Renewable Energy - Energy and the Environment - page 183

7.11 CONCLUSION

The renewable energy technologies that have been demonstrated to be technologically practical
sources of power are hydro, biomass, geothermal, wind, solar thermal and thermal electric, photo-
voltaic, and ocean tidal. Of these, hydro and biomass comprise almost the entire renewable installed
capacity in the United States in 1997, but the proportion of wind is increasing, especially world-
wide. Neither ocean wave nor ocean thermal electric power has yet emerged from the development
stage.
Hydro, biomass, and geothermal plants are able to supply electric power dependably on a daily
and annual basis. Wind, solar thermal, photovoltaic, and ocean tidal power have diurnal rhythms
and seasonal changes that do not necessarily match the demand for electric power. When linked
to an integrated power transmission system, they displace fossil fuel consumption, reducing air
pollutant and carbon emissions.
Renewable energy technologies are capital intensive, having capital costs per installed kilowatt
that are two to eight times those of fossil fuel plants. Furthermore, these plants may have low capacity
factors (the ratio of average to installed power), which increases the capital cost portion of the price
of electricity they generate, compared with conventional plants. The economic competitiveness of
renewable energy plants, compared to fossil fuel plants, is strongly dependent upon the costs of
capital and fuel.
The adverse environmental effects of renewable energy plants are generally less than those of
conventional power plants, but are by no means negligible. Hydro and tidal plants require extensive
changes to the natural hydrologic system, and biomass plants emit air pollutants. Because of the
low intensities of renewable energy, the size of a renewable power plant is larger than that of a
conventional plant of equal power, requiring more land area.

PROBLEMS

Problem 7.1
A proposed hydroelectric power station would produce maximum power when the volume flow rate
reached 100 m 3 /s at a head of 10 m. (a) If the turboelectric machinery operates with an efficiency
of 85%, calculate the maximum electric power output of the facility. (b) If the annual average
capacity factor of the plant is 65%, calculate the annual income from the sale of electric power if
the selling price is $0.03/kWh. (c) If the capital cost of the power plant is $1000/kW, calculate the
ratio of annual income to capital cost, expressing the result as %/y.

Problem 7.2
The annual average daily solar irradiance falling on agricultural land in the United States is about 10
MJ/m 2 per day. (a) If 0.1% of this is converted to biomass heating value, calculate the annual rate of
biomass crop heating value that may be harvested per hectare of crop land. (b) If the biomass heating
value is converted to electric power at an efficiency of 25%, calculate the annual average electric