26 July 2006

Energy Storage and Demand Alignment

In my previous post, I stated that only Solar PV could replace the most expensive 4% of the electricity production in the United States. But there are other technologies that might be competitive for this purpose. One technology is Strorage. The other technology is Demand Alignment.

Hydro pumped water storage is used in some locales to store energy produced by baseload coal and nuclear plants so that it can be dispatched during periods of peak consumption. Of course, it only works in some locations where one can acquire a couple of resevoirs at different heights.

Another technology that is slightly more cost effective as well as being usable in more locales is CAES (compressed air energy storage). This can also be used to time-shift baseload coal and nuclear power. More interesting is to convert wind, which is produced intermittently (and thus is less valuable than baseload or distpatched load) into dispatchable load.

See for example
http://www.princeton.edu/~ssuccar/recent/Succar_NETLPaper_May06.pdf .
The above paper suggests a model of converting Wind into baseload power by placing the CAES close to the point of wind production and then transmitting baseload power over a transmission line to the point of use. Apparently, if you are going to build a long transmission line, you want it to run at a high capacity factor. This is not exactly the approach we want to use for peak shaving.

The dispatchable CAES model probably involves storing energy near the point of use. http://sandia.gov/ess/Publications/Conferences/2002/SCHOENING%20-%20ShortVsLongStorage.pdf
suggests that the this approach would cost around $0.32/kwh when used to replace the most expensive 4% of generated electricity and around $0.15/kwh when used to replace the most expensive 20% of generated electricity. In other words, attempting to store cheap energy during off-peak hours for use during peak hours is about as expensive as current techniques to produce enrgy during peak hours. (Hmmm... the markets seem to work.)

The other approach is demand alignment. We may be able to find applications which are flexible as to when they consume electricity and which currently consume electricity during peak hours and shift their consumption to off-peak hours. California is strongly trying to move in this direction by installing smart meters that support real-time pricing so that market signals can be given to candidate applications. The primary candidate application is water pumping to pressurize municipal water systems and to irrigate crops.

It will take three to five years for California to implement demand alignment. Other localities are farther away. But this is one technology that might slow PV adoption in the U.S. by reducing the cost of electricity generated during periods of peak demand below the cost of PV.



Anonymous texasgrand said...

Since wind is 95% off-peak, storage is essential.

Demand and supply are the major components of the cost of electricity. If we lower peak demand, supply will increase and the cost of power will fall significantly.

The primary method available to reduce demand is to make ice when electricity is cheap. Melt the ice for air conditioning when electricity is expensive or in high demand. This is a simple alternative to spending billions building new coal fired electric power plants.

Thermal Energy Storage, TES systems have been in use in Texas since the 1920’s in Dallas when three churches installed systems. One of the original applications was to use a small inexpensive compressor to make ice all week long and then melt all that ice to cool the sanctuary for two hours on Sunday. A common TES system is using tank type water heaters (hot thermal storage) to avoid large instantaneous gas or electric water heaters.

So why don’t we find a TES air conditioner in every house and small business? The answer is also simple:
• Most electric rates are averaged so it is not less expensive to buy electricity when it should be cheap and it is not more expensive to buy electricity in high demand periods when the price should be exponentially higher.
• In very round numbers it costs thousands of dollars per kW (or ton of A/C) to fund the construction of electric generation plants, transmission and distribution (TD) infrastructure. There are no mechanisms to divert funds from coal fired generators to funding TES systems in your home or business. The current conservative estimate of avoided costs to build generation, transmission and distribution infrastructure is $1000. per kW per year. This adds up to more than $45,000. over the 15 year life of a 3 ton TES system.
Should we invest $45,000 in new coal generating plants or invest a fraction of that in your home TES system?

If the above economic rationalization isn’t enough to convince you, consider the following additional benefits on TES.
• Running your air conditioner at night to make ice for daytime use is much more efficient because the ambient outside temperature is much lower and you’re a/c unit operates more efficiently.
• Running the generating turbine at night is much more efficient for the same reason, lower nighttime temperatures.
• All power plants run more efficiently when they are fully loaded and demand is predictable.
• Transmission and distribution is more efficient at night.
A massive deployment of TES will postpone the need to build additional power plants for many years and lower the cost of power for consumers. We can land on the moon. Why can’t we make ice?

17 February, 2007 07:49  

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