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My PV project: frequently asked questions

My PV installation

  1. Can I produce my own electricity?

    If your home has a roof with some shadow-free space, a PV system can generate electricity for your consumption. With a roof area of 30m2 and using standard modules (15% efficiency), you can produce about 4050 kWh every year.


  2. Why should I produce electricity with a PV system?

    As a homeowner, you know the pain of constantly paying electricity bills. As electricity prices are expected to continue to rise across Europe, more and more people are feeling this increasing financial pressure. Furthermore, Europe’s uncertain energy security means that there is a constant threat of crippling rises in electricity prices.

    With a photovoltaic installation on your roof, you benefit from your own solar power plant. And it will give you substantial savings over its 25 to 30 year life. In fact, as conventional electricity prices are expected to continue rising in the coming years, the value of today’s investment in photovoltaics will only grow.

    PV is also a renewable energy source that produces electricity. Electricity can be used for all home appliances and lighting. Moreover, PV produces energy during periods of peak consumption. This reduces the load on conventional power stations, effectively reducing the price of electricity for all consumers.

    Besides, the following arguments apply:

    • The fuel is free: the sun is the only resource needed to power solar panels.
    • It produces no noise.
    • PV systems are very safe and highly reliable.
    • PV modules require low maintenance and can be recycled.
    • It brings electricity to remote rural areas. PV energy is produced locally, close to consumption.
    • It can be aesthetically integrated into buildings, covering roofs or facades.
    • The energy pay-back time of a module is constantly decreasing.
    • It creates thousands of jobs. The PV sector has an annual growth of 40%, thereby playing a major contribution in job creation.
    • It contributes to improving the security of Europe’s energy supply. PV systems offer greater self-sufficiency, reducing dependence on imported oil.
    • As PV energy is produced locally, close to consumption, the electricity usually does not need to travel long distances to be used, reducing losses and infrastructure costs and efforts.


  3. Doesn’t the manufacturing process of a PV system need more energy than what it itself produces during its lifetime?

    The energy payback time (EPBT) of photovoltaic (PV) systems is an important criterion in understanding the sustainability of PV. The EPBT is the amount of time a PV system has to operate in order to compensate for the energy required to fabricate the system itself. It takes the following actors into consideration: the impact of a product throughout the entire life cycle – from material sourcing, through manufacturing, construction, operation, dismantling and product collection and recycling.

    The technical lifetime of PV systems is 30+ years; hence they produce net clean electricity for more than 95% of their lifetime.

    For more information, please refer to Section DESIGN, Question 3.

  4. Do I have to change my boiler if I install a PV system?

    PV is a technology that generates electricity, not heat. Therefore, the existing heating system remains unchanged. As a measure to reduce emissions, it is worth to consider improving the home insulation and heating/refrigeration systems and installing solar thermal modules, which is separate from the photovoltaic system, or a heat pump to produce hot water.

  5. What happens if the sun doesn’t shine?

    A PV system needs daylight to work but not direct sunlight. Indeed, if a PV module is exposed to an artificial light, it will also produce electricity.

    Sunlight consists both of direct light and indirect or diffuse light (which is the light that has been scattered by dust and water particles in the atmosphere). PV cells not only use the direct components of light, but also produce electricity when the sky is overcast. It is a common misconception that PV only operates in direct sunshine and is therefore not suitable for use in temperate climates. This is incorrect: PV cells make use of diffuse solar radiation as well as direct sunlight.

    However, as the electrical output of a PV module is dependent on the light intensity to which it is exposed, it is obvious that PV modules will tend to generate more electricity on bright days than when skies are overcast. Nevertheless, PV systems do not need direct sunlight to work, so even on overcast days a PV module will generate some electricity.

    Normally, the PV system is connected to the electricity grid. Therefore, when more electricity is produced than is consumed this surplus is fed into the grid so it can be used by other consumers.
    When the weather conditions do not allow the system to produce enough electricity, the electricity will be provided by the grid.

  6. Can I sell excess solar electricity back to my utility?

    The owner of a PV system has two options: either to sell all locally produced electricity to the power utility (if a FiT is available) or to use the solar electricity to meet his own household demand, and sell any surplus to the utility.

    Solar power systems use PV technology to convert sunlight into electricity during daylight hours.

    If the PV system’s AC power is greater than the owner’s needs, the inverter sends the surplus to the utility grid to be used by others.

    If a home or office requires more electricity than can be provided by the PV system, the balance is provided through the grid connection. The utility provides AC power to the owner at night and during times when the owner’s requirements exceed the capacity of the PV system.

    In many countries the utility company purchases all PV electricity generated by consumers at a rate higher (FiT) than the tariff applied to consumed electricity. In this case a dedicated metering exists for ‘PV generation’ and a second metering for ‘power taken from the grid’. Each meter has a different tariff.

  7. Does my grid-connected PV system have to include batteries?

    Batteries are only essential if power needs to be ‘stored’ in case of a utility outage. Most grid-connected PV systems will send any excess generated electricity back to the utility, using the utility grid as backup (rather than batteries).

