This article will guide you through the technology which allows solar panels to generate electricity from sunlight. Although simple and robust, solar panels work based on complex physical processes.
What most laymen know about solar panels is that they provide free electricity. They are also sturdy and durable, capable of handling extreme weather and a surprising amount of physical force.
What makes these panels tick though? How do they generate electricity? How can they make you money off the surplus energy you can sell back to the grid?
- 1. What are Photovoltaic Cells?
- 2. The Construction of PV Cells
- 3. The Actual, step-by-step Process
- 4. Measures Meant to Optimize the Process
- 5. What is the difference between monocrystalline and polycrystalline silicon solar cells?
- 6. Flexible and Thin-film Solar Panels
- 7. How Long Does It Take to Install Solar Panels?
- 8. What is the FIT/SEG?
- 9. Do Solar Panels Work When It Rains and Snows?
- 10. Do Solar Panels Work When It is Cloudy?
- 11. Solar Batteries
- 12. What Does the Future Hold for PV Technology?
- 13. The Bottom Line
What are Photovoltaic Cells?
Light is made up of photons. When sunlight strikes the surface of a solar panel, it knocks free some electrons from the atoms that make up the surface.
These electrons are then captured by an electric field. Their movement is electric current. To capture the said electrons, electric tension, also known as voltage, is employed.
The phenomenon explains the term “photovoltaic”. PV means electric current resulting from the action of photons on a specially treated surface.
The Construction of PV Cells
Most solar panels use monocrystalline silicon technology. What this means is that the main component of the individual solar cells, which make up a panel, is silicon. Silicon is the base layer. Upon it, two other materials are layered/seeded, to create an electric field.
On top of the silicon layer, manufacturers use phosphorous. This layer adds extra electrons to the surface. Since electrons are negatively charged, this way, an overall negative charge is conferred to the top layer of the silicon.
The bottom layer is treated with boron, which reduces the number of electrons, lending this layer an overall positive charge.
The result is a charge difference between the upper and lower layers of the “sandwich”. This potential difference creates an electric field. The electric field is essential because it handles the capturing of the electrons. These electrons make up the electric current generated by the PV cell.
The Actual, step-by-step Process
- When sunlight hits the phosphorous-enriched surface, the photons break away electrons.
- These electrons are trapped by the mentioned electric field and are directed towards metal contacts. The organized movement of these electrons constitutes an electric current.
- After it is combined with the electron flows generated by other PV cells, the current is directed towards an inverter. The inverter is a device that turns DC (direct current) into the AC (alternating current) that most house appliances use.
- DC is suitable for the powering of smaller electronic devices. It does not work with household appliances, however. These require AC, which is what the inverter provides.
This is, in a nutshell, the way solar panels create electricity from sunlight. Of course, the actual composition of the panel is a little more intricate.
Measures Meant to Optimize the Process
The phosphorous-enriched surface is covered with an anti-reflection coating, to make sure that photons do not bounce off it.
On top of this coating, a layer of transparent adhesive is applied, followed by the glass cover. The glass cover is what lends the whole construction sturdiness and durability.
Usually, this cover is made of a special kind of glass that can withstand hailstones the size of golf balls. More precisely, the glass used for this purpose is optically transparent, lead-free glass. It has been tested to withstand the impact of a 35mm diameter ice ball, striking it at the speed of 30m/s.
The back of the ensemble is secured with a protective sheet. The role of this sheet is to deal with heat dissipation and the elimination of humidity.
Excess heat hinders the optimal functioning of PV cells. The same goes for humidity.
What is the difference between monocrystalline and polycrystalline silicon solar cells?
The monocrystalline construction uses a single silicon crystal. The polycrystalline one uses several shards/bits of silicon. Monocrystalline is the more popular construction on account of its superior efficiency.
Most “proper” solar panels use such construction. This variant is pricier than the polycrystalline solution. But efficiency trumps everything in the solar power game.
The described technology is amazing enough in regard to the actual manufacturing process. However, researchers have developed solar cells that are ridiculously thin and lightweight. Semiconductor technology generally lends itself well to miniaturization. That holds true for PV cells as well.
