off grid system help..

Re: off grid system help..

Welcome to the forum.

What you really have to do is get some definite numbers for the loads. The amount of power you need to supply is critical to designing a successful system, no matter what size.

Some of the items you mention could be run directly from 12 VDC, but if you already have the adapters et cetera for 120 VAC it's probably easier to power up a small inverter.

You have two bits of information to hunt down. One is the peak Watts you expect to use: everything that will be running at one time. The other is the Watt hours you expect to use. If you already have the equipment (sounds like you want to be able to keep the gadgets running while camping) you can spend about $30 on a Kill-A-Watt and plug 'em all in through it and see what you get while running everything through its charge and operating cycles. My guess is the number will be quite small compared to the whole house figures we usually deal with.

Eight 12 Volt 5 Amp hour batteries? Not 50 Amp hour? Sounds like you got a deal on some used or close-out batteries. Trying to keep eight batteries wired in parallel balanced may prove quite a trick. A lot to go through for 40 Amp hours. Even so, that's good for around 240 Watt hours, not including system losses.

The eight panels at 120 Watts each should supply quite a bit of power - well more than the batteries can take. About 50 Amps of current at 14.4 Volts and potentially 3 kW hours per day, depending on circumstances. Again more than 40 Amp hours of battery will handle.

So get a fix on the loads. Then re-work the battery capacity as it is the heart of the system. Then you can see if you've got enough panel to recharge and what sort of controller you'll need. The load Watts will also help pick the right size inverter.

Re: off grid system help..

These power consumption calculations are based on the numbers provided by the manufacturer, right? The reason I ask is that 70 Watts is actually quite a lot for a laptop computer. Half that would be normal. But they will label things as 0.6 Amps and 120 Volts or such.

However, proceeding from that information we have only bad news. Take the fan alone: 120 Watts * 10 hours daily is 1200 Watt hours. That's about half of what I run the whole cabin on, with refrigerator. The LCD screen (if 150 Watts can be believe, which it probably shouldn't be - again just numbers on the power supply) for 10 hours would be another 1500 Watt hours. If you run the two laptops @ 140 Watts for 8 hours that's another 1120 Watts. Do you see where this is going? Trying to supply 3.8 kW hours per day is a daunting task, and it likely isn't the right target number.

That is why I suggested the K-A-W meter so you can gets some real numbers. The maximum Amps at Voltage stamped on equipment is rarely accurate. It's frustrating, I know.