- What is a photovoltaic (PV) panel and how does it work?
- What are the main components of a PV solar home system?
- What are typical terms you get along?
A photovoltaic panel converts the
1. Technology overview
1.1 Silicon based technologies
There are basically two different types, mono- and poly-crystalline. The raw material for both is silicon.
1.1.1 Mono silicon
A boule is a single-crystal ingot produced by synthetic means. In the semiconductor industry, boules can be made by a number of methods, whereby the Czochralski process the most common one is, which result in a cylindrical rod of material. In the Czochralski process a seed crystal is required to create a larger crystal, or ingot. This seed crystal is dipped into the pure molten silicon and slowly extracted. The molten silicon grows on the seed crystal in a crystalline fashion. As the seed is extracted the silicon solidifies and eventually a large, cylindrical boule is produced. The efficiency of a mono-cell is about 20%.
1.1.2 Poly silicon
For poly-cells the raw silicon is melted and poured into a form. The advantage of this technology compared to mono crystalline, that the process is not so time and energy consuming, but the price for it is a reduction of the efficiency, which lies for poly-cells at about 16%.
1.2 Thin film technology
There are many different types of technologies on the market, where off 3 common ones are listed below:
- Amorphous silicon, this technology is often used for small tools like calculators. The efficiency is about 7%
- CIS-, CIGS Solar cells (copper-indium-gallium-diselenide). Not very common, but has for
- CdTe-cells are cheap in production but only reach an efficiency of about 10% so far.
2. Build-up of a solar panel
In the next
Which again are soldered together to a
To ensure the long
3. How does a solar cell work?
Some materials are called conductors, they allow electricity to flow through them very easily (notably metals). Other materials such as plastics and wood don't really let electricity flow through them, these are called insulators. A third group is called semiconductors, they are neither conductors nor insulators and silicon, the material solar cells are made of, is such a material. They don't normally conduct electricity, but under certain circumstances, they can do so. A solar cell is a sandwich of two different layers of silicon that have been specially treated, so they will let electricity flow through them. The lower layer is treated so it is missing electrons. It's called p-type or positive-type silicon, because of the missing negative electrons. The upper layer is treated the opposite way so it has too many electrons. It's called n-type or negative-type silicon. When a layer of n-type silicon is placed on a layer of p-type silicon, a barrier is created at the junction of the two materials and no electrons can cross the barrier so no current will flow. But if a light shines onto the sandwich, the light particles (called photons) give up their energy to the atoms in the silicon. The incoming energy knocks electrons out of the lower, p-type layer so they jump across the barrier to the n-type layer above and flow out around the circuit. The more light shines, the more electrons jump up and the more current flows.
Depending on the type of system certain components are required to operate the PV solar home system. On this
4. PV panel
As already described, there are many different types and sizes of photovoltaic panels, whereby the most common ones are the crystalline PV panels and there the one with 60 solar cells, which has the size of about 1650mm x 990mm and a weight of about 20Kg.
4.1 Thin film vs. crystalline
Both technologies are now for many years on the market and have their advantages. Within this technology groups there are also different types, which have slightly different abilities. But they all have some facts in common.
The thin film solar panels have a better diffuse and low light behaviour, which means that they are more efficient in harvesting the sun radiation in the morning and evening hours than a crystalline PV panel. The same counts for installations facing east or west, that's when the amounts of diffuse sun radiation will be higher.
They also have a better temperature coefficient. A solar panel produces less power when its temperature rises, with each degree the power output drops. For a crystalline PV panel it's about 0.4-0.44 %/K and a thin film PV panel about 0.25 %/K.
