The City of Surrey district energy network pipe network expansion project. Credit: City of Surrey
Mobile Thermal Energy Storage (M-TES) can be a viable and cost-effective way to harvest waste energy from industrial sources for use in district energy networks, according to an economic and technical analysis.
Waste heat from industrial sources, data centres, hockey rinks, and bioenergy facilities in rural areas can be harvested, stored as thermal energy, and then transported by tanker trucks to a district energy network (DEN). It can then be used to heat buildings and provide hot water for commercial and residential use, displacing the need to burn additional energy sources, such as natural gas.
The study—Integrating Mobile Thermal Energy Storage (M-TES) in the City of Surrey’s District Energy Network: A Techno-Economic Analysis—found that M-TES systems are cost competitive with common low-carbon energy sources such as biomass, renewable natural gas, and sewer heat recovery when the waste heat source is within 30 kilometers of the DEN and when using trucks fueled by electricity or renewable natural gas or diesel. The findings were published in the journal, Applied Sciences.
The research, led by Dr. Majid Bahrami’s team at Simon Fraser University’s Laboratory for Alternative Energy Conversion, was conducted as part of the PICS three-year opportunity project - Innovations in Mobile Thermal Energy Storage: Using Waste Heat to Power Communities; a collaboration between SFU, the City of Surrey, Canmet ENERGY and PICS.
The heart of M-TES is a thermochemical liquid sorption system proposed and designed by the project team. The goal is to deliver industrial waste heat to the City of Surrey’s district energy network, which already supplies space and water heating to many buildings ranging in size from 12 to 50-plus storeys.
The energy storage density (ESD) of the thermochemical solution is key to the feasibility of the system. Dr. Bahrami’s lab has several promising candidates, with potential to store energy up to ten times the density of hot water.
With M-TES system storage density of 0.7 MJ/kg, a single truck can deliver about 4,200 MWh/year which is about 7% of the projected demand of Surrey district energy network. Furthermore, the M-TES system is competitive with other low-carbon alternatives according to two key metrics, said PICS Scholar and report lead author, Ms. Maha Shehadeh.
Firstly, the cost of avoided emissions when waste heat energy is within 15 kilometres of the point of delivery using diesel truck M-TES is approximately $209 per tonne of avoided emission (tCO2e). This cost is lower than alternatives such as renewable natural gas ($319), biomass burning ($373), and sewer heat recovery ($423). The cost of avoided emissions harvested within 30 km is $385. Avoided emissions are calculated as the difference between the amount of CO2 emitted by the primary fuel source used in the DEN, in this case natural gas, and the emissions released by using the alternative, which is M-TES.
Secondly, the cost of energy delivered by M-TES operating in a 15-kilometre radius is about $42 per megawatt-hour (MWh), which is cost competitive with the use of available sustainable energy sources such as renewable natural gas ($60), biomass ($70), and sewer heat recovery ($80). The cost of one MWh within a 30-kilometre radius is $76.
Cost scenarios of M-TES have been evaluated for three different trucks; electric, renewable natural gas (RNG) and diesel-fueled trucks. Trucks fueled by renewable natural gas or electricity reduced the cost of energy, the cost of emissions avoided, and extended the practical range. The capital cost of M-TES, which includes the costs of a container, thermochemical solution, pumps, tanks, and two heat exchangers, is estimated at $100,000, plus the cost of a medium-duty truck.
The City of Surrey has been working with Bahrami's lab on the project since Sept 2019 and views it as one of the possible solutions in its transition to low-carbon energy. While the mobile thermochemical storage solution is cutting edge, it can marry easily with conventional district energy networks across Canada and around the world, Bahrami said. Buildings consume about 40% of the total primary energy in Canada, with approximately 70% of the buildings’ energy demand being for space heating and domestic hot water. In Canada, most of that energy is derived from fossil fuels, which makes low-carbon alternatives crucial to meeting national and local GHG emission reduction targets.