Storing solar energy for night use

This one is a giant leap forward that could bring solar power closer to mainstream. Until now energy from solar was possible only during the day with the suns rays hitting the solar cells.

Lets take a step back. The energy from the sun hitting the earth in one day is more than enough to fill all our energy needs for a year. The problem is that we have a huge surplus during the day and well nothing during the night. Many have tried to solve this with some sort of energy storage. Sofar all of those were expensive and inefficient.

A new and efficient way of energy storage was found by the scientist at MIT. It is not really new, it’s just electrolysis. The reaction takes place at room temperature, normal atmosferic pressure and pH. Everything is made possible by the use of cobalt metal and phosphate catalysts which are abundant and cheap.

So the idea is to store the excess energy by splitting water into hydrogen and oxygen. And produce energy during the night with a fuel cell.

More info…

 

Solar thermal – solar at night!

One of the big problems of solar energy has always been availability. There’s no sun on a cloudy day or at night. The solution would be to store the suns energy and use it when the sun is not available. Storing elecrticity in such quantities is very expensive. Another solution would be to use the electricity to produce hydrogen that can be latter used to produce electricity again. This process is not very efficient and storing hydrogen is both expensive and dangerous.

The proposed solution is to store heat which is both cheap and effective. The accumulated heat can later be used to produce electricity when it is needed.

The system uses an array of mirrors that reflect the sun’s heat onto a tank of water. The produced steam turns a turbine. Really simple – a good old fasioned steam engine. This works even at night because water can store heat for a long time.

 

The photovoltaic effect

The photovolataic effect is the means by which the photovoltaic cells ( the first generation of solar cell ) are able to transform sunlight into electricity.

A photovoltaic cell is made from a thin slice of semiconductor, usually silicon or galium-arsenide. Two special types of impurities called dopants are added to the semiconductor. The upper and lower part of the slice become respectively a p-type and n-type semiconductor. The n-type has a surplus of electrons while the p-type has a lack of electorns – also called “holes”. This electron imbalance forms an electric field in the semiconductor slice.

When an electron is hit by a photon it becomes free of the p-n structure leaving a “hole” or positive charge behind. Being in an electric field he negative electron and the positive “hole” begin to move in oposite directions creating an electric current. If we connect wires to the semiconductor we can run this current through a load ( light bulb, battery charger, etc ).

Of course not all the photons hit the electrons in the solar cell. Some light bounces right off the cell and some misses the electrons and passes right through. Also the semiconductors used today are able to absorb just about half the spectrum of sunlight, further limiting the efficiency of cells.

The efficiency of photovoltaic cells can be raised using different combinations of semiconductors to try to absorb the whole length of the sun’s specturm and also use thicker slices with more p-n junctions to catch the photons that pass thorough the first junction.

 

Solar power technology

Many of us might thing that solar cells are something new and cutting edge. Well the truth is that they have been around for decades. The buzz surrounding them now is caused mainly by the soaring gas prices and the green movement in general. The solar cells technology is at its third generation.

The first generation the classic photovoltaic silicon based cells still represents more than 80% of all the installations. They are highly effective but bulky and expensive.

The second generation tries to address the shortcomings of its predecessors. The lightweight and flexible thin-film solar cells are very low cost. They can be arranged in many different ways making their use much more suitable for urban settings. Despite their lower efficiency they are expected to dominate the solar market in a few years.

The third generation of cells are actually a group of technologies that are still being researched. The research is directed towards new materials like polymers and nanotechnology and away from silicon-based materials. The idea is to merge the flexibility and low cost of the thin-film cells and the effectiveness of the classic silicon based cells. I will try to cover the new technologies in a later post.