Frequently Asked Questions - FAQ


1. Why should I use PV?

Today's PV systems integrate easily with your home's existing electrical system. They produce clean energy no air pollution, no greenhouse gas emissions. And they can greatly reduce, or even eliminate, your electricity bills. Photovoltaic power systems can now be integrated into the fabric of a building, combining energy production with other functions of a building's external structure. Roof tiles, windows, facades, canopies and skylights can all be incorporated with PV technology and this combining of functions can lead to substantial cost savings A well designed and installed PV system is often considered a beneficial feature on a house and can increase the value of your property.

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2. Doesn't PV technology need bright sunshine to work properly?

The word Photovoltaic is composed of two terms: Photo - Photon which means "light" and Volt that is the name of the engineer Volta Co-inventor of electricity. A PV system needs daylight to work, not direct sunlight. Moreover, if a module is exposed to an artificial light, it will produce also electricity. However the electrical output of a PV cell is dependent on the intensity of the light to which it is exposed. Therefore it is certain that a module exposed faced to the sun of midday and by clear sky, will produce its maximum of output electricity (Watt peak = maximum power). You can indeed say that PV cells will tend to generate more electricity on bright days than when skies are overcast. Nevertheless, photovoltaic do not need to be in direct sunlight to work, so even on overcast days a PV cell will be generating some electricity. In practice, if a module can produce a maximum of 170 Wp (170 Watt peak) exposed to the sun, it will produce some between 130 and 150 in cloudy weather. You will collect more energy on a clear summer day but you will also collect energy on a cloudy winter day.

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3. How much electricity does a PV system produce?

It depends on several conditions. Orientation of the system (south), system inclination (what is the inclination of the roof), irradiance value at the location and last but not least, the weather. The following value can be assumed as a rough planning aid: 800-900 kWh per year for each kWp of installed power.

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4. Are solar power systems efficient?

Yes. Solar cells today have an efficiency of 15%, which is continually increasing. That does not sound much, but is actually quite a lot, as this already corresponds to 50% of the physically possible efficiency. Many conventional power stations have an efficiency that is still less than 40%, although the technology has been in use for 100 years. Comparing the efficiencies of fossil fuel and solar power stations is in fact fallacious as fossil fuels are limited, which means that they should be used as efficiently as possible. Solar energy, on the other hand, is practically unlimited.

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5. Can I install a PV system elsewhere than on a roof?

There are no limits for installing PV systems when a good exposure is achievable. Beyond roofs, some of the most common places used to implement PV systems are, for example: - facades, which offer huge possibilities for architectural integration and visibility; - sunshades; - canopies; - greenhouses; - noise mitigation barriers; - of course, the ground, especially for large scale applications.

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6. Do I have to install PV panels mandatory tilted and facing south, or am I allowed to different exposures? Is it mandatory to install PV panels tilted and facing south, or am I allowed using different orientations?

Certain shifts with respect to the optimum installation requirements for photovoltaic are allowed, without substantial efficiency loss. For instance, considering the mean latitude value for central Europe, a +/- 15? tilt shift can involve a slight 2% loss, while the same shift from the southern direction is merely capable of reducing a system's performance by 3%.

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7. What is the lifespan of a PV system?

PV systems are currently considered to have at least a 25 years lifespan. PV modules are covered with a long term performance guarantee (usually 10 years with less than 10% decrease and 20 years with less than 20%) by all the most important manufacturers. Guarantees for electronic components such as inverters can also be extended for several years beyond standard terms.

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8. Most PV modules don?t need to be cleaned and are easy to maintain.

Except for modules laid out "flat" on a roof, it does not have there cleaning necessary. The rain (in the areas where it falls) cleans the panels, those being generally laid out according to an angle of +/- 45? compared to the horizontal one. For the modules integrated in frontage, the problem does not arise. Maintenance question, only, the elements except panels (inverters and/or mini-power station) require a regular checking of production. Indeed, these elements have one less lifespan and are composed of significant parts It is obvious that the fixing of the modules in roof must be resistant to the wind, anchoring with the installation is thus important and must be composed of solid elements un-oxidizing.

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9. Do PV modules loose efficiency each year?

