Sparks

Ensuring renewables’ reliability

 By Nicholas Newman

As renewable energy becomes cost-competitive with conventional power sources, its market share has grown from 22 percent in 2012 to 29 percent in 2040 worldwide. However, for renewables to truly close the gap between present capacity and potential, the challenge of intermittency must be addressed…

Grid Solutions

Utilities have produced a variety of mechanisms for improving the reliability of renewables. These include the use of smart grids, interconnectors, peaking plants, energy storage and hybrid power plants. For many, storing clean energy power is the holy grail of the green energy revolution. However, high operating costs and limited storage capability of current battery equipment are handicapping this process. Smart grid technologies are aiding grid operators to match ever-changing output with demand in real time. A range of technologies is being used including improvements in weather forecasting and installation of smart meters.

How we support the Energy sector (Met Office - Weather)

Electricity grid interconnectors, which connect local and national power grids, provide another option. The British and Norwegian power grids are planning to build a 1400 MW North Sea Link interconnector across the North Sea. This planned £1.4 billion power link will enable increased production and use of renewable energy in both countries.

North Sea Link (power-technology.com)

Power generation

Utilities are using gas and diesel fueled peaking plants known as gensets to offer standby power when renewables supplies are scarce. A case in point is UK Power Reserve Ltd, which operates 40 small gensets with a total output of 693 MW, supplies the UK grid network. Hybrid power plants use a range of electricity generating technologies, designed to meet a wide spectrum of energy needs. For satisfying grid power needs at peak times, the proposed joint Pumped Hydro Storage (PHS) with solar and wind project in Prosper-Haniel in Germany provides a interesting example. Instead of locating the planned PHS scheme in a mountainous region like the Alps, the project sponsors have chosen a closed coal mine. The scheme consists of two lakes; one lake is located on the surface and the other some 1,200 meters below ground. In addition, a shaft links both lakes to a joint power plant and pump facility. To produce electricity, a million cubic meters of water drops down the shaft powering a turbine. When demand for energy is low, the turbine spins backwards and pumps the water back up from the underground lake to its companion on the surface. This enables the surface lake to provide water to produce electricity when it is needed. The electricity to power the pump comes from nearby wind and solar farms on the surface.

Coal mine in Germany turns into hydroelectric battery (mining.com)

On a smaller scale, William Ross Williams of CEO Altresco Companies states, “Hybrids are being deployed as part of micro-grids where resiliency is important. William adds, “This makes them ideal for serving remote communities, mines, business, and industrial parks.” For instance, CRONIMET Mining Power Solutions operates the world’s largest solar-diesel hybrid facility in South Africa. This unit has shown that a solar-diesel hybrid plant can reduce the diesel fuel used by over 30 percent.

Energy storage

The ability to store green energy affordably is likely to transform renewables prospects. In 2015, in the US, some 226 MW of energy storage capacity was installed. This is forecast to increase to over 2000 MW in 2021. At present, there are a number of energy storage solutions available, including established pumped hydro and pioneering thermal energy storage. Thermal energy storage uses molten salt to store energy produced from solar plants. Such examples of the use of this technology include Crescent Dunes in Nevada and Morocco’s Noor 1 projects.

Solar Thermal Storage Tank (G. Scott Davis)

Another option is the use of batteries, today’s big battery systems can only store enough power to satisfy a few seconds of global electricity demand states the IEA. The key to future success of this technology is reducing the cost and increasing the capacity of batteries. At present, Lithium grid scale batteries provide electricity users power at $321 per MW hour, as compared to $152 per MW hour for electricity using pumped storage hydro. However, investment costs are considerable for pumped storage as compared to grid-scale batteries.

Pumped Hydro Storage

Pumped hydro storage uses low-cost surplus off-peak electric power to pump water from a lower to a higher reservoir. At peak demand for electricity, the stored water is released through turbines to produce electricity, which is sold at a profit. Even so, in terms of the overall energy used, the losses of the pumping process makes the plant a net consumer of energy overall. However, the system increases revenue by selling more electricity during periods of peak demand. Examples of such pumped storage projects include the 450 MW Tam Sauk plant in the US and Iberdrola’s 2000 MW Cortes-La Meela in Spain, which is Europe’s biggest.

How does GE’s Hydro Variable Speed Pumped Storage technology work? (GE Renewable Energy)

Batteries

A battery production boom is underway primarily to service growing production of electric vehicles. As a result, the price of lithium-ion batteries has halved in price since 2014. It is expected that as more large battery factories are constructed, the price of batteries will fall further. Best known is Tesla and Panasonic’s Nevada Gigafactory, but this is only one of at least 14 mega factories being built across the world. Already, batteries paired with solar panels to produce electricity are in operation in the Chilean desert and Hawaii. In the UK, the utility Centrica is building a 49 MW battery storage facility at Roosecote in Cumbria. Britain alone is constructing 500 MW of grid battery storage nationwide. Such facilities deliver backup electricity and cut the need to build dedicated power plant capacity. Elsewhere, in Australia, some 6,750 home battery systems alone were sold in 2016. It has been forecast by 2020 Morgan Stanley analysts that about 1 million Australian homes could have batteries and solar panels. Nevertheless, worldwide, battery technology is not yet ready for households to turn their roofs into mini power stations.

New technologies have widened the opportunity for the power sector to improve the dependability of renewables. The future is likely to see the cost of renewables continue to fall alongside those of batteries. One thing is certain, we can expect the worldwide adoption of information technology to improve command and control of electricity inputs and battery storage solutions.

SEE MORE: Powering the energy storage revolution by Mike Scott

about the author
Nicholas Newman
Freelance energy journalist and copywriter who regularly writes for AFRELEC, Economist, Energy World, EER, Petroleum Review, PGJ, E&P, Oil Review Africa, Oil Review Middle East. Shale Gas Guide. https://nicholasnewman.contently.com/