|
Storage of renewable energy
One of the problems with renewable energy sources is that, in terms of time, demand of electricity often does not coincide with production. In other words it is not possible to produce solar energy at night or wind power when it is not windy. A climate, such as the Norwegian climate, is prone to seasonal changes with for example relatively a lot of sun during the summer when demand is low.
There are several different technologies for energy storage, but the most relevant are hydrogen, hydropower dams and batteries.
Hydrogen is considered by many as an important supplement to electricity as an energy carrier. Hydrogen as an energy carrier can contribute to renewable energy being used not only in stationary energy production but also in the transport sector. Hydrogen produces water as an end-product in a pollution- free cycle.
Research activity within hydrogen at NTNU, SINTEF and IFE is of considerable scope and covers the entire value chain from production to end use.
Batteries are storing the electricity electrochemically through reactions in different materials. Transmission of electrons between materials with different voltage potential makes it possible to use batteries as an energy storage media.
Rechargable batteries are most common in cellular phones, cameras and, lately, electrical cars. The most usual batteries used today are lithium-ion, nickel-metal hydride and lead-acid batteries. Lithium-ion is the one that is capable of storing most energy in terms of weight and size, but is also the most expensive one. Battery storage have a high efficiency of between 80 and 95 percent, but this method is in most cases too expensive for large scale storage of elektricity.
There is a wide research activity on lighter and cheaper batteries, as all the largest car makers have announced large scale production of electrical cars within the coming years.
Norway is in a special position when it comes to energy storage, because of the large hydropower capacity. Hydropower dams work as an energy storage because it is possible to store the water and use it when the electricity consumption is large. Other countries with less hydropower capacity is often pumping water into big reservoars.
Pump storage is the most efficient method of storing energy, and it is usually utilized by adjusting the daily variations between night and day.
Storage with compressed air is working more or less after the same principle as hydropower pump storage. Gas turbines are used to produce electricity and compress the air. When the electricity production is high and the consumption low, the turbines will use electricity to compress the air, and vica versa. It is possible to recover around 70-80 percent of the energy used to compress the air.
Compressed air is a relatively expensive technology. The storage time is limited and this type of storage is only used for daily variations. The oldest installation of this type was completed in 1978 in Germany. The compressed air reservoar is a cave 650-800 meters below ground level. The upper pressure level is 70 bars and at maximum power the turbines are delivering 290 MW in maximum three hours.
In a capacitor, the energy is stored in an electrical field, in contrast to batteries which uses redox reactions. Storage in capacitors has high efficiency because there is no phase changes or chemical reactions like in batteries. The life time of a capacitor is up to around one million cycles, in contrast to a couple of thousands in batteries. However the storage capacity is much less than for batteries.
A rotating wheel is storing the energy by motional energy. The diameter, mass and speed determines the energy storage capacity of the wheel. The rotating wheel is connected to an electrical motor, which also works as a generator. Energy is transfered to the wheel by increasing the rotating speed, the energy is transferred back by using the motor as a generator.
Energy can also be stored thermically as heat in almost any substances. Water is widely used as medium, as it has a large heat capacity and is easily transported through pipelines. Central heating is the most common area for storage of thermal energy in water. Water is heated by waste incineration, bioenergy, solar heaters etc., and distributed to buildings for heating.
SINTEFs research in relation to hydrogen as an energy carrier
IFEs research in relation to hydrogen
Norwegian Hydrogen Forum
Forsker Preben Vie, IFE, +47 63 80 63 60
Researcher Ann Mari Svensson, SINTEF Materials and Chemistery, +47 98 23 04 50
Professor Svein Sunde, NTNU, Department of Materials Science, +47 73 59 40 51
|
