In China’s arid northwest, a solar thermal plant faces a unique problem. It has nothing to do with sunlight.
The desert delivers heat in abundance. But in summer, that heat overwhelms the condensers.
This lowers efficiency right when demand peaks. Water cooling is impossible because water is too scarce.
A new simulation study proposes an unexpected fix. The plan captures intense winter cold to store underground.
Months later, it cools the plant through summer. It makes you wonder what this trick is like.
The cooling problem hiding inside a solar power plant
Concentrating solar thermal plants generate electricity like coal or gas plants. They boil water into steam to spin a turbine. Then, they condense the steam back into liquid.
That condenser step must dump heat somewhere. Usually, plants pull water from a nearby source or blow ambient air across the system.
Neither option works well in Dunhuang, Gansu province. Freshwater is too scarce for large-scale cooling.
Dry air-cooling sidesteps that issue but carries a high cost. When summer temperatures soar, the condenser cannot shed heat. Plant output drops exactly when the grid needs it most.
Dunhuang has an extreme seasonal swing. Winters are bitterly cold, and summers are brutally hot.
Could winter’s chill be stored underground for summer use? It makes one curious about what this climate-defying setup is like.
How borehole thermal energy storage works
The technology at the heart of the proposal is the borehole heat exchanger, or BHE. These are vertical pipes drilled deep into the ground.
A fluid circulates through them to exchange heat with the surrounding rock.
People already use this infrastructure for geothermal heating. Now, researchers are repurposing it for cold storage.
During winter, freezing air chills the circulating fluid. This fluid carries that cold energy downward into the borehole field. The ground absorbs the chill over the season.
Come summer, the process reverses. Warm condenser water routes through the same boreholes.
The ground is still cold from winter. It absorbs the heat and returns cooled water to the condenser.
This happens without drawing on scarce water supplies. Subsurface temperatures remain stable.
Rock and soil hold high heat capacity. The ground functions as a slow thermal battery. We naturally ponder what this subterranean vault is like.
Simulating a year of operation with TRNSYS
To test the concept, researchers used TRNSYS. This simulation program models energy systems dynamically.
It tracks how conditions change hour by hour. It avoids steady-state averages.
The simulation relied on Typical Meteorological Year data for Dunhuang. This data compiles historical hourly weather records.
Using it, the team identified the lowest ambient temperatures. They pinpointed the optimal window to charge the borehole field.
Key outputs included ground temperature evolution across the field. They tracked how much cold energy was stored and retrieved.
They also monitored fluid temperatures at the inlets and outlets. One can only imagine what this complex virtual testing is like.
Efficiency gains and water savings
The simulation results are highly encouraging.
The seasonal cold storage system raises plant efficiency by up to 1.54% compared to a conventional water-cooled condenser. It raises efficiency by up to 2.74% compared to a dry air-cooled condenser.
Those numbers may sound modest. At utility scale, a 10-megawatt plant runs across a full operating year. A 1% to 2% efficiency gain translates into meaningful extra electricity. The effect compounds over years.
The water savings matter just as much. Replacing evaporative cooling with ground-stored cold eliminates a substantial freshwater draw.
This is vital in a water-stressed region.
The concept aligns with China’s push to expand solar thermal capacity in its arid western territories. Land and sunlight are plentiful there, but water is not.
The data forces us to envision what this eco-friendly balance is like.
Does the economics add up?
The study includes a techno-economic assessment. It covers capital costs, maintenance, operational expenses, and the payback period.
Integrating the borehole system with the condenser unit is financially viable.
Borehole systems carry high upfront costs because drilling is capital-intensive. Once installed, however, operational costs are low.
Mechanical chillers require ongoing energy input and frequent maintenance. Over a long project lifetime, the borehole approach wins out.
The researchers acknowledge an important limitation. The entire analysis is simulation-based.
Real-world performance depends on subsurface geology and actual drilling outcomes. Models can only approximate these factors.
Field pilot data is needed to confirm these results under genuine conditions.
If a pilot succeeds, seasonal underground cold storage could become a practical tool. It will expand solar thermal power in water-stressed regions worldwide.
It is like freezing time itself, burying winter’s breath to conquer summer’s fire.
The study offers a complete review: Abbas, Z., Li, Y. & Wang, R. Numerical simulation of underground seasonal cold energy storage for a 10 MW solar thermal power plant in north-western China using TRNSYS. Front. Energy 15, 328–344 (2021). https://doi.org/10.1007/s11708-020-0676-1
Disclaimer: The content of this guide is not intended to replace professional advice or official sources. It is for informational purposes only and should not be used to make economic or non-economic decisions.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
