powering my desktop computer

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Hello. I was wondering if someone could make a general recommendation of thr minimum amount of solar panels and accesories I would need to power my computer and printer for 2 hours a day. Any advice appreciated. Thanks.

-- chaj (mac@ndre.w), December 21, 1999


It's emminently do-able. We do it all the time. However if it isn't planned right from the beginning you'll be disappointed. More info is needed but I'll take a stab at it....

First you need to analyze accuratly the amount of power you'll need. Having no idea what computer/printer/monitor you have I'll use my Win95 box for example.

The CPU of my homebrew 350mhz PII uses about 75 watts. The 17" Sony monitor on it uses 75 watts as well. It's hooked to an Epson 660 inkjet printer that averages about a 20 watt draw and a 5 watt speaker system. Total hourly power consumption will average about 175 watts, for 2 hours, 350 watt-hours. I'll divide this by the voltage (12vdc) and get roughly 30 ampere-hours. I''ll add another 15% for inverter/ battery inefficencies so we come up with about 35 ampere-hours per day to run this PC.

While you could run array direct it's better and cheaper to use a battery in the system. Actually a pair of golf cart batteries are almost ideally sized for this; they'll give you storage for 4 days of energy use at 35ah per day without draining the battery low enough to damage it and they're cheap.

Can you count on having sun? I can't. Many places a pair of 75watt panels would supply the energy needed sometimes but during cloudy weather, storms and the like you won't get it. I'd consider 2 solar panels marginal. 2-90 or 100 watt panels would be better (ignore the watt ratings of panels, look at amps). Ultimatly you need another charging source though. One option is your car. The charging system in it will charge batteries parallel with the vehicle battery (jumper cables work). This is wasteful of fuel but most folks have cars. I use a 5hp Honda motor mounted on a plate driving an automotive alternator. Windplants are also an option (such as the AIR403).

Here's an alternate though for you. A notebook computer might only use 30 watts, plus the example Epson printer, figure about 10ah per day for a couple hours computing and printing, probably less. Now you need one less panel, could maybe pass on the generator as well and the batteries would give you about 2 weeks use to a 30% battery state of charge (SOC).

Pretty soon you'd be using the power for other stuff...fess up! Electric light is so much better than candles or oil lamps (safer too). I'd get tired of cranking the Baygen so the radio would go online next. Also hate cleaning out my hand grinders after grinding coffee (coffee flavored corn meal?) so I have a Braun electric.

I've been living offgrid for a while. This computer is burning stored sunshine right now. Now I also use it for ham radios, the satellite TV, VCR, battery chargers, drills, etc. The stuff works very well but you have to plan it out to insure success. Also consider that you usually get what you pay for (if you're lucky). Don't expect decent power quality or long term dependability from a $40 inverter you bought at WallyWorld. But that's another subject.

You can do it and have all your needs fullfilled. We've published to how-to for 12 years now. There are lots of info files at our website and I suggest you download the file LOADCALC.PDF and study that for a good start.

The Good Stuff is at: http://www.homepower.com

-- Don Kulha (dkulha@vom.com), December 21, 1999.

Mr. Kulha

My profound thanks for your in-depth response. I thought there might be a way to get by with one 90 or 100 (thanks for the amp tip too BTW). This will be my most important prep item for the last week (besides filling my water "tanks"). Thanks again.


-- chaj (mac@ndre.w), December 22, 1999.

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