The table below shows an overview about the advantages and disadvantages of thin film PV panels:
Low efficiency (higher cost for installation and roof structure to install the same capacity as crystalline)
Good temperature coefficient
More space required to install the same capacity
Better low light behaviour
Higher initial efficiency degradation
Less dirt deposits due to the missing frame
More difficult to install and less stability because of the missing frame
Easier to produce
Lower live expectancy
Summarizing you can say that thin film PV panels are compared to crystalline PV panels less efficient, have a lower live expectancy and are more affected by environmental effects. Their advantages are the more flexible application possibilities due to the better low light behaviour. It mostly depends on the installation and the requirements which panel to use and one typical installation type for thin film panels are huge PV parks, where space is not the main issue.
4.2 Criteria to consider when buying PV panels
As described in section 1.1 first you should think of, which type of panel suits my needs most. In most cases for instants house owners or small businesses the crystalline is the most suitable technology and at the same time also the most common one.
There are worldwide plenty manufacturers of those panels and you should take a view minutes to think of what you are buying, because these panels come with a very long warranty of up to 25 years and you don't want to find out in 3 years time that your panel doesn't work anymore and you have to replace it, which can take sometimes a long time or even worse that the manufacturer of those panels doesn't exist anymore.
The following points should give a guideline what to think of, when buying PV panels:
CertificateSolar panels should be certified by a well known institute where the products of the manufacturers undergo standard tests to ensure a certain quality standard. For example there is the performance standard IEC 612125 in which the solar panel is tested among others for:
- hot spots
- temperature cycle tests where the panel is 50 and 200 times cooled down to -40*C and afterwards heated up to +85*C,
- Humidity freeze where the panel is also 10 times exposed temperatures of -40*C and +85*C at 85% humidity,
- Damp heat, 1000h at 85*C and 85% humidity
- Hail impact, 11 times ice balls with 25mm diameter and a speed of 23 m/s are directed at different spots of the panel
- mechanical load, 2400 Pa is applied for 1 hour on each side of the module
After those test the IEC 61730 takes place to ensure safety standards. This includes test for thermal hazards, fire resistance, mechanical hazards and electrical hazards. Before buying PV panels ensure that those products have a certificate. Some well known institutes are for example TUV Rheinland, TUV Intercert,...
WarrantiesPV panels normally come with a very long warranty. The product warranty of some manufacturer is up to 12 years and the performance warranty 80% for 30 years. That means the manufacturer is guarantying that his product produces after 30 years still 80% of its previous rated power.
A common product warranty is at the moment between 5 and 10 years and the performance guaranty of 80% for 20 years.
Manufacturing countryDo you want to support a local manufacturer and economy? There is a slow growing business for manufacturing of PV solar panels in South Africa, which provides certified products to the local market.
But most and also the biggest manufacturer are situated in China and export their products to the rest of the world. When you consider of buying one of those products you should also inform yourself if that company is one of the established ones and how many years of experience does that company already has in the manufacturing process of PV solar panels. Because you get also a lot fly by night companies, which already close down after a view years and what happens to your guaranty after that?
Regarding the guaranty it is also important to know how it is handled. Does that company have a branch in South Africa or a distributor who is handling it? Or do you have to claim it yourself in China?
StabilityIn areas with heavy winds the PV panels are exposed heavy mechanical loads, which can cause damage to the PV panel. So the size and there with the stability of the frame plays an important role. Most manufacturers designing the frame smaller to save aluminium and there with save production costs.
ExperienceAs already mentioned the experience of the manufacturer is very important, how long does the manufacturer already exist?
Is this a new product of that manufacturer?
Are there any negative or positive reports or news about the manufacturer like recall incidents or warranty claims and how were they handled?
Are there any references with this PV panels from the installer or in South Africa?
An inverter basically transforms the DC Voltage from the PV panels into AC voltage, which
- Grid tie inverter
- Bi-directional inverter
- Hybrid inverter
Grid tie inverterThis type of inverter transforms DC voltage, which is produced from the PV panels into the AC voltage and frequency from the local electricity network. This electricity can
This type of inverter got already an integrated MPPT to optimize the performance of the PV solar panels all time.
