Steadily increasing demand for electricity and power shortage incidents, issues of power quality, regular power outages and increases in electricity rates have led many customers of conventional power suppliers to opt for other high-quality, stable power sources. Distributed energy resources, which are small-scale local electricity generating units, can produce power near consumption points such as industries or homes as a substitute to or an advancement of the conventional power grid.

Distributed energy technologies include solar cells and wind turbines. Source: Pixabay

Introduction

Distributed energy resources represent a quicker and cheaper alternative to constructing fossil fuel-based power plants at a large scale and high-voltage transmission lines. They give customers the opportunity for reduced electricity bills, better flexibility of operation, good power quality, improved energy usage and energy independence. Environmental benefits can also be gained from the use of sustainable distributed energies and green energy technologies such as photovoltaics, wind turbines, biomass, natural gas turbines, geothermal systems, fuel cells and hydroelectric power.

The traditional power grid is changing because of the advent of these distributed energy resources as they allow bi-directional power flow and serve to decentralize electricity markets. Distributed energy resources can also include inverters (power electronics devices that convert DC into AC), electric vehicles, more controlled loads such as hot water systems, energy storage and behind the meter non-renewable and renewable power generation. Simply put, behind the meter means power that is produced at the end user’s end. In comparison, the power that is produced at the grid station is referred to as the front of the meter. The distributed energy resources web does not end here; it also includes the latest technologies such as data services and smart meters. All these individual elements of distribution energy resources function together to develop distributed generation.

Distributed energy resources technologies

Microturbines generate power in the range of 25 kW to 500 kW as small-scale combustion turbines. They are developed from turbines found in aircraft auxiliary power units or turbocharger systems available in big trucks. The traditional combustion turbine is being used both for centralized power production and distributed energy generation. These produce power in the range from 500 kW up to 25 MW when working as a distributed energy generator and can produce up to 250 MW when working as a centralized power generator. Dual fuels (a mixture of fuels) and natural gas are used to feed such combustion turbines. The latest combustion turbines utilizing single-cycle are generally 20% to 45% efficient when working at full load and are less efficient when working at a load lower than full load.

Another distributed energy technology is the internal combustion engine that transforms energy stored in a fuel into mechanical energy, which in turn moves the shaft of the engine. This rotational movement is converted into power using a generator connected with the internal combustion engine. They come in small units such as 5 kW for residential backup power to large 7 MW units. The external combustion engine, a Stirling engine, is also a distributed energy technology. These use an inert working fluid such as hydrogen or helium and are sealed generators, and are also available in small sizes ranging from 1 kW to 25 kW.

Fuel cell-based on-site electrical generators are highly efficient, clean and quiet, and harness electrochemical processes to produce electricity from fuel. These units can also offer a thermal power source for absorption cooling or space and water heating. Research has demonstrated fuel cells to reduce power service costs by 20% to 40% when compared with traditional power service.

Another interesting distributed energy resource technology is uninterruptible power supply (UPS) systems or energy storage devices. They generate no net power but can supply energy for short time intervals. Utilities use them to correct flicker, voltage sags and surges that may be generated from load switching. Solar or photovoltaic cells use sunlight energy to produce power when arranged into flat plate structures, which can be installed in sunny locations or on rooftops. They produce power without any moving parts, need little maintenance and work quietly without pollution.

Wind turbine distributed energy systems exploit wind energy to generate electricity. A turbine with fan blades is fitted at the tip of a tower designed to tap winds at fast speeds. An individual wind turbine can produce power ranging from a few kW to over 5 MW for domestic use.

Currently, distributed energy resources manufacturers and developers are exploring ways to use a combination of these technologies to boost the reliability and performance of generation equipment. For example, wind turbines can be combined with diesel backup generators and battery storage systems, Stirling engines and solar cells can work together and solid oxide fuel cells can be integrated with a microturbine or gas turbine.

Conclusion

Distributed energy resources offer numerous advantages to both the consumers and the utility. Consumers can pay lower electricity bills as the power produced can be sold back to the national grid. They can also be rewarded for permitting their storage systems to assist in balancing the grid, particularly at peak times, and increase overall power supply system reliability.