  8. How do I know what size PV system I need?

    The best indicator for sizing a PV system is your historical electrical usage, or the number of kWh (kilowatthours) consumed each year. It is especially important to determine an annual average for kWh usage, because many families experience seasonal peaks in usage. This average gives a starting point for comparing the energy output of various systems.

    Depending on the technology a PV system of between 7m²-15m² (1KWp installed) can produce for instance about 1000kWh every year if you live in Munich and 1400KWh in Malaga.

    The calculation for a system size can easily be made if you know your yearly electricity consumption.

  9. Do I need to contact my electricity supplier when installing a PV system?

    This depends on the country legislation in question. For example, in Germany the system’s connection point needs to be requested to the supplier. It will usually be the same as the point where electricity is purchased, but if the system is bigger than the capacity of the grid at that point there may be complications. In Spain the process is similar but requires a long time. In Portugal, there is a simple online application to be filled out for small systems.

    Contact the photovoltaic association in the country concerned for specific details about the process.

  10. Can I expect a positive return on investment from my PV system?

    The cost of PV technology has dropped dramatically in the past ten years, thanks to government incentives or subsidies in some countries, PV systems may be the most cost-effective power solution.
    PV systems allow electricity rates to be locked at current prices. With fossil fuels likely to become more expensive in the future, purchasing a PV system today is a smart economic move.

    In some countries there is the possibility of benefiting from FiTs or investment incentives. When installing a PV system at home, all electricity generated can be injected and sold to the electricity provider at a higher price than the price paid in one’s monthly bill. This mechanism enables the investment to be paid back in a short time. Germany has best developed the FiT and leads the PV market worldwide. Spain, Italy, France and Greece have also developed this system, and electricity consumers, aware of the importance of renewable energies, are gradually switching to solar power, receiving a compensation for their effort.

    Moreover, in light of decreasing solar electricity costs and increasing costs for conventional electricity, solar power systems will become increasingly economically viable. During the next 5-10 years solar electricity will become cheaper (depending on location and electricity prices) for private households than conventional electricity.

  11. Do PV systems need to be cleaned?

    Most PV modules only need to be cleaned when it doesn´t rain for a long period of time. When installed on roofs, the PV modules are installed with a tilt angle and the rain cleans the panels. For modules integrated in facades, no cleaning is necessary.

  12. Can I step on one of the PV modules on my roof?

    PV modules are most often encapsulated in two layers of tempered low iron glass or between glass and tedlar (a polymer) so they are stronger and less rigid than glass, in order to withstand, for instance, the most severe hail impacts.

    There are many public projects where PV has been integrated on the floor and therefore walking on the modules is not a problem. However, PV modules are normally not designed to be walked upon.

    It is recommended to protect the modules with wooden planks before walking on them, as you would protect a skylight or other glass roofing material.

  13. If I install a PV system on my roof, will it attract wasp nests?

    PV modules are generally very dark in colour (blue or black, depending on the technology) and can become quite hot. A PV module with an efficiency of 12% converts 12% of the incident energy into electricity and most of the rest of the energy is converted into heat!

    Wasps like warm but not hot environments. The most common wasps in Western Europe ventilate their nests once they reach 35°C, and die at 40°C.

    Whilst wasps may be attracted to build their nest under roof-mounted PV modules or sunshades (or shutters and roof eaves) the wasps will probably not survive the mid-summer temperatures under the PV modules.

  14. What if a PV roof/facade develops a leak or is damaged by hail?

    This should be covered by the home or building insurance. Some insurers will automatically cover the system as it is considered to be just another part of the house and its contents and no modifications are required to the contract. However, it should be checked with the insurer if they can cover your system or whether a new clause is required in your contract.

    Other elements of the system may require attention; inverters generally come with a one-year factory warranty, although some manufacturers have developed fee-paying extended warranties.

    The electrical connections should be covered by the installer’s professional insurance – the guarantee should always be specifically checked with the installer. For larger systems, specific contracts may be negotiated.

  15. Do I need a building permit to install a PV system?

    Depending on the regional legislation,  a building permit to install photovoltaic panels may be needed. For BIPV systems it depends as well on the building legislation and the type of BIPV application you are going for, e.g. roof or façade application. In any case please contact your city council or your arechitect and solar energy professional to learn about all the details.

  16. How should I select a Renewable Energy Professional?

    When selecting a solar energy professional, look for a company that has experience installing (or other professional services you desire) the type of solar energy system you seek. Ask them how many years they`ve been in business, ask what licenses they hold, and get (and check) references. Also ask if they have any specific manufacturer or industry training or certifications. Solar energy systems are an asset that properly installed should provide many years of reliable service. You want a qualified professional. Get several bids, but picking the lowest bid is not necessarily the goal. Choose experience and quality too. Also compare warranty and service policies offered by competing bids.

  17. Does it make sense to install a solar system if we are moving in a couple of years?

    It probably does. Most real estate experts currently believe that given the concerns about energy costs a solar system will significantly raise a home's value. However, this very much depends upon the local market so you should probably confirm this with an experienced local real estate agent before making this decision if you know you are planning to sell in a relatively short period of time.