Design Help

Re: Design Help

Let's just look at the batteries needed for one fan @ 1530 Watt hours per day. Divide by 24 Volts (as that is likely a more favourable system Voltage than 12) and you get 63.75 Amp hours - call it 64.
At 50% Depth Of Discharge maximum, that requires 128 Amp hours of battery at 24 Volts.

To recharge that you'd need 12.8 Amps of peak potential current @ 28.4 Volts charging: 363.52 Watts.
Since panels don't actually produce their rated Wattage you have to factor that in: 363.52 / 0.77 = approximately 472 Watts of panels.

In terms of "harvest" you might expect those panels to produce up to 1452 Watt hours per day, based on 4 hours of "equivalent good sun" so you'd probably need even more panel to match the actual consumption. Using Icarus' famous fast formula: 1530 Watt hours needed * 2 = 3060 / 4 hrs sun = 765 Watts of array to account for all the losses inevitable in a system.

Those fans; 24" with 1/2 HP motors by any chance? They'll probably hit about 10 Amps on start-up, possibly more. Motors do not have a fixed run current and the especially don't have a fixed start-up current. Fortunately fans are easier to start than pumps.

So for three fans you'd probably want a 4 kW inverter at least. Plus a minimum of 384 Amp hours of battery and probably 2 kW of array to recharge them (with about a 45 Amp MPPT charge controller).

You can look at some of the different types and prices of equipment at our host's store, to get an idea of costs: http://www.solar-electric.com/

Re: Design Help

I don't think those fans are designed to be run directly from solar panels. You'll need batteries to supply consistent power and a charge controller to regulate the charging. If you want to use 24 Volt panels to charge a 12 Volt bank you'll need to use an MPPT type controller.

Time is a big factor here. One 40 Watt fan running 24 hours is 960 Watt hours. That's about 80 Amp hours @ 12 Volts, so would require at least 160 Amp hour battery to run it.
To make up for that 960 Watt hours you'd have to determine how much sun you can expect. You'll get a calculation like this: 960 Watt hours / 4 hours "equivalent good sun" per day = 240 Watts of panel after efficiency losses. Probably 300 Watt array. That also works out very close to providing the peak potential charge current for the 160 Amp hour battery (comes to 15.6 Amps by my estimation).

However, if you can't actually get 160 Amp hours of battery you may need to increase everything.

And that's per fan.

Re: Design Help

Sorry; the questions all start to run together after awhile and I get confused about which specific situation I'm looking at.

If the fan manufacturer says it can run off a panel they should also say how much panel.
Otherwise you'd be looking for something that could supply the roughly 48 Watts averaged over the daylight. That would likely be about 60 Watts of panel. It may be difficult to find one that meets that exact number, so you could go down a bit and possibly lose some fan performance or go up a bit and spend money on Watts you'll never use.

Note also that small panels tend to be quite expensive on a per Watt basis. I think your original plan was to run two or three fans? In that case running multiple fans from the same panel becomes more feasible financially. For instance two of them could be powered by one 135 Watt Kyocera which is less $ per Watt than two small panels. You don't want to go higher than that or you'll find you get "24 Volt" panels which will probably exceed the V-max for the fans.