Dutch company Ecovat is negotiating to build its first commercial scale underground water storage tank for district heating company Mijnwater starting in the first quarter of 2020.
The 20,000m3 storage tank can use several energy sources such as heat pumps and waste heat from a factory to be stored for up to three weeks, providing heating for 3,000 homes. By storing surplus generated energy using a 'barrel in barrel' principle and using it in times of scarcity, sustainable energy use is optimised. The Ecovat can also be used for cooling the homes.
This will be Ecovat’s first commercial application, although Ecovat has interest from several other district heating companies and has some ongoing demonstration projects. The first Ecovat will take about nine months to build, although construction of the second Ecovat could start after three months construction of the first.
“The possibility of making optimal use of renewable energy demands flexibility. The amount of sustainably generated energy is growing and consequently the call for flexibility does too. Energy storage enables us to use our energy in a flexible way. The Ecovat energy storage system is the missing link here: affordable thermal energy storage across the seasons,” says Ruud van den Bosch, technical sales manager.
“Ecovat enables the 5th generation DHC system of Mijnwater B.V. Heerlen to substantially cover peak loads with waste heat; it turns waste into value instead of burdening the environment,” says Louis Hiddes, director of Mijnwater.
One major benefit of the Ecovat is that it can be built completely underground and near buildings. This means it can be built in many cities without any visual impact. Further, its scale (30 metre diameter and more) and good insulation, makes it very efficient.
Longer duration facilities for seasonal storage of up to six months, where solar, waste and geothermal sources of heat can be stored in the summer for delivery over the winter, may in future allow district heating companies to provide winter heat without using any fossil fuels at all.
Savings of €97,000 to €167,000/yr per Ecovat system can be made as a result of avoided investments compared to households with heat pumps powered with electricity bought from the grid, according to independent research agency Berenschot.
The Ecovat hardware can be coupled with a network balancing system that uses machine learning to respond to energy market signals based on the weather forecast. This will allow more renewables to be integrated into the grid, as well as increasing the efficiency of power plants. However, opportunities to capitalise on these pricing dynamics are still relatively modest. The Netherlands has around 15% renewables penetration so weather-related fluctuations have an as yet limited effect on intra-day and day-ahead prices, and while prices in the balancing mechanism are more volatile, volumes there are quite low.
Ecovat is participating in the Horizon 2020 research project Flexible Heat and Power (FHP) with a demonstration thermal storage project in Uden, North Brabant. The facility is designed to store heat for six months with an efficiency of 90%. The 1,500 m3 (88,000kWh) system is linked to a dry cooler which simulates the heat demand. It is working with system operator Enexis to test integration with the distribution network and test whether having the flexibility of storage will allow for the deferral of investments in the grid.
The FHP project has another demonstration project in Sweden with regional energy company Karlshamn Energi, which owns the local heating system, operates the power grid and has wind and solar generation. Flexibility resources such as heat pumps or ventilation system in larger buildings are fitted with the FHP interface solutions and respond to the overall voltage control scheme. The goal is to use demand side response to maximise the renewable output and avoid curtailment.
Heating in the Netherlands predominantly uses natural gas, but pressure is mounting to diversify from this fuel source after earthquakes restricted use of the large Groningen gas storage facility. District heating companies using more renewables may be more attractive to potential customers, which will also drive the need for more storage. The government is reviewing its price cap on heating tariffs, which may lead to some additional incentives.