News about Solar, Wind and alternative green power technologies

The major constrains with renewable energy sources is its inconsistent or irregular supply. For example, solar energy supply is subject to seasonal changes, the absence of sunshine during the night and cloudy days. It is not feasible to produce solar energy during the night and wind energy cannot be generated if there is no wind. These variables influence the amount of electricity that can be produced from renewable energy. The only solution to surpass these limitations associated with alternative sources of energy is to establish technologies enabling energy storage.

The energy storage technologies suggested are:
1. Hydrogen
2. Batteries
3. Pump Storage (hydropower dams)
4. Compressed Air
5. Thermal Energy
6. Rotational Wheel
7. Capacitors

1. Hydrogen

Hydrogen is increasingly being considered as a vital energy carrier of electricity. The use of hydrogen as an energy carrier could make it possible to introduce renewable energy into the transport sector. The best aspect of using hydrogen as an energy carrier is that it is pollution free; its end-product is water.

NTNU, IFE and SINTEF are studying how hydrogen can be introduced into the value chain of renewable energy production.

2. Batteries

The use of battery technology would allow electricity to be stored. The energy can thereafter be transferred from the batteries to other materials in various voltages. Batteries are well-known energy storage mediums.

Rechargeable batteries like those used in cellular phones, laptops, cameras and more recently in electrical cars are examples of how efficient batteries are as a storage medium. Nowadays, most batteries are made of nickel-metal hydride, lithium-ion or lead acid. The most efficient material used is Lithium-ion based on the capacity to store energy in a compressed size battery. However, it is also the most costly one. Batteries are able to store energy at an efficiency of roughly 80 to 95 percent. Yet, the cost of using batteries for large scale storage of electricity is simply too costly.

There are apparently wide researches carried-out on batteries. This is mainly motivated by all car makers which are in the quest for cheaper and lighter batteries for electrical cars.

3. Pump Storage (hydropower dams)

Countries like Norway have a particular advantage when it comes to storing energy. Their competitive advantage is based on the colossal hydropower capacity present. Hydropower dams can be used as a source to store energy. The dams can store water and this source of hydropower can be harnessed when the demand for electricity expands. Other countries less fortunate than Norway usually pump water into large reservoirs.

The so-called Pump storage is a very effective way to store energy. It can be used to supplement energy variations that prevail during day and night.

4. Compressed Air

Another principle similar to the hydropower pump storage is the compressed air. There are gas turbines used to generate electricity as well as to compress the air. During intervals when the electricity production is above normal and consumption is relatively low, the turbine will use the electricity to compress air. Almost 70 to 80 percent of the energy required to compress the air can be recovered.

However, compressed air is a costly technology. It is also meant for short time storage intervals usually maximum a day. The earliest use of compressed air technology was in 1978 in Germany. This compressed air reservoir was constructed roughly 650 to 800 meters below the surface. The immense pressure that the turbine delivers is 290 MW for up to 3 hours.

5. Thermal Energy

Thermal energy is energy derived from heat, and it can be stored in various substances. One commonly used medium is water; it is easy to transport hot water through pipelines. Water can be heated by solar heaters, bio-energy and other means. It is usually used as the central heating medium in house systems. Thermal energy can easily be stored in water.

6. Rotational Wheel

The use of motional energy to store energy is what the rotational wheel is based on. The speed, mass and diameter of the wheel determines the storage capacity of the rotational wheel. The rotating wheel is linked to an electrical motor which acts as a generator. The energy is transferred into the wheel by increasing its rotational speed. The energy is afterward converted back by electricity by utilizing the motor as a generator.

7. Capacitors

A capacitor is used to store energy in an electrical field. This is different from batteries as they make use of redox reactions. The use of capacitors is remarkably efficient and as there are no chemical reactions or phase modifications. The life-time of a capacitor is much longer than for a battery. However, the storage capacity is much higher in a battery.

Sources: Centre For Renewable Energy, SINTEF, IFS, Norwegian Hydrogen Forum