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Lead-Acid Batteries by Richard Perez
n 1970, we realized that our dreams depended on cheap land. The only desirable property Iwe could afford was in the outback. Everything was many miles down a rough dirt road and far from civilized conveniences such as electricity. The 40 acres we finally bought is 12 miles from the nearest paved road, telephone, or commercial electrical power. We were ready to do without. This is not, however, an account of doing without-- it is a story of having
one's cake and eating it too.
We solved the problem of the rough road with a 4WD truck and countless hours of mechanical maintenance. The electrical power problem was not so easy to solve. We had to content ourselves with kerosene lighting and doing all our construction work with hand tools. The best solution the marketplace could offer was a motordriven generator. This required constant operation in order to supply power, in other words expensive. It seemed that in America one either had power or one didn't.
We needed inexpensive home power. And we needed it to be there 24 hours a day without constantly running a motor. We decided on a 12 volt battery system. A lawnmower motor driving a car alternator recharges the batteries. To this we added a homemade control system. Later, we installed an inverter. We now have all the power we need, both 12 volts DC and 120 volts AC.
This information on batteries is based on my over 17 years of actual experience with battery based alternative energy systems.
The battery is the heart of all alternative energy systems. A battery is a collection of cells which store electrical energy in chemical reactions. Not all batteries are the same. They have evolved into different types to meet different needs. We are primarily interested in the true "Deep Cycle" lead-acid battery. This type is the most cost effective for home energy storage. In order to discuss these batteries, we need to agree on certain terms. The more we know about batteries, the better we can use them, and the cheaper our power will be.
Voltage is electronic pressure. A car uses a 12 volt battery for starting. This voltage is the addition of the six lead-acid cells which make up the battery. Each individual lead-acid
cell has a voltage (or electronic pressure) of about 2 volts. Commercial household power has a voltage of 120 volts. Batteries for alternative energy are usually assembled into packs of 12, 24, 32, or 48 volts.
Current is the flow of electrons. The rate of this flow per unit time is the ampere. A car tail light bulb draws about 1 to 2 amperes. The headlights on a car draw about 8 amperes each. The starter draws about 200 to 300 amperes. Current comes in two forms-- direct current (DC) and alternating current (AC). Regular household power is AC. Batteries store power as direct current (DC).
Power is the amount of energy that is being used or generated. The unit of power is the Watt. A 100 watt lightbulb consumes 10 times as much energy as a 10 watt lightbulb. The amounts of power being used and generated determine the capacity of the battery pack required by the system. The more electricity we consume the larger the battery must be. The power source must also be larger to recharge the larger battery pack.
Battery capacity is the amount of energy a battery contains. This is usually rated in ampere-hours at a given voltage. A battery rated at 100 ampere-hours will deliver 100 amperes of current for 1 hour. It can also deliver 10 amperes for 10 hours, or 1 ampere for 100 hours. The average car battery has a capacity of about 60 ampere-hours. Alternative energy battery packs contain from 350 to 4,900 ampere-hours. The specified capacity of a battery pack is determined by two factors-- how much energy is needed and how long must the battery supply this energy. Alternative energy systems work best with between 4 and 21 days of storage potential.
Home Power 1 November 1987
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