Frequently Asked Questions about Solar Energy

The surface of Earth steadily receives radiation from Sun. The total amount of energy absorbed by atmosphere, oceans, land, and biomass is approx. 3 850 000 exajoules (EJ) per year. The total World energy consumption is max. 600 exajoules. If we were able to utilize all the incoming solar energy, it would take only 80 minutes to cover World's energy needs for the entire year.

Photovoltaics is about the conversion of light into electricity. Photons are light particles that carry a small amount of kinetic energy. When the light hits a special kind of semiconductor, some photons bump into electrons. These collisions inside the material free the electrons to a higher-energy state. Loose electrons and holes appear. Electric charge (voltage) builds upon the electrodes of P and N layer of the semiconductor. The accumulated energy can be collected from + and - electrodes as a flow of electric direct current.

The term photovoltaic cell and photovoltaic panel/module are often confused. The cell is one semiconductor plate 16 cm x 16 cm made of 0,1 mm thick silicon. It’s the smallest unit that produces electricity. Several dozen of cells connected together make the solar panel. Photovoltaic cells are connected in series (rows). Individual series of cells in the module are then connected in parallel. Silicon solar cells are usually black or blue color. But you can have other colors on special request.

A solar panel is a passive flat device which absorbs sunlight by its surface. It transforms sunlight into heat or electricity depending on the type of solar panel you have. Solar panels are connected into series. Individual series of modules are connected in parallel. You want to install your panels to some sunny place with no shadow. Because the shadow is the biggest enemy of solar panels. The safest and sunniest place is mostly on the roof of your house.

Solar panels will work everywhere on Earth. How good will be the output depends on your location. There are very sunny places on the planet, as the irradiation map shows. That is good for the economy of your investment. Solar panels love the sunshine but hate the heat. That's why even the colder areas are very suitable. If the electricity is a matter of life and death, you will appreciate solar panels even in the coldest places on the planet. There are apps on the internet that can calculate average daily or yearly energy yield according to your location. You can try PVGIS if you're from Europe, Asia or Africa. For more regional solar maps try SOLARGIS.

Yes, you can achieve significant financial profit or savings if you place photovoltaic or thermal panels on your roof. Thanks to the panels your energy bill gets lower and above that, you can get subsidies, feed-in tariff, tax bonus, green tags or nothing - it depends on which country you live in. If you also purchase a battery your house will be secured against the blackout. This is a pretty cool feature whose financial benefit is not easy to quantify. It works like an insurance, which you will most appreciate in difficult times. And finally, the acquisition of solar panels means a certain environmental benefit. It's an investment in our planet and in our children and it's practically impossible to financially evaluate. It is also an investment in your lifestyle, status, and feelings. You will have the double pleasure whenever the sun shines.

We indicate the power output of photovoltaic panels in Watt peak units (Wp) or kilowatt peak units (kWp). That represents the maximum output produced by the PV panel when tested. The tests are performed under standard testing conditions (STC). It means with a light source at an irradiation energy of 1000 W/m2 and ambient temperature of 25 °C. These conditions are similar to direct sunlight irradiation on a clear sunny day without clouds.

You can divide the solar panels into two groups according to the type of energy they produce. Thermal panels make heat and photovoltaic panels make electricity.

Thermal solar panels can be in the form of black rectangular plates and also tubes called heat-pipes. They are made of metal and covered with glass. Panels designed to heat pool water are made of plastic. Thermal solar panels can heat water, antifreeze mix and also air.

Photovoltaic (PV) solar panels can be in the form of thin rectangular or square plates. The base of the module is plastic or glass. On the base is the active layer of semiconductors covered by glass. The aluminum frame reinforces the panel and its layers. The semiconductors are usually from crystalline silicon. Alternative materials are amorphous silicon, CIGS, sulfur, or organic substances. We refer to alternative solar panels as thin-film.

Thermal solar panels are quite cheap, almost immortal and very efficient. They convert up to 80% of sunlight energy into heat. Therefore you don't need such a big area of modules. You can start with 2 or 3 panels to heat hot water for your household. But thermal panels need direct sunlight otherwise there is no energy yield. Some kinds of thermal panels must be continuously cooled, otherwise, they overheat.

Photovoltaic panels are lightweight and they can work even in dim lighting or rainy weather. They have no electronics or moving parts inside. The direct current comes right from the semiconductors. PV modules can't overheat. In opposite to thermal panels, PV panels have lower efficiency (8% to 25%). Therefore you need a larger area of panels on your roof. You will need the inverter or charge regulator with a battery to utilize the electricity for your household.

