Canemure Best Practices: Harnessing renewable energy and excess heat through heat storage

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Heat storage increases the flexibility of the energy system, reduces the need for peak power plants, and improves the possibilities for utilising surplus and environmental heat.

Harnessing renewable energy and excess heat through heat storage ▼▼

Storage of heat assists in the utilisation of surplus heat and environmental heat, which reduces emissions caused by incineration.


When connected to a district heating network, heat storages contribute to the realisation of a carbon-neutral energy system.


Various heat storage technologies allow for a wide range of uses and applications.


Towards Carbon Neutral Municipalities and Regions


Heat storage helps electrify heating and reduce emissions Heat storage increases the flexibility of the energy system, reduces the need for peak production, and improves the possibilities for utilising surplus and environmental heat. Incineration and emissions can be reduced particularly in heating Seasonal with heat pumps, which collect heat from the ground, air, water bodies and the storages, surplus heat of industrial processes, buildings, data centres and waste water such as large treatment plants. Heat pumps consume electricity that can be produced water storages cleanly with wind, solar, hydro and nuclear power. The fluctuation in the and medium-deep increasing wind and solar power can be controlled inexpensively with the help of heat pumps and heat storage (Rinne & et al., 2019). Heat geothermal boreholes, storages are also cheaper to build than electricity storages. can be used to store heat

produced in the summer for the The length of the storage cycle and uses of heat storages vary. For example, they can balance daily peak powers for short periods heating needs of autumn and winter. of time or store heat for several months. Seasonal storages, such as large water storages and medium-deep geothermal boreholes, can be used to store heat produced in the summer for the heating needs of autumn and winter. Most of the surplus heat derived from the cooling of buildings and solar energy is available in summertime, when heating needs are at their lowest. Heat storage facilities relying on direct electric heating can contribute to the frequency control and demand response of the electricity grid, improving the cost-effectiveness of the storage facility. The heating and electricity markets are set to become increasingly integrated with the electrification of heating. Increasing renewable energy in electricity production will increase the demand for load response and other electricity control services. Heat storage can reduce the use of peak production plants and fossil fuels, and increase flexibility in the energy system. It would also facilitate the exploitation of renewable energy sources and waste heat, given that surplus production can be shifted to the hours of high demand when supply is high.

Types and examples of heat storage Water-based heat storages Water allows the storage of heat from low to very high temperatures, up to over 100 degrees, by pressurising the storage cavern naturally in the bedrock by means of groundwater pressure or by using pumps, for example. The water is layered according to the temperature, meaning that the heat storage cavern can have sections of different temperatures. Water stores heat well and has a relatively high specific thermal capacity. Water is inexpensive, easy to pump and works well with heat exchangers. Thanks to these factors, water can be used to store very large quantities of heat, provided that there is ample storage space. In Vaasa, Vaskiluoto has Finland’s first thermal energy storage facility taking advantage of former underground oil caverns. It has a charging and discharging capacity of 100 MW, a storage capacity of 7–9 GWh, a water temperature of 45–90°C and a volume of 210,000 m3. The storage will help reduce the use of coal by 30 % in district heat production, because it will enable the more efficient use of power plant production. Heat from other sources, such as wind and solar energy, can also be stored in the thermal energy storage facility. (Vaskiluodon Voima Oy, 2020) Vantaan Energia Oy intends to build a pressurised underground seasonal thermal storage facility. It will have a charging and discharging capacity of 200 MW, a storage capacity of 90 GWh, a water temperature as high as 150°C and a volume of 1,000,000 m3. This capacity corresponds to the annual heat demand of about 40,000 residents. The facility will store renewable and surplus energy from the summer season. What plays a key role is the higher pressure provided by the rock caverns, allowing the water to be heated to 150 degrees in such a way that the water remains in liquid state. This allows for a greater heat capacity. Although some of the heat will be wasted in the rock, in the long run the total energy efficiency of the heat storage’s use will increase to 85 %. (Vantaan Energia, 2021a) Upon completion, the storage is expected to be the world’s largest seasonal heat storage. (Vantaan Energia, 2021b)


