Appendix - Solar Glossary

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Array: Collection of PV panels connected together to form an array of solar panels.

Volts: The measure of electrical voltage. In fluids – this would be similar to flow-rate.

Amps: The measure of electrical current. In fluids – this would be similar to pressure.

Watt: The unit of electrical power is the watt. There are 1,000 watts in a Kilowatt (KW). If 1,000 watts is used for one hour it is 1 Kilowatt Hour (1 KWH).

Power: Electrical power (P) equals electrical pressure in volts (E) times current in amperes (I), and is expressed as: P = E x I. For example, with 110 volts (E), and a current flow of 10 amperes (I), then: P = 110 x 10 = 1,100 watts (or 1.1 Kilowatt)

Electrical Horsepower (hp): Motors are generally rated in horsepower or fractional horsepower. The relationship of mechanical horsepower to electrical horsepower is:

1 foot-pound of force is equal to 1.356 watts.
550 foot-pounds per second is equivalent to 1 mechanical horsepower.

The equivalent rate of electrical power would be: 1 electrical horsepower = 550 x 1.356 = 746 Watts A motor that has a rating of 220 volts and 20 amps, then you can determine its horsepower (H.P.) by the following relationship: H.P.= watts / 746 = volts x amperes / 746 = (220x20) / 746 = 5.898

British Thermal Units (btu): Heating appliances use ratings in British Thermal Units or BTUs.

A BTU is the quantity of heat needed to raise the temperature of 1 pound of water one degree Fahrenheit.

The BTU is also equal to 778 foot-pounds,1055 watt seconds, and 0.000293 kilowatt hours.

Fuel Conversion:

How would you convert from one form of energy to another? It is common to convert gasoline, natural gas and propane powered generators to Kws; electricity, natural gas or propane heaters to BTUs. For example, a 5 KW generator may use 1.5 gallons per hour at full load. That’s 5 KWH at the cost of one and a half gallons of gas. Using previous information you can convert 5 KWH to horsepower, or to BTUs from the following information:

Natural gas is converted to BTUs at 1,000 BTUs per cubic foot.
If a generator uses 100 cubic feet per hour to generate 5 KWH, the cost of 1 KWH is equal to the cost of 20 cubic feet of gas. Note that some sources use the value of 750 BTUs per cubic foot.

Propane converts to BTUs at 2,500 BTUs per cubic foot.
The calculations would be the same as natural gas. However, the fuel use rate will be less because of the higher conversion factor. You don’t get an improvement of 2.5 times, however. The efficiencies are different, and the cost of propane is higher than natural gas.

Electricity converts to BTUs at 3413 per kilowatt hour.
In the example above, 5 KWH times 3413 is equal to 17,065 BTUs. If the cost of electricity is 0.08 per KWH, then the cost of 5 KWH is $0.40 and you can relate this to the cost of energy in BTUs. Fuel Oil conversion to BTUs is another useful quantity. The standard unit is 100,000 BTUs per gallon.

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