Thermal Energy Storage and the Benefits of Distributed Power Storage

As the total electricity consumption in the US is projected to continue rising, innovative use of technology can more efficiently use the existing generation capacity to meet this increase in consumption without having to build additional power plants, by shifting the peak demand of electricity usage.  In effect, level out the load curve by shifting the consumption of electricity from peak hours (i.e., during the day) to off-peak hours (i.e., during the night). 

A large percentage of peak demand is generated by the summer time use of residential air conditioners.  Residential air conditioning accounts for the largest percentage of total electricity consumed in the home, approximately 16.0%[1].  During hot summer days, meeting the electricity demands from residential air conditioners can be problematic for utilities, which may be required to build additional power plants just ensure that the electricity demanded at peak hours during a couple of the hottest summer days can be met.

This is where the use of innovative technology, such as thermal energy storage, can shift the timing (peak hours to off-peak hours) of electricity usage from air conditioners and thereby reduce the need to expand generation capacity.  A company called Ice Energy is attempting to do exactly that, by using ice. Ice Energy recently signed a contract with Southern California Public Power Authority to provide 53 MW of storage in the form of rooftop air conditioner units that use off-peak electricity to make ice that is then used during the day to provide the cooling[2].  These units thereby reduce the electricity required during peak demand by relying on the ice instead of an electric compressor to cool the air. 

The use of these types of thermal energy storage systems can be considered a type of distributed energy storage because they are located at the load instead of the source.  This can have several advantages over a centralized power source (e.g., a gas peaking power plant) in that they require no additional infrastructure, no permitting or siting requirements, and they only require electricity that is already available.      

As the US grabbles with how to satisfy increasing energy consumption, deal with potential climate legislation, and meet the rising cost of energy production (the current price for a 300MW coal-fired power plant is about $1 billion[3]) the use of distributed energy storage systems could help address all of these challenges, at least partially. 


[1] http://www.eia.doe.gov/emeu/recs/recs2001/enduse2001/enduse2001.html

 [2] http://greeninc.blogs.nytimes.com/2010/01/27/storing-energy-as-ice/?scp=3&sq=energy&st=cse

 [3] http://www.jsonline.com/business/29482814.html

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6 Comments

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6 responses to “Thermal Energy Storage and the Benefits of Distributed Power Storage

  1. bhgully

    Interesting stuff, I had no idea people were considering such methods. Would be very neat to take a look at the technical details/efficiencies of such designs.

  2. juliaharvey

    Definitely an interesting idea. I wonder if it would be feasible somewhere like Texas, where temperatures at night during the summer don’t drop significantly. Also, I wonder how much energy savings we could incur by not cooling our buildings to near-frigid levels.

  3. utpqd

    This is a very interesting idea and I can see how a system like this (found at the load) could potentially cut electric utility costs for companies with larger stores. I worked in the utility industry over the summer and and learned that the benefits of consuming off-peak electricity add up quickly. These benefits are part of what’s driving the new smart metering, which will allow customers to program appliances (washer, dryers, dish washers) to run during off-peak demand. Secondly, by designing this system at the load (ie: the company’s facility), the company will most likely own the equipment, as opposed to the utility company, who owns the power lines and transformers. By owning their own equipment, the company can better spec the equipment to maximize its benefits, rather than the utility company choosing what is most beneficial for the utility. All in all, this sounds like a decent approach to cutting costs for air conditioning, but I too would like to know the efficiencies of operating in different climate zones across the country. California gets pretty cold at night, but in Central and South Texas during the summer months…not so much.

  4. reidrb

    For an example of thermal energy storage at UT, check out the huge tank currently under construction behind Simkins dorm here on campus. That’s a four million gallon chilled-water storage tank, acting on a very similar concept to the ice units you posted about. At night, when the cooling demand on campus is low, the campus chilling stations fill the tank with 39 degree water. During the day, as cooling demand fluctuates, that 39 degree water will be distributed to campus and help level the load on the large centrifugal chillers in the chilling stations. The tank will store 41,000 ton-hours of chilled water (potentially offsetting about 10MW of electricity during 4 hours of peak demand).

    UT chose to build this tank for one of the exact reasons you mentioned: instead of increasing the size of their power plant just to ensure the peak summer cooling load is met, the power plant can remain the same size and handle an increasing campus cooling demand by filling the tank at night.

  5. dhjohnston

    I’m friends with Sarah Nathan, the Sales Rep for ICE Energy — the company is based out of CO, but she’s based out of Austin. Great gal, and the company is partnered up with about 1/2 dozen stimulus projects. Austin Energy was looking at working with ICE Energy to do something similar to the downtown communal chiller that’s been a big hit. However, the cost-benefit analysis apparently didn’t shake out to AE’s satisfaction.

    Neat little factoid about the ICE Box from ICE Energy — the coils were designed to snuggly wrap around a Coors light bottle.

  6. The idea of making ice during off peak hours is sound. Having said that we should make sure that we are not wasteful with our hard gotten ice. The principal cause of the peak electricity demand at UT and throughout is the demand for air conditioning on hot summer afternoons. How foolish we’d look to allow our buildings to heat up just to show how our a/c units and our ice inventory could overcome the heat. It’s worth looking at the amount of heat entering our buildings through the windows, particularly the infrared portion of sunlight. LBNL is on the trail of this one. During the 2013-2015 period they will study and document the physics and the economics and the practicality of window attachments, especially the externally mounted attachments.

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