PTES explained: the key to future-ready heat solutions

What is Pit Thermal Energy Storage?

Pit Thermal Energy Storage (PTES) is a large, insulated, water-filled heat storage system built below ground, capturing surplus heat from renewable sources such as solar thermal plants or industrial processes and storing it for when required, both in the short or long-term. For long-term seasonal storage, energy collected throughout the year is stored as heat, then released during winter months when there is a higher demand, thus providing efficient, fossil free heating for homes, businesses, and district heat networks all year round. Short-term storage can be used regularly to buffer the heat required to feed the heating networks or industrial processes. This also allows for greater renewable and waste heat to be collected throughout the year.

PTES can bridge the gap between the fluctuating generation of renewable heat and the steady, year-round demand for energy. By balancing this seasonal difference, PTES makes renewable heat supply stable, efficient and independent of fossil fuels.

How does Pit Thermal Energy Storage work?

A PTES consists of an excavated pit lined with high-performance geosynthetics that ensure watertight and thermally stable storage. The pit is filled with water, which serves as the heat storage medium, with the water then being heated through solar thermal collectors, industrial heat exchangers, Power to Heat from renewable energy such as wind farms, waste to heat plants, or any other heat source that is readily available, which will charge the thermal store, acting as a thermal battery. The stored heat is then extracted through a heat exchanger system when it is needed during either high demand or ore regularly if designed into the district heating network.

Insulation layers at the top, and if necessary, on the sides, will minimize thermal losses, while precise temperature monitoring ensures efficient operation and long service life.

Why does Pit Thermal Energy Storage matter for the energy transition?

Heating and cooling account for nearly half of global energy demand. To achieve Net Zero, renewable energy generation alone is not enough — technologies are required that store energy when it is readily available and release it when it is needed most.

PTES provide this missing link in the renewable heat value chain, enabling:

• Decarbonization at scale, by integrating renewable heat into district and industrial systems

• Energy independence, by reducing reliance on imported fossil fuels

• Cost stability and local value creation, through efficient use of local renewable resources

• Long-term performance, proven by more than a decade of successful operation.

Building Reliable Storage Systems with ENERVIA by Solmax:

Under the name ENERVIA, Solmax delivers the materials and expertise that make PTES systems reliable and long lasting. Our high-temperature resistant geomembranes, protective layers and insulation systems ensure impermeable, efficient, and safe storages — designed for decades of operation under demanding thermal conditions.

With ENERVIA, we provide the foundation for sustainable heating systems that support communities and industries in reaching their decarbonization goals.