A rendering illustrates how the NETenergy thermal battery integrates with a commercial rooftop air conditioner.

Thermal battery keeps cool while saving green

For a lot of people, the term “energy storage” raises images of traditional batteries that work in electronic devices. But energy storage comes in different forms. 

NETenergy in Chicago develops thermal energy storage technologies, which work in a similar way to electric batteries except they store thermal energy and help cool buildings. 

Recently the business announced a collaboration with the National Renewable Energy Laboratory. NREL granted NETenergy an exclusive field limited license to develop and commercialize a hybrid HVAC thermal energy storage system that uses NREL’s intellectual property. 

The innovation

An illustration of the thermal battery.
An illustration of the thermal battery. Credit: NETenergy / Courtesy

The thermal storage technology uses phase-change materials — substances that release or absorb significant energy when they change states (e.g. solid to liquid) and provide useful heating and cooling. The NETenergy thermal battery integrates with cooling systems to essentially generate and store cold energy at night when energy demand and prices are low. The stored energy can help air conditioners during the day when energy demand and prices are high. The initial target market is large commercial buildings. 

The proprietary phase change material in the thermal battery is made of wax and graphite. It has a couple of unique characteristics. First, its freezing temperature is 42 degrees Fahrenheit. It also has a high thermal conductivity, meaning it freezes and thaws quickly — 10 times faster than water. The quick state changes create fast thermal battery charging and discharging.

“It’s the combination of these two characteristics that allows our thermal battery to be integrated very effectively with air conditioning systems,” said Mike Pintar, NETenergy co-founder. “One problem with water or ice as a storage medium is the freezing point is too low for effective integration with air conditioning systems. The compressor has to work too hard to reach that low temperature. The other problem is the thermal conductivity is too low.”

Key benefits

This system reduces energy consumption and carbon emissions. It could also prevent utilities from having to construct and maintain “peaker” power plants that only get used a few times a year. The leading benefit customers will notice is saving money, considering peak energy prices are usually two to six times higher than off-peak.

“We’re not trying to shift the whole peak period energy consumption to off-peak. That would require too large of a battery and would be too inefficient,” Pintar said. Instead, the battery maximizes demand and consumption during the peak period. It’s a similar concept to a hybrid car’s electric battery assisting the combustion engine and maximizing efficiency in different situations. 

The partnership

NETenergy has been working with NREL for about five years on testing and validating this technology. They first collaborated through the Wells Fargo Innovation Incubator (IN2), through which they received funding.

“We at NETenergy were experts on the thermal storage material, but we did not have the expertise as it related to the HVAC side of the equation,” Pintar said. “So we used this [IN2] funding to help us figure out how to integrate our thermal storage battery with an air conditioning system. From this program is where the [intellectual property] was developed by NREL, which we have exclusive license to.” 

Hard tech ups and downs

NETenergy experienced a lot of the same challenges as other startups, such as moving as quickly as possible, finding the right partners, and finding the right target markets. But it also has additional barriers as a hard tech business.  

“We’re a hardware company, so it’s a more capital-intensive industry. And the technology has to work,” Pintar said. 

“There’s no opportunity to release patches once the product has been released. You have to perfect it as much as you can both in the lab and in the field before you can produce a commercial product.” 

But being Midwest-based has helped ease some of the hard tech and startup challenges.

“The Midwest has been very beneficial to us as we have a lower cost of real estate,” Pintar said. “Since we are a manufacturing company, we’ve had the ability to find lots of high-quality resources in the Midwest that are experts in HVAC, energy storage, and chemical engineering. And Chicago is a central hub so we have had opportunities to meet with executives from Fortune 500 companies very easily.” 

What’s next

NETenergy is in late-stage research and development. The next step is to run pilot projects to test the technology on multiple buildings in multiple locations, then they will develop prototypes and do field testing. After that, they hope to proceed toward commercialization with industry partners.

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