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.

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From a million miles up, the problem with the power grid is that it is an over-spanned control system with no buffers. Thirty years ago, the grid had safety margins to handle volatility in demand; today, those margins are razor thin. Until recently, large predictable generators (coal and nuclear) supplied most electricity; our current plans are to replace them with intermittent sources. The brittleness of a large system without buffers is about to increase.

Energy storage is attracting a lot of attention today as a way to manage volatility and the lack of buffers. Fast start generation to back up volatile energy sources so far looks more expensive, in terms of fossil fuels consumed, than not using the volatile sources at all. Even the perfection of fast-start technologies will not address the episodic surpluses of energy generated by renewable sources.

The problem with grid-scale energy storage is that the solution set is too constrained. Grid-scale storage must either be electricity, or be something quickly convertible to electricity. The sheer scale required makes every solution expensive, or hard to site. The risk avoidance that we require of regulated utilities keeps the adoption of innovations slow. It will be difficult and expensive to buffer the grid.

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 deploy must be big enough to support transmission or distribution scale of operations. For example, pump storage, wherein water is pumped up in height, 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.

Microgrids, closer to the customer, have more options. A microgrid is restricted in size and in connections to the grid. Each of those connections should be metered. The smallest microgrids are buildings themselves; each commercial building or residence can be managed internally as its own microgrid. Microgrids do not have to limit themselves to storing electricity; microgrids can store any resource that provides a service to their customers.

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. Microgrids are close enough to the customer to store services other than electricity, services that customers actually want.

Behind every meter there is a microgrid, which exists to supply the wants of its customers.  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.

[an error occurred while processing this directive] 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. Water pressure is maintained 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-managing building water pressure in response to grid prices is effectively energy storage. Thermal storage can be in basements or rooftops. We could even consider some data center strategies to be storing up business process for use later.

Local buffers increase the value of local generation and energy harvesting. A wind generator on a building can be used internally to support any service buffer in the building rather than only for sale to the grid. We may even want to consider whether we want wind to pump water directly in a building rather than to generate electricity to run a pump for local pump storage.

Any system that uses energy to produce a service, can provide a buffer for the grid if that service can be buffered. There is no reason at all to limit our concepts of grid energy storage and buffers to electricity and batteries—and many opportunities open up if we do not. All these new services and new energy buffers should be responsive to smart grid signals.

Systems in smart or automated buildings are close to the occupant and under the control of the owner. System integrators in smart buildings know more about how to value each local service than grid operators ever will. Take control of your customers’ micro-grids, and plan now to offer service buffers, taking advantage of the smart grids needs for buffers.

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