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One promising and ever-evolving technology is photovoltaic systems that can generate electricity, drawing on solar energy like solar systems. Solar cells, commonly called photovoltaic cells (semiconductors), are "devices" that convert solar energy directly into electricity through the photovoltaic effect. The operation of photovoltaic systems is based on the fact that solar radiation can change the properties of certain materials (semiconductors) by generating electricity through the "photovoltaic effect". In the photovoltaic effect, the sunlight falling on a semiconductor of two layers creates electrical potential between them. This voltage can actuate a voltage and power proportional device or be distributed to the electrical system. The set of photovoltaic elements connected electronically to each other is called a photovoltaic generator and the set of photovoltaic generators connected to each other is called a photovoltaic array. The photovoltaic array is the most important part of the photovoltaic system and is accompanied by appropriate electronic circuits for controlling and managing the energy produced, as well as a storage system (batteries). The electricity produced is continuous voltage and depending on the application can be converted to alternator with the help of a voltage inverter. The efficiency of photovoltaic systems is increased by the use of frame rotation systems that follow the sun, however the installation of such systems can significantly increase the cost of investment. Ongoing technological developments in the field aim to maximize the efficiency of these systems and at the same time reduce the cost of the generated kilowatt-hour in order to make photovoltaic systems one of the most important technologies for solar energy exploitation in the near future.

Feed in Tariff systems

In the last decade, the majority of photovoltaic stations in Greece are feed in tariffs. This is due to the very encouraging subsidies provided to date by the state and the EU. either by subsidizing the initial capital or the price of electricity sold by the individual. Consequently, the installation of a solar power station, in addition to its significant environmental benefits, as it exploits a renewable energy source (solar), is a guaranteed and efficient investment.

In these systems we have a set-off of energy accounting (the indications of the two meters are converted into money and deducted from each other, the difference being credited to the consumer). Photovoltaic systems are mainly installed in domestic consumers, in craft industries or in parcels. In the past decade, the vast majority of photovoltaic systems installed in Greece were in plots. However, in recent years, mainly after July 2009, when the Ministerial Decision on Home Photovoltaics on Roofs and Roofs was adopted, more and more home consumers are installing them in their homes.

This shift in home systems is due, on the one hand, to the subsidy on the price of electricity produced, and to the fact that income is tax-free and guaranteed for 25 years, and on the other to the fall in the price of photovoltaic panels which has made the investment particularly attractive and affordable. . Suffice it to say that with a capital of around € 13,000 a household can secure up to € 2,000 annually tax-free income guaranteed for 25 years. The maximum limit for a home system is 10kWp and set off at a rate of 0.12 € / kWh (Fall 2014). Larger parcel systems have enjoyed lower tariffs but due to economies of scale the return on investment is excellent. Even with the new reduced tariffs, the return on a photovoltaic roof investment yields less than 7 years of initial capital.


Photovoltaic net metering systems

Since October 2013 it has been a law of the Greek state to self-consume energy generated by RES and to offset it with energy consumed by the public grid. In this case we have the energy offsetting of incoming and outgoing electricity. In short, using two meters eliminates the energy generated by the PVs from the energy consumed by the user from PPC. The shape of self-production has been used abroad for many years with excellent results for both the user and the public network.

Distributed self-production has many advantages, notably reducing transport losses but also relieving households and businesses of high energy costs. Suffice it to say that 4-8,000 € can meet the electricity needs of an average Greek house for 30 years. The expected Ministerial Decision setting out the details of the self-production program has been signed since January 2015. The power limit is set at 20kWp and if the agreed power is high at 50%. The set-off is annually and part of the fees are included.

The basic parts of a net metering system are the same as a tariff system (photovoltaic and interconnect inverter). The method of calculating a self-generating system consists of a thorough study of the electrical consumption of the building and the reverse calculation of the required power of frames that will produce the above data.

Depreciation of a photovoltaic net metering can be done in less than 5-6 years depending on its size. For example, a 20kWp photovoltaic that costs less than 23,000 + VAT will save over 30,000kWh annually, ie over 5,000 €. If we are talking about a business (hotel) which will deduct the capital of 23,000 € by 26% then the depreciation becomes much shorter.

Photovoltaic systems stand alone

Stand-alone systems provide electricity without interconnection with the electricity grid. They receive the energy from the sun with the help of photovoltaic panels (or wind turbine - wind) and pass it on to the batteries. From there the energy is distributed to the electrical loads after being converted into a suitable form by a voltage inverter (DC to AC). Autonomous systems are mainly used in buildings that do not have PPC such as cottages, caravans, mobile homes, cottages that are either illegally constructed or are away from the public network.

Many times depending on location and wind power there is a power generator and the system is called a hybrid, and very often a battery charger is added to charge with the help of a liquid fuel generator. In addition to the panels, an important part of such a system is the charge controller that controls the charge and discharge of batteries and batteries.


The design and installation of a standalone system is extremely demanding and it is suggested that an experienced engineer be selected for their development. The calculation of a system of autonomy consists mainly of a good record of the user 's consumption with particular attention to the seasonal period of maximum use and how the building operates. Battery selection is perhaps the most critical part of designing a standalone system as they have a finite life span which varies considerably depending on the type and quality of the battery. So there are two major categories of closed and open type batteries. The former have shorter life spans (3-5 years) but do not require maintenance while the latter longer life spans (5-15 years) are more demanding in maintenance.

Depreciation of a stand-alone photovoltaic can be done even from the first day of operation, in cases where the cost of interconnection with PPC for example exceeds 50,000 € and a stand-alone photovoltaic system costs 40,000 € not only the user wins the fixed assets but also the original interconnection costs.


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