How to make alternatives more viable
Monday, 9 July 2007
Mike Sccott
Electricity has many qualities, but easy storage is not one of them. Today's electricity market operates on a "just-in -time" system that avoids the need for storage - power companies simply built an entire infrastructure capable of meeting the highest demand for power, even though this was only needed for a relatively short space of time.
In a world of high fuel and infrastructure prices, planning obstacles to building more power stations and fears over energy security and climate change, this is not desirable. While electricity itself cannot be stored, it is easy to store energy in other forms and convert it to electricity when needed.
Energy storage cuts the need for new generating and transmission capacity by allowing power stations to run more efficiently.
Energy storage also significantly improves the reliability of the grid, which is vital in a computer-run economy, where small variations in power output can trigger disruption to machinery and plant costing millions of dollars.
Furthermore, it can play a big role in making renewable energy viable. Wind is the most developed renewable energy, but it does not blow all the time. Worse, it often blows in inverse relation to peak power demand so wind generators get a lower price for their electricity than companies able to sell their power at peak times.
Extra capacity is needed to compensate for periods of low wind while, conversely, if the wind exceeds forecasts and more power is generated than predicted, it is often just discarded to maintain the stability of the system. If the power can be stored and sold at peak times, making the energy "dispatchable", the economics of renewables becomes much more attractive.
In small electricity markets, the capacity of the grid system limits the potential of wind generation to grow. "The transmission system can cope with very little variation in power output from second to second," says Hugh Sharman, of Denmark-based energy consultants Incoteco. "Wind cannot be forecast with any great degree of accuracy and if you put more wind on to the system, it increases frequency variations, which are very bad for power quality."
As a result, certain markets cannot fully exploit their wind resources. These are often islands with lots of wind but weak or non-existent grid connections to other markets and few other power generating resources.
New Zealand, Shetland, the Faroe Isles and the Canary Islands are among the locations where wind is unable to meet its full potential. "In the Shetlands, for example, they could generate wind for E30/MWh against the ElOOJMWh they have to pay to meet their power needs with diesel," Mr Sharman says.
Pumped hydro storage is the largest and oldest large-scale technology. Water is pumped from a hydro-electric plant's lower reservoir to the upper reservoir in off-peak hours, to be released at peak times. This is the most developed and best value proposition, but most available sites have been developed or have high environmental and financial costs, long lead times and must be in remote areas, given their size.
Compressed air energy systems (CAES) can provide big efficiencies for gas turbines. About two-thirds of the energy produced in a gas turbine is used to pressurise the air for combustion, according to the US department of energy. CAES systems use off-peak electricity to pre-compress the air, which is then stored in an underground reservoir and released at peak times to feed the turbine. Decoupling air compression from turbines increases the amount of power that can be produced per unit of fuel by two to three times.
The storage technology closest to commercialisation (apart from pumped hydro) is redox flow batteries. Tests in Ireland suggest that flow battery technology from VRB, a Canadian company that uses technology based on vanadium, could significantly increase the amount of installed wind capacity the grid can carry. Graham Brennan of Sustainable Energy Ireland says the system can deliver guaranteed power at a very high quality, overcoming one of the key obstacles to wider adoption of wind. "It may also allow deferral of grid improvements, reducing the cost of transmission by millions of euros."
.................................................................
Under syndication arrangement with FE
Electricity has many qualities, but easy storage is not one of them. Today's electricity market operates on a "just-in -time" system that avoids the need for storage - power companies simply built an entire infrastructure capable of meeting the highest demand for power, even though this was only needed for a relatively short space of time.
In a world of high fuel and infrastructure prices, planning obstacles to building more power stations and fears over energy security and climate change, this is not desirable. While electricity itself cannot be stored, it is easy to store energy in other forms and convert it to electricity when needed.
Energy storage cuts the need for new generating and transmission capacity by allowing power stations to run more efficiently.
Energy storage also significantly improves the reliability of the grid, which is vital in a computer-run economy, where small variations in power output can trigger disruption to machinery and plant costing millions of dollars.
Furthermore, it can play a big role in making renewable energy viable. Wind is the most developed renewable energy, but it does not blow all the time. Worse, it often blows in inverse relation to peak power demand so wind generators get a lower price for their electricity than companies able to sell their power at peak times.
Extra capacity is needed to compensate for periods of low wind while, conversely, if the wind exceeds forecasts and more power is generated than predicted, it is often just discarded to maintain the stability of the system. If the power can be stored and sold at peak times, making the energy "dispatchable", the economics of renewables becomes much more attractive.
In small electricity markets, the capacity of the grid system limits the potential of wind generation to grow. "The transmission system can cope with very little variation in power output from second to second," says Hugh Sharman, of Denmark-based energy consultants Incoteco. "Wind cannot be forecast with any great degree of accuracy and if you put more wind on to the system, it increases frequency variations, which are very bad for power quality."
As a result, certain markets cannot fully exploit their wind resources. These are often islands with lots of wind but weak or non-existent grid connections to other markets and few other power generating resources.
New Zealand, Shetland, the Faroe Isles and the Canary Islands are among the locations where wind is unable to meet its full potential. "In the Shetlands, for example, they could generate wind for E30/MWh against the ElOOJMWh they have to pay to meet their power needs with diesel," Mr Sharman says.
Pumped hydro storage is the largest and oldest large-scale technology. Water is pumped from a hydro-electric plant's lower reservoir to the upper reservoir in off-peak hours, to be released at peak times. This is the most developed and best value proposition, but most available sites have been developed or have high environmental and financial costs, long lead times and must be in remote areas, given their size.
Compressed air energy systems (CAES) can provide big efficiencies for gas turbines. About two-thirds of the energy produced in a gas turbine is used to pressurise the air for combustion, according to the US department of energy. CAES systems use off-peak electricity to pre-compress the air, which is then stored in an underground reservoir and released at peak times to feed the turbine. Decoupling air compression from turbines increases the amount of power that can be produced per unit of fuel by two to three times.
The storage technology closest to commercialisation (apart from pumped hydro) is redox flow batteries. Tests in Ireland suggest that flow battery technology from VRB, a Canadian company that uses technology based on vanadium, could significantly increase the amount of installed wind capacity the grid can carry. Graham Brennan of Sustainable Energy Ireland says the system can deliver guaranteed power at a very high quality, overcoming one of the key obstacles to wider adoption of wind. "It may also allow deferral of grid improvements, reducing the cost of transmission by millions of euros."
.................................................................
Under syndication arrangement with FE