Submitted to: Solar Energy
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2013
Publication Date: N/A
Interpretive Summary: The world is currently in a transition phase for generating electricity. Most electricity is currently generated with either polluting fossil fuel sources (e.g. coal, natural gas, and diesel fuel) or with uranium. Most countries are trying to transition to the use of clean renewable energy fuel sources (wind, solar, biofuels). One renewable energy source which has seen tremendous growth in the past few years is solar energy. There are two types of solar systems used for generating electricity. One solar type concentrates the heat of the sun by 70 to 100 times to heat oil, and transfer the heat of that oil to water. The water is converted to steam, which then can be used to generate electricity in a steam turbine. The other type of solar is to use the photons from the sun to energize the electrons in a solar cell, and the flow of electrons produces electrical power. Several of these solar cells can be connected to make a photovoltaic (PV) module. Several PV modules can be connected together to make a PV array. Decreased cost and increased efficiency of PV arrays are needed to transition more rapidly to renewable energy. One of the best ways of improving the efficiency of the PV array is to lower the temperature of the PV modules. When the PV array temperature decreases 4 degrees Fahrenheit (F), the PV array power output will increase 1%. At the USDA Conservation and Production Research Laboratory near Amarillo, TX a 2.4 kilowatt PV array was installed, and instrumented to measure PV array power output, PV array temperature, solar radiation, air temperature, and wind speed. On a sunny day in August when the wind speed average was 8 mph, the PV array temperature reached 143 degrees F in the afternoon. On another day in August, it was found that when the wind speed increased to 18 mph the PV array temperature decreased to 125 degrees F, and the PV array power output increased 2.5%. There was not a 4.5% increase in PV array power output (i.e. due to 18 degree F decrease in PV array temperature) because the solar radiation also decreased 2% on the higher wind speed day. most likely the solar radiation decreased with increased wind speed due to more dust in the air. Similar results were observed in November. Additional research on cooling PV arrays (besides ways to increase the wind speed) could result in fewer numbers of PV modules required (lower cost).
Technical Abstract: Thousands of solar photovoltaic (PV) arrays have been installed over the past few years, but the effect of wind speed on the predicted performance of PV arrays is not usually considered by installers. An increase in wind speed will cool the PV array, and the electrical power of the PV modules will increase as the temperature decreases. Data were collected on a grid connected 2.4 kW PV array (ground mounted, fixed and two-axis tracking) at the USDA Conservation and Production Research Laboratory near Bushland, TX. The data collected was: AC power, DC voltage, and current (e.g. DC power), PV module, and air temperatures, solar irradiance in plane of PV array, and wind speed at 2, and 10 m heights. For clear (cloudless) days with approximately the same air temperature, and irradiance, it was shown that an average wind speed increase of 4.5 m/s (10 mph) resulted in a 4 to 5% increase in system efficiency. However, the average AC power only increased 2.5%. The AC power increase was only half the system efficiency increase due to a 2 % reduction in solar irradiance for the higher wind speed days. The solar irradiance may have decreased with an increase in wind speed due to increased amount of particulates (dust) in the atmosphere.