The solar system uses the energy of the sun and converts it into electricity. Rightly, the question arises what happens to PV systems in winter, when the number of hours of sunshine is less and the sun, which is already lower, is more often covered by clouds. Let’s take a look at how the PV system works in winter!

Operation of the PV system in winter

The assumption that the performance of the PV system decreases somewhat in winter is basically true. However, it is a misconception that it would be useless, as it can produce energy even in such conditions.

A solar system, as the name suggests, works as a system. This is evident not only in its structure, but also in how we see its usefulness. In summer, PV systems can usually produce more energy, meaning they produce in excess thanks to the radiant sunshine. This surplus is fed back into the network, i.e. “pitched in”. Then, when winter comes and the output drops, the energy produced is replaced by the consumers from the “community network”, i.e. by connecting to the central system, they supplement the available electricity according to the demand.

What affects the power generation of a PV system?

The operation, performance and efficiency of the PV system depend on several environmental and non-environmental factors.

Among the non-environmental factors, the most important are:

• the orientation: in which cardinal direction the plane of the roof points,
• the angle of inclination: what is the angle of inclination of the roof, what angle it forms,
• shading: how much shadow is cast on the system due to its location?
• the type: it is important whether the solar cell is polycrystalline, monocrystalline or thin film.
• the quality: an important factor is the quality of the solar panel, the inverter and the design of the installation.

Environmental factors that affect performance:

• the number of hours of sunshine: how many hours the sun shines in a given period,
• the altitude of the sun: how high the sun is,
• climate: what are the temperature conditions in the given area.

In the following, we will look at these individually and see where the cold is an influencing factor, i.e. what the operation of the PV system in winter depends on.

The number of hours of sunlight and the height of the sun

How long a PV system is exposed to sunlight affects how much energy it ultimately generates. In winter, the sun shines less each day, so the number of hours of sunlight is lower, which can contribute to the decrease in energy production.

An important factor is the height of the sun in the sky, as this affects the angle of incidence of the sun’s rays falling on the system. As the sun is lower, the angle of incidence is less, which means it cannot produce as much energy as it would under ideal conditions.

The temperature and efficiency of the PV system in winter.

In winter, efficiency is a key issue in solar energy production. Some PV systems are extremely sensitive to temperature changes. Neither too hot nor too cold is good for them, because then their efficiency decreases.

In general, monocrystalline and polycrystalline solar cells withstand temperature drop best, while thin-film solar cells respond less well. However, when it comes to temperature rise, thin-film panels hold up much better.

Cloud and fog formation and winter performance

The type of PV system also determines the performance value. There are some that provide average performance even in cloudy weather, but there are also those that are less able to take advantage of the scattered light. Types that belong to the former category have a good chance to pass the test even in winter.

With regard to types, it can be said that the performance of monocrystalline solar cells decreases significantly in cloudy weather, so it is not recommended to install them in regions with a low number of hours of sunshine.

Where the sun shines less, lower temperatures also cause problems. As we wrote above, thin film systems cannot tolerate this drop in temperature and their performance degrades. The best choice for this is the polycrystalline solar cell, which can tolerate both stray light and low temperatures. Its indicators react less strongly to environmental influences.

In Germany, the solar module types have almost the same performance. Matched with summer production, the surplus and deficit complement each other when needed. We can see that the energy production of the PV system is influenced by several factors. If we take them into account, we can build a system that works well all year round.

Let’s start with the bad news: According to the current state of the art, all PV systems widely available on the market operate with relatively low efficiency. And now the good news: efficiency does not equal performance. In other words, as long as our solar system performs as it should, i.e., when operating optimally, it lowers our electricity bill and covers our total annual electricity consumption, the efficiency levels at which it does so are negligible.

Efficiency of the PV system: absorbed and emitted energy

Of course, there is a correlation between power and efficiency, but they are by no means synonymous and the low efficiency of a PV system should not be a cause for concern at all.

PV systems convert sunlight into electricity. Solar cell efficiency essentially expresses the ratio of the amount of light energy that arrives at the surface of the solar cells and the amount of electricity generated from it. Let’s take a look at what this all means in practice, using the most common types of PV systems.

Monocrystalline solar cell

The monocrystalline solar cell consists of one silicon block and therefore has a very high efficiency: On average, it can be around 21%. However, due to the larger silicon block, the manufacturing costs and thus the price are relatively high.

Polycrystalline solar cell

The polycrystalline solar cell consists not of one large silicon block, but of several smaller ones. Its efficiency is lower, although only slightly, and is about 20%. The production is cheaper, which is also reflected in the price.