In a general way, the modules lose very little potential of production, at least during the first years of use. The loss of production usually intervenes after 20 to 25 years and is estimated at a ratio of +/-20 %. However, for common financial calculations (pay-back) it is of use to consider an average loss of 1% per annum.

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10. Are PV modules guaranteed?

On modules, the manufacturers in general propose guarantees of productivity between 20 and 25 years. On the accessories (inverters) the guarantee does not exceed 10 years. However the majority of the modules of the market today have a correct production (minimum 80 %) up to 30 - 35 years.

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11. Can I walk on 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 flexible and less rigid than all glass. This is to provide the modules the strength to withstand the most severe hail impacts. PV modules are however not designed to be walked upon. It is recommended to protect the modules with lengths of wood before walking on them, as you would protect a skylight or other glass roofing materiel.

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12. Are PV panels heavy? What kind of loads does a PV installation involve on a building? How heavy are photovoltaic modules? Does the support structure need to be reinforced?

Standard photovoltaic modules are relatively light, around 10 to 15 kg per square metre. This means that in most circumstances there is no need to reinforce existing structures. Made-to-order modules may be heavier - insulated double and tripled glazed modules, often used in sunroofs and atriums will be 2 to 3 times heavier. Other factors that may affect the weight of a photovoltaic system are the type of module frame and the selected connection method. It is essential that photovoltaic installations comply with local building regulations and safety codes.

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13. How much light does a transparent PV roof element let through?

Transparent PV modules are generally one of two principal types : - normal cells in a double glass frame, the gaps between the cells are transparent. - thin films deposed on a glass surface ; the PV layer is thin enough to let a certain amount if light through. The gaps between normal PV cells in a double glass module can be increased or decreased to change the transparency level of the module. Generally, the gaps between cells are such that the transparency is between 5% and 30%. A classic double glass module will have a transparency of roughly 4% to 5%. The transparency of thin film modules depends on the transparency of the support and the thickness and type of cell used. It is normally around 5% to 10%. Nearly any degree of transparency desired can be made to order, but it is common to balance the natural light gains against potential overheating due to increased thermal gains.

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14. If I install PV on my roof will it attract wasp nests?

PV modules are generally very dark coloured (blue or black, depending on the technology) and can become quite hot. Remember, 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. So whilst wasps may be attracted to build their nest under roof mounted pv modules, or PV awnings or sunshades (or shutters and roof eaves) the wasps probably won't survive mid-summer temperatures. (The commoner types of wasps are not particularly dangerous unless disturbed, and the person is allergic to their stings).

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15. What if there is a problem with the system?

Roof-integrated photovoltaic have several distinct functions, as a structural element, as part of the building envelope and as an electricity generator. The potential problems are: - If a photovoltaic element no longer produces electricity or, under identical conditions, produces much less electricity than before, it is generally covered by a production guarantee against a drop in efficiency of more than 20%. - If a photovoltaic module has a fault due to a manufacturing defect, certain manufactures will repair or replace the module under a 10-year warranty. Ask your supplier if your modules or photovoltaic elements have a factory warranty.

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16. What if a photovoltaic roof or wall develops a leak? What if a photovoltaic element is damaged by hail?

These questions are difficult to answer, as they come under 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. But check with your insurer if they can cover your system, and 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 your installer's professional insurance - ask your installer what sort of guarantee they can offer. For larger systems, specific contracts may be negotiated.

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17. How much CO2 will a solar roof save?

How much CO2 a solar roof saves will depend on many factors, including : - the energy source the solar production is replacing (coal, gas, hydro-electric, nuclear...); - the quantity of energy produced by the solar roof (depending on the roof's location, orientation, inclination and shading); - the "energy habits" of the solar roof owner (does the solar roof owner use less energy now that they are aware of the cots of producing electricity ? Or do they see their production as a "bonus" so that they can use more electricity than before?) The first point is the most important - if your electricity comes from a coal fired power station, each kWh you use will release around 1 000g of equivalent carbon (various greenhouse gases converted into 'equivalent carbon units' for comparison).

