Supermarkets as batteries in smart grids

Chalmers University of Technology

​Getting along and taking turns are concepts we learn early in life, and the balance between supply and demand for energy requires a similar mindset – the supermarket on the corner may not need to run their refrigerators at full power while you brew your morning coffee, and maybe you can lower your indoor temperature whilst away from home. An increasing share of renewable energy sources requires for us to consider existing energy as our common asset.

​On a typical weekday morning, hundreds of thousands of Swedish households are preparing for a new day. You brew coffee and make breakfast, shave or blow-dry your hair, charge mobile phones and laptops. During this time, power peaks are created in electricity consumption, which means that the electricity grid runs at high pressure, something that creates problems in grids with a large proportion of renewable energy sources hard to regulate, such as solar, wind and wave power.
– This is where the research on smart grids comes in, and part of the solution for these morning hours for example, could be that supermarkets hold back on cooling to balance supply and demand for electricity in the grid. This would mean that when people leave home for work and school, there is a surplus of electricity in the grid – which is saved in the supermarkets’ refrigerators and freezers, and an environmentally friendly virtual battery has been created, says Tommie Månsson.
Swedish supermarkets account for 3 percent of Sweden’s total electricity consumption, of which the refrigerators solely account for about 1.5 percent. Tommie Månsson, a soon to be PhD at the Department of Architecture and Civil Engineering, has in his research project investigated the potential of using supermarkets and their cooling systems to balance the electricity grid and thus increase the opportunities for a larger share of renewable energy in the electricity grid.
– My contribution to the smart grids of the future are models for estimating the storage capacity for supermarkets, ie how long store refrigerators can be switched off without damaging the food, Tommie says.

Users balance the electricity grid

When you turn off the refrigerators, that in turn affects the entire building’s energy system, so in order to be able to use the flexibility in an efficient way, you first need to know the current situation. When you know the temperature development and performance, you can make mathematical models and together with user data create forecasts.
– Overall, these parts become a whole that enables a concept called “Demand Response” for supermarkets, which refers to how the user side – in this case the supermarket – adapts to the energy available in the electricity grid. Demand Response is a prerequisite for creating smart grids with a large proportion of renewable energy, Tommie explains.

Studies on in-store refrigerators make for unique dataset

After experiments in a lab environment where researchers created input values for the thermal performance, the next step was to look at how customers interacted with refrigerators in a supermarket. The partner was the German groceries giant REWE, and for a month Tommie and his colleagues performed studies in a store with about eighty refrigerators to study the speed at which customers opened the refrigerators, at what angle, how long the doors were open at each opening and how it affected temperature development.
– The result was a unique dataset that is important for research because the temperature development of the chilled foods determines the capacity of a demand-response system. The fact that the refrigerated goods are heated thus reduces the capacity and the possibility of contributing to the electricity system, says Tommie Månsson.

Technology with a bright future

Tommie believes that the potential for applying his results is high. Models, input data and technology already exist, which means that in the next step it is a matter of putting it together into a system and looking at the whole and optimizing.
– Much more reserch could be done on behavioural patterns and how it ultimately affects the electricity grid, but in terms of the technical part, pilot studies would be the next step in determining what technical and economic barriers exist in managing grocery stores. In addition, we need to understand that we must start handling the in the grid as our common asset, Tommie Månsson concludes.
Text: Catharina Björk
Tommie Månssons will defend his doctoral thesis “Supermarket refrigeration systems for demand response in smart grids” on December 11th, at 10 a.m.

Scientific articles connected with the project:

Funding

The PhD project “Supermarkets as thermal buffers for renewable electricity grids” was mainly funded by Climate-KIC
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