Thin film solar cell

The thin-film solar cell is also based on silicon, but is manufactured by an evaporation process in which only a thin layer of it is applied to the surface of the structure. This makes its production not only cheaper, but also much faster than its monocrystalline and polycrystalline counterparts. Unfortunately, it shows a significant drop in efficiency: only 6-8%.

It can be seen that the differences are sometimes smaller, sometimes larger for some types. In the long term, these can lead to significant yield losses. At the same time, the issue should also be studied from the point of view of cost implications in order to get a realistic picture of total costs and payback.

The problem of measurement

Before photovoltaic manufacturers launch their solar modules on the market, they carry out a so-called “final measurement” in which they illuminate the solar modules in a measurement chamber with artificial light of a specific spectrum and then measure the level of the output current and the value of the DC voltage. Since the spectrum of the artificial light source cannot completely match the spectrum of the solar radiation, the result obtained in this way is not exact, but only approximate values.

Cell efficiency = PV system efficiency?

The cells inside the solar panels do not work with the same efficiency, they are classified according to different aspects during production, and then a kind of mixed set is formed. The average efficiency of the cells cannot fully correspond to the efficiency of the whole panel. This value can not be determined accurately or reliably in this way.

Alignment and inclination

The angle of inclination between 30 and 40 degrees is the most favorable for the system, as it ensures the optimal angle of incidence of 90 degrees. It is also possible to install the panels on a flat roof, in which case the same conditions apply as for installation on the ground, with the difference that the solar panels are distributed at a more favorable height.

The longer the panels are exposed to the sun, the more energy they can produce. A southerly orientation is most optimal; a southeasterly and southwesterly orientation can expect a loss of about 5 percent, while a westerly orientation can expect a loss of 10-15 percent. None of these have a significant impact on the payback of the investment. We pose a real problem only when the roof is oriented to the north. In this case it is not recommended to install the PV system on the roof. At the same time, there is no such orientation that would be a reason for exclusion, at most the installation conditions change accordingly. Finally, a PV system can be placed on a garage or other outbuilding, on the roof of a covered terrace or even on the garden ground.

Ideal or optimal?

In terms of conditions, the ideal state for PV systems is like the perfect happiness of man: It exists almost only for a moment. For example, we might think that the higher the heat, the better the efficiency: on a hot day, we can produce more electricity with our private mini solar power plant. However, this is not really the case. Most solar panels work most efficiently at 25 degrees Celsius. Therefore, manufacturers measure solar cells with 1000 watts of rectangular irradiation at 25 degrees Celsius, which is optimal in all respects, an environment that very rarely occurs in reality or only for short periods of time.

There are types of products that produce relatively high power even in cloudy weather, while in others productivity drops more drastically. So when it comes to efficiency, you can’t think in terms of black or white. However, it is certain that certain environmental factors have at most a slightly different impact on the operation of the overall system. The efficiency of PV systems is constantly changing due to various environmental influences.

Under the given circumstances

The use of solar energy is also affected by humidity, cloud cover, smoke, smog and temperature values, the geography of the area and the angle of incidence of sunlight.

Of course, the efficiency of PV systems is much higher in summer than in winter, but there are also differences depending on the landscape. For example, in the lowlands, there are more hours of sunshine in summer than in the mountains due to cloud cover. In winter, on the other hand, the opposite is true: due to the fog that falls on the flat terrain, the sun’s energy is better utilized in the mountains. Smog can also become a problem from time to time around larger cities. Regardless, it is important to point out that PV systems produce energy everywhere and at all times of the year, just to varying degrees. Of course, it would be possible to create a system that is incapable of doing this, but it loses its raison d’être on the design table even before it is implemented.
Despite the fact that the layer of snow blocking the light path slides off more easily from clean, dust and dirt-free panels, and efficiency is also better, you do not have to worry about the separate cleaning. On the one hand, the rain always solves this problem for us, on the other hand, cleaning is strongly discouraged, because the panels can be easily damaged. We can also improve our electricity production with a rotating support structure. However, careful consideration is absolutely necessary here, as these devices significantly increase investment costs and their maintenance also requires a greater financial outlay compared to almost maintenance-free fixed support structures.

Smart System: smart solution?

One of the weak points of PV systems is that the overall system is tuned to the module with the lowest power. If a shadow falls on a module or leaves remain permanently attached to the surface after a strong storm, the efficiency of the overall system decreases. Smart systems can improve the efficiency of the PV system. They optimize the system and coordinate the operation of solar modules with different tilt angles and locations. In addition, they also indicate possible faults.

An installed smart system can lead to an increase in performance of 5-25%, depending on individual conditions.

The types of photovoltaic systems now paint a very colorful picture, so even less experienced customers can easily get lost in the dense solar panel field. In today’s article we take a look at what types we find on the market and what advantages and disadvantages they have.

What is a photovoltaic system?

