In a virtual power plant, intelligent and centrally controlled biomass, hydroelectric and storage plants balance out the volatility of solar and wind plants

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The amount of electricity produced using renewable energy sources is subject to fluctuations, making the network unstable. Conventional plants can be used to balance the situation but their problem is their negative CO2 balance and lack of flexibility. Virtual power plants can ensure stability by automatically combining renewable energy sources based on availability, writes Dag Hoeft

Supplies of fossil fuels are running out. Extraction methods which are more complex and have a higher level of risk, such as fracking, are increasingly being used.

The unexplained problems surrounding its long-term storage and the associated financial and political uncertainties make nuclear energy a difficult option. There is an urgent need for environmentally-friendly alternatives.

There are numerous renewable energy sources that can be used. One possibility is solar energy, although it can only be produced during the day and is dependent on the weather.

Wind energy has been around for centuries, but the drawback is that availability and intensity are neither constant nor predictable. In addition, the noise produced and shadows cast by the rotors of modern wind turbines have affected their acceptance by society.

While hydroelectric energy can be stored and accessed quickly, availability is limited in some European countries due to geographical conditions. For political reasons, it is sometimes practically impossible for larger barrage and pumped-storage power plants to be built.

Geothermal energy has also remained rather a niche energy source in some areas of Europe.

Energy from biomass can also be stored and made available quickly via combined heat and power (CHP) plants. However, the associated land requirement competes with food production. The deforestation associated with the cultivation of biomass outside Europe should also be regarded extremely critically.

There is a need for conventional plants to regulate the demand for energy in order to balance out the volatility of renewable energy sources and keep the energy network stable. For example, in Germany that regulation is achieved by using power plants fired by hard coal and lignite, although these have an extremely negative CO2 balance. They may be old and inflexible, but they have already been written off financially, making them very cost-effective.

The alternative would be gas-fired power plants, which are easy to control and more favourable in terms of the CO2 emissions that they produce, but they are more expensive to run. A surplus of renewable energy has suppressed gas-fired power plants in favour of more profitable coal-fired plants.

Virtually networked

New intelligent strategies for production, storage, distribution and consumption are required. Virtual power plants – where different sources of renewable energy can be intelligently networked – provide the answer. Control and information technology enables the relevant energy sources to be combined automatically, based on availability.

Instead of comparatively slow coal-fired and nuclear power plants, in a virtual power plant, intelligent and centrally controlled biomass plants and hydroelectric and storage power plants balance out the volatility of solar and wind power plants, thus ensuring a stable energy supply.

Further potential for improvement lies in the intelligent integration of consumers. For example, sewage treatment plants use sewer gas itself to cover part of their energy requirement.

If a sewage treatment plant is integrated in a virtual power plant and there is a surplus of energy, the production by the sewage treatment plant can be stopped and the sewer gas can be stored in an appropriate gas storage facility or CHP plant. The sewage treatment plant will then get its energy from the grid, thus helping to ensure stabilzation in the process.

If the network requirement increases, the sewage treatment plant can supply additional energy from the sewer gas stored earlier. Pumped-storage power plants can also store mains energy and feed it back if required; however, due to the multiple energy conversions, the level of efficiency is limited.

This intelligent networking of different energy sources means that operators will be able to join the lucrative market of control energy with minute and quarter-hour reserves and thus improve their amortization and profitability. The higher the number and the greater the variety of energy sources there are, the better.

As soon as virtual power plants can provide the capacity required, fossil fuel ‘backup power plants’ can finally be shut down. The result will be a sustainably improved CO2 balance with no limitations in respect of energy availability.

Virtual power plants can ensure stability by automatically combining renewable energy sources based on availability

Credit: Mitsubishi Electric Europe BV

The availability and intensity of wind power is neither constant nor predictable

Credit: Thinkstock

Automation know-how

Sadly, there are no ready-made virtual power plants. Every installation is designed to meet individual requirements based on the specific type and number of participants. A variety of approaches can be taken in order to formulate a suitable solution.

Experienced specialists can help to configure a reliable and economical production setup while taking into account the trend for sustainability in society and the environment.

Powerful automation components with optimized energy consumption form the basis of any control system. Mitsubishi Electric’s portfolio ranges from complete converter substations for connecting wind and solar energy systems to the network, through PLCs for small applications or with several thousand inputs and outputs and intelligent remote terminal units – smartRTUs for short – for communicating securely and wirelessly with a master station, to contactors and fuse elements for controlling and protecting valves and drives as well as HMI devices in a wide variety of designs.

There are also powerful energy-saving inverters for controlling drives. Feedback capability and the possibility of temporary storage complement the design possibilities for energy-optimized control systems.

Powerful, finely scalable SCADA systems enable individual electricity generating facilities to be linked in order to create intelligently co-ordinated virtual power plants. Mitsubishi Electric offers products such as the process control system PMSXpro and the Mitsubishi Adroit Process Suite lifecycle software tool (MAPS) for ensuring that installations respond quickly and flexibly to demand from the grid and controlling the renewable energy power plants connected to them according to their utilization and capacity.

Like MAPS, PMSXpro also offers many options for centralized and decentralized plant operation, while also being certified to the VGB power plant standard.

Developing a renewable energy supply, including plants, networking and distribution networks, has to be financed. With the interest rate being so low at the moment and government bonds being barely trustworthy and offering little return, along with risky property and securities transactions, investing in renewable energies could offer a profitable option.

Dag Hoeft is Process Industry Technical Sales Consultant, Factory Automation – European Business Group at Mitsubishi Electric Europe