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Daedalus was the mythical great architect and artificer of the classical world. Today, embedded intelligence is enabling the most profound changes in the way we create and use buildings since his day.

Building Intelligence meets the Intelligent Building. The Intelligent Building negotiates with the Intelligent Grid. How will this transform how we interact with the physical world?

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Tuesday
Dec082009

Distributed Energy Grids can use Diverse Energy Storage

But there’s no way to store energy, he said. What he should have said is that there are few ways to store energy at grid scale. Grids, and microgrids, have two approaches to storing energy. They can store it in something that produces electricity, or they can store it in any format that provides a service to its customers. The closer we get to the end users of energy, the more options we have to store energy. The most critical short term goal of smart grids might be to transfer as many incentives for energy storage to the end nodes of the grid as possible as soon as possible.

Very few of us want electricity—we want instead to have a modern life-style. This means we want ready access to sanitary services, whether clean water or working waste disposal. We want light, and heat (or cooling). We want our appliances to provide whatever services we bought them for. Digital electronics provide us with the most direct conversion of electricity to desirable service, but even there we may be able to store services.

Behind every meter there is a microgrid, which exists to supply the wants of its customers. The customers of transmission and distribution grids only want electricity, and they want a lot, so these grids are limited in how they can store energy. Any storage that these grids do use, must be big enough to support the transmission or distribution scale of operations. For example, pump storage, wherein water is pumped up in the air, and used for hydro-generation later, is a very efficient way to store the energy in electricity for later use. Transmission-scale pump storage, though, must be as big as a small lake. There are a limited number of locations to place a lake with a down-hill water supply where filling and draining the lake is an acceptable option. We may have used all of them in North America already.

There are not many more options for distribution scale storage in traditional local microgrids. Non-traditional microgrids, however, distribute more than electrical energy. District energy grids distribute thermal energy, whether in the form of heat (steam) or of cooling (chilled water). These systems can pre-cool (or pre-heat, although this is less common) water for distribution. Thermal storage lets district energy microgrids shift energy use to off-peak hours. In a modern transactive grid, such shifting can be part of demand response. Microgrids with significant thermal storage may be able to run entirely on site-based alternative energy during peak hours. They may be able to store off-peak generation converted to thermal energy.

Non-energy utilities have their own grids supported by the distribution grid. A significant service in cities is the supply of water, and water pressure. This is done by pumping water high into the air, using energy-intensive pumps. Water towers can easily become locations for energy storage, off-loading electrical use until when energy is cheap, and the pumps can run inexpensively. This local pump storage is not used to generate electricity, but within its limits is an effective way to shift energy use to times when energy is cheaper and more plentiful.

When the microgrid gets down to the size of a single commercial building or home, all sorts of energy storage options become available, if only we do not confine ourselves to electrical storage. High rise buildings pump water to so toilets will flush. Thermal storage can be in basements or rooftops. Some data center strategies could even be considered to be storing up business process for use later.

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