However, if your original electricity comes from a hydro-electric power station, it is producing much less carbon equivalent emissions (less than 10g). So clearly the amount of CO2 you will be saving is very dependant on the source of your 'normal' electricity. For example, in France every kWh of electricity is estimated to produce 0.12kg of Co2 whilst the European average is approximately double that (INESTENE figures) - the difference is due to the large percentage of French electricity supplied by nuclear power.

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18. Is solar energy more expensive than conventional energy?

From a long-term point of view, solar energy is much cheaper than conventional energy. However, solar energy is still currently somewhat more expensive as new technical processes need to be developed and financed. Therefore, as was previously the case with nuclear energy, renewable energy sources will initially require subsidies to enable them to become competitive. Solar energy is already well on the way: whereas the costs for conventionally generated energy have constantly increased in recent years and ? faced with finite resources ? will continue to increase by a considerable extent, increasing mass production has enabled the cost of solar energy to drop by an average of 5% per year. The lowering of subsidies for new plants of 5-6.5% per year, which is laid down by the Renewable Energy Sources Act (EEG), is also forcing further cost reductions.

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19. Can the solar industry also grow without government subsidies?

The solar industry will become capable of a high level of growth without government subsidies in the foreseeable future. Given the increasing costs of conventional energy sources and the decreasing costs of renewable energy sources, as well as a growing export market, solar thermal could achieve this within the next five years and photovoltaic in 10-15 years. Until then, the market introduction of solar energy is dependent on statutory frameworks if it is to become competitive and survive in the global market. Until then the industry requires investment security for developing solar power manufacturing plants and for their high development input, and, until then, consumers require legally secure incentives to invest in installing solar systems.

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20. How long will the construction of new solar power systems continue to depend on an increased statutory feed-in tariff?

In the light of decreasing solar electricity costs and increasing costs for conventional electricity, solar power systems will become increasingly economic during the next few years. During the next 10-15 years, solar electricity will become cheaper for private households than conventional electricity. A considerable advantage of solar electricity is that it is mainly produced around midday when conventional electricity is particularly expensive. Solar electricity largely replaces expensive peak-load electricity at preferential customer prices, which is why it would be wrong to compare it with cheap base-load electricity. Thus solar power will become independent of subsidies much earlier than might seem at first glance. With stand-alone systems remote from the electricity grid, it is already worthwhile using solar technology today. With continually rising heating costs, the production of solar thermal heat using solar collectors is already on the threshold of profitability.

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21. Is it at all worthwhile using solar energy in our latitudes?

Definitely! In Germany for example, the average annual solar irradiance is 1000 kWh per square metre; that corresponds to the energy content of 100 litres of oil. Thus more than half the amount of solar energy is attained that we find in the Sahara. With efficient solar power systems, this is sufficient to generate a considerable volume of electricity and heat from solar power here ? it is just that in southern regions profitability is reached somewhat more quickly. It is worthwhile producing solar energy in Germany, not least because this makes Germany less dependent on energy imports from crisis regions.

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22. Can renewable energy sources guarantee a secure power supply despite their dependence on the weather?

The future of power supplies consists in a mixture of renewable energy sources and intelligent load management in combination with short-term electricity storage. This will enable renewable energy sources to ensure a secure, climate-friendly and sustainable power supply. Solar power is particularly available during periods of peak load demand (midday and in summer) and is excellently complemented by wind power, whose peak values are principally reached in winter. Biomass, hydropower and geothermal energy are continually available and balance out any deficits. Economic experts from the German Institute for Economic Research (DIW) and the Deutsche Bank are now recommending a greater promotion of renewable energy sources as this will reduce dependence on both the world markets for fossil fuels and on politically instable regions, while providing protection against the increasing costs for the economy and consumers.

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23. Is it possible to introduce renewable energy sources in consensus with the energy providers?

Only with difficulty, since expanding the market share of renewable energy sources represents direct competition for the major energy supply companies. They themselves are only slowly entering the new energy market, since their written-off conventional power plants and existing grid monopoly for end customers means that they can achieve considerably higher profits than with renewable energy sources during the market introduction phase. Here, however, they are acting against the interests of the customers and society because they are neglecting to secure a sustainable energy supply. Political regulations such as the EEG must therefore give renewable energy sources a chance and ensure more competition in the energy market.

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