The growth of renewable energy is causing headaches for national grids.
Wind and solar power are intermittent by nature but the increasing dependence on them has complicated the process of being able to guarantee a power supply, say utilities that model these trends.
Engineers are looking at innovative ways to plug the power gap by harnessing advanced technology.
Among the solutions is the conversion of cold storage chains into giant virtual batteries known as “thermal storage”. Some of the most significant trials for this are in the US.
PJM, the country’s largest independent grid operator, aims to capture 192MW of “flexible energy” in one of the largest demand-management programmes in US wholesale markets. Refrigeration makes up a small portion, 2 per cent, of this but the ball is in motion: even Walmart, the US retail giant, is conducting trials in “refrigeration batteries”.
Virtual storage works by managing energy use. Big power users interrupt their demand — in this case because frozen materials can hold low temperatures for a period without degrading. This allows the normal energy requirement to be reduced and switched to other users, so cutting the pressure to the grid at times of peak demand.
In this narrow sense, the freezers act as virtual batteries by freeing up energy supply on the grid rather than, as with an actual battery, discharging power. This software-controlled system in effect turns fridges into power assets.
The idea behind cold storage “batteries” is not new. It has existed for decades as an emergency resource for grid operators.
Cooling, not heating, is the main concern of many US commercial building owners, driving as much as half of peak demand on a hot summer day. What has changed is the scale of investment in virtual storage, which is attracting the attention of food retailers and energy companies that can see economic benefits.
Battery companies are working with supermarket chains to bring these energy assets online while mainstream energy companies such as Shell are pushing into the virtual power market through investments in battery installation companies.
“In an increasingly renewable world, you are looking at a situation where you will need more flexibility in your power system, such that we get to a point where load is following supply, rather than the norm today, where supply follows consumer demand,” says Elta Kolo, an analyst at Wood Mackenzie Power and Renewables, a US consultancy.
Almost a fifth of global energy consumption derives from the cooling applications including air conditioning and heat pump systems. Most goes to the cold chain, the temperature-controlled supply route that keeps food fresh and safe.
Done well, converting fridges into batteries could save the economy millions of dollars in energy costs by curtailing demand. This year, trials undertaken by Lincoln university and Tesco, the UK supermarket chain, showed how systems developed by software company IMS Evolve can self-regulate the flow of electricity and link to the grid. The £5.2m project suggested it is possible to reduce the grid load by 160MW for 30 minutes a day.
Frank Jones, chief executive of IMS, says: “Refrigeration of food is a fundamental part of their [food retailers’] asset base. Competition from players like Amazon has made supermarkets think very seriously about how they use their assets.”
The next frontier in flexible capacity is cold warehouses. “The thermal inertia in those systems is enormous,” he says. On the US west coast, Southern California Edison has signed a contract with Ice Energy for hooking up 1,800 ice storage units at industrial and commercial customer sites for the provision of more than 25MW of power capacity to the utility.
Meanwhile, energy company Axiom has installed three “refrigeration batteries” at Whole Foods Market stores across the western state since 2017. Axiom has won venture capital backing from Royal Dutch Shell for the project, as part of the oil company’s strategy of diversifying into new energy arenas.
Not everyone in the industry is completely convinced, however. “Virtual batteries can’t absorb energy. All you can do is turn consumption up or down, you can’t put more energy back on to the grid,” says Alan Greenshields, chairman of Innolith, a Swiss company involved in grid balancing. Even so, the interest of grid operators, retailers and even oil groups in exploiting cold storage shows how modern techniques are carving out a profitable role for demand management and helping to accommodate more sources of renewable power.