If anyone asked about the ideal energy conversion system, you would hardly find one better than a photovoltaic system (PV system). You will find in it the perfect instrument to harvest the most abundant source of energy on this planet: the solar energy.
The quantity of solar energy that reaches the earth is 10,000 times bigger than how much fossil and nuclear fuels we use. The actual PV cell is built entirely by silicon (the second most abundant element on the earth) and it has no mobile parts so, theoretically (if not practically) this type of cell could run without problems an infinite period of time.
If you plan to install a photovoltaic system in your own home (which by the way is extremely easy), in this article you will find information about how efficient are the different types of PV cells and how much money you need.
PV cells: how everything works
A PV cell is an optoelectronic device, using solar light to generate power. The semiconducting material (silicon) absorbs the photons in sunlight. Consequently, electrons are excited from their current atomic orbital and they travel through the cell until they reach an electrode.
Current flows through the material and electricity is captured. In order for this process to work, the chemical bonds in the material are vital, so silicon is used in two layers, bonded together with boron and phosphorus.
The power produced by a single cell is almost insignificant; therefore more cells are bonded together in large arrays with better efficiency.
Types of PV cells
Depending of the crystalline nature of the semiconductor (usually silicon), there are three types of PV cells:
- Monocrystalline silicon cells;
- Polycrystalline silicon cells;
- Amorphous silicon cells.
Monocrystalline silicon cells are produced by casting pure silicon through a very complex and expensive process. But, in terms of efficiency, this type of photovoltaic system cells is the best, with more than 10% better than the others. They also generate more electricity on a smaller surface.
Polycrystalline silicon cells are easier to build and a lot less expensive than monocrystalline cells. But they are not so efficient because the silicon molecules are too small and the electrons don’t travel as easy through the material. However, the specialists are constantly working on the fabrication process and they are obtaining bigger and bigger silicon molecules in order to increase efficiency.
The amorphous structure is a very irregular one, which doesn’t help the electrons reach their objective therefore the cells have very little efficiency.
When we talk about solar cell efficiency, we can think about many different things: reflectance efficiency, thermodynamic efficiency, conductive efficiency or fill factor.
If we want to evaluate practical performance of the PV cell we take into consideration mainly the fill factor, which is a ratio of the maximum obtainable power to the product of the open circuit voltage and short circuit current. In 2009, typical solar cells had a fill factor ~ 0.70. Cells with high fill factor have less internal losses.
The theoretical power efficiency of crystalline silicon cells was limited to about 33.7% (in 1961) but some French and German scientists have obtained (in a laboratory) 46% efficiency in 2014.
On the other hand, in the real world, the PV cells have an actual efficiency of about 17% and it is expected to rise to 20% in the next 10 years. In countries like the USA, Germany, Italy, Spain, Switzerland are already functioning large PV cells power plants that generate megawatts of electricity. Imagine how many PV cells you need, if a single one generates approximately 1.5 W of power.
The price of a solar module is constantly dropping, as many countries are manufacturing large quantities of PV cells and also the costs of the whole manufacturing process is reducing due to technological advance. After the recession in 2008, the price of a solar module has reached €1 per peak watt in Germany while in China a crystalline module is worth $0.60 per peak watt.
So, if you are planning to build your green home, covering your entire roof with PV cells and combining solar energy with a windmill and a micro-hydropower system will provide you with energetic independence.