Low Voltage Living

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If you're just about ready to give up your power bill, maybe it's time to look into... Low Voltage Living

Do you sometimes feel as if you're at the mercy of your mailbox and the monthly utility bill it contains? You're not alone: Power company per-kilowatt-hour (kwh) rates are pushing up over 15e in some parts of the country-enough to suck better than $ 100 out of many people's monthly budgets-and there's not the slightest reason to suppose that we've seen more than the tip of this financial iceberg. Maybe it's just about time to abandon ship!

The alternative-a personal electrical system using a renewable resource-can offer you an insurance policy against the inexorable escalation of utility electricity prices. Researchers such as Hunter and Amory Lovins (see the Plowboy Interview in issue 88) have argued persuasively that investments in conservation and renewable energy are among the wisest that anyone can make. But there are other equally convincing arguments for making the move toward electrical independenceamong them, the personal satisfaction that can be gained by taking control.

The power grid that public-owned utilities and the government have supplied us with is a marvel of reliability. And the awesome size and complexity of that system make it hard to recall just how simple an electrical supply can actually be. But, in fact, a small, well-conceived home power station need be no more complex than an automobile's electrical system.

In the following paragraphs, we're going to give you an overview of what we've found to be the simplest, least expensive method of achieving electrical independence. We've been working with low-voltage, direct-current power systems for a number of years now and have found that they offer a practical combination of low initial cost, expandability, flexibility, simplicity, and reliability. For people on a limited budget who are willing to conserve, low-voltage living is assuredly the most sensible way to cut the utility umbilical.

WHAT IS LOW-VOLTAGE LIVING?

For our purposes, low-voltage means producing 12-volt direct current (VDC) and using it at that level whenever possible. For technical reasons, low-voltage electricity limits the size of a given appliance and the total amount of power that will be available in a day. Therefore, to keep the system simple, we've more or less arbitrarily decided that the largest 12-volt appliance we'll use will draw 150 watts and that the maximum amount of power that will be produced in a day is 3,000 watt-hours . . . or 3 kilowatt-hours (kwh). As you'll soon see, there are ways around both of these restrictions, but a low-voltage house hold will still end up being one that uses far less electricity than the norm of about 900 kwh per month.

Much of the margin between 900 kwh per month and 90 can be made up simply by not using electricity to power major heating appliances (a water heater, stove, or space heater, for instance). Solar energy is a good choice for water heating . . . gas or wood can be used for cooking . . . and passive solar heatingbacked up with a little wood in the stoveshould keep you comfy.. Those three changes alone will trim at least 500 kwh/month from the U.S. average. But before we get too deeply into how to use electricity in a lowvoltage house, we'd better figure out where that power will come from in the first place.

TAPPING NATURE'SPOWER SYSTEM

To a great extent, the alternative power source you choose will be determined by the resource you have available. As attractive as hydropower is in comparison with wind or solar, it requires that you have flowing water that goes downhill some distance. For those of you who have the luxury of choosing, the following chart sums up the relative advantages of each system, and should give you a basic idea of what natural and financial resources are required.

To withstand high-amperage 12-volt DC power, switches should be equipped with 47microfarad capacitors wired in parallel to tame arcing between the contacts. Use only snap (as opposed to silent) switches for DC power.

The success of your project will hinge on correctly estimating your renewable resource. With hydropower, you must accurately measure the fall and flow, and the volume of water must be figured at the hourly minimum to prevent installing equipment that will demand more water than is available. Average annual wind speed will determine the size of wind machine you need to buy. If your site has a 10-mph average, you'll need a 2,000watt plant, but at 15 mph you can get by with only 1,000 watts capacity. The number of photovoltaic (PV) panels you might need will also be profoundly affected by the area in which you live. In New Mexico, for example, 20 panels will provide 3,000 watt-hours per day, but 30 would be needed to do the job in overcast areas in upstate New York.

STORAGE

The weakest link in any low-voltage electrical system is almost always its batteries. Why? Well, usually because they're the wrong type for the application, they're improperly sized, they're poorly monitored, or they don't receive adequate maintenance. This information was covered thoroughly in TJ Byers' article in MOTHER NO. 74, page 114, but we're going to review a few of the key points again.

First of all, you must choose the right type of battery for your generating method. There are essentially three types: lead-calcium, leadantimony, and pure lead. Lead-calcium cells should be cycled through only about the upper 30°70 of their total capacity, which makes them suitable only for consistent power sources, such as hydro. Their advantage is that they're quite efficient. Lead-antimony batteries can be deeply discharged without rapidly degrading but aren't quite as durable as pure lead cells. Unfortunately, the latter are more expensive. Both of the last two lose some power just standing around waiting. In any event, you must not use auto batteries . . . heavy-duty, deep-cycle cells are mandatory for reliability.

What's more, a battery bank that's too small or too large for the generator output and your use will have its life span cut severely. Batteries are designed to be discharged and recharged at certain rates, and using or replacing too much too quickly will damage them. Likewise, a huge battery bank that's underutilized and receives only a tiny charge will deteriorate.

Monitoring and maintenance consist of checking the specific gravity of each celi once a week, keeping a daily eye on the system's voltage (which is an indicator of charge), cleaning the terminals whenever they become corroded, maintaining the fluid level, and providing a shelter where the temperature will stay between about 40 and 90°F.

The battery bank should be centrally located, to avoid long runs of expensive cable, and must be well-ventilated to prevent toxic and explosive gases from accumulating. If you have a remote point where you need powersuch as a well-consider locating a slave battery (or batteries) at that location. The amperage demands from a well pump are much greater than the peak charging current, so placing the battery at the point of use will allow the heavy current to be transmitted a short distance. The modest charging current can make the long haul from the generator or centrally located bank.

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