Figure 1.1 Energy Basics
1 watt
0.1 horsepower
100 watts
1 horsepower
1 kilowatt
(kW)=one
3
thousand (10 )
watts
1,875 watts
3-9 kW
1 Megawatt
(MW)=one
6
million (10 )
watts
500-1000 MW
1 Gigawatt
(GW)=one billion
9
(10 ) watts
1,121 GW
1 Terawatt
(TW)=one trillion
12
(10 ) watts.
Power v. Energy
1 kWh
International System of Units (SI) unit of power defined as one joule per second. Also equivalent to 3.4 imperial unit British thermal units (btus).
The amount of mechanical power a human can sustainably generate, equivalent to approximately 75 watts. This is in contrast to the average
amount of waste body heat a human generates of approximately 100 watts or 350 btus at rest.
Electricity consumed by an average incandescent light bulb. However, incandescent light bulbs produce more heat than light. A compact
fluorescent bulb that produces the same amount of light as a 100 watt incandescent bulb consumes less than a quarter of the energy to produce
that same amount of light, approximately 23 watts.
Amount of power a typical draft horse could generate—33,000 foot-pounds per minute.
One kilowatt of power is approximately equal to 1.34 horsepower. As a rule of thumb, the mean residential average electricity consumption in the
United States is 1,000 kWh/month. As there are 8,760 hours per year, the U.S. average annual household consumption of approximately 8,800
kWh is almost double that of the UK average of 4,700 kWh per year.
Typical U.S. hairdryer and approximately the amount of supplemental heating capacity needed for a 2,000 square foot home built to Passive
House building standards (See Chapter 7).
Average range for home solar PV array to meet U.S. electricity needs.
Typical unit for measuring utility scale electricity generation facilities.
10-20 MW—typical industrial-scale solar project or single dish system unit.
50+ MW—typical CSP plant.
150 MW—typical industrial scale terrestrial wind farm in the United States.
(Also equivalent to 0.5 – 1.0 GW) Capacity of large coal plants in United States. U.S. nuclear power plants have capacities between 500 and 1,300
MW.
This unit is sometimes used for large power plants or power grids. The installed capacity of wind power in Germany was 25.8 GW in 2010.
U.S. total electric nameplate capacity in 2009 (Providers = Utilities 62%; Independent producers 35%; Commercial/industrial 3%).
The total power used by humans worldwide is commonly measured in this unit: approximately 132,000 TWh in 2008. Lasers and lightning can
produce up to 1 terawatt for very short periods of time.
The terms “power” and “energy” are often confused. Using the metaphor of water going through a hose: “Power” would indicate the diameter of
the hose (e.g., 1 kW), and “energy” would be the volume of water the goes through the hose during a particular time period (e.g., 1 kWh), or in
other words, the volume or amount of energy consumed or generated. As another example, when a light bulb with a power rating of 100W is
turned on for one hour, the energy used is 100Wh. This same amount of energy would light a 50-watt bulb for two hours or a 25-watt bulb for four
hours. Power station capacity is rated in watts, but annual energy sales would be in watt-hours. MWa means megawatts per year (or annually).
A kilowatt-hour is the amount of energy needed for a steady power of 1 kilowatt running for one hour. 1kWh is equivalent to 3,600,000 joules;
3,410 btus; .00008598 tonnes of oil equivalent; .00614 barrel of oil equivalent; .001228 of hard coal; or 860 kilocalories. See, e.g., Unitjuggler.com