Electricity storage: holy grail of the renewables industry

Storing electricity reliably, safely and cheaply has long been the holy grail of the alternative energy industry.

Vast amounts of energy – and money – are wasted in electricity grids the world over as suppliers struggle to keep the lights on while coping with the vagaries of demand.

If energy could be easily stored, this waste would stop and renewable energy sources such as wind power – that are intermittent by nature – would find a surer place in the electricity mix.

When wind power is generated at night, demand is lower, and the intermittency and unpredictability of the wind means that fossil-fuel power stations must be kept on standby in case it does not blow.

Chris Stubbs, director at WSP, an environmental consultancy, says: “Energy storage can play a key role in overcoming the intermittency of renewables. That is vitally important if renewables are to become a viable means for powering our economy.”

Widespread, reliable and cheap energy storage would also provide a big boost to the “smart grid”, a new form of electricity grid that contains much more communications technology than the old system, thereby allowing energy companies to manage supply and demand much more effectively.

Mr Stubbs says: “Implementing a smart grid and remote ‘load shedding’ can temporarily cut demand when the supply drops, but quick-reaction fossil-fuel plant would still be necessary to safeguard energy supply against the intermittency inherent in renewable sources. The critical factor is flexibility and, most significantly, flexibility without the expense of high carbon and cost.” Greater use of energy storage could provide a significant amount of the flexibility needed.

Some of the ideas being explored for storing energy include “pumped storage”, using fuel cells, and harnessing the power of fleets of electric vehicles.

Pumped storage is an option where hydroelectric power is used.

The technique involves diverting electricity generated at times of low demand to pumping water up to a storage reservoir behind the turbines, or into another reservoir, such as one at a higher level, where it can then be released as needed at times of higher demand, or when other renewables such as wind or solar power are less productive.

This seems inefficient, because of the energy involved in pumping the water uphill, but it forms an effective means of load balancing when demand is lower than supply.

It is also one of the few readily available options for the storage of large amounts of potential electrical power, and one of the most convenient, as modern pumped storage systems can start generating electricity almost instantly when it is needed.

Tidal energy systems could be used in a similar way, as seawater can be pumped back to storage reservoirs behind tidal barrages or into tidal lagoons, to be released later.

Countries with large fleets of electric vehicles can also benefit from their storage capacity.

The batteries of electric vehicles are usually set to recharge overnight, when they are driven less and when electricity demand is lower.

As these vehicles are plugged into the grid, they provide an important means of soaking up excess generation capacity – for instance from wind turbines, which frequently produce more power at night than in the day.

But if there were a sudden surge of demand at night, energy could potentially be recovered from the vehicles’ batteries to be used elsewhere on the grid. Owners could also make their vehicles available for such “borrowing” when they were not in use for extended periods.

Fuel cells offer a different means of achieving widespread electricity storage.

Excess energy at times of low demand can be turned to generating hydrogen, which can then be stored for use in fuel cells, principally to fuel vehicles.

However, in spite of years of development and successful trials in several countries, hydrogen fuel cell technology is still in its relative infancy, and it is likely to be many more years before it is in widespread use.

These forms of electricity storage are all likely to be needed, and they should be considered in conjunction with the much higher levels of renewable energy that will be required to “decarbonise” the electricity supply, which experts say will be necessary if global targets to reduce emissions by 50 per cent by 2050, compared with 1990 levels, are to be met.

Mr Stubbs says: “Making use of pumped storage and other forms of energy storage such as hydrogen storage and fuel cells can help supplement renewable generation assets for short periods when demand starts to outstrip supply.”

Without such forms of storage, the dreams of renewable energy companies of replacing fossil fuel generation will be impossible to achieve.

Source: Fiona Harvey, Financial Times