Creating a sustainable energy source for your home or business starts with a good understanding of power conversions and ends with a plan to build your power system.
http://www.powerstream.com/Amps-Watts.htm
So, let's go through how to apply this information. I have a power drill that uses a rechargable battery. On the charger, it reads 18V/DC charger. The details show "output 21 Volts to 500 mA" = 10.5 watts output for the charger while it is running.
The key measurement for power production is Kilowatt hours. The kilowatt hour, or kilowatt-hour, (symbol kW·h, kWh) is a unit of energy equal to 3.6 megajoules. Energy in watt hours is the multiplication of power in watts and time in hours. The most common use of the unit is when energy is delivered by electric utilities to consumers. In this case electricity use is usually billed in kilowatt hours (kW·h, W h): 1 kW·h = 1,000 W·h.
More examples:
A heater, rated at 1,000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3,600 kilojoules) of energy.
Using a 60 watt light bulb for one hour consumes 0.06 kilowatt hours of electricity.
Using a 60 watt light bulb for one thousand hours consumes 60 kilowatt hours of electricity.
If a 100 watt light bulb is on for one hour per day for 30 days, the energy used is 100 W × 30 h = 3,000 W·h = 3 kW·h or 10.8 million joules.
The key consideration when creating a sustainable energy system is to deterimine the maximum amount of energy needed so that your system can handle the maximum load. If you are creating a system for a community, the maximum load will have to be considered for the entire community and designed so that the system can handle the load.
Average annual power production or consumption can be expressed in kilowatt hours per year; for example, when comparing the energy efficiency of household appliances whose power consumption varies with time or the season of the year, or the energy produced by a distributed power source. One kilowatt hour per year equals about 114.08 milliwatts applied constantly during one year.
The energy capacity of a battery is usually expressed indirectly in ampere hours; to convert watt hours (W·h) to ampere hour (A·h), the watt hour value must be divided by the voltage of the power source. This value is approximate since the voltage is not constant during discharge of a battery.
