PV explained and its components
A photovoltaic panel converts the sun radiation into electricity. This is achieved through solar cells, which are put together to a solar panel. The principal of the photovoltaic panels is based on the photo effect and was already discovered 1839 by Alexander Becquerel. At this stage the leading technology on the market is silicon based, with a market share of about 80%. The second most common technology with about 10% market share is thin film based, where of CdTe is the most common technology. That's why the focus of this Website will be on the crystalline solar panels.
1.1 Technology overview
Silicon based technologies
There are basically two different types, mono- and poly-crystalline. The raw material for both is silicon.
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%.
Source: http://www.waferpro.com
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%.
Source: https://www.crystec.com
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 thin film a high efficiency of about 17,4%. The problem with this technology is the indium, which is expensive and limited.
CdTe-cells are cheap in production but only reach an efficiency of about 10% so far.
1.2 Build-up of a solar panel
The centrepieces of a solar-panel are the solar-cells. Normally a semiconductor crystal boule is cut with a diamond saw into circular wafers. In a following process the wafers are cleaned and receive a coating, which gives the solar cells their typical appearance. The thickness of a solar cell is about 0,2mm.
Source: http://tindosolar.com.au
In the next step these cells are soldered together to a so-called string.
Source: https://www.dgs.de
Which again are soldered together to a so-called matrix, which looks like the PV-Solar panel we know. Below you find a typical setup of a PV-Solar panel.
Source: http://www.pveducation.org
To ensure the long-life span of the solar panels (some companies offer already 30 years warranty) the solar cells must be protected from environmental influence. A typical PV panel has a glass sheet on the site facing to the sun and a back sheet on the rear. This back sheet is often a tedlar foil with embedded aluminium. All these components are imbedded and hold together with an encapsulate, which is often an EVA foil.
Source: http://www.kern-tech.com
1.3 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 shine 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. Here we explain some of the main components and points that should be considered when purchasing the equipment.
2.1 PV panel
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.
In this chapter we will look a bit closer where the advantages of the different panels are and what to look at when you buy PV panels.
Thin film vs. crystalline
Source: http://www.exsolar.co.za
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:
Advantages
Disadvantages
Cheaper
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.
Criteria to consider when buying PV panels
The most common PV panels are the crystalline type. 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 must 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 some thoughts, when buying PV panels:
Certificate
Solar 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
Warranties
PV 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 between 5 and 10 years and the performance guaranty of 80% for 20-25 years.
Manufacturing country
Do 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 manufacturers are situated overseas 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 from the country of origin?
Experience
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/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?
2.2 Inverter
An inverter transforms the DC Voltage from the PV panels into AC voltage, which is used in households. In South Africa an inverter has to meet the requirements of NRS 097-2-1. Depending on the requirements and size of installation there are different types of inverters.
- Grid tie inverter
- Bi-directional / Hybrid inverter
Grid tie inverter
This 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 then be used in your own household and excess electricity feed into the local electricity grid. Note, before you connect or feed back into the local grid you or your installer must talk to your municipality. To be able to be credited for the excess energy there must be a special meter installed, which can count the electricity consumption both ways. For more details on the regulations from the Electricity & Energy dep. in NMB please visit Renewable Energy Guideline 2021
This type of inverter stops operating during load shedding to avoid electricity feed into the grid, while it is switched off.
Bi-directional / Hybrid inverter
As the name already says, this inverter works both ways. On one hand it inverts the DC voltage from your batteries into the set AC voltage and frequency from your grid supply (230V 50Hz). On the other hand, it got a build in charger which converts your AC into the DC voltage of your batteries.
This type of inverter 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 failure, it switches automatically to your battery backup like an ups. A hybrid inverter operates also during load shedding, due to internal switches that avoid a feed into the municipal grid. That means if there is load shedding during the day your PV panels still produce electricity, which can be used in your household or to charge your battery backup.
Efficiency
Common ways to measure the efficiency of an inverter are: peak efficiency, Euro efficiency and CEC efficiency.
The peak 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.
Warranties
Usual warranties for inverters are between 3-5 years. Some manufacturers also offer extensions to their normal warranty period at additional costs.
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?
2.3 Maximum power point tracker (MPPT)
A MPPT ensures that your solar panel works always at its best operation point. These MPPTs are normally already built into the inverters and one has to match the voltage range of the MPPT with the voltage of the PV array.
But for example, in cases where the PV panels should charge the battery directly, they can make a huge difference to other charge controller like PWM.
A MPPT can track the input power from the solar panel and the voltage from your battery bank and then re-adjust the voltage for the highest amp output to charge the battery.
2.4 Batteries
For those who are interested in installing a battery backup or to be off grid there is the question what type of battery should I use?
There are many different types of batteries available, and one must think carefully which one to choose.
For a small PV system backup, common battery types are AGM, GEL or lithium-ion batteries which offer a long-term solution with low maintenance.
The dimensioning of the AGM or Gel battery is very important for the life expectancy of the system. A battery is rated in Amp-hours and the capacity of it depends also on how fast the energy is withdrawn. A battery rated C20=100Ah has 100Ah when the energy is withdrawn in 20 hours. If I know want to withdraw the energy faster, let’s say in 5 hours the capacity drops down to about 86Ah. The capacity depends also on how fast I withdraw the energy.
A battery should not be emptied completely, because it shortens the life expectancy of the battery dramatically. For this the lifetime over the depth of discharge (DOD) is of interest. This is often a graph and shows you how often you can discharge the battery to a level XX before it has only 60-80% of its original capacity left. To keep the life expectancy of a battery high it is recommended to not discharge AGM or Gel batteries completely due to the dramatic loss in cycle life. For example, let's look at the data sheet below:
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 system there are specific testing conditions, the EN 61427 and a battery is ideal tested under these conditions.
3. What are typical terms you get along
| 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
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| Pitch / Slope |
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| Back ventilation |
PV panels heat up during operation an can reach easy 60°C and a higher temperature means less performance. To allow an 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. |
| Shading |
It is important to ensure there are no obstructions that will block the sunlight from reaching the Solar PV array. Small areas 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
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| Hot Spot |
The Hot-Spot-Effect describes the overheating of an area in a solar panel due to unequal light radiation and occurs when there
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| Watt peak |
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:
In most
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
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