Manufacturers give a 25-year warranty for silicon photovoltaic panels. Modules must be still able to operate after 25 years, and furthermore, the performance of the PV panels may not be less than 80% of nominal power. So the real lifespan of the photovoltaic solar panels could be even more than 40 years. And quality thermal panels are made of galvanized metal, copper pipes, mineral insulation, and glass. They are literally immortal.

Monocrystalline photovoltaic cells can achieve slightly higher efficiency compared to polycrystalline cells. Both types of materials process the light somewhat differently. But the variance is more about the academic debate. The customer sees only that the monocrystalline cells are black and the polycrystalline cells are blue. So the real difference between the two is just a matter of aesthetic taste.

You need approximately 6,5 square metres of mono or polycrystalline photovoltaic modules to make it 1 kWp. You need approx. 8 to 16 square metres of thin-film photovoltaic panels for the same total output.

Thermal solar panels are more efficient, therefore you need only 1,25 m2 to achieve the power of 1 kW. Thanks to higher efficiency, thermal panels are more suited for roofs with limited space.

The front side of each solar panel is glass. So the rain will wash away dust, dirt, pollen and bird poo. Or snow, if it's snowing where you live. However, there is one condition for this self-cleaning function. You have to put your solar panels sufficiently inclined, at least 15° (27%). You can also wash your solar panels if you can easily reach them. Total energy yield will increase by 1% to 5% if you are in dusty areas.

You can use flat roofs or sloping roofs of any inclination and orientation. You can place the panels on the walls, on the balconies or on the ground. The building can have any roofing, there is a specific fastening system for all roof types. Panels can be integrated into the roof, the panels then have the function of roofing. Different mounting variants may vary in price. Mounting above the roofing is usually cheaper than roof integration. You can also install solar panels on land. But installation on your house is usually cheaper and the panels don't occupy your living space.

To maximize energy yield, place the solar panels in the exact south orientation. Your modules are still optimally oriented when their orientation is from southwest to southeast. The optimal inclination depends on the latitude of the place where you are. The best inclination is 0° to 5° when you are on the equator. The best inclination is 40° to 45° when you are around the polar circle.

The tracker is a mechanical device that rotates and tilts the solar panels so that they are always optimally inclined and/or oriented to the sun. You can have single-axis or dual-axis trackers. Tracking helps to maximize the energy yield. Thanks to the dual-axis tracker you can get up to 35% more energy compared to fixed installation. The downside is the higher maintenance cost of the solar installation. Trackers are designed exclusively for installation on land.

No, the accumulators are not necessary, if you plan to build a grid-connected photovoltaic installation. If you can't eat up all the power from PV modules, the rest can be fed into the grid. You have the possibility take the energy from the grid when solar panels are off - e.g. during the night.

You will definitely need batteries if you plan to set up an off-grid installation. Accumulators then act as a buffer and store the energy for later use.

Ideal conditions for producing energy are when exposed to direct sunlight on a sunny day with the completely cloudless sky. Thermal solar panels stop working when the rain comes. Photovoltaic modules continue operating, but performance drops down by 50% to 95%.

Solar panels operate in the exterior and are exposed to all weather conditions. They can survive hailstorms unless they are extreme. Manufacturers test solar panels for impacts of ice balls of 25 mm in diameter and speed of 80 km/h. There is a standard IEC 61215 for these tests. You need to have insurance cover for damage caused by extreme weather conditions.

An inverter is a device that converts direct current (DC) into alternating current (AC). Solar panels and batteries operate on direct current. On the other hand, the electric grid operates on alternating current. The inverter is a bridge that allows you to use energy from PV modules and batteries in your house. You need the inverter when you want to use standard 120V or 240V AC appliances. You can find inverter in either off-grid and grid-tied PV systems. Without the inverter, you wouldn't be able to feed the power into the network. Well known manufacturers of inverters are SMA, Fronius or Victron

Charge regulator is a component of PV off-grid or hybrid systems when batteries are part of the setup. The regulator controls voltage and an electric current that charges the battery. Battery charging is quite a delicate process that needs to be controlled in order to secure long life to the battery.

MPPT stands for "Maximum Power Point Tracker". The MPP tracker is an algorithm, which is a part of solar inverters and charge regulators. It searches for the optimal ratio between voltage and electric current coming from photovoltaic modules. MPPT maximizes the power output from PV modules, especially in poor lighting conditions. The MPP tracking can add up to 30% of the annual energy output from solar panels. If possible, always choose devices with MPPT.