Photovoltaic systems convert solar energy into electricity that can also be used in the home. They function as part of a complex solar panel system consisting of the solar panels themselves, the structure supporting them, cables and the inverter that converts the energy.

The process works briefly as follows: sunlight falls on the surface of the solar panel, which absorbs it. The energy transfer releases electrons that begin to flow, creating an electric field and voltage. This energy, direct current, is converted by the inverter into alternating current, which can then be used to charge and power various electrical appliances, heating, cooling and lighting.

However, before we take a look at the different types of PV (solar panel) systems, let’s first clarify a common, confusing difference, which is the difference between a solar panel and a solar collector.

Solar panel vs. solar collector

Although their names are very similar and both use the sun’s energy, there is a big difference between the way solar panels and solar collectors work. While the former produces electricity thanks to the photovoltaic effect, that is, directly uses solar radiation, the latter heats the fluid circulating in the system. Therefore, the solar collector is used for heating and hot water production.

Now that we know what photovoltaic systems, or solar panels are and how they work, we will present the types available on the market, as well as the advantages and disadvantages of the types of PV systems.

Types of solar cells

Basically, we distinguish between two main categories: There are crystalline solar cells and solar cells based on thin-film technology. Let’s look at these first and then present some alternative solutions.

The crystalline solar cells

The technology used by crystalline solar cells is quite mature, being the oldest and most popular type. This is due to the fact that they operate at high efficiency and can provide good performance. By the way, their name comes from the fact that the panel is made of silicon cells.

There are two types, monocrystalline and polycrystalline, which actually differ in the way they are manufactured.

Monocrystalline solar cells

Monocrystalline solar cells are made by dividing a silicon block into equal parts, octagons. This makes them easy to recognize when placed next to other types. The technology can achieve an extremely high efficiency of up to 21%, which is why it owes its popularity.

It performs best when exposed to direct sunlight rather than diffused light, which has several disadvantages, such as the fact that its performance decreases in cloudy weather and it is very sensitive to the angle of inclination and orientation. Since its price is higher than the polycrystalline version, it often lags behind the competition for financial reasons.

Polycrystalline solar cells

Polycrystalline solar cells use several silicon blocks that are also divided into equal parts, but in this case they are square. They are most easily recognized by their purple color and square cells.

Unlike monocrystalline solar cells, these solar cells use stray light very efficiently, so they perform well even in cloudy, slightly shady locations. The price, however, is that direct sunlight is not handled as well, although their efficiency is only minimally behind mono, about 20%. As for the price, it is also important to point out that the production and purchase price of polycrystalline solar cells is cheaper than other crystalline solar cells.

Thin-film, amorphous solar cells

In addition to crystalline solar cells, the thin-film solar cell is another defining type. Silicon still does most of the work here, but it is evaporated onto the surface and a very thin layer is formed. Let’s look at the advantages and disadvantages!

The advantages are clearly strengthened by the fact that thin-film solar modules are not too sensitive to heat, which means we don’t have to worry about the PV system letting us down on a hot summer day. Likewise, they’re not too picky about orientation, which is especially important when conditions aren’t the best. And what makes it even more interesting is that it can be manufactured at a much lower cost.

The downside, however, is that power and efficiency are lower, so more panels are needed to achieve the same result. In addition, their lifespan is also shorter and so is the manufacturer’s warranty.

A very popular subtype is the amorphous version. Amorphous solar cells differ in that they are made of an amorphous crystal, while semiconductor silicon is made of silane gas.

Hybrid

The special feature of hybrid solar panels is that they combine the advantages of a solar panel and a solar collector, so that the system can produce both hot water and electricity. In addition to the panel system, there is also a water system that is also suitable for cooling the solar panels, which can avoid the reduction in power due to heating.

Polymer

Polymer solar cells represent a novel line that is inexpensive to produce and flexible to use. However, their disadvantage is that the technology is not yet mature, as evidenced by the fact that their efficiency is low and large-scale production has not yet begun.

Solar roof tiles

There are also so-called solar tiles, which are very practical, because the roof tiles themselves perform the function of solar panels. However, this solution is currently available only at a very high price.

Insular or networked

In addition to the types of solar modules and PV systems, it is also important to mention that it does not matter how the modules form an overall system. This is possible in two ways: islanded and networked.

In the case of islanded systems, the property is completely independent of the power grid and the excess energy is stored in batteries. In the latter case, on the other hand, the plant is connected to the grid, which means that it is recharged here and any excess production and deficits are compensated from here. Therefore, it is also necessary to purchase an electricity meter that measures in two directions, which can be used to monitor production and consumption.

Photovoltaic systems are the most accessible means of generating green energy. Thanks to various subsidies, users have increasingly widespread access to this environmentally friendly technology.