MEDIUM VOLTAGE INSULATION TRANSFORMER REMOVAL (ADJUSTMENT TO CEI 0-21)

We perform the adaptation of your photovoltaic system to the CEI 0-21 standard, thus allowing the removal of the insulation transformer (galvanic separation) and obtaining significant money savings.

What can you do

Photovoltaic plants with power exceeding 20 kWp entered into service before the entry into force of the CEI 0-21 standard (as of 01 July 2012) had to be connected to the grid through an isolation transformer (galvanic separation) due to the standard Enel DK5940. The insertion of an isolating transformer allowed to limit the input into the grid of any direct current component generated by the photovoltaic inverters. This control was then integrated directly into the inverters, from the first July 2012 which had to comply with the CEI 0-21 standard.

The presence of an isolation transformer obviously causes a loss of energy due to the efficiency (less than 1) of the same transformer. Moreover, since the transformer is connected to the grid even during the switch-off time of the photovoltaic system (for example at night), this has a consumption of electricity from the exchange / sale counter. This consumption is accounted for in the bills of the network operator.

It is therefore evident that the elimination of the isolation transformer in a photovoltaic system produces an economic saving. Let's see how it is possible to perform the removal of the transformer without having any kind of problem with E-distribution and the GSE.

The steps to be taken are as follows:

• CEI 0-21 Inverters adaption
  • It is not always possible but can be done with an update of the inverter firmware. It is necessary for the limitation imposed by the CEI 0-21 standard on the input of the continuous component in the network.
• Interface Protection System (S.P.I.) replacement with a CEI 0-21 compliant model
  
  • Necessary for a complete adaptation of the photovoltaic plant to the CEI 0-21
• Installation of a reinforcement device (D.D.R.)
  
  • Necessary to disconnect the system in case of failure to open the interface device (D.D.I.)
• Installation of a continuity system (U.P.S.)
  
  • As required by CEI 0-21 necessary to power the Interface Protection assembly (SPI, DDI and DDR) for a time of not less than 5 seconds
• Insulation Trasformer removal
  
• Drafting of a technical report to be sent to the GSE and the distributor, accompanied by updated wiring diagram, of the new operating regulations
  

  
  

What can be economic savings

Consider a 100 kWp plant. The production estimated annually for this plant, for example with Rome location, is about equal to 140,000 kWh / year. Suppose we have used an isolation transformer of 130 KVA and consider it always connected to the network. We can estimate the following consumption:

• Energy consumption from the transfer / exchange meter
  • The typical consumption of a transformer of this power is about 0.5 kW. So considering this consumption for the hours of shutdown of the photovoltaic system, or about 10/12 hours a day, we can consider: 0.5 kW x 10 hours / day = 5 kWh / day -> 5 kWh / day x 365 days = 1.825 kWh / year . Considering an average cost of 0.26 euro / kWh in the bill we can calculate the savings as follows:
    Savings = 0.26 euros / kWh x 1.825 kWh = 474 euros / year

• Eliminazione perdite per trasformazione energia prodotta
  • Considering that the transformer in question has an average loss in load (during the production of the photovoltaic system) of about 2.5%, we can estimate the loss of energy produced dissipated by the same transformer: 2.5% x 140,000 kWh / year = 3.500 kWh / year Considering a fourth Energy Account for imposing on a building with an incentive rate of 0.338 euros / kWh we have:
    Earnings = 0.338 euros / kWh x 3.500 kWh = 1.183 euros / year

Therefore we can consider, in conclusion, that for a 4 Conto Energia plant, on a building, with 130 KVA isolation transformer and an incentive tariff of 0.338 euro / kWh, the saving that can be obtained by removing the transformer is about 1,650 euros / year. Considering the remaining incentive period (for example 13 years, with the date of entry into operation of the 2011 plant) we can obtain a saving + gain of around € 21,000.

CONTACT US FOR TECHNICAL ANALYSIS OF YOUR PHOTOVOLTAIC PLANT

We are available for individuals and installers for technical inspection and expertise also for legal disputes use. 
Contact us info@st-ingegneria.com