Cottage Solar-Electric Systems, What is Requried?

May 5th, 2008 · No Comments

I am thinking about building a “Farmhouse Micro” office out behind my house, but the perfect spot is too close to the neighbor’s house to get a permit for a permanent building. The solution seems to be to build a “temporary” structure without permanent electricity, gas or plumbing.

This got me to thinking. What would it take to use solar power to run just a computer in a small disconnected house? So I did some research.

My Desktop computer is an Apple iMac with a big LCD monitor. The computer draws as much as 175 Watts according to How Stuff Works. They claim that a typical desktop computer with large monitor consumes as much as 250Watts.

The same article suggests that a laptop computer only uses 15W, clearly a better answer, but let’s roll with the desktop problem and see how it turns out.

To get a sustained 250W even when there is no sunlight (I am writing this post at midnight), you first have to take care of the battery storage problem. There are solutions available for Lithium Polymer and NiCad, but they are not readily documented online so let’s stick with regular, old Lead-Acid batteries. Every site I visited recommended sealed, deep-cycle batteries for this. Wholesale Solar recommends Interstate 220 aH batteries which cost around $250 each, and it looks like we will need 2 of them.

Cost: $500

Next we will need an inverter to change the DC power coming from the solar panels to AC for use by the computer, and maybe a low-wat LED light or two. There are a lot of these out there but the Outback VFX3524.

Cost: $2,000

The Charge Controller regulates the voltage and current coming from the solar panels going to the battery. solar panels can output more than the Voltage specified and a charge controller keeps the batteries from getting damaged. The Outback MX60 is a highe-end option and there are cheaper out there but let’s estimate high.

Cost: $600

The System Controller / battery monitor provides a digital readout on the system and battery performance.

Cost: $250

We will need a couple of Breakers, a temperature sensor, a breaker box and a variety of connectors and cables. Estimated Cost: $250, or $500 if you use an integrated enclosure like the Outback.

Cost: $500

For the solar panels we want to be a little more particular. Instead of using standard, rigid panel systems like the very popular Mitsubishi 125 Watt, 12 Volt Solar Electric Panel, (around $600 each), we will get a series of flexible panels and install them in the “valleys” of a standing-seam metal roof. There are videos around about this type of installation, but pricing is not available online. Since 20W flexible strips are listed for $300, it seems reasonable that 250W with a volume discount should be around $3000.

Cost: $3000

Total cost …. $6850 + installation.

Maybe running an extension cable from the kitchen is a smarter idea.

… or, if you just want to do it the easy way, Silicon Solar (and others) offer off-grid kits one that produces 495W costs about $6000 without batteries.

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