A key question when installing a net-metering self-consumption photovoltaic system is whether batteries will be placed. This question we will try to answer in this article.

The price of batteries has escalated significantly in recent years and their price is expected to decrease even more in the future, mainly due to its use in electric cars, but also in energy storage systems for electricity generation. But the de-escalation of these prices is not yet as rapid as that of photovoltaic panels.

In today’s terms, the cost of a photovoltaic net metering system that includes batteries (mainly lithium ions) is about 40% to 50% of its price without batteries. The key question is whether these costs are paid back over a reasonable period of time

The benefit of the battery in photovoltaic net metering

To answer the above question we must see what we will gain if we place a battery in photovoltaic net metering.

Let’s first look at the various implications of battery placement in the Net metering philosophy

The key points of Net Metering in Greece with and without batteries are:

  1. All energy produced by the PV systems is used for the user needs.
  2. In case that the solar energy is not enough,
    • without batteries: the user will also use the gird to extract energy
    • with batteries: rest of the energy will be drawn from the batteries. When the energy of the batteries is not enough, the rest of the energy will be taken from the public grid.
  3. In case that the energy produced by the PV systems exceeds the used needs,
    • without batteries: the excess energy is fed to the grid
    • with batteries: the excess energy will be used to charge the batteries and when they are fully charged, the excess energy would not be lost, but will be fed into the grid
  4. For three years, the energy that you fed into the grid is subtracted from the energy that you got from the grid, so you will be charged only for the net amount of energy that you got from the grid.
Energy Consumption Photovoltac curve
Energy Consumption Photovoltac curve

Based on the above, the installation of the battery will increase the rate of self-consumption, ie the percentage of production of photovoltaic Net metering system  that leads directly to consumption, without being fed into the network.

As mentioned in detail in the article “What we save with a photovoltaic net metering”, the increased rate of self-consumption, increases our savings in Adjustable Energy Charges – energy department ②. ④, ⑤ and ⑥ of the electricity bill. As mentioned in the above article, in a household three-phase consumer the percentage of these charges in the total bill is about 24% in electricity bills before the increases of the summer of 2021 and 10% in electricity bills based on the March 2022 prices.

So if we assume the same average household three-phase consumer with a family of four with two children and an annual consumption of 8000 kWh, the average self-consumption rate will be about 40%. By installing batteries the average self-consumption rate is expected to increase to about 70%.

That is, the placement of the battery increases the self-consumption rate by 30%

So, since the rate of regulated charges was 24% on bills before the summer 2021 increases and 10% with March 2022 prices, our ultimate benefit from batteries will be:

• 24% x 30% = 7.2% in bills before the increases of the summer of 2021

• 10% x 30% = 3% on bills with March 2022 prices

The above percentage is very small and in this example corresponds to about 120 € per year. If we take into account that the battery will increase our cost by an amount that exceeds € 3,000, it means that the payback period of the battery costs exceeds 25 years!

So the economic benefit of placing a battery in a photovoltaic Net-Metering system is small in relation to its cost. The profit from the placement of a battery in a photovoltaic Net-Metering system will have a long payback period, a fact that at present and as long as the legislation of net metering remains as it is , makes the installation of a battery unprofitable in Greece.

It should be noted that, in addition to the above, there is the possibility and under certain conditions, with the installation of a battery, the photovoltaic system can also function as a backup system, providing energy to consumption in case of power outage. But this is something different and goes beyond the purposes of this article,

Of course all of the above are assumptions and depend on the consumption profile, the size of the battery etc

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