What Is a ‘Sand Battery’?
A “sand battery” is a high temperature thermal energy storage that uses sand or sand-like materials as its storage medium. It stores energy in sand as heat.
Its main purpose is to work as a high-power and high-capacity reservoir for excess wind and solar energy. The energy is stored as heat, which can be used to heat homes, or to provide hot steam and high temperature process heat to industries that are often fossil-fuel dependent.
As the world shifts towards higher and higher renewables fraction in electricity production, the intermittent nature of these energy sources cause challenges to energy networks. The sand battery helps to ambitiously upscale renewables production by ensuring there’s always a way to benefit from clean energy, even if the surplus is massive.
The first commercial sand battery in the world is in a town called Kankaanpää, Western Finland. It is connected to a district heating network and heating residential and commercial buildings such as family homes and the municipal swimming pool. The district heating network is operated by an energy utility called Vatajankoski.
The term “sand battery” was introduced to grand audience by a BBC News story published the 5th of July 2022. The story was written by BBC News’ Environmental Correspondent Matt McGrath.
Read the story: BBC News: Climate change: 'Sand battery' could solve green energy's big problem
Watch the video: BBC News: How the world's first sand battery stores green power
Frequently Asked Questions
What is the structure of your heat storage?
It is an insulated silo made of steel housing, filled with sand and heat transfer pipes. Additionally, equipment outside the storage is required, such as automation components, valves, a fan, and a heat exchanger or a steam generator.
How do you heat the sand?
With electricity from the grid or from local production, in both cases from fluctuating sources such as wind and solar. We charge it when clean and cheap electricity is available. The electrical energy is transferred to the heat storage using a closed loop air-pipe arrangement. Air is heated up using electrical resistors and circulated in the heat transfer piping.
How hot is the sand?
The maximum temperature in the Kankaanpää heat storage is about 600 degrees Celsius. However, the temperature may even be higher depending on customer needs. In practice, the maximum temperature of a sand-based heat storage is not limited by the properties of the storage medium, but by the heat resistance of the materials used in the construction and control of the storage.
How do you get heat out of the heat storage?
The heat storage is unloaded by blowing cool air through the pipes. It heats up as it passes through the storage, and it can be used for example to convert water into process steam or to heat district heating water in an air-to-water heat exchanger.
Why do you use sand?
Many solid materials, such as sand, can be heated to temperatures well above the boiling point of water. Sand-based heat storages can store several times the amount of energy that can be stored in a water tank of a similar size; this is thanks to the large temperature range allowed by the sand. So, it saves space and it allows versatile use in many industrial applications.
What kind of a sand you are using?
The heat storage is not very sensitive to sand grain size. We prefer high density, low-cost materials that are not from scarce sources. Someone else’s dirt could be our heat storage medium. We prefer to use materials that are not suitable for construction industry.
You can read more about our thermal energy storage medium from this blog post: Polar Night Energy’s Sand Battery Doesn’t Cause Sand Shortage – Thermal Energy Storage Medium Explained.
Does it matter what the grain size of the sand is?
Not much, we prefer to use those grain sizes that are not suitable for construction industry.
How is the heat storage insulated?
The heat storage is made of steel and insulated with standard, heat resistant insulating materials. The insulation is all around the heat storage between the outer steel layer and the inner one.
How long does the sand stay hot in the winter?
It can stay hot for months if needed, but the actual use case of the heat storage in Kankaanpää is to charge it in about 2-week cycles. The heat storage has its best range of use when it is charged and discharged 20 to 200 times per year, depending on the application.
You can read more about the efficiency of the thermal energy storage from this blog post: Sand Battery’s Efficiency Explained – Polar Night Energy’s ‘Sand Battery’ Has Efficiency Up To 95 Per Cent.
Is the outer surface of the heat storage hot?
The surface of the storage is not hot, because the heat stays inside the storage—where it should be.
Can it store electricity?
Not as such, as it stores energy in the form of heat. The heat can be converted back to electricity using turbines like the ORC-turbine or a steam turbine. This requires additional investments to the turbine technology, and the conversion to electricity has inherent losses, thus complicating the economical side.
Is this a new technology?
Well, yes and no. The idea of heating sand to store energy is not new. Our way of doing things and commercializing it in large scale applications is.
Can I buy your heat storage for my house?
No. We don’t have products for individual homes yet.
Who are your clients?
We serve a wide range of different businesses and industries. For example, energy utilities, residential & commercial building operators, food & beverages, textile & clothing, chemistry & pharma, metal production and pulp & paper and other industries.
How can our company start a heat storage project with Polar Night Energy?
Please contact our Product Sales Manager Matti Ulvinen: send an email to matti.ulvinen@pne.fi or call +358 40 838 5767.
(UPDATE: We’ve been getting a lot of attention after our sand battery went viral. Due to a massive amount of requests and messages, our reply times can be very long. We appreciate your patience. Thank you!)