Courtesy:Shetland College

In the Shetland Islands, not currently part of the UK’s electricity grid, the main power plant, an oil-fired unit is reaching the end of its service life. But, the Islands have some of the best potential for wind generation in the world.

The local electrical utility, Scottish and Southern Energy (SSE), deciding to take advantage of the substantial wind energy potential by developing a smart grid and making use of smart energy storage systems. As part of its energy storage solution, SSE is fitting 1,000 homes on the Islands with smart electric thermal storage heaters and hot water tanks reports its supplier, Dimplex.
 
The issues facing SSE on the Islands’ wind project are similar to those of other renewable energy projects: when there is enough demand from customers relative to the energy being produced, the electricity from the wind turbines goes toward meeting that demand.
When demand drops relative to production, or there is too much electricity being generated, there is a need for some type of, what can be known as, "Demand Side Management" or more simply, storage.

For the Shetland project, SSE selected an active grid network, connected to multiple energy storage systems. SSE will use some of the excess power electricity from the wind turbines  supplying reduced-rate electricity directly to customers with  next-generation storage heaters installed.

The utility will manage demand from a central location by sending commands to the various devices, while guaranteeing an acceptable level of comfort for the residents.

SSE outlined several requirements for the energy storage system needs. The heaters would have to be continually energised accepting a trickle charge to a default level, while being able to respond rapidly to an increased charge to meet the requirements of the coldest days, or support the electrical network’s frequency response.

The heaters would have to accept power continuously at varying power levels and be extremely well insulated to minimise static heat losses; the units would have to be compatible with SSE’s interactive demand management system and be cost effective.

Dimplex, claiming to be the world’s largest storage heating manufacturer, developed a smart storage heating system that met all of SSE’s requirements. The heaters work with SSE’s smart grid system and other ZigBee based system specifications to accept surplus wind power when available, store this as heat energy to meet the homes’ heating requirements, no matter how harsh the Shetland Islands’ weather.

An American pilot

The full danger of excess renewable energy supply appeared in a the US in a June 2010 emergency, when a severe storm through the Bonneville region between Oregon and Washington so loaded the transmission network that the authorities had to turn off all fossil fuel generation, give electricity away to neighbouring networks and even cut local nuclear plant production by 78% reports  the New York Times.

As a result, the Bonneville Power Administration, decided to recruit volunteers with home appliances to link up, allowing a pilot remote control to balance supply and power. Now if excess supply threatens the grid, a control room operator dials a volunteer's water heater and raises the thermostat by 60 or more degrees, and ceramic brick in a nearby electric space heater can be warmed to hundreds of degrees. Devices then act as thermal batteries. Microchips run both systems, ensuring that tap water and room temperature hardly vary.

Goal of Bonneville’s pilot programme is to gain know-how in charging and “discharging” water and space heaters, and assess how much response operators can count on as the use of such thermal batteries expands.

Threat of excess supply now threatens to destabilise an electric grid system just as much as a shortage. California is now committed to getting one third of power from renewables by 2020, much harder to do if it has to turn off wind machines on best generating days, simply to prevent the grid from being overwhelmed.

Bonneville began advertising for volunteers to accept extra electricity, mainly from homeowners with electric heat and with newer water heaters. Plumbers install a mixing valve on water heaters to keep faucet temperature safe, while new wiring and a small computer keeping track of energy flows.

The agency says that some 200 homes will have the adapted water heaters, space heaters or both. In hundreds more homes, it is installing more traditional controls, that allow it to turn water heaters off. Portland General Electric, another regional utility is also to begin a similar program paid for by the federal Energy Department.

Currently devices collectively absorb the output of only a handful of wind turbines. A 100-gallon home water heater can store about 26kW hours, or a day’s worth of electricity for a typical house, but less if the house relies on electricity for heat.

Ceramic bricks in the space heater can store 40kW hours, or more in some larger configurations. Heat can be drawn off by passing air and delivered to living spaces by a fan, with bricks functioning as thermal batteries.

Some equipment dates from the late 1980s, designed for cheap “time of use” rates. But broad area coordination by a utility, managing regional flows is new.

An open question that remains is who pays for installations that are carried out on a larger scale? Additional ways of compensating consumers may be needed to get the thousands of volunteers required to make systems effective.

If installations benefit everyone by improved stability, cost might be spread among all ratepayers. But if installations mainly benefit wind generators, because they never have to unplug turbines, it is arguable that industry might have to foot the bill.