This type of inverter
Bi-directional inverterAs the name already says, this inverter works both ways. On one
This kind of inverter can be used with a battery bank and without PV panels to avoid load shedding. For more details please see also What type of system do I need?
Hybrid inverterThey combine the functions of the other two inverters. This type of inverter got a built in MPPT to optimize the output of your PV panels at all times and can charge your batteries as well as supply your house with the required power or feed excess energy into the grid. In cases of a grid
5.1 Criteria to consider when buying an inverter
The inverter can be considered as the heart of a solar system and plays a very important role in the performance of your system. The build in MPP tracker in an inverter have different operating voltages, which have to be considered when designing you solar home system also the amount of MPP trackers differs from brand and size of the inverter. The following points should give you just a guideline on what to look at when you buy an inverter but the actual design and layout of the solar system should be done by a professional.
Manufacturing countryDo you want to support the local manufacturer and economy? There are some local companies producing here in South Africa. The advantage can be a fast response or replacement when a failure accurse.
WarrantiesUsual warranties for inverters are between 3-5 years. Regarding the warranty it is also important to know how it is handled.
Does that company have a branch in South Africa or a distributer who is handling it?
Or do you have to claim it yourself from the manufacturer in the country of origin?
What are the response times for an exchange or repair of the inverter?
EfficiencyThe efficiency is very important for an inverter and most of them have even three different ones: peak efficiency, Euro efficiency and CEC efficiency. Which one is most important when considering which inverter to buy?
Many people look only at peak efficiency, but the truth is that this number does not reveal the actual performance of the inverter, because this efficiency is measured at one point when the inverter is performing at its best. But your inverter may only operate for a short time of the day at its peak efficiency. The Euro/EU efficiency and CEC inverter efficiency are ‘weighted’ efficiencies. These figures measure inverter performance across the range of the inverter’s capacity. This gives you a better idea about the inverter’s operating profile over the course of the day.
6. Maximum power point tracker (MPPT)
For example a
A standard PWM charge controller without MPPT makes no adjustments in
This technology is used in most charge controllers and helps the battery to reach full charge by pulse charging.
For those who are interested in installing a battery backup or to be off
There are many different types of batteries available and one must think carefully which one to
For a small PV system backup the battery types AGM or GEL would be a good choice.
The dimensioning of the battery is very important for the life expectancy of the system. A battery is rated
A battery should not be emptied completely, due to the fact that it shortens the life expectancy of the battery dramatically. For
If you discharge the battery to 100% it will last only about 500 cycles. But if you discharge this battery only to 50% of its capacity it will last 1500 cycles.
When it comes to the cycle life manufacturer like to use the standard that suits their batteries best or even use their own standards. But for batteries which are used for a PV
|Solar PV orientation (Azimuth)
||In order to produce the most electricity, the Solar PV panels should be orientated north. It is not absolutely necessary for the array to face directly north. There will be only a small percentage power loss, as a result of moving a few degrees east or west of north. For
|Pitch / Slope
||PV panels heat up during operation an can reach easy 60°C and a higher temperature means less performance. To allow a air ventilation underneath the PV panel it should always be installed with a distance to the roof ideal would be a distance of min. 10cm.
||It is important to ensure there are no obstructions that will block the sunlight from reaching the Solar PV array. A small amount of shading can reduce the performance of the whole system, not just that of an individual shaded module. Shading can occur from obstructions like neighbouring buildings, trees
||The Hot-Spot-Effect describes the overheating of an area in a solar panel due to unequal light radiation and occurs when there
||The rated output of solar panels is measured under Standard-test-conditions (STC). That means the real output can be higher or less, depending on the sun radiation
|Standard test conditions (STC)
The performance of a solar panel is measured under Standard-test-conditions:
One also has to consider that 1.000 W/m2 are not always reached. In the morning, evenings or on cloudy days it will be less and so the performance of the solar panel. On the other hand on a sunny