Photovoltaic energy for production or consumption
Once established the convenience of the realization of photovoltaic system, it is very important to understand the mechanisms that function in energy production and the consumption or selling of produced energy.
For all plants connected to the electric system of distribution ( grid- connected) are possible 2 technical solutions for the connection: an exchange on the site or a production.
If we have the exchange mechanism, the user produces the energy and uses it or put it all or in part to the system, depending on charges ( electricity, household appliances) connected in every moment when the system works. The energy not used at the moment is being put in the network and it is always possible to use it if it is need. At the end of the year is being prepared a balance between the electric energy used and produced. If the all annual usage is higher than the production, the user have to pay the difference to the administration. If the production is higher than the usage, the user will have 3 years to use the difference and the part not used would be lost. It is obvious that the system have to be get into proportion for the predictable consumption of the user because the difference isn’t paid.
If the user have a mechanism of the production and don’t use immediately the energy produced, so the energy goes to the network and is paid with the market prices or with a rate of fixed market. If the user needs more energy that he is able to produce, he has to buy it from the network with prices of the distributor. In practice the energy produced is consumed ( saving money) and sold immediately, with an only difference that selling and buying have different prices: now the energy is sold with 9,6 c€ every kWh and bought 12 to 18 c€ every kWh, depending on the type of contract with a distributor.
It’s evident that domestic user has all convenience to use the exchange mechanism ( not if the house is a seasonal location), but a company could have more convenience, also fiscal, in using of a producer contract or auto producer ( consumption >= 70 % of production). A company that works a lot during a night can prefer the exchange program because the major part of energy wouldn’t be available in that period.
The exchange mechanism can be performed up to 20 kWp of power, even if it should be an increase up to 200 kWp but are still attended right legal dispositions.
It is obviously possible to make a photovoltaic system only for a selling of produced energy but this hypothesis is convenient for the medium- large systems ( more than 50 kWp).
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