Photovoltaic and storage, because the battery is (almost) never worthwhile

In Italy, the development of photovoltaics is still very low. If we exclude condominiums, where photovoltaics are still possible but not always easy, even for the heights, there are hundreds of thousands of single-family homes without panels on the roof. Only in the last few months, due to an unexpected spike in lighting costs, many people have woken up from their numbness and tried to take action to understand how much the installation of a suitable system on the roof of their home could cost.

The costs are not high, especially for a classic 3 kWh system where we are in the order of 4,000 euros with the appropriate deductions, yet most people gets stuck in front of a much higher estimate than what the right price should be. The prices have gone up, it is true, but the reason for the often exaggerated estimates is simple: everyone tries to place, together with the photovoltaic system, even the battery, the famous accumulation. A battery that often leads to double the initial estimate, bringing the costs of the systems to prices close to 20,000 euros, 10,000 if there is a discount on the invoice.

The battery is obviously sold by focusing on the fact that photovoltaics only produce during the day, and that obviously it cannot reduce consumption in the other hours of the day, but the reality is that the battery is practically never worthwhile.

There is only one case where the photovoltaic battery is convenient: when it has been included in a towed incentive under the 110% bonus. The state paid, the battery came for free.

Although an incentive has been created (ridiculous in the delivery methods) to facilitate the installation of domestic storage batteries, and although the deduction also exists, the substance does not change and a small calculation is enough to understand that the battery will practically never pay for itself. She will do it when she is old now.


Before moving on to the numbers, it is good to remind everyone, because no installer does it (especially those who try to sell systems with batteries), is that there is an incentive that compensates the owners of photovoltaic systems for the excess electricity that is fed into net. Or rather, there are two: one is the exchange on the spot and the other is the RID.

The on-site exchange reimburses consumption in the time slots of the day where the plant does not produce

The exchange on the spot can be considered as a kind of virtual battery, where you are paid for the energy that is “exchanged” with the grid.

How on-the-spot Exchange works

Let’s take a practical example by taking an “X” system that generates 500 kWh in a month, where of these 100 kWh are consumed by the house, the typical “self-consumption”. During the hours of the day, when the plant is producing, the owner uses the washing machine, the dishwasher, has the refrigerator on and several connected appliances, and these use 100 kWh of the 500 kWh photovoltaic generation in a month. The 400 kWh that are not consumed are fed into the grid as an excess.



Obviously, the system does not work early in the morning after sunset and in these time slots, either for the oven in the evening, or for the air conditioner on hot summer nights, the house draws about 150 kWh throughout the month to compensate for the failure. production. This energy, which is not produced by the plant and therefore is not free, is purchased at the price set by the contract with the supplier.

Let’s say that a user has a contract locked at 0.20 euro / kWh: for those 150 kWh he will spend 30 euro of raw material necessary to meet the needs of the house during the night hours.

This is where on-site exchange comes into play: having fed 400 kWh to the grid throughout the month, the 150 kWh that is recovered later are considered exchange energy, and the GSE will pay them. How many? It depends on the price of energy on the wholesale market, and in the situation we are in the price is high but in the past years it was much lower. The exact calculation to quantify the exchange on the spot, which is paid annually, is very complex but we can assume for this year an average of 0.3 euro per kWh.

Those 150 kWh “exchanged”, which we paid 30 euros to the operator on the strength of our still competitive fixed rate, will be re-paid 45 euros. We are in a very particular period, where the cost of energy so high represents an advantage for those who produce, but it has not always been this way: we often find ourselves in a situation of almost equal or slight disadvantage. However, it changes little: the exchange on the spot it is practically a sort of battery with a yield close to 100% todayand as long as it exists as an incentive (theoretically a few more years) the situation will not change.


There is still a portion of energy missing, the one we have not exchanged and we have not consumed: they are 250 kWh, and the user can choose what to do with it. We are faced with a surplus that is also valued at a value close to the PUN (average single national price), and every 31 January you can choose whether to request the reimbursement of the surpluses every year or set them aside for the following years using them for the exchange.

