How it works

Terrajoule technology is not the expected solution to the worldwide need for expansion in reliable, dispatchable, distributed and renewable energy.  A particular distinction from the expected is that Terrajoule technology does not require massive investments in new science, new materials, and new manufacturing capacity to reach large and economic scale.

In fact, Terrajoule exploits an old-fashioned technology: “Universal Unaflow” reciprocating steam piston engine technology that reached its historical pinnacle in the 1930s.  These engines were produced for decades by the dominant Skinner Steam Engine Company of Erie, Pennsylvania, and others.  They embodied the technology sophistication of 300 years of steam engine evolution that drove the industrial revolution.

Steam engine technology is from the past, but was never obsoleted as a flexible and efficient means to convert thermal energy to electricity at the distributed power scale.  Steam engines lost to cheap diesel on the one hand, and to centralized steam turbines powered by coal on the other.  Neither diesel nor centralized power have retained their economic advantages, and solar concentrator technology has advanced.  The wheel turns.

Here are the components of a terrajoule distributed solar power system:

    • Solar concentrators to produce steam.


These are proven and under constant improvement.  Terrajoule can use any of the available third-party concentrator technologies: Parabolic trough; heliostat/tower; linear fresnel (CLFR).

    • Steam engines to convert the solar power in steam to electricity.

HP engine
At its full-scale field demonstration site (shown above), Terrajoule has proven that steam piston engines can be built today, and still work as efficiently (or more so) as they did in 1930.  These are not steam turbines.  Steam engines are efficient at sub-megawatt scale, whereas steam turbines are not.  More importantly, steam engines are able to efficiently produce output power across a wide range, and independent of inlet and exhaust steam pressure.  This is something a turbine simply cannot do.  It is fundamental to distributed power applications, and is key to Terrajoule’s breakthrough in storage cost.

    • Energy storage is achieved via a “steam accumulator” built with insulated steel pressure vessels and filled with water.

tank container

Since it is impractical to store gaseous steam for later use, the steam is condensed into the mass of water where its energy is stored.  When needed, the stored energy flashes the water back to steam.  The energy lost in this steam-water-steam phase change cycle is less than 2%.  Terrajoule’s proprietary architecture allows for energy storage at below 18 bar, while achieving the efficiency of inlet steam at 42 bar.  At 18 bar we exploit the sweet spot for pressure vessel pricing that is driven by the worldwide Liquid Propane Gas storage industry (however there is only water, and no propane, stored in Terrajoule’s vessels).  The result is storage at less than 20% of the cost of batteries, with no degradation, no cycle limits, no toxic or rare materials, and a useful life of at least 25 years.

 Low cost, robust storage changes everything