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7 CHAPTER TWO ENERGY TECHNOLOGIES AND TYPES OF IMPACTS This section of the report describes the energy technologies produce steam, which drives a turbine, usually for the pur- of interest and the types of impacts that they may produce. pose of supplying commercial power to the grid. Three CSP This chapter also summarizes the types of information avail- designs are parabolic troughs, power towers, and dish engines able for assessing existing impacts of energy technologies on (NREL 2010a). airports and aviation, including reviewing the regulatory def- inition of airspace that is used to evaluate potential impacts. Parabolic troughs continually track the sun and concen- trate the sun's heat onto receiver tubes filled with a heat trans- fer fluid (see Figure 2). The fluid is heated up to 750°F then ENERGY TECHNOLOGIES pumped to heat exchangers that transfer the heat to boil water and run a conventional steam turbine producing electricity. The energy technologies that are analyzed in this report are solar power [both photovoltaic (PV) and concentrating solar Parabolic troughs have been producing 350 MW of utility- power (CSP)], wind turbine generators (WTGs), and traditional scale electricity at a site in the Mojave Desert for more than power plants. The report also considers issues associated 15 years (NREL 2009). with the new electric transmission infrastructure necessary for delivering the electricity from these new facilities to high Whereas parabolic troughs focus sunlight to receivers energy consumption load centers. located on each individual unit, power towers focus all the facility's sunlight to a single receiver (see Figure 3). The power tower facility is comprised of individual heliostats (mirrors) Solar Photovoltaics and Concentrating Solar Power that track with the sun. Each heliostat reflects sunlight onto the central receiver at the top of a tower. As with the para- A solar PV system is made up of various components that bolic trough, a heating fluid transfers heat to create steam to collect the sun's radiated energy, convert it to electricity, and drive a turbine and produce electricity. A 10 MW power tower transmit the electricity in a usable form. The main component pilot project is operating in Barstow, California (DOE 2008). is the solar panel, which is typically comprised of 40 individ- ual solar cells made from silicon that convert sunlight into A dish engine, also referred to as a dish stirling (Figure 4), electricity (see Figure 1). The panels are held in place by a is a stand-alone parabolic reflector that concentrates light onto frame that is either fastened to an existing structure or placed a receiver positioned at the reflector's focal point. The col- atop a stand that is mounted on the ground. Panels are covered lected heat is utilized by an engine located at the focal point. by a thin layer of protective glass and the panel is attached to They typically use two axes tracking to maximize potential a substrate of thermally conductive cement that traps waste solar radiation as its position in the sky changes (NREL 2010a). heat produced by the panel and prevents it from overheating. There are no commercial scale dish engine facilities in oper- Several panels connected together in series are identified as a ation. However, there is a 150 kW demonstration project at "string" and often operate as a single generating unit. Multi- DOE's Sandia National Laboratories (NREL 2011). ple strings assembled into one solar facility are referred to as an "array." Other types of PV technologies include thin film As with traditional fossil and biofuel-fired power plants, and multi-junction versions. Solar PV systems may consist CSP facilities boil water and drive a steam turbine. There- of just a few panels providing electricity to a single building fore, they are equipped with either an evaporative wet or dry or cover tens to hundreds of acres and transmit electricity to cooling system. the power grid. Utility-scale solar plants are connected to the electricity grid by networks of transmission towers and high- voltage electrical lines (NREL 2010a). Wind Turbine Generators CSP systems use reflective mirrors in large arrays to focus WTGs convert air blowing across the earth's surface into the sun's energy on a fixed point producing intense heat, which electricity. The WTG's rotor is comprised of the rotor hub is then converted to electricity. The most common means for and typically three blades (see Figure 5). Behind the rotor is producing electricity in these systems is to heat water and attached a box called the nacelle, which encloses the turbine

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8 FIGURE 3 Power Tower at Sandia National Laboratories (courtesy: Dr. Clifford Ho, U.S. DOE, Sandia National Laboratories). FIGURE 1 Solar PV on roof [courtesy: Harris Miller Miller & Hanson Inc. (courtesy: HMMH)]. and other equipment necessary for generating electricity. The nacelle sits on top of a tower. The WTG is secured to the ground using concrete and/or bolt anchors depending on the composition of the substrate. WTGs may be sited as single units providing local power or in expansive wind farms comprised of hundreds of units that contribute electricity to the electrical grid. Utility-scale wind turbines constructed on land can be as high as 500 ft above ground level to the blade tip height. Large wind farms are connected to the grid through traditional electric transmission infrastructure comprised of transmission towers and high-voltage lines (NREL 2010b). Utility-scale wind turbines are operating in 37 states, with Texas, Iowa, and California the top three states in generating capacity (AWEA 2011). FIGURE 4 Dish stirling at Sandia National Laboratories (courtesy: Dr. Clifford Ho, U.S. DOE, Sandia National Laboratories). Traditional Power Plants Traditional power plants utilize conventional fossil fuels and biofuels to make steam and drive a turbine to produce elec- FIGURE 2 Parabolic solar collector (courtesy: HMMH). FIGURE 5 Wind turbine schematic (courtesy: HMMH).