Types of solar panel
Different types of solar PV installations require slightly different components. However in the next two sections we have explained in detail all the main components that will make up your solar PV array and provide you with 100% renewable, free electricity.
The solar panel
This is the key component of any solar photovoltaic system, which takes the sun’s energy and converts it into an electrical current.
The process of converting light (photons) to electricity (voltage) is called the solar photovoltaic (PV) effect. Photovoltaic solar cells convert sunlight directly into solar power (electricity). They use thin layers of semi-conducting material that is charged differently between the top and bottom layers. The semi-conducting material can be encased between a sheet of glass and or a polymer resin.
When exposed to daylight, electrons in the semi-conducting material absorb the photons, causing them to become highly energised. These move between the top and bottom surfaces of the semi-conducting material. This movement of electrons generates a current known as a direct current (DC).
There are three main types of solar panel (as well as the hybrid version) currently in commercial production, all of which are based on silicon semiconductors.
Monocrystalline solar cells
This type of solar cell is made from thin wafers of silicon cut from artificially-grown crystals. These cells are created from single crystals grown in isolation, making them the most expensive of the three varieties (approximately 35% more expensive than equivalent polycrystalline cells), but they have the highest efficiency rating – between 15-24%.
Polycrystalline solar cells
This type of solar cell is also made from thin wafers of silicon cut from artificially grown crystals, but instead of single crystals, these cells are made from multiple interlocking silicon crystals grown together, hence they are cheaper to produce, but their efficiency is lower than the monocrystalline solar cells, currently at 13-18%
Amorphous solar cells
These are the cheapest type of solar cell to produce, are relatively new to the market and are produced very differently to the two other types. Instead of using crystals, silicon is deposited very thinly on a backing substrate.
There are two real benefits of the amorphous solar cell; firstly the layer of silicon is so thin it allows the solar cells to be flexible and secondly they are more efficient in low light levels (like during winter).
This however comes at a price; they have the lowest efficiency rating of all three types – approximately 7% – 9%, requiring approximately double the panel area to produce the same output. In addition, as this is a relatively new science, there is no agreed industry wide production technique, so they are not as robust as the other two types.
Hybrid solar Cells
This is not a type of solar cell in its own right; instead it is a combination of both amorphous solar cells and monocrystalline solar cells. These are known as HIT solar cells (Heterojunction with Intrinsic Thin Layer – is a bit of a mouthful!), and have higher efficiency ratings than any of the other three types of solar cell alone. In addition, they are also better suited in sunnier climes, where temperatures often exceed 250C, creating up to 10% more electricity.
At TheGreenAge, we feel that for most installations polycrystalline cells are most suitable, as they provide value for money while still also being relatively efficient.
Solar PV Inverters
All the electricity produced by the solar panels is produced as direct current (DC), which compares to the electricity that is distributed through the grid and we use in our homes, which is alternating current (AC). For this reason most solar photovoltaic systems are now connected up with some type of inverter, which changes the DC to AC, allowing the individual to sell the electricity back to the grid (in grid tie systems) or to be used easily in the homes.
There are 2 major types of inverter that can be installed in your solar photovoltaic system:
1. String inverters (also known as central inverters)
These are used in grid-tied systems where the solar panels are wired together in series, which is known as a string of panels. Each string of panels is connected to a string inverter, which converts the DC current to AC for use in the home and selling back to the grid. You can imagine each string as a mini power station, producing electricity.
The main issue with string inverters is that if one of the panels in the string fails or produces less electricity (from things like shading), this impacts the output of all the panels. They will operate at the output of the worst panel, so a small amount of shading or debris on your solar array can disproportionally reduce the total output of your entire solar photovoltaic system.
They also have relatively short lifespans when compared to micro inverters.
The benefits include simple wiring and that you can use thinner wires within your solar PV system, so less copper is used which makes the system cheaper. Buying one string inverter (which is normally the case of most home solar PV systems) is also considerably cheaper than buying multiple micro inverters.
2. Micro inverters
These are a newer technology and service each solar panel individually, so each panel requires its own micro inverter and acts as an individual power station. As a result, micro inverters do not suffer the same performance reduction as a result of shading because any power reduction in a particular solar panel is handled by one micro inverter, having little effect on the combined power output from the entire solar photovoltaic system.
Micro inverters are much more expensive than the string inverters. However much of this cost is offset by the increased performance (25% more power produced using micro inverters) and the fact that they are more reliable than string inverters (warranties for micro inverters are up to 25 years).
Buying inverters for your solar PV system
As a tip when looking for which inverters to buy, ideally you want your alternating current (AC) to match that provided by the utility companies. Waveform relates to the quality of the AC signal that an inverter produces. Cheaper inverters will provide modified sine wave signal, while the more expensive versions will produce the pure sine wave signal. Some appliances (such as computers) simply don’t work unless they are powered by a pure sine wave signal, so we recommend strongly that you spend a little more to get this type of inverter.
Grid tie inverters differ slightly from your regular inverters in that the AC pure sine wave signal has to be perfectly coordinated with the waveform from the grid. As such, these tend to be more expensive than the typical inverters that you buy. They also have a built-in safety feature to cut off power from the solar array if the electricity grid goes down for any reason.
It is also worth noting that most inverters now also have ‘Maximum Power Point Tracking’ (known as MPPT) installed within them, which helps to maximise the electrical output of your solar photovoltaic array system.
The principle of MPPT is to extract the maximum available power from the photovoltaic module by making them operate at the most efficient voltage (known as the maximum power point voltage). The algorithm included in the MPPT inverter compares the output from the photovoltaic module with grid voltage and then fixes it at the most efficient voltage, to allow you to export the maximum amount of kWh of electricity back to the grid. An MPPT charger in your solar photovoltaic system will improve your power gain by 20-45% in the winter and 10-15% in the summer.
- All Solar PV panels are rapidly decreasing in price due to better production techniques and increased competition between manufacturers and suppliers.
- Monocrystalline solar PV cells are the most efficient type of solar PV cell (rated between 15-24%), so smaller panels can produce equivalent amounts of electricity compared to other solar cell types.
- Polycrystalline solar PV cells are easier to produce than the monocrystalline solar PV cells and therefore cheaper to buy, still providing decent efficiency levels (13-18%).
- Amorphous solar PV cells are the easiest to produce and as the silicon is deposited on any surface, these panels can be made into any shape.
- Hybrid solar PV combine amorphous and monocrystalline cells giving you the advantages of both of these two types of solar cell.
- Polycrystalline and amorphous solar PV cells are less efficient than monocrystalline, and therefore bigger panels are needed to produce the equivalent electricity output.
- The technique for building monocrystalline solar cells is more difficult and this is reflected in the higher price of this type of panel.
Have a look on page two for more components of a Solar PV system…
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