How does Terrajoule Technology work ?

Terrajoule harnesses heat energy from the sun to produce electricity, day and night.

  • Mirrors concentrate sunlight on pipes.
  • The concentrated solar energy boils water to make high pressure steam.
  • The steam is expanded in a steam piston engine, causing the engine’s crankshaft to rotate.
  • The crankshaft drives an electrical alternating-current (AC) generator to produce electrical power.
  • To match the timing of the solar energy supply (daylight) to the electricity demand, heat energy must be stored for later use.
  • To store the energy contained in steam for later use, steam is condensed by injecting it into water that is contained in an insulated steel pressure vessel, thus capturing the energy of the steam by heating and pressurizing the water.  When electricity is needed, the heat in the water flashes part of the water, converting it back into steam.
  • The steam retrieved from the steel pressure vessel is then used to power a steam engine, which powers an electricity generator to provide power on demand.

For more information, see Unexpected Technology.

 Is the technology proven ?

The technology is proven, both in performance and durability, by decades of use of each of the three system elements. Terrajoule validated the concepts and the calculations underlying its performance model with a proof-of-concept system in the California Central Valley. The tests and measurements were completed in 2015.

The three system elements and their basis of proof are as follows:

  • Solar concentrators consist of parabolic troughs that track the sun. Many examples of this technology have been in continuous use for over 30 years. Terrajoule’s partner SkyFuel, Inc., supplies the world’s most efficient, reliable and low cost parabolic trough system, extensively tested and verified for performance and longevity by the USA National Renewable Energy Laboratory (NREL).
  • Energy storage is via pressurized saturated water contained in steel pressure vessels. These are industrial steam accumulators, used for decades to provide industrial steam across a wide range of flow rate.
  • Steam piston engines are supplied by Terrajoule’s partner Spilling Technologies GmbH. The product line has been manufactured and continuously refined for over 60 years, with 75 heavy-duty engines in current operation. The reliability and O&M costs are low and predictable.

For more information, see Unexpected Technology.

How does Terrajoule Technology differ from the available solar thermal technologies ?

Terrajoule technology is designed to provide distributed-scale power on demand, 24/7.

Other solar thermal technologies are designed to provide utility-scale baseload power.



Other Solar Thermal

Distributed scale: 2 MW to 10 MW and more Centralized utility scale: 50 MW to 250 MW
Dispatchable power: Rapid slew rate, < 20 seconds from zero to full power;
Rapid response < 1 second;
Baseload power: Limited range of output power, slew rate limited by large turbine specification
Low cost storage from 12 to 48 hours via Terrajoule proprietary storage technology:
Pressurized hot water
Higher cost storage: Two-tank molten salt system that supports extended hours of operation at a single output power level with only “on-off” dispatch capability
Thermal-to-electrical power conversion: Reciprocating steam piston engines driving an AC electrical generator Thermal-to-electrical power conversion: Steam turbines driving an AC electrical generator

For more information, see Unexpected Technology.

 How do the costs compare with the other renewable technologies ?


PV Solar Panels + Batteries

~50% of PV + Li-ion Batteries for power station units with 6 hours of storage at peak dispatchable power (24 hours storage at average power)
~2 times Terrajoule LCoE for power station units with 6 hours of storage at peak dispatchable power (24 hours storage at average power)
Storage cost of net electrical output storage capacity, normalized for replacement over 25-year life:
~20% of lithium-ion battery costs;
Both Terrajoule and Lithium-ion costs will maintain a downward trend
Storage cost of net electrical output storage capacity, normalized for replacement over 25 year life:
~5x Terrajoule costs;
Both Terrajoule and Lithium-ion costs will maintain a downward trend
Charge/discharge cycle limit:None Charge/discharge cycle limit:
Depends on battery technology;
Cycling for 24/7 power causes 20% degradation and 10-year life in lithium-ion batteries
Capacity degradation during useful life:None Capacity degradation during useful life:
Depends on battery technology;
Lithium-ion typically 20% over 10 years
Toxic or hard-to-obtain materials:None Toxic or hard-to-obtain materials:Depends on battery technology
Energy storage configurable independent of power output:Yes Energy storage configurable independent of power output:Depends on battery technology

 What is the storage medium used ?

Terrajoule uses pressurized hot water, in an operating range from 2.5 bar(a) to 18.25 bar(a) (approximately 22 psig to 250 psig). The water is contained in insulated steel pressure vessels, certified as ASME Section VIII compliant. Each vessel has a volume of approximately 48 cubic metres.

