There has been a lot of talk lately about renewable energy not being up to the task of supplying reliable baseload power. The sun doesn’t always shine and the wind doesn’t always blow, detractors claim, so how can utility companies expect to rely on either? Pintail Power, based in Silicon Valley, says its new patented Dispatchable Solar Combined Cycle technology is the answer.
If you follow renewable energy news, you are familiar with the concept of “time shifting.” In essence, that means collecting electricity from renewable sources when the sun is shining and the wind is blowing and storing it for use later in the day. Time shifting strategies include pumped hydro — using excess power to pump water uphill during the day and letting it flow back downhill later, spinning electrical turbines along the way.
Battery storage systems like those provided by Tesla to South Australia are gaining in popularity. Concentrated solar power uses the energy of the sun to heat a storage medium — usually salt — and then using that stored heat later to generate steam to run conventional turbines. Some people even want to build a railroad to nowhere in the Nevada desert. Filled with rocks, it would go up a mountain when excess power is available and generate electricity when it rolls back down the track later.
A pintail is a duck, and the duck curve is a well known concept to utility engineers. If you draw a curve that represents the demand for electricity over the course of a 24 hour day, the shape resembles a duck. The duck curve has become more pronounced lately in places like California, which often has more renewable power available than it can use.
The company announced in a press release on December 5 that its new Dispatchable Solar Combined Cycle technology “greatly enhances the performance and cost-effectiveness of thermal storage by dramatically increasing the efficiency by which this stored energy is converted back to electric power. Our patent pending technologies deliver breakthroughs in the cost-performance ratio, and enable bankable projects that can be sited anywhere, constructed quickly, and scaled to meet demand.”
William Conlon, CEO of Pintail Power says, “This is the first of a new class of hybrid power systems designed to overcome the Duck Curve — essentially the challenge of PV solar over-generation during the day and the need for fast ramping energy to meet customer demand as the sun sets. DSCC creates synergy by using thermal energy storage to integrate conventional and renewable power, increasing the amount of solar energy delivered by 25% and reducing the cost of energy by 32%. Bottom line: customers benefit from a more efficient and more responsive system while significantly reducing the cost of energy.”
I’m an OK writer but I am no engineer. So I reached out to Bill Conlon to help me gain a better understanding of the process. In an email, he told me, “A Combined Cycle Power Plant (CCPP) uses the exhaust heat from a combustion turbine to make steam that produces additional power in a steam turbine. CCPPs are the current state of the art for efficiency and energy cost for thermal (fossil fuel) generation.”
The influx of electricity from solar panels is reducing capacity factors fore CCCP’s, Conlon says. “One approach to this challenge is the Integrated Solar Combined Cycle to merge solar-thermal-generated steam with the steam produced from the turbine exhaust. For various technical reasons, the ISCC has minimal economic and environmental benefit over a CCPP.”
Here is the meat and potatoes of the Pintail Power technology. “The DSCC invention changes how the turbine exhaust heat is used,” Conlon says.
“In the conventional CCPP (and the ISCC) roughly two-thirds of the exhaust heat is used to evaporate the water, with the rest used to heat water up to the boiling point and then superheat the steam.
“Instead of evaporating steam using exhaust gas, DSCC boils the water externally. It still uses exhaust heat, but now only for heating water and superheating steam, using the two-thirds of the energy formerly used to boil water. This means we can use 3 times as much steam with the same combustion turbine exhaust energy, to produce three times as much overall power from the steam turbine part of the CCPP.
“Solar thermal energy, which can be stored cost-effectively in molten salt, can be used to boil the water. The net result is that much more solar energy can be productively used than in ISCC – up to 30 times more. Because much more power is produced with the same amount of fuel, the fuel efficiency is dramatically improved over the conventional CCPP.”
Conlon says the technology will work especially well for customers in the Middle East and China. Any system that helps overcome the “sun don’t always shine, wind don’t always blow” objection is good news for renewable energy advocates. Not every storage solution is appropriate to every location and situation. Pumped hydro, for instance, may work well in mountainous regions like Switzerland but not so well in the Sahara Desert.
Having access to yet another strategy — like the hybrid system pioneered by Pintail Power — will help drive the clean energy revolution forward and reduce the amount of fossil fuel needed to generate electricity. That’s good news for the earth and everyone on it.
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