Flexible and Thin-film Solar Panels
These cutting-edge PV cells are much thinner than a human hair and much lighter than a sheet of paper. They are also flexible. Why would we need to achieve this sort of PV cell sophistication? Such panels can be built into construction materials (as we have already seen with PV roof tiles) and even clothing at one point.
Flexible solar panels are already available. While these are not the ultra-thin ones mentioned, they fit boats, cabins, trailers, and cars, where large, flat surfaces are not available.
Flexible solar panels should not be confused with thin-film solar panels. The latter may represent the peak of solar cell technology. They offer scores of advantages over their more cumbersome peers, but they are not as sturdy and durable. As such, thin-film solar panels are not suitable for rooftop, residential use.
The Strengths of Thin-film Solar Technology
Still, due to the fact that less material goes into them, such solar panels are cheaper and often more versatile. Some of their main advantages are:
- They are portable and lightweight. That makes them suited for powering sheds, tents, and cabins out in the woods, off the grid.
- Durable, organic materials are used in their construction. That said, the expected lifespan of a thin-film solar panel is much shorter than that of a “legacy” one.
- Thin-film solar panels are cheaper.
- Due to the above factors, such panels see wider applications.
- Most such solar panels are transparent.
- Their performance is not dependent on weather conditions.
How do Thin-film Solar Panels Work?
The basic principle that allows solar panels to turn light into electricity is the same in thin-film panels as in regular ones. There are obvious differences in construction, however.
Instead of the layers described above, thin-film solar panels consist of a number of films. These layers are designed to absorb different parts of the spectrum of light.
There are three types of thin-film solar panels, depending on the type of semiconductor they use.
– Cadmium Telluride(CdTe) and Cadmium Sulfide(CdS) are at the core of some of the cutting-edge thin-filmPV cells. They make up the Negative- and Positive-doped layers needed for the process to take place. A gold contact at the bottom carries away the resulting stream of electrons.
On top of the Negative-doped Cadmium Sulfide (CdS) layer, there is a high resistivity oxide coating. It isfollowed by a low resistivity oxide coating and then the protective glass or plastic.
– Other new thin-film solar panels use copper indium gallium diselenide (CIGS). A company has developed CIGS material which is essentially an ink, containing the right nanoparticles.
CIGS can be applied to metal foil or glass. In the latter case, an additional layer of molybdenum is required to create an electrode.
The efficiency of these new technologies has already reached the 20 percent mark. And it is expected to reach 50 percent at one point. Researchers have already created solar panels with 46 percent efficiency. Such panels are experimental for now. Their technology is too pricey for mainstream users.
The highest efficiency has been achieved with multi-junction cells. Cells featuring 4 or more junctions are currently the best experimental performers.
The progress of the solar panel industry has been spectacular over the last decade. The first PV cell was created in the late 1800s, and its efficiency was less than 1 percent. Bell Labs achieved PV cell practicality with its 1954 creation. The efficiency of that cell was around 5-6 percent.
Hoffman Electric reached 14 percent efficiency in 1960. In 1992, University of South Florida researchers created a PV cell with an efficiency of 15.89 percent. 2015 was the year when Panasonic announced 22.5% efficiency with its PV cells.
Thus we expect it to take many years until the efficiency reaches 50% for the retail market.
– Amorphous silicon (a-Si) technology recreates the silicon wafer construction depicted above. It is a transfer of existing technology to the thin-film realm. Its efficiency capped at about 20 percent, this approach is already obsolete.
How Long Does It Take to Install Solar Panels?
There is no clear-cut answer to that question. Installation time depends on many factors. Of these, the most obvious one is the size of the PV system that is to be installed.
As a basic starting point: it may take the installers one day or two days to set up all the necessary elements, depending on system size/complexity.
In the UK, the installation itself should be included in the quoted price of the system. That is to say that the client will likely not have to pay extra for it.
Solar Panel Installation Phases
- The most time- and work-intensive part is the fitting of the frame for the panels. There needs to be enough free surface area available on the roof to accommodate the needed number of such frames.
- The second phase is the installation of the actual panels.
- The fitting and connecting of the inverter is the last element to fall into place.
