Self-production with photovoltaics
With the installation of a photovoltaic system, the user from simple consumer also becomes energy producer, that is, the one who energy field is called “Prosumer”. By originating an exchange of energy with the electricity grid from both directions, the need arises for a bidirectional meter, i.e. capable of measuring both the incoming and outgoing energy generated by the photovoltaic system.
During the day, approximately from 6.30 in the morning until 6 pm on average (4.30 in winter and 7.30 in summer) the photovoltaic system produces electricity. During these hours it is possible to consume the electricity self-produced by the panels, without having to purchase it from the distribution network. If, for example, you produce 10 kWh in one day and consume 6, the remaining 4 kWh are fed into the electricity grid, resulting in an economic advantage.
When the sun goes down, the photovoltaic system stops producing energy, but your home will continue to consume: for example with the refrigerator or the mobile phone charged. The energy you need at night will have to be taken from the grid.
Photovoltaic system with storage
The accumulation (or storage) systems for photovoltaics have the function of storing the energy produced in excess of consumption to make it available during the night or when the solar panels do not produce energy to cover the entire requirement required at home at that time.
An adequate storage system, therefore, allows you to use all or most of the energy produced by the photovoltaic system (if consumption reflects the storage capacity of the batteries), without having to contact the electricity grid and significantly reducing energy withdrawals from the grid and consequently bill costs.
It is advisable to purchase a storage battery if, for example, the house remains empty during the day and therefore consumption is concentrated towards the evening, when the photovoltaic system stops producing energy, or if you plan to buy an electric car to be recharged at night.
On-the-spot trading with the GSE
The State allows you to enter into an on-the-spot metering contract with the GSE1 (Gestore Servizi Energetici). This procedure exploits all the energy fed into the electricity grid by the owner of a photovoltaic system, taking into account not only the electricity lent to other users, but also the energy that is taken from the grid for one's own consumption.
Therefore, after paying for consumption outside the production of the photovoltaic system, the owner of the system will receive economic compensation between inputs and withdrawals from the GSE.
The kWh consumed when there is no self-production, for example at night, will be reimbursed by the electricity grid in the form of an exchange on the spot. Those in excess and remaining in the electricity grid (our famous piggy bank) are identified as a surplus which is paid by the GSE; the value of electricity is established by the authority for electricity and gas.
To receive the refund, it is necessary to wait about a year from the installation of the photovoltaic system, because the GSE proceeds with the disbursement of the subsidy on an exchange basis on a six-monthly basis (as an advance) and on an annual basis (as an adjustment).
1 governed by Resolution 570/2012/R/efr AEEGSI.
How to calculate the savings linked to photovoltaics
As already mentioned above, the economic benefits of photovoltaics are of two types. The advantages related to self-consumption and those related to on-site exchange.
By self-consumption we mean the energy absorbed by the household utilities that comes directly from the production of the photovoltaic system. Therefore, the greater the self-consumption, the greater the savings on the bill, as the consumption that is taken from the electricity grid and invoiced by our energy supplier is reduced. On average, it is possible to estimate that 30% of the energy produced by a photovoltaic system is self-consumed. This percentage can even reach 70% if a storage battery is also combined with the system.
To have some numerical reference we can make this example. Let's assume we install a 6KWp high-efficiency photovoltaic system in the province of Rome, in a house that consumes 3,000KWh per year. The average production expected from the plant is approximately 8,500 kWh (for other simulations, refer to the photovoltaic geographical information system). Therefore, self-consumption, in the absence of a storage battery, will be approximately 900KWh. The remaining 7,600KWh will be fed into the electricity grid.
How much is the saving from self-consumption worth in economic terms?
Using the prices published by Arera for the domestic user protection service valid for the third quarter of 2022, we obtain savings on bills thanks to self-consumption equal to €325 per year, savings that rise to €750 €/year if a storage battery is installed2.
It is possible to be able to determine the self-consumed energy, the energy fed into the grid and taken from the grid. In fact, in the photovoltaic system connected to the grid there are two meters: a production meter which measures the electricity produced by the solar panels and a bidirectional exchange meter which measures both the electricity fed into the grid (when there is in excess of self-consumption) and that withdrawn from the network (when the system does not produce any or is unable to satisfy all the requests from the home).
