May 21, 2019


Changes in guaranteed photovoltaic prices have reduced the return on an investment, but autonomous systems remain the next day in the household sector.

The energy self-sufficiency of a home every day becomes even more timely due to current economic conditions and excessive property taxation as well as due to the imminent increases in electricity.

Despite the reduction in the guaranteed price for production, domestic systems continue to be the future of the energy sector.

Either through net metering or other future proposals, the energy autonomy of the home will be retained as an end in itself as it is the only solution that can meet the economic and environmental requirements of the coming years

It is therefore important for every interested consumer to know every detail about a photovoltaic system, as well as the options available to him at this time, so that he can prepare himself also for the future challenges.

  What is an Autonomous Photovoltaic System?

It is a system that can supply electricity to any installation or device, using solar energy, without depending on any power supply network.

Such facilities are primarily located in homes, cottages, warehouses, boats, etc.

Parts of an autonomous system

 – Photovoltaic panels:

They are the devices that convert solar radiation into electricity. A Photovoltaic Panel is a frame containing interconnected solar cells and generates electricity when it receives solar radiation.

Traditionally, for low power systems, monocrystalline panels with open circuit voltage of 12Volt – 17Volt were used. Today, though, the architecture of the autonomous systems (hybrid, island, etc) has been improved, we can use any type of panel without any limitation.

– Charge regulator: It is the device that is inserted between the panels and the batteries.

The charging regulator ensures that the current produced by the photovoltaic panels loads batteries in a uniform manner and constant voltage and controls the level of charge.

– Batteries: Stores the energy produced so that it can be used when required. Batteries for photovoltaic systems are specially engineered to have a long life and to withstand multiple charging and discharging cycles. It may be closed or open type. Liquid open type batteries are considered the most reliable, but they cost almost twice the closed type and need regular maintenance. In recent years, closed-type batteries (AGM, GEL) have improved features and are increasingly used.

– Inverters: They are devices with electronic and electrical devices, which convert the direct current into alternating, suitable for consumption. In an autonomous photovoltaic system, the inverter is supplied with a direct current from the batteries. Many modern inverters can also be powered by an AC power source (PPC, power generator) to charge the batteries.

There are even inverters that play the role of a network administrator. They have the ability to manage at the same time:

– The current produced by the photovoltaic panels or a small wind turbine and has already been converted to alternating from the local inverter.

– The power from an external source (PPC, generator).

– Charge the batteries

– Consumption supply

– Mounting brackets: They are usually made of aluminum and used to fix the photovoltaic panels on them.

– Electrical equipment: It consists of the wiring connecting the panels to each other, the wiring connecting the panels to the inverter and the wiring connecting the inverter to the power consumption network.

Annual consumption

In order to properly begin collecting the information needed to properly design the autonomous system that will properly meet your needs, you must know the annual consumption of your home in kilowatt hours (kWh).

So take 4 consecutive PPC accounts (representing a full year) and add the current consumption you had. This set will be the first essential information.

FOR EXAMPLE: We have a residence that has the following consumption in the 4 PPC accounts:

1st 4month = 900 kWh

2nd 4month = 820 kWh

3rd 4month = 750 kWh

4th quarter = 800 kWh

Total = 3,270 kWh

Appliance and consumption recording

Another very important element is the devices that you operate and their consumption. Record all the electrical appliances you use in your home (lamps, kitchen appliances, TVs, video etc) and note their power. (Power is usually written on each device and measured in watts or kW).

If on this list you fill in the time it is used daily next to each appliance, then multiplying its useful time will give us the kilowatt hours (kWh) consumed daily and annually.

Study to define the appropriate system

By knowing precisely the devices we use, their power and their daily use, we can turn to the specialized professionals who can produce such energy studies and suggest the right system that will meet your needs.

In order to properly cover the abovementioned household consumption, a stand-alone system has been specified which includes the following materials:

– 12 photovoltaic panels 250W, total power 3kWp

– 1 inverter for integrated management of the stand-alone system (island)

– 1 inverter for converting direct current to alternating

– 8 Closed-type batteries 12V, 200Ah

– Aluminum brackets to support frames

– Electrical equipment and wiring

The above system installed will cost around € 11,000 (including 23% VAT).

The participation of the materials at the above cost is approximately the following:

– Photovoltaic Panels: 25%

– Batteries: 25%

– Inverters: 35%

– Stands and wiring: 15%

Note: In this system, the role of the charge controller is played by the inverter manager (island).


  1. In order to properly design a stand-alone photovoltaic system to meet the needs of a home, it should be “grounded” on the basis of electricity production in the winter months and not on the basis of average monthly production, otherwise otherwise in the winter months there is a clear lack of energy. The current system will produce approximately 4,000 kWh per year. During the winter months it will cover the house’s consumption, while in the summer it will have a surplus of energy.
  2. In all cases where an autonomous system is planned to cover the annual operation of a dwelling, it is proposed to install an oil generator in parallel to meet the energy requirements in adverse conditions (eg over 2 days without sunshine , demand for electricity in addition to what was planned, etc.).

System depreciation

We should be aware that our energy consumption (kWh) also includes several other charges that are noted below, as reported in the PPC accounts.


Gen. T., et. Al., 2093/92

  • CPC (L.3336 / 05)
  • VAT 13%

All above together with VAT represent a charge on the cost of the current value of 68%. So, in order to calculate the actual cost we charge for each kilowatt hour, we should add the cost of electricity billing, all charging charges and VAT. and let this be divided by the kilowatt hours we consumed.

Of course, in addition to all these charges, the PPC accounts are charged with municipal taxes and fees, the Real Estate Fee and the well-known “poll tax” EYTID. For example :The above building for the 3,270 kilowatt hours (kWh) paid the following:

-3,270 kWh X 0,0815 € / kWh = 266,51 €

-Other charges = 129.58 €

-F.A. 13% = 51.49 € Total = 447,58 €

Consequently, each kilowatt hour (kWh) cost 447.58 / 3.270 = 0.137 € / kWh


As is clear from the above, the full autonomy of a regular residence is not the ultimate economic solution for the consumer at the moment (taking into account the cases where the PPC network can be connected), given that the depreciation of the investment over time. However, it continues to be the only advantageous solution, and its overall prospects for the future remain strong, with no stress on bills and increases.

In addition, housing autonomy is much more advantageous with very small consumption (eg cottages usually used only in the summer and without high demands on energy etc.)

System Tracking

Charge controls and inverters provide various indications and alerts about the system’s operation and the battery charge level. Below, we provide examples of rational use of energy to help you reduce energy consumption:

– Washing machine

We set the washing switch at 30 ° C, as most of the energy consumed by the washing machine is used to heat the water.

– Lighting

Replace common lamps with special low-power lamps to consume up to 5 times less power. We do not let the lights light up where they do not need.

– Electronic devices

We close the devices, such as TV, DVD and stereo, from the switch and not from the remote control. When in standby, the devices continue to consume power. We remove the chargers from the socket after charging them.

– Electrical devices

We replace old energy-intensive devices with new energy class A. Tip: replacement of kitchen with gas / gas cooker.