Connection of the heat storages to the district heating system

District heat plant

Cold district heat back flow Hot district heat outflow


4 8

Heat pump

7 1


Heat exchanger


1. Hot water storage cavern, seasonal.

4. Small mineral-based heat storage, short term.

7. Shallow geothermal borehole, geothermal heat.

2. Pressurised hot water storage cavern, seasonal.

5. Medium mineral-based heat and power storage, short and medium term.

8. Energy piles, geothermal heat and seasonal storage.

3. Warm seawater storage cavern, seasonal.

6. Intermediate depth geothermal borehole and heat storage, seasonal.

A storage making use of the natural heat of sea water is planned for Kruunuvuorenranta, Helsinki. Its operation requires heat pumps for the utilisation of thermal energy, given that sea water temperature is quite low in comparison. The storage, which will consist of former underground oil caverns, will be filled with warm sea water in the summer. This will then be used to generate district heat by means of a heat pump. The storage will have a discharge capacity of 3 MW, annual production of 6–7 GWh, a temperature of 2–24°C and a volume of 300,000 m3. (Helen Oy, 2018)

Mineral-based heat storages The advantage of technologies using sand and other minerals to store heat is that some minerals can be heated to several hundreds of degrees in the same manner as an electric sauna stove without vaporising the minerals. This can also be coupled to electricity storage, whereby the hot water vaporised by the mineral rotates a turbine. Polar Night Energy Oy has developed a sand-based heat storage in which electrical energy is stored as heat. Together with Vatajankoski Oy, the company is building a heat storage facility that will be connected to the Kankaanpää district heating network. The storage’s discharge capacity will be 100 kW, storage capacity 8 MWh and temperature 500–600°C. The aim is to prime the 60-degree waste heat recovered from a datacenter to a temperature of 75–100 degrees before feeding it into the district heating network. The storage was tested in 2021 and is expected to become fully operational during 2022. (Vatajankoski Oy, 2021) An electrothermal energy storage based on volcanic rock, where electricity is stored as heat, operates in Hamburg, Germany. Electrically heated air is blown into the storage of volcanic rock, heating it up. When the grid needs more electricity, the heated rock is used to boil water which is used to run a steam turbine. The storage has a capacity of 130 MWh, a temperature of 750°C and a mass of 1,000 tonnes. (Siemens Gamesa Renewable Energy, S.A., 2019) A similar heat storage facility could serve as both an electricity and a heat storage facility in Finland, when the mild temperature waste heat from the steam turbine would be used in heating.



Lappeenrannan Energia Oy is set to begin the operation of a salt-based thermal battery. The battery is charged with electrical energy by heating the salt, because the Areas should be designated salt binds more energy to the phase transformation as it melts. In daily use, the battery for decentralised heat has an efficiency of 95–97 %. The thermal battery is also suitable for the production of production infradistrict heat for the industrial sector, where high temperatures and steam are required. structure already The discharge capacity of the thermal battery is 300 kW and its temperature is 300°C. The in the urban total annual amount of district heat produced by the battery depends on how many hours of low-cost electrical energy there are during the year. The district heat produced by the thermal planning battery will replace district heat produced with natural gas. (Lappeenrannan energia Oy, 2021) The phase. battery is expected to be taken into use during 2022.