Whoever decides for the refund, since it is a profit and not an exchange, will have to insert this quota in the tax return because it is taxed. Even the RID, in these months of “high” prices, represents for those who have a photovoltaic system, and therefore are a producer, a small sum that helps to quickly amortize the cost of the system itself.


This is what happens to those who today build a system without a battery connected to the grid and registered with the GSE: they do not have to worry too much about the energy they consume at night, when the plant does not produce, because even if you pay it in your bimonthly bill once a year, the reimbursement of the GSE will arrive, which will compensate part or all of the expense. The exchange on the spot, better to say, is not accessible to those who have made a system using 110%.

We add the battery to our plant, the simulation


What happens if we decide to buy a battery for the “X” system? A well-sized system, in a good location and with a 10 kWh battery will have managed approximately 3200 kWh over the course of a full year. The battery has charged and downloaded almost completely every day, doing the job for which it was installed.


Those 3200 kWh are energy that the house has taken from the battery, and that without the battery it would have taken from the grid at a rate of 0.20 € / kWh: the cost to buy those 3200 kWh would have been 640 euros.

As we have said, there is an on-site exchange: those 3200 kWh that we can buy from our manager are “exchange” and will then be paid back to us.
In reality, 3200 kWh will not be paid back, but 3500 kWh will be paid back for a simple reason: those 3200 kWh that the battery has managed are the result of a loss in the storage process. The accumulation is usually eaten from 10% to 15%, and therefore if the system produced 3500 kWh about 300 kWh were lost in dissipation during the conversion, and only 3200 kWh remained in the lithium cells.
Without the battery we would have fed 3500 kWh into the grid.

Wanting to be conservative, and assuming as an exchange price on the spot 0.15 euros per kWh (now there are many more) those 3500 kWh that we have entered we will be paid 525 euros.

As we wrote, the reimbursement amount is variable and depends on the price of energy: in August the GSE paid about 0.5 euro per kWh and in September about 0.4 euro per kWh, but in recent years the prices were much lower. Today, however, there is no doubt that, for those who have a contract with a fixed price and the purchase price is convenient, there are only (economic) advantages to enter the network compared to accumulating at home.


Let’s go back to the battery: the presence of the battery in the house prevented us from buying energy at night, energy that we would have paid 640 euros, but it also prevented us from being reimbursed by 525 euros because we could have fed that energy into the grid. 525 euros which, as we have written, is a conservative and variable figure.

In practice, over the whole year, the battery led us to a saving of 115 euros: with the battery the 3200 kWh cost us nothing, but with the exchange on the spot they would have cost us only 640 euros with 525 euros refund, 115 EUR.


A 10 kWh battery today, with the appropriate deductions, costs about 4500 euros, and calculating a saving of 115 euros a year it takes 39 years to repay the investment. Even if we had saved 200 euros a year thanks to the battery, the battery would have paid for itself once the guaranteed return expired, approximately 20 years.

A battery does not pay for itself today


Accumulation is useless today: the numbers say so. It will be so as long as there is the on-site exchange, which was supposed to be abolished but which seems to be progressively reduced in the number of beneficiaries starting from 2024. For those who are making implants today, however, it seems that there will remain a sufficient period to amortize at least the cost of the installation. Today it is not possible to know what will happen in 3 years, but surely the energy fed into the grid will be paid in some way, whether it is the energy communities or another form of incentive there will always be a return for those who produce and distribute on the grid.

In three years there will be more batteries, the prices will be different, there will be cars that work as domestic storage: there is plenty of time to think about it and also to understand how the energy / price issue will evolve.

Today a battery, associated with a system regularly connected to the grid, is only a cost, not an investment and above all it is not a way to save. If you manage to have it for free, as part of a 110% renovation, the situation changes.

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About Eric Wilson

The variety offered by video games never ceases to amaze him. He loves OutRun's drifting as well as the contemplative walks of Dear Esther. Immersing himself in other worlds is an incomparable feeling for him: he understood it by playing for the first time in Shenmue.

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