Energy Services Bulletin - Topics from the Power Line: Many choices for water districts looking to go solar

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Many choices for water districts looking to go solar

Question:

One of our customers, a large metropolitan water district, is interested in using solar energy to power some of their remote operations. Do you have any examples of such projects?

Answer:

There are several examples of water district pumping stations in California and Nevada that have installed, or are now building, photovoltaic arrays at pumping stations, water recycling plants, vehicle refueling stations and offices.

In addition to photovoltaic systems, your customer may also want to consider concentrating solar thermal and concentrating photovoltaic technologies. Power generated by non-concentrating PV arrays is more expensive than power generated by conventional power plants in most locations. On the other hand, concentrating solar power is becoming cost competitive with conventional power, depending on scale. The cost effectiveness of concentrating solar systems can be greater than that for non-concentrating system at capacities of a few kilowatts and more.

Your customer should not overlook other types of renewable generation systems. Micro- and mini-hydropower systems in fish-free distribution and drainage runs may be a viable option for a water district. Wind might also be considered, depending on resources in your area. The Power Line can supply information on these opportunities, as well.

Water-sector facilities with PV systems

PV arrays offer several advantages for businesses and industrial facilities that want to build on-site generation. The systems are relatively easy to install and connect; siting PV arrays is easier than conventional power plants; and solar plants can be expanded incrementally. On the other hand, solar-generated electricity still costs more than electricity from conventional plants in most places.

Concentrating photovoltaic systems use low-cost lenses or mirrors to focus sunlight on photovoltaic cells. Concentration can improve cost effectiveness because fewer high-cost PV panels are required. Nevada Power installed a concentrating photovoltaic array at their Clark PV Station, but there are no examples of concentrating PV systems at water districts.

The Las Vegas Valley Water District (LVVWD) solar project consists of photovoltaic arrays at six reservoir and pumping station sites. Built by Sunpower, the arrays range from 330 kW to 851 kW with a combined power of 3.1 MW. This is the largest photovoltaic project built by a public agency in the United States.

LVVWD also completed a solar hydrogen refueling station for its fleet operations in April 2007.

California offers several examples of water districts that have installed solar arrays. West Basin Water Recycling Plant, just south of Los Angeles International Airport, built three solar arrays totaling 590 kW. The Semitropic Water Storage District in Kern County completed a 1-MW system, and the Idyllwild Water District recently dedicated a 42-kW solar PV system. It serves a 50-HP system that pumps water from six wells to an aeration plant that removes iron and manganese, then to a filtration plant and on to storage.

Small-scale generation with solar thermal energy

When discussing power generation, "small-scale" generally refers to systems of a few megawatts or less. However, this would be considered large-scale for a water sector facility.

Solar parabolic troughs, parabolic dish and concentrating PV systems may be a good fit for water district projects. A nice summary of concentrating solar projects is available in A Look at the U.S. Concentrating Solar Power Market, a PowerPoint presentation by Fred Morse of Morse & Associates.

Activity in this area has picked up in recent years, after a long period of stagnation. Slide 7 gives a list of concentrating solar projects that have been completed or are in progress, as of December 2006. As an update, the 64-MW Nevada Power Solar One project was completed in 2007. Projects on this list include parabolic troughs, parabolic dish and concentrating PV projects.

Parabolic troughs with Organic Rankine Cycle

Arizona Public Service Company's Saguaro Generating Station is an example of solar trough technology. (Photo by Carol Shipman, APS)

If the water district has pumping stations or other facilities of about 1 MW or more, an organic-cycle parabolic trough system may be an option. The National Renewable Energy Laboratory (NREL) report Solar Trough Organic Rankine Electricity System (STORES) Stage 1: Power Plant Optimization and Economics summarizes the advantages of small parabolic trough systems:

A small solar trough power plant could be built quickly and provide local value.
STORES would focus on the retail market rather than wholesale, because local value and prices may be higher.
Such plants could be modularized with proper optimization to achieve economies of production.
If the market existed, the plant could be automated and scaled up or down, depending on the customer's needs.

Arizona Power Systems’ Saguaro parabolic trough power plant has been in operation since December 2005. At 1 MW, this is a small plant for a power generation facility, but is the same size as some large water district pumping stations. Organic rankine turbines are more cost-effective at this scale than the steam turbines typically used in larger plants.

Organic rankine cycles use an organic fluid—in this case pentane—as a working fluid instead of steam. The solar field typically accounts for about 75 percent of the capital costs.

Parabolic trough systems are available for large commercial, industrial and institutional operations.

Manufacturers of parabolic troughs include:

Acciona (formerly Solargenix)
Solucar (formerly Industrial Solar Technology Corp.)
Solitem

Parabolic dish with Stirling engine

Facilities requiring 3 kW or more should consider installing a parabolic dish and Stirling engine system. Parabolic dish systems have been in the development phase over several decades and only recently have begun to be installed in commercial-scale operations.

Parabolic dish Stirling Energy Systems will be providing San Diego Gas & Electric with 300 MW of power generated from 12,000 dishes with Stirling engines. A 500-MW parabolic dish project will also be installed by Southern California Edison.

STM Power's SunDish system has been operating at the Salt River Landfill near Scottsdale, Ariz., for almost a decade. Each SunDish system produces 22 kW by reflecting and concentrating the sun's rays onto the receiver of a Stirling engine that operates a generator producing 480 Volt, 60 Hz, power. The landfill facilities and the SunDish support system use the resulting electricity.