Management of the photovoltaic system with different orders of priority

The energy produced by the solar panels will be managed with different orders of priority:

• The one that comes from the panels is favoured, and when there is no demand for electricity, the system charges the batteries.

Figure 1

•  When the batteries are charged, the system feeds them into the national grid (this function in figure 1 above was not drawn. This function in figure 1 above was not drawn due to different inverters, different philosophies; for now, let's focus on how to use our system at total capacity.
• Conversely, when household appliances require electricity, priority will be given to photovoltaic production.
• When the panels don't produce (like night), the batteries will be used.
• When the accumulators are discharged, the system takes current from the external electrical network thanks to the minimum voltage contactor, which read the reference voltage from batteries. If the batteries start to flat, the contactor closes and sends energy from the network directly to the inverter. The minimum voltage contactor will open as soon as the batteries are charged, which means when the FV panels will produce energy again. The contactor is always connected to the internet; it can inform when the change over has taken place, including how many Kwatts it withdraws.

Connecting the FV panels installation to the electricity grid to sell electricity

By following my instructions step by step, you will be able to design a photovoltaic system and, if you want, could independently purchase the photovoltaic panels, the support structures, the inverter, the Charge Controller (if with accumulation), and the wiring, which you will make available to the technician who will carry out the installation, reducing the overall cost without sacrificing quality, or create a comparison with the quote that the companies offer you. I always recommend that you install the hybrid inverter. For any help, send an email on the website here

Before moving on to the configuration and calculation of the photovoltaic system in self-consumption, I would like to clarify.

There are at least three reasons for changing the energy with PV panels

• In Italy, the cost of the electricity bill varies between € 0.20 and € 0.30 per kWh (in my case: 0.30) while the production cost of photovoltaics varies between € 0.05 and € 0.10 per kWh.
• Tax deductions.
• clean energy and not fossil fuel

To get an idea of the years needed to balance the energy used and cost, you can see the examples below:

Energy gain point (payback) = Energy produced / Energy saved (years)

Generally:

• With Monocrystalline Silicon photovoltaic panels: from 3 to 6 years
• With polycrystalline silicon photovoltaic panels: from 3 to 6 years
• With amorphous silicon photovoltaic panels: from 2 to 3 years

Another data is the amount of energy that a photovoltaic system produces compared to the energy used in the production phase.

• With Monocrystalline Silicon photovoltaic panels: 4-8 times
• With Polycrystalline Silicon photovoltaic panels: 4-8 times
• With amorphous silicon photovoltaic panels: 10-12 times.

Therefore, self-consumption should always be convenient. I say that because if it does not happen, it could be due to incorrect installation.

An FV system made satisfactorily should be at first the immediate use of self-produced electricity, and only the one which one not needed should be placed on the network, but if, for example, all the energy produced was mistakenly put on the network and then take it back instantly when is required from the devices, this would be counted by the bidirectional meter in both direction input and output. Since the one withdrawn from the electrical network costs is more than the one placed on the network, it could nullify the savings.

Therefore, as mentioned above, the user must consume first of all the self-produced energy, and only when it is not available from FV panels, withdraw it from the national grid, while when the user does not need to use power or is in abundance: then it's possible to send it Network.

  Figure 2

Figure 2 above shows the correct layout of the system, as it allows the self-consumption of self-produced energy before it is fed into the grid, and the correct positioning of the electricity meters (photovoltaic energy meter and bidirectional meter) which allows the correct count of self-consumed energy, the fed into the network, and energy which is taken from the network.

How to calculate self-consumption

Self-consumption = total energy produced by photovoltaics - energy fed into the grid

Formula to calculate the savings on your bill:

Bill savings (€) = self-consumption in kWh x 0.25 (€)

(0.25 is an average gross price of energy in the bill which I have taken as reference).

Example:

• Energy produced = 2,500 kWh (year)
• Energy fed into the grid = 1,000 kWh (year)
• Self-consumption = 2,500 - 1,000 = 1,500 kWh (year)
• Savings on the bill = 1,500 x 0.25 = 375 euros (year)

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