Solar and Ice-based Energy Storage

100+ year-old Alamo Heights Independent School District upgrades energy technologies as student population grows.

The Alamo Heights Independent School District (AHISD) serves the Texas communities of Alamo Heights, Terrell Hills, Olmos Park and a portion of north San Antonio. Originally established in 1909, AHISD has a rich history that is deeply ingrained within the local community and has evolved from a rural district to a suburban district. In 2010, the 9.4 square mile district started an initiative to increase sustainability and reduce utility costs.  

Facing reductions in budgets and the need for upgrades to address a growing student population, the AHISD turned to the community. In 2010, community voters approved a $44 million bond for the school district. These funds were then earmarked to help improve technology in classrooms, expand the high school’smusic building, increase the number of overall classrooms, implement technologies that would help reduce operating costs and address the numerous needs listed in the district's bond proposal. 

 AHISD explored many options on how to implement the newly obtained funds. The use of geothermal energy and tri-generation were discussed, but ultimately the deployment of solar generation and ice-based thermal energy storage was decided upon. 

AHISD installed a 500 kW solar system split between two campuses, Alamo Heights High School and Woodridge Elementary, through CPS Energy’s Solartricity program. The system generates $235,000 annually, with all energy being sold back to CPS Energy at 27 cents per kWh. Separate from this program, the AHISD decided to install another five solar arrays at four campuses and the maintenance building. The energy produced by these arrays, totaling 400 kW and generating 40,000 kWh of energy per month, is used by the district to power daily operations. Payback on all the arrays is between 12 and 14 years. Although the renewable technology will prove beneficial for both utility and school district, there was still a need to reduce energy costs by lowering demand (kW). 

AHISD relies partially on the grid for electricity use, and the grid is mostly made up of fossil fuels. Fossil fuels are not just a form of energy. They are a form of stored energy. Renewables, on the other hand, are energy. So, when renewables were added to the schools, peak demand didn’t necessarily go down. The sun didn’t always shine. The school ended up using the grid as a backup source of generation when renewables were unavailable. When a school is unable to generate enough energy from solar, it draws from the grid, which usually occurs during peak demand hours when the least efficient power plants are running and electricity is most expensive.  

As a strategy to reduce peak demand and compliment the solar installation, CALMAC’s IceBank energy storage tanks were recommended by the Brian Uhlrich of DBR Engineering Consultants and came online in 2012. The energy storage system creates cooling in the form of ice at night and then stores it within the energy storage tanks when demand is low and energy prices are discounted. The next day during peak demand hours, the ice is melted to cool students and teachers inside of a building. Through a third party automated control software, demand (kW) targets can be set and the ice will be utilized once within 10 percent of the programmed target. This provides a flat, more attractive load profile to the utility and controls district energy costs.

Fine arts building

AHISD also identified that ice-based energy storage would help with the expansion of the high school’s fine arts building, one of the major projects that was included in the bond proposal. Enrollment in AHISD’s music programs had tripled since the opening of the music program. It was to the point that the orchestra program students were using the foyer as a classroom, making expansion a top priority.

Lowell Tacker, AIA, LEED AP, principal with LPA Inc. was chosen to help bring the expansion of the fine arts building to fruition. This addition and renovation project added a building that could serve as a direct link between the existing practice facility and auditorium. The extra square footage that was added as a result of the project could be cooled using cooling that was created at night and stored in the ice-based energy storage tanks. This would allow the district to meet the extra cooling demand of the new structure without upgrading to bigger chillers to meet the new load. 

“This was the first project that I’ve worked on involving a thermal storage system,” Lowell said. “Given the size and usage of the campus we felt a thermal storage system appropriate. The best thing is we have actual usage data to back up the numbers. We added over 40,000 square feet, and the energy costs per square foot have gone down considerably. For any project of this scale and usage, there’s no reason not to use consider energy storage technology.” 

The decision to use the bond funds to target energy efficiency upgrades and lower operating costs has proven itself extremely wise, as the AHISD has roughly $422 less per student today from traditional state funding than it did at the start of the projects in 2010. The district is able to generate revenue through its solar program and has reduced peak demand in buildings with energy storage. 

Currently 240kW of energy storage is being used. Energy storage is responsible for providing air-conditioning to 325,442-square feet split between the five buildings on the high school campus. Through the use of CALMAC’s technology, AHISD has reduced peak demand energy consumption by roughly 21 percent at Alamo Heights High School in its first year of operation. This decrease in peak energy usage from the grid comes despite the high school increasing the size of its fine arts building by over 12,000 square feet.

“The use of CALMAC’s ice-based energy storage tanks has really allowed us to capitalize on the most cost-effective energy from the grid,” said Mike Hagar, assistant superintendent for business and finance at AHISD. “Despite fiscal pressure, we identified a need to become smarter with our energy purchases in order to reduce operating costs and reallocate them to other important areas. We had heard about energy storage in the past, but the technology has exceeded expectations.”

Through community support, AHISD was able to make a big impact to its energy future by implementing energy storage and renewable energy technology. These chosen strategies have allowed the district to generate revenue and reduce peak demand. The proactive actions of the AHISD has set the foundation for a much more cost-effective and sustainable future. 

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