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WHAT IS PHOTOVOLTAIC?

The term "photovoltaic", commonly referred to as PV, is derived from a combination of "photo", the Greek word for light, and "Volta," the name of the Italian physicist, Alessandro Volta, who invented the chemical battery in 1800. The PV effect is the direct conversion of solar energy into electricity. This process does not generate heat like solar domestic hot water or solar pool heating systems do. It also differs from the process used in solar thermal power plants, where concentrated solar energy is used to produce team that activates a turbine connected to an electric generator.
PV power systems do not have any moving parts. They are reliable, require little maintenance and generate no noise or pollutants. PV systems are modular – the building blocks (modules) come in a wide range of power capabilities, from a fraction of a watt (e.g. solar watches and pocket calculators) to more that 300 W. Modules can be connected to achieve the power that your application requires. Some demonstration PV power plants have several megawatts of power, although most installed PV systems are much smaller.

WHICH ARE THE ADVANTAGES OF PV POWER SYSTEMS?

Users of PV power systems appreciate their quiet, low maintenance, pollution-free, safe and reliable operation, as well as the degree of independence they provide.
Why else should you consider buying a PV system?
If you are some distance from an electrical grid, it may be cheaper to generate your own power rather than pay to extend transmission lines from the grid. Diesel, gasoline or propane generators are the conventional alternatives, but many people find them noisy, polluting and costly to run and maintain. It also makes little sense to turn on a 5-kW generator to power a few 100-W light bulbs. PV systems reduce the negative aspects of generators by using them only as a backup.
When capital cost is an issue, or when photovoltaics alone are not enough to replace an existing generator, you can use a wind generator as part of a hybrid PV system, thus reducing the use of the generator. Such an intermittent charge system is more efficient than a generator running continuously at low load. In addition to saving fuel and lowering maintenance costs, you will increase the generator’s life span. Also, since the PV panels and battery banks are modular, you can expand the PV system gradually as your budget or needs increase.

WHAT'S THE DIFFERENCE BETWEEN GRID CONNECTED AND STAND ALONE SYSTEMS?

Grid connected means that the PV system is connected to the mains supply usually within a building. The electricity produced is either used within the building or is exported to the National Grid. A Stand Alone system on the other hand produces electricity that is usually stored in one or more batteries. The electricity is then used as and when required with the PV module constantly re-charging the battery.  

WHAT'S THE DIFFERENCE BETWEEN SOLAR THERMAL AND SOLAR PHOTOVOLTAIC?

Solar thermal uses solar panels to heat water whereas a solar photovoltaic (PV) system produces electricity from sunlight. There are two types of "solar panels": electrical and thermal. The electrical type is general referred to as a "photovoltaic module" or a "solar module." It is a solid state device or assembly of solid state devices and produces electricity only. This is the type we carry. The thermal type of panel (which we don't carry) generally consists of water piping, glass and insulation and is generally much larger in size (often 4' x 10').

WHAT DOES IT MEAN "NOMINAL POWER" OF A PHOTOVOLTAIC SYSTEM?

The Nominal Power of a PV system is the electrical power of a system given by the addition of the single nominal power of each photovoltaic module of the same system, measured in standard conditions (temperature of 25°C and radiation of 1.000 W/m2).

WHERE WE CAN INSTALL A PHOTOVOLTAIC SYSTEM?

Best condition suggested:

• In Italy the optimum direction and inclination for photovoltaic modules are south and 30° respectively;
• Exposure between 45° more or less from south and inclinations of between 5 and 60° can be considered acceptable;
• An inclination of less than 5° would lead to the accumulation of dust on the modules, with a negative effect on the energy yield;
• Large inclined surfaces facing in a suitable direction are the ideal supporting surfaces on which to install photovoltaic systems; the modules can be installed on the same plane as the surface, making the anchoring structures less sensitive to the action of the wind and enabling the whole available surface to be exploited;
• The photovoltaic modules must be installed in such a way as to avoid as much as possible that they will be even partly in the shade during the day, otherwise the energy yield of the whole module will be cancelled out at such times;
• On flat roofs, in the case of installation in several parallel south facing rows, the free distance between two rows should be 2 to 2.5 times the maximum height of the modules (difference between the top of the module and the base on which it rests);
• For reasons connected with operation of the inverters for converting direct current into alternating current, photovoltaic modules are installed in groups facing in the same direction and tilted at the same angle. The minimum size of each group must be not less than 10 m2 (better still 15 m2), referred to the surface area of the collector; "groups" of different sizes and exposed in different ways from one another are in any case permissible.

