01-11-2016, 02:30 PM
1463035971-SolarEnergy1460483699272.ppt (Size: 2.67 MB / Downloads: 5)
Putting Solar Energy to Use: Heating Water
Two methods of heating water: passive (no moving parts) and active (pumps).
In both, a flat-plate collector is used to absorb the sun’s energy to heat the water.
The water circulates throughout the closed system due to convection currents.
Tanks of hot water are used as storage.
Heating Water: Active System
Heating Water—Last Thoughts
Efficiency of solar heating system is always less than 100% because:
% transmitted depends on angle of incidence,
Number of glass sheets (single glass sheet transmits 90-95%), and
Composition of the glass
Solar water heating saves approx. 1000 megawatts of energy a yr, equivalent to eliminating the emissions from two medium sized coal burning power plants.
By using solar water heating over gas water heater, a family will save 1200 pounds of pollution each year.
Market for flat plate collectors grew in 1980s because of increasing fossil fuels prices and federal tax credits. But by 1985, when these credits were removed and fossil fuel prices were low, the demand for flat plate collectors shrunk quickly.
Heating Living Spaces
A passively heated home uses about 60-75% of the solar energy that hits its walls and windows.
The Center for Renewable Resources estimates that in almost any climate, a well-designed passive solar home can reduce energy bills by 75% with an added construction cost of only 5-10%.
About 25% of energy is used for water heating.
Major factor discouraging solar heating is low energy prices.
Power Towers
Parabolic Dishes and Troughs
Direct Conversion into Electricity
Photovoltaic cells are capable of directly converting sunlight into electricity.
A simple wafer of silicon with wires attached to the layers. Current is produced based on types of silicon (n- and p-types) used for the layers. Each cell=0.5 volts.
Battery needed as storage
No moving partsdo no wear out, but because they are exposed to the weather, their lifespan is about 20 years.
Efficiency
43% of photon energy is used to warm the crystal.
Efficiency drops as temperature increases (from 24% at 0°C to 14% at 100°C.)
Light is reflected off the front face and internal electrical resistance are other factors.
Overall, the efficiency is about 10-14%.
Cost of electricity from coal-burning plants is anywhere b/w 8-20 cents/kWh, while photovoltaic power generation is anywhere b/w $0.50-1/kWh.
Does not reflect the true costs of burning coal and its emissions to the nonpolluting method of the latter.
Underlying problem is weighing efficiency against cost.
Final Thought
Argument that sun provides power only during the day is countered by the fact that 70% of energy demand is during daytime hours. At night, traditional methods can be used to generate the electricity.
Goal is to decrease our dependence on fossil fuels.
Currently, 75% of our electrical power is generated by coal-burning and nuclear power plants.
Mitigates the effects of acid rain, carbon dioxide, and other impacts of burning coal and counters risks associated with nuclear energy.
pollution free, indefinitely sustainable.