FAQ

Heating home with a PV system ?

Generally not, due to differences in the system efficiency. Thermal collectors 80%, and PV modules approx. 14% efficiency. In practice that means that to achieve an power of 4.5kW of energy, requires surface of solar collectors approx 6m², and PV technology approx 33m². But due to the price drop of PV technology and in some countries, specific structure of the feed-in-tariff (prefered self consumption above 30% of generated electricity), it may be interesting.

Advantages of heating with PV systems are obvious:
 

PV is an simple electric system (thermal systems with high pressure and temperatures requires appropriate handling)

almost in every solar tank, can be installed an electric DC-warmer, powered by an PV system

PV systems works in a broader light spectrum band, producing energy even in very weak solar exposure, but proportionately less

unified system easy for maintenance, not two in different technologies (Thermal/PV)

But nowadays from an economic point of view, it is preferred to produce hot water on the basis of thermal heating solar systems. The differences in the efficiency are to big, differences in prices of technology also. Solar thermal systems are about half cheaper than the PV technology, calculated in EUR per 1Wp. The PV technology produces a very universal energy - electricity, which is much more useful and transferable, than the thermal energy. But each solar system during the winter months has an supporting character, that should not be forgotten.

Failure of PV inverter

This is probably the most common cause of disfunction in a photovoltaic system. A PV inverter is subject to wear and may be sensitive to external influences such as heat, dust, moisture, etc. Furthermore fluctuations in voltage or current problems, both from your PV systems, as well as from outside, such as nearby firms, farms, biogas plants or wind turbines. If an PV inverter fails after a relatively short period after start-up your PV system (under warranty) you lose usually the feed-in tariff during the downtime. After the warranty period an replacement inverter, generally is an small part of costs, compared to the whole system costs.

If there is a failure indication (on the display of the inverter), the error code can be interpreted according the user manual. There are often displayed codes only for references or operating system status, that have nothing to do with disfunction of the photovoltaic system. E.g. morning and evening when the inverter is in on or off status again (indicated by yellow or red LED's). This may also appear, if an PV inverter operates at its limit of the rated power range. If this message appears only in the cold but sunny and clear days, that's absolutely normal. If this message appears in the hot summer days, the inverter is probably undersized.

Adjustments and maintenance of PV inverters, should be made by specialized professionals.

Grid failure, failure of the PV system

While a grid failure the inverter will immediately, within miliseconds, interrupt the transfer of electricity into the local grid. The PV inverter monitors the local grid and until recovery of the local grid parameters (eg. Hz frequenz), transfer of electricity will be resumed.

Dirtiness and dust on the PV modules

The modules are cleaned by rain, when they are mounted on a inclined roof there is an self-cleaning effect. Leaves from nearby trees should be removed, if firmly fixed. Shadowing of individual cells of a module, has significant influence on energy yield losses and may result in hotspots. Every five years, the modules should be checked in general inspection.

PV power decreases over the time

The degradation of the modules (decrease in efficiency over the lifetime of the modules) should be noticeable after several years, except for thin film modules. If the PV power goes back in a shorter time, the system should be examined more closely. The simplest reason may occur through extraordinary contamination of the modules, especially for systems operating in the vicinity of factories, agricultural or railway. Otherwise, If no errors are found, the modules should be "flashed" by the manufacturer or at an laboratory, so their performance can be determined.

Different performances of PV-strings, with the same number of modules

If similar strings (within the PV system) are unshaded and otherwise the conditions are equal and the different performance occur shortly after installation, the most obvious is that a module has been forgotten to connect. This happens more often than you think.

Hot Spots

Hot-Spots are areas in the solar cells (within a module) resulting from permanent shadows on the solar cell. It occurs in the solar cell an ohmic resistance and heat, which can lead to damage or even destruction of the cell. To reduce this effect, it can not be completely avoided, in the PV modules are installed protecting bypass diodes, which disconnects the faulty circuit. An hot spot can be detected as a brownish stain and can burn even through the cell and the module rear wall (eg. in similar size to an 1or 2EUR coin). The problem can occur in modules located very close to pipes or antennas as source of permanent shadows, which should be avoided at all cost.

Broken solar glass (thermal expansion)

PV - Glass breakage occurs primarily when one or more modules are mounted without strain, without avoiding the accordance with thermal expansion. This happens especially if the installation instructions have not been met. Under heat the framework of modules and mounting system expand upon heating, adequate clearances must be maintained. If modules are mounted directly to each other without a gap, problems are inevitable. The same applies to the mounting system. The rails must not exceed a maximum length specified by the manufacturer. Faulty installation may take some time to be perceived by later module glass cracking or creaking of the mounting system or PV modules. Glass breakage often occurs during the first year after installation of thin-film modules and in this time visual inspections are particularly recomended. Here it is again noted that a cross-bar assembly helps to counteract this phenomenon.

Thermal - In the case of solar collectors, the flexible connections of solar collectors adapt the thermal expansion. But the max. amount of connected solar collectors in one section (collectors battery) should not exceed 8 solar collectors. If needed, another section of solar collectors can be created, up to the next 8 solar collectors in one section. The sections can be connected with an elastic dilatation of several cm (25-50cm) eg. to an industrial (bigger) thermal solar system.

Hailstorm on PV modules

The modules are mounted of hardened special glass. It is bombarded with ice balls for testing purposes, according IEC standard, which are carried out with ice balls of 12.5 mm to 35 mm in diameter and the impact velocity has a maximum value of 140 km / h. Therefore hailstorm means low risk for PV modules and may have an cleaning function.

Tracking systems ?

Tracking system allows to receive up to 30% more energy yields, because the system tracks the sun continuously. It should be weighed exactly which PV technology will be mounted on the tracking system. There are technologies where direct sunlight is preferred, ideally for higher energy yields, then there are PV technologies, which would not use it efficiently. An tracking system for flat roofs are also not recommended and the financial benefits of higher energy yields with the higher costs for construction and infrstructure need to be calculated. Generally tracking systems have advantages in middle and large scale projects, where the maintenance of such systems is subject to an scale effect. For single tracking systems, due to the high integration costs and maintenance (motors, software, monitoring) are rarely recommended. Usually installed for esthetic purposes - there is no doubt, looks definitely modern and futuristic.

Insurance of your PV system?

An important component of any PV system is it's insurance. Already from the time of delivery or after takeover from installer ? It is important to clarify the insurance, before mounting the system. Extremely rarely happens, but it can not be excluded, eg a lightning strike during the mounting works, in unfinished PV system, then who is liable for this damage? General your PV system should be covered by an home or property insurance, usually requires a message to your insurance company and his confirmation in written form. The most harm can result from lightning, over voltage or fire. Eventualy technical defects of the system components are covered by producer warranty.