WHAT’S THE CORRECT SIZE OF A PV SYSTEM?

The utilities present in the building are analysed, the minimum and maximum limits for adopting renewable energy sources according to the regulations are checked and the specific requests of the principals are interpreted.
Lastly, the necessary output power of the system is converted into square metres of photovoltaic surface area. The building designer will have the sometimes far from easy and sometimes stimulating task of identifying a convenient position in terms of productivity of the system, but which must be compatible with the architectural characteristics of the building. For this reason it is advisable and often important to take the "photovoltaic need" into account starting from the earliest design studies.
This type of approach, which is in any case positive, ensures the availability of a suitable place for installing the photovoltaic system, does however have the limit of being conditioned by a contingent assessment of how large a photovoltaic system should be installed. This limits the possibility of subsequent up-grading of the system.

HOW MUCH ENERGY CAN A PHOTOVOLTAIC MODULE PRODUCE?

Electrical energy is generally measured in kilowatt-hours (kWh). Thus, if a module produces 100 Watts for 1 hours, it has produced 100 Watt-hours or 0.1 kWh. The amount of energy produced on a given day will depend on location, shading, and module orientation (direction and tilt).
In a good area for solar power (such as Phoenix, Arizona), a properly oriented module which produces 100 Watts at noon on a clear day will produce an average of about 0.5 kWh/day in January and 0.8 kWh/day in May and June. (Fluctuations result from the amount of variation in direct sunlight on a typical day).
In a relatively "poor" area for solar power (such as Albany, NY), the same module will still produce about 0.25 kWh/day in January and 0.6 kWh/day in July.

HOW MUCH DOES PHOTOVOLTAIC ELECTRIC ENERGY COST?

The cost of photovoltaic energy is obtained by adding together investment costs (planning, photovoltaic system, inverter and/or batteries, other auxiliary equipments) running costs (maintenance, technicians) and additional costs (taxes and insurance). Generally, governments provide incentives, funding and various concessions, which unfortunately sometimes come up against bureaucratic obstacles. If we take as an example the most common systems, which use modules in mono or polycrystalline silicon, with an efficiency of 12-14%, the average cost in Italy is approximately 8000 Euros/kWpeak for small systems (a few tens of kWpeak) and can cost as little as 5500 Euros for 1 MWpeak systems. Modules built with a special technology can reach a 20% efficiency with a corresponding increase in costs; modules in amorphous silicon, with a 6-8% efficiency, cost less. The cost of the photovoltaic kWh generated, plus investment and maintenance costs, must also take into account the number of kWh generated in a year, the lifetime of the system (usually estimated at 25 years), real interest costs, etc. In Italy, the final amount can vary between 0.3 and 0.5 Euros/kWh; the cost paid by the average private consumer to the distributing company is around 0.15 Euros/kWh. (source: ENEA)

HOW LONG DO PHOTOVOLTAIC (PV) SYSTEMS LAST?

A PV system that is designed, installed, and maintained well will operate for more than 20 years. The basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than 30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly.
Experience has shown that most problems occur because of poor or sloppy system installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of the electronic parts in the balance of systems (BOS): the controller, inverter, and protection components. Batteries fail quickly if they're used outside their operating specification. For most applications (uses), batteries should be fully recharged shortly after use. In many PV systems, batteries are discharged AND recharged slowly, perhaps over a period of days or weeks. Some batteries quickly fail under these conditions. Be sure the batteries specified for your system are appropriate for the application.