Exactly how much time it will take installers to complete the job also hinges on the supporting structure they will use.
The support structures used consist of aluminium profiles and stainless-steel fastening elements.
Supporting structures used for rooftop solar panels are simple and quick to install. They are fixed and will keep the solar panel facing in the same direction, at the same angle at all times. The angle needs to be set carefully, to maximize capacity.
Support structures for ground-based solar panels are usually anchor block-based. For panels mounted on office/residential buildings, the ballast-based solution may be used.
More complex PV systems come with trackers and weather stations of their own. The role of the tracker is to determine the exact position of the sun. It then positions the panel so that the incoming photon rays hit its surface perpendicularly.
Weather stations offer estimates on the expected production of electricity. They also warn of possible situations when production falls below certain levels. Such solutions are only really used for industrial-level solar farms, however. Rank-and-file solar panel owners should therefore not worry about them.
Whom Can You Contact to Install Your Solar Panels?
There are scores of companies out there willing to sell you solar panels and to install them. It is important however to find an MCS approved entity.
On the one hand, this will give you, the consumer, peace of mind regarding the quality of the work done.
MCS approval is also needed for qualification into a scheme such as FIT or its successor: the SEG.
The solar panel providers/installers recommended on these pages are MCS-approved. Reviewed entities without MCS certification are tagged as such.
Can I Install Solar Panels Myself?
Given that installation costs make up around 10% of the quoted costs of a solar panel system, some may be tempted to attempt installation on their own.
A decent handyman should find it relatively easy to install such a system. Even to design and size it. There is plenty of information available online in this regard after all.
That said, taking matters into your own hand is not recommended. Here is why:
- You will likely want your residential solar power system to be hooked up to the national grid. Only qualified specialists are legally allowed to perform such operations. Above and beyond that, the physical risks associated with a DIY hook-up are immense.
- You may only qualify for a power buy-back scheme such as FIT or SEG, if you have your system installed by a certified company.
There are DIY plug-in solar panel kits out there, which blur these clearly defined lines. As the technology matures, more and more companies will launch such products.
Such solutions may fit some off-the-grid location, but certification is required if you intend to connect them to the grid.
What is the FIT/SEG?
The Feed-in Tariff Scheme (FIT) is on its way out. FIT was introduced in April 2010. It requires electricity suppliers to pay for the generation and export of solar electricity.
From April 1, 2019, the Scheme has stopped accepting new applications. Those who already applied, however, will continue receiving FIT payments. Solar panel owners whose MCS certificates have been issued before March 31, 2019, can still apply for FIT payments, until 31 March 2020.
Under FIT, solar panel owners receive payment for their electricity exports to the grid, as well as for the electricity they generate and use up.
The export tariff is around 4.77p/kWh, and the generation tariff is 6-13.99p/kWh.
The Smart Export Guarantee is set to replace the FIT in January 2020. It will compel electricity suppliers with more than 150,000 consumers, to pay an export tariff for the electricity delivered into the grid by consumers’ PV systems.
Down the line, the SEG may even reward consumers storing electricity and making it available for the grid during times of peak demand. Exact export and storage tariffs have not yet been set.
FIT participants do not qualify for the SEG.
Do Solar Panels Work When It Rains and Snows?
Solar panels do not need direct sunlight to work. They work in overcast weather too, just not as efficiently as they would on a sunny day.
In certain regards, rain may even be helpful: it can wash away the dust and debris accumulated on the surface of solar panels. Thus, when the sun comes out aftera rain, the panels may work better than they did before.
If it so happens that rain falls while the sun is out, the PV array should work at close to full efficiency.
Snow is a different matter. If enough of itfalls on a solar panel, it can block sunlight completely, shutting down electricity production. Even a little snow will impact performance.
Winter is an interesting season for solar panels. On the one hand, plummeting temperatures may improve solar panel performance. Below 77 degrees, the voltage output of solar panels increases. On the other hand, with winter come shorter days and less sunlight. Thus, the overall performance of solar panels still decreases.
Solar panel owners are advised to clear snow from their PV arrays as quickly as possible. In case the rest of the roof remains covered in snow, more light may end up falling on the panels, due to reflection.