Geothermal storages Geothermal wells are generally drilled in the ground to produce heat, but the thermal capacity of bedrock and mineral soils is also taken advantage of in the storage of heat. Heat can be stored by directing it into the boreholes, from which the heat can then be extracted when necessary. Geothermal wells can be drilled to different depths depending on the desired properties. Together with its partner QHeat, Vantaa Energia Oy is having a geothermal well of intermediate depth and a geothermal heating plant built in Varisto, Vantaa. The depth of the geothermal well will be about two kilometres. The heat is generated by pumping cold water into the well, where it is heated to 30 degrees by the Earth’s crust. The temperature of the water will be increased to 80 degrees with the help of heat pumps, which makes the water suitable for the district heating network. In addition to producing geothermal heat, the geothermal well also serves as a heat storage. Therefore, the heat generated by a waste-to-power CHP plant during the summer can be stored in the geothermal well and in bedrock for winter, for example. (Vantaan Energia Oy, 2020) Heliostorage Oy has developed a method for storing heat in bedrock. Several boreholes 35–45 metres deep are drilled in the rock, forming nested circuits and heat storage circuits in which either water or glycol circulates. This allows for storing the heat with highest temperature in the middle of the area, while the temperature of the storage decreases towards the edge. As an alternative source of heat for the storage, the company offers a solar collector integrated into a building’s roof, which allows charging of the storage during the summer. In winter, the heat storage provides 30–70-degree heat. (Heliostorage Oy, 2022) Heat can be stored in a layer of clayey soil, for example, with energy piles. This is often economically viable as well, given that a building requires pile-driving in any case. The operating principle of the heat storage is similar as in other low-depth rock and soil solutions. (Rakennustietosäätiö RTS, 2020) Authors: Teemu Helonheimo, Karoliina Auvinen, Teemu Meriläinen Finnish Environment Institute SYKE References: Helen Oy. (31. 05 2018). Uutta voimaa -blogi, Jättimäisillä luolalämpövarastoilla joustavuutta ja lisää uusiutuvaa energiaa. Noudettu osoitteesta Helen Oy: j%C3%A4ttim%C3%A4isill%C3%A4-luolal%C3%A4mp%C3%B6varastoillajoustavuutta-ja-lis%C3%A4%C3%A4-uusiutuvaa-energiaa Helen Oy. (21. 12 2021). Helen lopettaa hiilen käytön yli viisi vuotta suunniteltua aiemmin. Noudettu osoitteesta Helen Oy – Ajankohtaista: Heliostorage Oy. (2022). Our products. Noudettu osoitteesta Heliostorage: Lappeenrannan energia Oy. (23. 06 2021). Uusiutuvaa sähköä käyttävä lämpöakku vähentää CO2-päästöjä. Noudettu osoitteesta Lappeenrannan energia – Ajankohtaista: uusiutuvaa-sahkoa-kayttava-lampoakku-vahentaa-co2-paastoja Rakennustietosäätiö RTS. (2020). RT 103137 Lämpöenergian kausivarastointi. Rinne, S.;& et al. (2019). Clean district heating – how can it work? Aalto University publication series BUSINESS + ECONOMY, 3/2019. Noudettu osoitteesta Siemens Gamesa Renewable Energy, S.A. (12. 06 2019). World first: Siemens Gamesa begins operation of its innovative electrothermal energy storage system. Noudettu osoitteesta Siemens Gamesa – Newsroom: Vantaan Energia. (2021a). Lämmön kausivarasto. Noudettu osoitteesta Vantaan Energia: Vantaan Energia. (2021b). Maailman suurin lämmön kausivarasto Vantaalle. Noudettu osoitteesta Vantaan Energia: fossiiliton-2026/maailman-suurin-lammon-kausivarasto-vantaalle/

Vantaan Energia Oy. (2020). Vantaalla hyödynnetään ilmastoystävällistä geolämpöä jo ensi vuonna. Noudettu osoitteesta Vantaan Energia: Vaskiluodon Voima Oy. (29. 09 2020). Tulevaisuuden lämpövarasto otettiin käyttöön Vaasassa. Noudettu osoitteesta Vaskiluodon Voima Oy – Ajankohtaista: Vatajankoski Oy. (20. 05 2021). Iso askel kohti hiilineutraalia kaukolämpöä. Noudettu osoitteesta Vatajankoski – Ajankohtaista: Cover photo: Adobe Stock Layout: Satu Turtiainen, SYKE & Marja Vierimaa Helsinki 06/2022 ISBN 978-952-11-5500-0 (PDF) ISBN 978-952-11-5499-7 (print)

Finnish Environment Institute | |

LIFE17 IPC/FI/000002 LIFE-IP CANEMURE-FINLAND This best practices -brochure has been carried out with the financial contribution of the LIFE Programme of the European Union. The best practices -brochure reflects only the CANEMURE project’s view, and the CINEA/Commission is not responsible for any use that may be made of the information it contains.

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