Friday, April 20, 2007

Solar Electric (Photovoltaic System) on a Limited Budget

Recently I mentioned that it is possible to build a photovoltaic (PV) system on a very limited budget. Here are some ideas for doing that, and some thoughts about how useful a small system can be.

PV System Diagram:

Because of the abundance of system components that operate on 12-Volts (charge controllers, batteries, inverters, etc.), choosing to build a 12-Volt DC system will result in the lowest overall system cost. By converting the DC voltage to AC and boosting it to 120-Volts, ordinary household appliances can be powered by the system described here.

Although lightning protection, fusing, and mounting hardware are not shown, this is a complete system, and a true bargain hunter should be able to put it together at a very low cost. The most expensive system component is the solar panel itself. Keep in mind that to get the most from your system, you’ll want to get the largest solar panel that your budget will allow. Here are a few options for the budget-minded:

Check ebay, flea markets, and your local newspaper for used panels.

Watch for sale prices, perhaps on discontinued solar panels. Websites are listed at the bottom of this article.

Purchase individual solar cells and build your own panel. For cell pricing and how-to information, click on the links at the bottom of this article.

If you’re lucky enough to find used panels at a good price, grab them. Since solar panels have a life expectancy in excess of twenty five years, you’re likely to get a bargain.

Solar panels can be mounted on a pole, or on a roof, as long as they are aligned perpendicular to the sun. Wood, or metal, can be used as a mounting structure or frame. Use wiring that is heavy enough to carry the expected maximum current. Ground the panels to protect them, and your other equipment, from lightning strikes.

If you’re starting with just one panel, the output of that panel will probably be below 5-Amperes in full sunlight. If that’s the case, you need not choose an expensive charge controller. As with the solar panel, you might find a bargain on ebay. If you choose to purchase a new charge controller, prices start at about $30.00. Again, check the websites listed below.

If you choose to build your own panels from individual cells, a 36-cell panel will produce the correct voltage for a 12-volt system. Wire individual cells in series. Larger cells will produce more current than smaller ones, but the maximum current will be no greater than that produced by the smallest cell in the series string. Stated another way; for maximum efficiency, all cells should be the same size. Be sure to do a good job sealing the assembly from moisture to ensure long-life from your finished solar panel.

Used batteries are available from several sources. You might check with your local telephone company for rechargeable deep-cycle batteries, or with any business that has a lot of computers. Batteries used in UPS systems are often replaced before they reach the end of their useful life. While you should use only deep-cycle batteries, you could actually use any lead-acid or gell-type rechargeable. You might get them from junked cars, lawn tractors, or motorcycles. With some scrounging, you shouldn’t have too much trouble getting more battery capacity than your small system can handle. Test batteries by charging them and by making sure that they are able to maintain their charge for several days.

If you happen to find several 12-volt batteries, you can connect them in parallel in order to increase the amp/hour capacity. By connecting batteries in parallel (positive to positive and negative to negative), the voltage does not change. As you search for bargain batteries, keep in mind that it is not a good idea to connect batteries of different types together. Connecting several batteries to positive and negative bus-bars makes it easier to isolate individual batteries, and therefore easier to identify those that fail in the future. Bus-bars can be salvaged from junk fuse boxes, hand-made, or purchased new from a hardware store. Check this blog’s archives for additional battery information.

The final system component is the DC to AC inverter. If your budget will allow it, choose a True Sine Wave Inverter big enough to handle all of the loads you’ll want to connect simultaneously. For example; two 25-Watt light bulbs, a 60-Watt TV, and a 35-Watt fan will result in a need for an inverter rated at not less than 145-Watts of continuous power. If budget constraints force you to settle for a Modified Sine Wave Inverter, the inverter store (link included below), has one for $25.00.

Using ideas presented here, you may be able to put together a 50-Watt system for under $200.00. If so, and assuming 4 hours of sunlight per day, your system should produce about 200-Watts of power each sunny day. That may not sound like a lot, but it can be a big help when the grid power fails. One 13-Watt compact fluorescent light will burn up to 13 hours on that. Or it could power a TV, a fan, and some light for several hours each evening. If your battery is oversized with respect to the capacity of the solar panel, you’ll be able to store up power to use when you need it. While it may take several days to fully recharge your batteries, perhaps you’ll have enough stored power to get you through a short-term grid power failure. An oversized battery bank is good to have in a weekend cabin or camper as well. Although it may take several days to fully charge the battery bank, your goal should be to have enough stored power to last for the entire outing.

Once you’ve experienced the benefits of a small system during an actual grid power failure, you’ll probably want to enlarge the system so that it can do more. If you use the system on a daily basis, you’ll notice a small reduction in your electric bill. Check this blog’s archives for tips and information.

If you choose to build a small system, please let me know. I would like to write about your experience in an effort to help others. Bookmark this blog and check back often.

Solar John

Purchasing New Equipment:

Building your own solar panels:


Patti said...

Reading your blog is the first time I've actually been able to figure out how to start putting my little system together - I can do it!!!
If you have time, could you look at the questions I posted on the NAWS forum?

Jason said...

Very nice post, I enjoyed reading it very much. I installed a small solar system that cost a TOTAL of $600 in my sisters off-grid home. Before this they didn't even have lights !!

Anonymous said...

It is useful to try everything in practice anyway and I like that here it's always possible to find something new. :)

Dominic said...

Thanks for the information, we will link to your article!

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New Solar Panel Technology

Thesolar said...

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Remi said...

I would like to congratulate you on the knowledge you've written on today. Thank you.