Do Solar Panels Work When It is Cloudy?
They most certainly do. If they did not, the UK would hardly be a workable place to install them. Powerful direct sunlight triggers excellent electricity generation. The UV rays also damage the panels though, leading to faster performance decline.
What can you expect wattage-wise on a cloudy day? Solar panels will deliver some 10-25% of their rated wattage during such weather conditions.
The good news is that solar panels in the UK are sized according to the specificities of the local weather. What’s more, those who size them and determine exactly how many are needed, also take into account the daylight hours, sun hours as well as the shade patterns of the exact location where the panels are installed.
As long as all these issues are factored in, a PV array should work just as well as any other, regardless of the challenges presented by the weather.
In some cases, solar panel performance may spike on a partially cloudy day. This response is due to the “silver lining” effect of the clouds intensifying the light of the sun when it passes over their edge.
Electricity storage technology (batteries) has progressed even faster than solar panel technology.
Storage costs have been dropping at impressive rates.
Nowadays, it makes perfect economic sense for solar panel owners to augment their renewable energy capabilities through batteries.
Cheap storage also allows for arbitrage when selling energy back to the grid. Through the SEG, PV system owners might be able to take advantage of arbitrage indeed.
Solar Battery Types
Solar batteries use the same technology employed in batteries. There are three types of batteries:
- Lithium-ion – currently the most wide-spread and technologically sound solution
- Saltwater – a new technology hailed for the depth of discharge it offers.
What You Need to Know About Solar Batteries
The value of a solar battery is determined by a handful of factors. These factors are:
- Power and capacity. Capacity defines the maximum amount of electricity a battery can store. Power, on the other hand, tells you how much electricity a battery can deliver at a given moment. As far as capacity goes, most batteries are stackable.
- Depth of discharge signifies the actual amount of electricity you can use from your battery, without damaging it. Batteries need to retain a charge at all times to function optimally.
- Round-trip efficiency describes the electricity you can get from a battery, as a percentage of the electricity it took to charge it.
- Battery life. Over time, batteries lose their ability to retain a charge. The number of charge/discharge cycles it takes to degrade the battery to a point where it is no longer useful is the lifespan of the battery.
- Manufacturer. Some manufacturers build better quality batteries than others.
- Cost is always a factor as well.
What Does the Future Hold for PV Technology?
It is already profitable for homeowners to invest in PV panels, and it will certainly be even more profitable in the future.
That said, if humanity is to meet its goals of gaining some 30% of the electricity it uses from the sun, the current, silicon-based technology may have to give way to something more efficient.
Silicon itself displaced another, less efficient, technology. Charles Fritts created the first PV cell. In 1883, he used selenium covered with a layer of gold, to achieve around 1 percent efficiency.
Silicon was the real breakthrough. In the 1950s, at Bell Labs, Gerald Pierson and Calvin Fuller worked on silicon transistors. As they experimented with gallium-doped silicon, they immersed the semiconductor in lithium. The resulting PV cell had an efficiency of around 5 percent.
Technical difficulties tied to the electrical contacts and the way their p-n junction behaved, prevented them from improving the efficiency.
Significant improvements only came about well into the 90s and later: the 2000s.
Much of the progress registered over the last couple of decades came as a result of the replacement of amorphous silicon with crystalline silicon.
As mentioned, new materials are already pushing the efficiency limits of PV cells. Other improvements are lined up.
- A completely new family of materials called perovskites might soon replace silicon solar panels. Not only would tandem perovskite solar cells be more efficient than the current technology, but such solar panels would be cheaper as well.
- Perovskite films are made with a mixture of lead and tin, fine-tuned with a chemical compound called guanidinium thiocyanate.
- Organic solar cells and quantum dots are also explored as potential PV technology. But their efficiency is currently too low to make them noteworthy contenders.
- Other potential innovations include floating solar farms, building-integrated solar panels, PV fabric, as well as PV noise barriers alongside highways.
The Bottom Line
The technology that goes into solar panels explains quite well why they cost as much as they do.
Being able to withstand extreme weather and to keep working in adverse conditions is no small feat. This is one of the main reasons why solar energy has become feasible in areas such as the UK.