you take some time and study many of the posts on this form and educate yourself before you purchase.
    The 15 watt panel you have on order, will put out less than one amp in full sun. Hardly more than enough to MAINTAIN a battery, and useless for recharging a battery with a daily load. No where near enough power to run an inverter with it's associated losses and a 110 volt fan.
    Also, mixing an old battery with a new one in the same circut will drastically shorten their lives.
    But don't give up - study, learn and then plan your system.
    Good luck.
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: Solar Power Novice

    I think your scheme would probably work, although you may be disappointed with the run time you get off a single car battery. It would seem that a 15W panel is not enough to run the system continuously, given the inefficiencies of using a charger and inverter.

    If this project has educational and entertainment value for you, then any adjustments will be part of the fun.

    But if all you really want to do is cool your building, you might consider some of those conventional wind-powered turrets, or passive ridge vents. And spray paint the roof white, or reflective silver. In an article recently in the local paper in Honolulu, there was a claim that you can save 11% of your cooling costs just by having a white roof.
  • System2System2 Posts: 6,290 admin
    Re: Solar Power Novice

    After installing an solar attic fan on my house this summer and seeing how efficient these units remove heat build up, I would highly recommend the simplicity of these units for heat removal. They come on when the sun comes up and go off when the sun sets which corresponds to the time that heat needs to be removed. Of course if you need to remove heat after dark, then some type of full blown solar system would be needed.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar Power Novice

    roderick is right, the wind powered ones are better unless you usually don't have wind. there's nothing wrong with using both types at the same time, but at different places on the roof. at least with the solar type you could wire some auxilary power to run it with a switch and a fuse inline.
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