A group of Australian engineers in California USA are about to run a live demonstration of a solar technology that rivals all others when it comes to a total system solution. Using thermal solar heating, s rejuvenated steam engine technology, and a storage system that is a fraction of the cost of any other, they have a solution can have a ROI within three years without a subsidy.
Idiotically the complete system demonstrated will have a 100KW out put 24 hours per day, with a peak output of over 300 Kilowatt during the day. As the industry well knows, solar is cheap to deploy, however storage is the Achilles Heal. Typically any type of storage is over $1000 USD per kWh capital cost. Some systems in the future my reduce this to sub $200 USD. The DGS Terrajoule has reduced this to $60 per kWh. This project will demonstrate the ability of the DGS to convert, store, and discharge renewable energy without fossil fuels or large-scale chemical battery energy storage and show that the renewable energy can be used for on-demand power generation as backup to key nodes or provide peak power mitigation.
The Terrajoule DGS system is comprised of three major subsystems: the Solar Collectors, Steam Driven Generator Unit, and Superheated Water Energy Storage.
- Solar Collector Subsystem. Solar concentrators generate steam while the sun is shining. A portion of the received energy is converted immediately to output power and the balance stored for later (night-time) use. For collectors, industry-standard RP-3 parabolic troughs, circulating oil Heat Transfer Fluid (HTF) through heat exchangers to produce superheated steam at 42 bar pressure and 315 degrees C, are currently used.
- Steam Driven Generator Unit. The steam is converted to mechanical rotating shaft power via a modular steam engine, which is operated at constant, increased, or decreased output depending on load requirements. It is a multistage expansion system with four stages, the first stage consuming steam at up to 42 bar / 315 degrees C and the fourth stage exhausting into a sub-atmospheric condenser at approximately 0.063 bar and 37 degrees C. The design of each engine stage is derived and updated from a Skinner Universal Unaflow design, used for stationary and marine power through World War II. The engine drive shaft is used to drive a standard electric generator.
- Energy Storage. Energy storage is embedded in the system via superheated water, stored in an insulated pressure vessel at operating temperatures between 130 degrees C and 170 degrees C (corresponding to pressures between 2.7 bar and 7.9 bar). The pressure vessel used is an insulated commercially available 30,000 gallon LPG storage tank. Insulated with 12 inches of standard building insulation, the daily energy loss is less than 2% of stored energy. A single 30,000 gallon storage tank will store sufficient thermal energy that, converted by the engine system to electrical energy, provides 1,200 kWh of electrical energy. Multiple tanks provide energy storage as required.
The DGS system can provide on-demand clean distributed power generation with minimal maintenance and operating cost. It operates as an off-grid, standalone on-demand power source up to 24 hrs per day, and as an economical grid-connected power source that will continue providing power during interruptions of grid power, during sunlight, in cloudy conditions, and after dark.
Target markets include customers who understand the difference between capex and opex” and who will buy products based on realistic payback times. He adds that, “Straight solar power doesn’t address the farmer’s energy problem — they want power when they want it.” Terrajoule’s initial target market is the more than 300,000 electric and diesel-powered irrigation pumps in the solar-rich western US. Bisset says the technology will work in other applications, for example manufacturing plants, off-grid locations including mines, and even entire towns.
Terrajoule’s systems have a modular unit size of a 300 kilowatt peak/100 kilowatt flat output over the day. Customers need to use the system 1,000 to 2,000 hours per year and consume more than one megawatt-hours in order for the Terrajoule system to be economical. Most Western United States agriculture users fit this profile, according to Bisset. Most factories fit this profile, as well.
Because the system is CSP, it still needs a relatively high DNI, and “California’s Central Valley is more than adequate,” according to Henkel-Wallace, the VP of Engineering.
Henkel-Wallace provided some numbers on cost and efficiency:
- Storage has a capital cost of $60 per kilowatt-hour of storage capacity, the typical configuration provides 12 hours of storage.
- The firm foresees the levelized cost of energy (LCOE) as under 10 cents without government assistance with a three to five-year payback.
- CSP troughs have an efficiency of approximately 70 percent and the steam cycle efficiency is above 30 percent for an overall system efficiency of 22 percent.