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Greening the Local Grid

Smart solutions for distributed renewables.

Fortnightly Magazine - February 2011

adjacent power pools to take advantage of diverse generation mixes also offers a viable solution strategy. Greater diversity of resources, including geographic diversity of a single type of generation resource, increases the overall predictability and reliability of the system. But this may require adding significant transmission infrastructure with its associated financial and environmental costs.

A further example of mechanisms to address the impact of intermittency is the application of new technologies to allow more visibility into the operation of the power grid. This is especially applicable for the distribution system, and can also provide control over the system to ensure system stability, performance and reliability.

The broader interpretation of proposed smart grid solutions can support all of these potential solution themes, but currently available and emerging technologies can specifically assist with demand response, energy storage and grid operations based alternatives. These solutions include new devices (sensors, switches, controls) out on the electric system itself; equipment and applications that engage consumers; energy storage technologies that allow renewable energy to be produced when it’s available and used when it’s needed; as well as more integrated control and operations.

The Demand Response Solution

Energy usage isn’t constant. Except for a very few number of users—such as 24x7 server farms, or constant industrial multi-shift processes, energy consumption goes through a well-understood pattern. The pattern changes according to customer type, geography, day of the week, or season. But by aggregating the profiles for various customer classes, an overall system profile can be obtained. Utilities have relied on all available generation, interconnection resources, and traditionally built peaking plants to meet the demand at peak conditions. Demand response offers a different solution to this problem; rather than increasing available generation capacity to meet peak, the utility can reduce the load and lower the peak to meet available generation capacity. This option provides a much more economic and environmentally low-impact solution to meet peak conditions, which tend to occur less than 5 percent of the days on average.

For industrial or commercial customers, demand management solutions are customer-specific and usually involve shutting down processes or production lines. In office buildings, it could be cycling the air handlers and lowering lighting. For residential consumers, traditional demand response solutions focus on direct load control where the utility uses a combination of a special purpose communication network and customer premise equipment to control appliances. Due to the preponderance of residential loads, most utilities peak in the early evening when people return home from work. Much of this is A/C in warmer climates and space heating in cooler zones, with cooking and general appliance use contributing to the peak. Direct load control programs have proven effective, and this proven basic load control technology remains very viable today, and a key tool for utilities to manage peak energy consumption.

Recent advances in technology have also resulted in more customer-interactive and perhaps arguably friendlier solutions such as controllable programmable thermostats (PCT) which function in a manner similar to DLC in that they allow the utility to control the A/C units, but these allow the customer to