Polar Works-Inlet Cooling Technology Overview-Thermal Energy Storage

Thermal Energy Storage

Thermal Energy Storage (TES) is a subset of the refrigeration-based inlet cooling technologies. TES can significantly lower the size of a refrigeration system, and also lower the parasitic electrical load of the refrigeration cycle during peak revenue hours. TES is typically employed at power plants that are peakers, or which have significantly differing revenue structures for off-peak vs. on-peak power.

For example, if a peaking gas turbine operates only 4 hours per day, it doesn't make much sense to build a refrigeration plant that operates at full load for only 4 hours a day too. This is because refrigeration, unlike electricity, can be "stored." So, it makes more sense to build a refrigeration system that is sized at about 20% of the peak load, and slowly make and store cooling capacity, discharging that capacity under peak conditions.

TES can also be used for base-loaded plants, while using the storage volume to "peak-shave" the highest cooling load during mid-day. This cooling storage can be built back up during the cooler evening hours, when it is more efficient and economical to make the refrigeration.

The power generation equivalent to TES is hydro pumped storage.

Cooling capacity is typically stored as ice or chilled water in VERY large tanks. TES is difficult to employ at sites that have severe space restrictions. These tanks also have a significant first capital cost. So performing the financial analysis for these projects can be a little involved, although most consulting energy engineers can supply at least rudimentary financial calculations of the TES benefit.

Alternatives to TES

An alternative to TES is to use gas-engine driven chillers, or gas-fired absorption chillers for the peak load. The higher first unit cost of these refrigeration systems is offset by the high capital costs of the TES tanks and infrastructure. Either way, the high electrical parasitic load of a standard vapor compression refrigeration system is displaced by these "gas cooling" alternatives.

A gas engine chiller is an ideal solution for a site that has limited run hours per day, and limited operating hours per year. A gas-fired absorption chiller can make sense for sites that have longer operating hours.

An additional benefit to TES and gas-cooling technologies is that the changes to the site's electrical infrastructure can be minimized. One challenge to back-fitting electric vapor compression to most sites is the placement and connection of a large transformer for the new electrical loads. With TES and gas cooling technologies, the electrical load of the new equipment is significantly reduced, and there may be sufficient capacity in the plant's existing motor control centers for the smaller loads.

The Polar Works system can also be used in a TES mode. In fact, we can store desiccant cooling in the same way that we can store refrigeration, so that the leverage benefits of the Polar Works Inlet Air Cooling system can also be employed in the same way in a TES mode.

At Polar Works, we expect to see more novel approaches to the inlet cooling industry due to the new financial rules being played out in the deregulated electrical market. TES and gas cooling technologies will take a more prominent role in advanced cooling projects.