Furthermore, it is very often possible to monitor the performance of the system in real time thanks to simple apps provided by the system manufacturers.
2Values calculated considering Arera variable prices for the third quarter of 2022, in relation to a residential domestic customer with 3 kW of committed power and annual consumption equal to 3,000 kWh.
How to access in-place trading
Producers who intend to join can activate the service via Single Model or with standard mode.
The Single Model
It is a simplified procedure that allows you to interface only with network managers. The GSE will then activate the Contract and to communicate the code and the link to view it to the user on the portal named Scambio Sul Posto – SSP, accessible by GSE Customer Area, only after receiving the data in the Single Model from the network operators.
The Single Model can be used by manufacturers of photovoltaic plants with the following characteristics:
- made at end customers who already have active low voltage withdrawal points;
- having power not exceeding that already available for withdrawal;
- having a rated power not exceeding 50 kW;
- for which access to the Net Metering regime is requested at the same time;
- made on the roofs of buildings in the manner prescribed by Legislative Decree no. 28/11;
- absence of additional production plants on the same withdrawal point;
The standard mode
Producers who want to join the Net Metering must submit, within 60 days from the date of entry into operation of the plant , a specific request by using the service named Scambio Sul Posto - SSP accessible by GSE Customer Area and then stipulate a contract with the GSE for the regulation of the exchange. The contract, for a calendar year, is tacitly renewable. The Exchange On The Place - SSP portal must also be used by the producers adhering to the contract for the subsequent phases of technical, economic and administrative management of the service. The contract generally expires on 31 December of each year.
How does in-place trading work?
The metering on the spot aims to obtain a sort of economic compensation between the energy fed into the grid and that withdrawn. We speak of economic compensation between injections and withdrawals as we do not refer to the quantity of energy but to its economic value, to the charges and services normally charged in the bill. Furthermore, if at the end of the year the energy input is higher than that withdrawn, a contribution relating to these surpluses will also be recognized.
The energy introduced is that detected by the GSE, while that withdrawn is that invoiced by the energy supplier in the bill
In detail, the two forms of contribution are as follows:
- the trade contribution (Cs);
- any surpluses (in the event that the energy input is greater than the energy withdrawn in the current year).
How these contributions are calculated:
Let's start from the first, which has a fairly complex formulation
Here is the formula: Cs = min (Oe ; Cei) + CUsf x Es
where:
- Cs: exchange account contribution.
- Oe: Cost of energy withdrawn from the grid, expressed in euros. It is given by the multiplication between PUN and KWh withdrawn (the kWh withdrawn are equal to consumption – self-consumption). The PUN (acronym for Single National Price) is the reference wholesale price of electricity that is purchased on the Italian Power Exchange (IPEX - Italian Power Exchange) market. For more information, consult the article "What is the PUN".
- Cei: Countervalue of the energy fed into the grid, expressed in euros. It is given by the multiplication between the Hourly Zonal Price and the KWh entered (the kWh entered are equal to production - self-consumption) in the same hours. This price is the one formed on the electricity market and varies according to the time in which the energy is fed into the grid and the market area in which the plant is located. For more info, consult the website of Electricity Market.
- CUsf: Flat-rate exchange fee. It is expressed in euro cents per kWh. This value quantifies some network costs and general system charges normally paid in the bill. This is the parameter that "identifies" the advantage of on-site exchange, reimbursing part of the costs paid by the user in the bill. The fee is indicated in the tables shown in the documentation available on the GSE website “Technical Rules – On-the-spot Exchange Service.
- Ex: amount of Energy exchanged. Expressed in kWh, it is the minimum value between injections and withdrawals.
The second contribution, on the other hand, is calculated only when the volumes entered are greater than the withdrawals. In particular: Surpluses = Cei - Oe
The above definitions have been reported in a simplified form; they vary according to some parameters (for example according to the type of meter) and for an accurate consultation, please refer to the aforementioned document available on the GSE website "Technical Rules - Exchange Service on the spot.
