Prime Attraction

A solar array in Weslaco, Texas, helps the treatment plant run off the grid during the day and draws interest from academics and other municipalities.
Prime Attraction

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The City of Weslaco's South Wastewater Treatment Plant has been getting attention for its 302 kW solar array: On most days, the plant runs completely off the grid in the daytime, saving the city $16,500 in electrical costs annually.

Located five miles north of the Mexican border in the Rio Grande Valley of Texas, Weslaco has seen 15 percent growth in the past 10 years to a population of 37,000.

The city is split into two watersheds and has wastewater treatment plants on the north and south sides of town.

The 2.5 mgd South plant and the recently expanded 4.75 mgd North plant provide secondary treatment using the activated sludge process with oxidation ditch aeration. The effluent discharges to the Arroyo Colorado and ultimately the Laguna Madre, a lagoon along the coast of the Gulf of Mexico. Biosolids are land-applied or landfilled.

The terrain is relatively flat, and the city has 52 lift stations. CH2M HILL OMI is contracted to operate the plants; David Salinas, public utilities director, and a crew of four maintain and operate the collection system, which includes 128 miles of pipe.

A home for solar

When funding from the American Recovery and Reinvestment Act of 2009 (ARRA) became available, Weslaco considered installing a solar array at City Hall. Instead, officials chose the South plant as a better location for multiple reasons.

The treatment plants, as the city's largest energy consumers, stood to benefit most from renewable energy. The South plant had more space on 40 acres of vacant, city-owned property, while the North plant was landlocked between an expressway, a shopping center and an airport.

Contractors felt a South plant installation would get more community visibility and interest. "Not everyone likes to see a wastewater treatment plant in their neighborhood, but the solar array shows we are being good stewards of the environment," Salinas says.

In June 2012, Meridian Solar installed 1,316 SCHOTT solar panels on three acres next to the South plant. The array produces 302 kW DC, which is converted to 260 kW AC. On most sunny days, the array harnesses enough power to operate the facility and return 21 kW to the grid. The ARRA grant provided $1.3 million for the project, and the city added $200,000. Payback on the investment is projected at 15 years.

Salinas sells surplus power to local energy provider Reliant. The array generates power during daytime peak-demand hours and goes back onto the grid at low-demand times. "We're actually off the grid when energy is at a higher cost, so we're negotiating with the utility for a rebate because we are saving on peak consumption," Salinas says.

Eco-tourism influence

Weslaco considered wind turbines as renewable energy sources but dismissed the idea for its potential harm to the region's eco-tourism industry, which draws significant dollars to the Rio Grande Valley. Tourists visit to view the migration of subtropical birds, monarch butterflies, dragonflies and rare waterfowl. Wetlands once drained for farming have been restored, creating Estero Llano Grande State Park.

"With wind turbines in the valley, there were concerns about the impact on the migrating birds," Salinas says. "Solar arrays are more bird-friendly."

Interest in the solar array has brought academics and representatives from other area municipalities to Weslaco. The facility has hosted tours for engineers from the Texas Public Works Association and students from South Texas College and the University of Texas-Pan American. Public Works officials have been visiting to ask Salinas for advice. The answers they receive may be somewhat surprising.

"They want to know how it was funded and the ROI," Salinas says. "But unless you get a grant to help fund it, I don't recommend a solar array without understanding that it won't give you a return on investment right away. Arrays have a short life expectancy, maybe 20 years at the most, and many have a return on investment of 15 to 20 years."

Doing the right thing

Salinas feels the key motivation for investing in solar power should be the environmental benefits and reduced dependence on nonrenewable energy. "ROI shouldn't be the main goal of a solar power project," he says. "If anything, the main goal should be to truly believe and act on environmental stewardship. We need to stop doing what we've been doing for the past century. We need to consider the people here after us."

Since the South treatment facility has reached 75 percent capacity, the Texas Commission on Environmental Quality requires Weslaco to begin designing an upgrade. The city is now determining its capacity needs and how to optimize energy efficiency, such as by installing premium-efficiency motors. Construction on the upgrade is expected to begin in 2015.



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