“tell me how much and when you consume and I’ll tell you how much I’ll save you”

Not all photovoltaic systems are the same and the electricity requirements of different realities also differ considerably.

In order to obtain the maximum potential from a self-consumption photovoltaic system, the size of the photovoltaic system should be the optimal result between:

  • distribution of user loads
  • plant producibility

With the 110% superbonus, the (erroneous) logic of using all the space at one’s disposal, without any assessment of the real value of self-consumption, has spread.

Electricity bill analysis

Electricity bill consists of items that lead to the final price of the kWh taken from the grid, the three main ones being: sales services/network services/taxes.

In general, the bill is also divided into three different time slots:


  • Monday to Friday from 8 a.m. to 7 p.m.


  • Monday to Friday from 7 a.m. to 8 a.m. and from 7 p.m. to 11 p.m.
  • Saturdays from 7 a.m. to 11 p.m.


  • Monday to Saturday from 00.00 to 7.00 and from 23.00 to 24.00
  • All hours on Sundays and public holidays

How do you define value for money?

Reference will be made to data on:

  • energy withdrawn per year (referring to the share that can be self-consumed)
  • cost of kWh drawn from the grid
  • expected output of the system according to the area of installation
  • cost of the system, which varies according to the type of installation and the quality of the material used

Cash flow is the flow of income and expenditure accumulated over the years in different situations.

Example of a photovoltaic system on a building, without Superbonus, but with 50% tax deduction 

Without photovoltaic system = outlets for drawing energy from the grid.

With a photovoltaic system in “Scambio sul Posto” and tax deduction=


  • plant costs
  • costs of only the energy still withdrawn when the photovoltaic system is not self-consuming


  • feed-in tariff contribution for energy fed into the grid
  • tax deduction of 50% of the investment cost spread over 10 years (alternatively, credit transfer/discount on invoice)

Savings on self-consumption energy are not calculated as a direct cash inflow, but are an economic benefit that is implicitly included in the calculation as a lower outlay on the electricity bill.

In order to assess the profitability of the investment, the overall benefit of the intervention is measured, i.e. the difference between the cumulative cash flow of the situation with the photovoltaic system and that without the photovoltaic system.

Payback time is the point at which, in terms of costs, the situation with a photovoltaic system is better than the situation without a photovoltaic system.

A photovoltaic system is not a purely speculative investment, but an economic benefit on the user’s electricity consumption; whoever invests in a photovoltaic system today is insuring himself against the unforeseen events of tomorrow’s energy market, mitigating the effects of fluctuations in the cost of the kWh drawn.

The overall economic benefit, which is significantly higher than the initial investment, is calculated at the end of 40 years (in the case of Maxeons) and takes into account on-site exchange and cumulative cost savings.