Each vessel stores enough thermal energy to enable the system to store and deliver over 500 kWh of net electrical energy.
Energy is stored in the storage medium by directly injecting steam into the vessel. The steam condenses by direct contact with the water. To retrieve energy the heat in the water flashes the water back to steam.


 Are steam pressure vessels a safety hazard?

No, there is no safety hazard. All pressure vessels and piping are certified compliant with USA ASME Section VIII or Section I as appropriate, or equivalent standards in other regions.

Costs of PV solar panels and batteries keep coming down.  Will Terrajoule costs keep pace?

Yes, the pace of Terrajoule cost reduction will exceed that of PV solar panels and batteries. Both PV solar panels and batteries have already enjoyed the benefits of high volume production, whereas Terrajoule is at the beginning of its volume curve.

What storage value do Terrajoule power plants bring to utilities?

Terrajoule’s power is dispatchable on demand, unlike PV and unlike CSP with molten salt storage (like all large turbine systems, CSP cannot be powered up or down quickly or efficiently). Further, Terrajoule power has outstanding capability for rapid ramp up and down, with ramp times measured in seconds rather than minutes or hours.

Therefore, Terrajoule offers several levels of benefit to utilities:

  • Terrajoule plants dispatch power to meet variable demand day or night. This means that Terrajoule capacity can expand its penetration of a grid without the limits to penetration associated with intermittent PV solar panels.
  • Terrajoule can respond to market price signals and dispatch power accordingly, to fill in the demand-supply shortfalls that result from normal changes in demand, and that are exacerbated by high penetrations of intermittent solar and wind.
  • Terrajoule can respond rapidly to direct signals from a utility. Since Terrajoule systems can be controlled remotely, it is possible to aggregate large amounts of Terrajoule dispatchable power, and respond to utility requests to dispatch power not only when but also where it is needed on the grid. This is high quality spinning reserve with a rapid ramp capability.
  • Terrajoule systems have high inherent inertia, with rotating mass driving AC generators, not inverters, so it is clean and inherently well suited to reactive loads on the grid.

Can air cooling be used in Terrajoule Power plants ?

Air cooling is the default configuration. At sites such as water treatment plants where there are evaporation ponds, these can be used for cooling with an enhancement to electrical output.

Isn’t steam engine technology inefficient?

Terrajoule steam engines are highly efficient over a wide operating range, with an average conversion efficiency of thermal to electrical energy over 20%.

There is sometimes a misconception that steam engines are inefficient because historically, different steam engines evolved for different purposes. For example, steam locomotive engines were often less than 10% efficient. These were usually non-condensing engines with atmospheric exhaust, optimized for power-to-weight ratio, not efficiency.

Marine and distributed power generation steam engines were more efficient. By 1914 many engines were well-documented performing routinely with efficiencies approaching 25%.

Large steam turbines (e.g. 200 MW) achieve efficiencies above 40% in continuous operation, yet there are substantial losses involved in daily startup and shutdown.

The bottom line is cost efficiency and the value of the electricity. Thermal efficiency is one of several factors. Terrajoule modular power serves broader markets, enabling a higher rate of volume-driven cost reduction. Terrajoule serves different markets, distributed rather than centralized, adding value by reducing transmission and distribution costs and providing valuable localized grid stabilization services.

How do Terrajoule O&M costs compare?

Terrajoule forecasts O&M costs of less than 1% of system cost per annum.

Is storage needed?  With net metering it doesn’t seem to matter.

Solar power, primarily from PV solar panels, has been enormously successful. However, that very success is approaching overproduction of power in the middle of the day in many markets, while contributing nothing to the evening ramp in demand or power after dark when the demand is typically the highest. The result is reduction in the value of un-stored solar power, while the value of dispatchable solar power is increasing.

For any application that is off-grid, or where the grid itself it intermittent, and diesel is used extensively, storage is required.

The capital needed to scale up new solar technologies has been prohibitive.  How is Terrajoule different?

All components of a Terrajoule system are mature products or parts produced within existing large supply chains. There are no new materials or manufacturing processes, and there is no need to build new factories to meet multi-billion dollar demand.

This contrasts with many new renewable energy technologies where the development of new materials, equipment, manufacturing processes and manufacturing capacity must be financed. Since the cost of such development and capacity must be amortized, there is a significant impact on the delivered cost of the energy system. By utilizing innovation in architecture and controls, rather than materials and processes, Terrajoule avoids this problem.