Everyday we receive plenty of questions about our technology. Here we tried to answer the most frequent ones.


Why is it important to have alternative storage technologies to Li-ion Batteries?

While Li-ion batteries are a proven solution and commercially available, it will be important to consider other storage technologies and encourage their development. Li-ion batteries may be a solution in the near term for short duration in a smaller scale, but they have some serious limitations as we consider a larger scale use in the future. We have seen that in applications requiring a lot of cycling, li-ion batteries degrade rapidly, requiring the replacement of the battery pack. We also predict that there will be increased competition from the electric vehicle market expansion for the key raw materials required. From an environmental point of view, the problem of large-scale battery recycling has not been fully solved. One of the key aspects of the thermal energy storage technology developed by E2S Power is that the storage system doesn’t degrade substantially over time, and the materials required are readily available and recyclable.

How does the thermal energy storage technology developed by E2S compare with other storage technologies?

The total LCOS cost of TWEST for utility scale applications is very competitive compared to batteries and other storage solutions as we are taking advantage of valuable existing equipment and assets. Our design is a compact “all in one” unit and, unlike other energy storage solutions, does not require additional equipment, separate storage or auxiliary systems. One key aspect of our design approach is simple plant integration and simplified project execution.  Some of the other energy storage technologies have additional project complexities due to the amount of equipment, auxiliary systems, materials and special working fluids.

We believe that total costs should be considered on an equal basis for a true comparison.  When looking at the cost of Li-ion batteries, for example, the complete project cost needs to be included, not just the battery pack. This includes inverters, power electronics equipment, required housing and climate control, in addition to construction costs and the interconnection to the grid. By utilizing existing power plant equipment, infrastructure, and sites, we are able to keep our costs down. If you consider a 25-year life and taking into account capital costs and the degradation and replacement cost of batteries, the levelised cost of storage of the E2S Power storage system is estimated to be one third of Li-ion batteries.

Can your system provide ancillary services such as frequency response, load following, reactive power?

Yes, by using the existing synchronous steam turbine generator, we are better equipped to provide grid support and ancillary services compared to batteries. Furthermore, the advantage of our system compared to the existing plants is that we do not have boiler drums which limit the start up times and cycling capabilities. Our system is much more flexible than most of existing coal-fired plants and can be started or shut down very rapidly if needed without any life penalty.

What is the long-term performance degradation of the system?

We expect to have less than 1% of recoverable performance loss within the 2,000 cycles interval. The storage material and the steam generator are designed to have negligible degradation over time. The recoverable degradation is mainly expected to be due to electrical connectors and typical auxiliary and balance of plant equipment.

When you store the energy how much is the daily energy loss?

We expect to have less than 1% of loss per day – which can easily be recovered during off peak hours to maintain the full system charge.

What is the roundtrip efficiency of your system?

The storing efficiency which is defined as conversion of electrical energy into heat is very high, about 99% as we have efficient heat transfer through radiation and therefore very low losses in this process. The roundtrip efficiency depends on the existing steam cycle efficiency, typically around 40%. As mentioned, when looking at life cycle costs, there are also other factors that need to be considered, such capital costs, lifetime degradation, need for replacement, and opportunity to use existing infrastructure.

What is the maintenance schedule for TWEST?

We have designed the key components for 30 year life. However, as with any power plant equipment regular inspections are needed and we recommend to have visual and borescope inspection yearly and a major inspection every 6 years or 2,000 cycles.

Can you use the TWEST for gas-fired plants?

Yes, in fact our system can be used to generate steam for steam cycles in coal plants and combined cycle plants.