|HOLMAN, ADAM - West Texas A & M University|
Submitted to: Windpower
Publication Type: Proceedings
Publication Acceptance Date: 1/17/2012
Publication Date: 8/1/2010
Citation: Vick, B.D., Holman, A.J. 2010. Increasing the percentage of renewable energy in the Southwestern United States. In: Proceedings of the 2010 American Wind Energy Association Annual Conference, May 23-27, 2010, Dallas, Texas. 2010 CDROM.
Interpretive Summary: According to the Energy Information Agency, during 2008, about 50% of the electricity generated in the United States was from coal and 20% was from natural gas. The burning of coal causes acid rain in the northeast, and the natural gas price increases over the past decade indicate that supplies are limited. Therefore, the United States needs to begin transitioning from finite fossil fuel energy sources, such as coal and natural gas, to renewable energy sources like wind and solar. In 2008, the percentage of electricity generated in the United States from wind was 1.3% (it was only 0.1% in 1998), and solar was less than 0.1%. Wind generated electricity has been increasing in the past several years because it is relatively inexpensive. Wind farm generated electricity normally costs utilities in the United States less than 6 cents per Kilowatt hour which is about one-half of what the retail customer pays. The main problem with wind generated electricity is that it doesn’t blow all the time. Also, at the typical height of the turbine blade rotor hubs in a wind farm (200 to 300 feet tall), the wind speed is higher during the late night hours, so the highest winds occur when the utility loading is low and the lowest winds occur during the afternoon when the utility loading is high (e.g., almost an exact mismatch between wind farm electrical generation and utility electrical load required). We found that by adding solar power plants to wind farms (i.e. instead of installing just wind farms) in all of the southwestern states (Arizona, California, Colorado, Nevada, New Mexico, and Utah), the combination improved the match to the utility electrical load during the year and during the day. Also, solar power plants were almost always a good match to utility loading on the highest peak utility loading day of the year which, in the Southwestern United States, is typically on a very high temperature day. We also found that all the types of solar power plants (parabolic trough, power tower, Dish Stirling, and photovoltaic) would help achieve a high percentage of renewable energy in the southwest. The parabolic trough and power tower plants can use thermal storage which greatly improves the match of potential electrical generation and electrical power needed by the utility, and also partially compensates for periods during the day when the wind does not blow and/or the sun does not shine. Also discussed is a recommended new policy to be adopted by the electrical utilities which will allow excess renewable energy to be put into the utility grid and, at the same time, to be taken out of the utility grid and stored in batteries, pumped hydro, or compressed air energy storage systems. Otherwise, as the percentage of wind and solar power production increases, the balancing of the electricity generated from the other power plants becomes too difficult or even impossible to manage. All of these concepts are important for residents and utilities in the Southwestern United States because they will help the transition from finite fossil fuel energy resources to inexhaustible energy sources such as wind and solar power.
Technical Abstract: An analysis was performed on the states in the Southwestern United States to determine methods to increase the proportion of wind and solar generated electricity in those states to levels as high as 40% of total electricity used. This analysis was performed by comparing the monthly and diurnal electrical load in each state to the electrical generation by wind farms and to the solar resource. Electrical utility loading was also compared to electrical generation by concentrating solar power (CSP) plants with and without storage for California. In order to meet the high electrical load in the evening for most states, CSP plants with storage capability (i.e. parabolic trough and power tower) are required. In addition, wind energy generated during the late night and early morning hours needs to be stored to match electrical loading. There are some locations in the Southwestern United States where the wind and solar resources are both excellent (capacity factors above 40% for both), so the efficient CSP plant storage system (97% efficiency) can be used to compensate for the intermittent production of electricity by both systems, but normally this is not the case. However, establishing a procedure/policy of supplying to the utility grid excess energy from wind farms during utility low load periods (e.g. late night and early morning) and extracting it for storage systems should help in achieving a high percentage of renewable energy use in the Southwestern United States. Also, if high renewable energy proportion is to be achieved, two-axis tracking systems like Dish Stirling and photovoltaic (PV) arrays will be required to add additional solar energy in the fall and winter when the parabolic trough method is insufficient for meeting utility electrical load requirement.