Wednesday, August 6, 2008

Solar Electric Power Generation

Today, solar photovoltaic (PV) systems are at work converting the suns radiation directly to electricity. PV generated power has three main advantages over all other types of remote power generation: Free Inexhaustible Power, Simplicity Low Maintenance, PVs provide electricity to rural homeowners, ranchers, and farmers for TV, VCR, stereo, landscape and security lighting, pumps, electric fences, and livestock feeders, without connection to the power company. Some farmers use PV powered pumps for watering of livestock on remote grazing areas. PV systems power street, billboard, bus stop, and highway sign lights, navigational buoys, and emergency telephones throughout Florida.
Small PV systems provide portable power for camping equipment, computers, fans, pumps, and test equipment. PV cells are used in calculators and watches. Photovoltaic power is practical where access to utility company lines is costly, and for low power/portable needs. Industry improvements have reduced the cost of PV systems to 25-50¢ per kWh. This is still considerably more than the 7-10¢ per kWh of utility power. The U.S. Department of Energy (DOE) goal is PV power at 12¢ to 20¢ per kWh before 2000. To take advantage of the economies of large scale production, the DOE announced a new strategy to
accelerate the use of PV power. The DOE Solar 2000 plan calls for an increase in PV use by a factor of ten by the year 2000. Use of PV power is increasing by over 25% each year, and has been for the past few years. PV power systems range in price from $75 to $40,000 depending on how much electricity the user needs. The box below shows how system cost varies.
PV systems are a poor economic investment if power is readily available: the annual rate of return is around 1%. However, in outlying or isolated locations, connecting to faraway power lines can cost more than a complete PV power station!
When using PV power, it is especially cost effective to replace inefficient appliances with modern energy efficient ones -- allowing selection of a less costly PV system. Since PV cells produce DC voltage, the use of DC (instead of conventional AC) pumps, fans, refrigerators, lights, etc. makes sense. Use of DC appliances reduces the cost of the PV system since they
are typically more efficient and require no invertor capacity. (The invertor is the part of the PV system that changes the PV cells DC voltage to AC.) In most cases, it is not yet economical to power cooling and heating equipment with PV power since these are seasonal loads. Heating and cooling accounts for over half the residential energy use of a typical Florida family. PV power systems are modular, so they easily grow with the users budget and electricity needs. PV system size is measured in watt-hours per day (WH/D). Typical system cost is around $3 per WH/D of system capacity. The smallest systems (around 200 WH/D) can cost up to $5 per WH/D, while very large systems (10,000 WH/D) cost less than $3 per WH/D. Storage batteries are required for power at night and on overcast days. The required size and cost of a PV system can be estimated
using the Sizing Worksheet given in cost comparison Table which can be obtained from PV modules distributors. Utility bills can be used to determine the WH/D of electricity currently consumed. Most bills give "average kWh used per day," simply multiply this number by 1000 to obtain WH/D. Or, (1) take the total kWh on the bill, (2) divide by the number of days in the billing period, and (3) multiply by 1000 to obtain WH/D.
Using this method, one can see that a conventional small home, with a $65 monthly electric bill, would require 25,000 WH/D of PV capacity to go completely solar using the same appliances and lighting. The great cost of such a system emphasizes the importance of using efficient lighting and appliances, natural gas for cooking and heating, and fans for cooling.