Researchers at Carleton University in Ottawa are working to prototype an innovative, solar-driven heat storage system that could one day free remote communities in Northern Canada from reliance on costly and toxic diesel.
Applying their scientific enthusiasm to practical, sustainable solutions that are attuned to community values, the multidisciplinary team is partnering with the municipality of Cambridge Bay in Nunavut to custom-build a solar-driven adsorption thermal energy storage system (SATES).
A SATES is a version of an STES, or a “sorption” thermal energy system, relying on the scientific principle that when certain molecules become attached, or disattached, to other kinds of molecules, such processes release heat. The SATES system being built by Carleton will collect the heat released by reversible sorption reactions, which involve the breaking, and re-formation, of very weak chemical bonds between an “adsorbent” (typically a powder of some sort) and an “adsorbate” liquid, usually water.
Held in tanks, the materials are separated using solar energy in the summer, explains Carleton Newsroom. Come winter, they are recombined to release heat. The following summer they are once again separated by solar energy, and on the cycle goes. One researcher noted that STES have the “charming advantages of high energy storage density and negligible heat loss during storage periods.”
Curiosity-Driven Research
Funded by a five-year Natural Sciences and Engineering Research Council (NSERC) Alliance grant, Carleton mechanical and aerospace engineering professor Jean Duquette and his team are pursuing a heating system purpose-built for Cambridge Bay, designed in consultation with the community. On completion, the SATES would ease lives in a place where many diesel alternatives aren’t feasible.
“Permafrost makes geothermal exchange heating systems impossible, solar energy is hard to generate during the long, dark months of winter, and batteries aren’t capable of storing sufficient amounts of electricity through extended periods of extreme cold,” notes Carleton Newsroom.
The project is grounded in the needs and values of local residents, but its existence owes to a kind of “curiosity-based” research that can be difficult to pursue when funding demands immediate application.
“A lot of the time, curiosity is where the drive comes from,” Duquette told Carleton Newsroom. “It is not from the needs of industry, but from academics who have ideas for things that do not exist yet.”
“A great idea can be great for Canada, great for the community, and have benefits down the road,” he added. “Not only for the researchers, but for Canadians in general.”
The SATES project is no longer in the realm of “things that do not exist yet,” but a fair number of things remain to be tacked down, and the NSERC grant allows Duquette and his team the breathing space to make that happen.
One problem they are tackling is the cost of materials used in a typical STES—like one in Munich that since 1996 has heated a school during the day and supplied a jazz club with air-conditioning at night. STES use an eye-wateringly expensive adsorbent powder called zeolite 13x. The mineral’s high cost makes small applications rare, effectively disqualifying it as an option to run an adsorption heating system for a single home, Carleton Newsroom writes.
Zeolite 13x is also “definitely not readily available in the North,” Prof. Ronald Miller, chair of mechanical and aerospace engineering at Carleton, told The Energy Mix in an interview. Miller and Duquette are focusing on the project’s engineering dimensions, while Stephan Schott, a professor at Carleton’s School of Public Policy and Administration, is working with Maya Papineau, an associate professor of economics, to quantify the environmental and socio-economic impacts of the proposed SATES system.
Engaging to Find Local Solutions
While declaring the cost of using zeolite 13x to heat even a single building in Cambridge Bay “ridiculous,” Miller affirmed his team’s commitment to design a SATES system that can provide benefits beyond eliminating diesel. He said the researchers are taking “a very practical approach,” zeroing in on a replacement adsorbent that can be manufactured locally at a fraction of the cost of zeolite 13x—namely, activated carbon.
Also known as activated charcoal, activated carbon is produced by cooking carbon-based matter (wood, for example) at very high heat in the absence of oxygen. That process creates an intricate lattice on the surface of the burned material, hugely increasing its overall surface area and making it highly adsorbent—that is, very much inclined to attract and hold other molecules, like water vapour, in weak chemical bonds. By one estimate, a single teaspoon of activated carbon has greater surface area than a football field.
The individual heat-generating bonds between activated carbon and water vapour are weak in aggregate, but “the amount of energy stored can be significant,” Miller says.
Activated carbon is not expected to measure up to zeolite 13x’s efficiency, but Duquette told Carleton Newsroom that 70-80% efficiency yields with the cheaper adsorbent will mean it is “still a viable heating solution.”
Schott said the research team will ask the community what local carbon sources might be used as feedstock for the activated carbon during a workshop later this year, with fish waste as one possibility.
“Currently, most of that waste material is used as dog food in the community,” Schott told The Mix in an email. “We don’t want to compete with that and will see if there is additional waste that could be redirected.”
On Carleton Newsroom, Schott emphasized the team’s commitment to a diesel alternative that Cambridge Bay itself can maintain and expand. Local sourcing and production of the activated carbon will be essential to that process.
Cambridge Bay residents will be directly involved in the pilot through focus groups, Papineau said. “We will be speaking with residents to get feedback and insights on how they feel about their current home heating technologies, what needs they have that are not currently being met, and insight into what characteristics their ideal heating system has,” she said in an email. The focus groups will also be asked to share their impressions about the impacts of diesel on their community.
The team will reach out to organizations like the local Hunting and Trapping Association learn about seasonal demand variations, given that many Cambridge Bay residents spend much of the summer out on the land.
