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Study of savings with a self-consumption PV installation.

The physicist Mariano Sidrach de Cardona, professor at the University of Malaga and vice president of the Renewable Energy Foundation, has studied the possible savings on electricity bills in Malaga. In this article we have the results.

Photovoltaic systems allow consumers to generate part of their consumption on their own. It is therefore important to know how these systems work and what options are available. In this study, REAL cases are visualised to help make the right decisions for consumers in the future. The evaluation is based on a system in operation in Malaga, and is based on real data of production, consumption and energy exchanged with the electricity grid. All data are from 2020 and 2021.

The study looks at the energy performance of the photovoltaic system, and how it has impacted on electricity bills. To this end, a simulation has been carried out comparing the cost of one year's bills in a home without a photovoltaic installation, with the real value paid in the bill of a home with an installation in operation. It also analyses the impact of the new electricity tariffs and whether incorporating a storage system has a significant impact on savings.

The following table shows the energy balance of the installation.

Table 1: Monthly average daily energy balance

The average daily consumption is 12.8 kWh with peak values in January for heating and August for air conditioning. As can be seen, during the year analysed, the PV system produces approximately the energy necessary for the consumption of the house, making it a zero-emission house. On average 54% of the energy produced was used directly (self-consumption), which means a self-sufficiency of 47%. An important fact to note is that the self-consumption values are optimised by the fact that in practice a user ends up adapting (over the years) to consume most of the energy in the central hours of the day, achieving higher percentages of self-consumption.

PV production is lower in winter than in summer, so there is always energy bought from the grid, and also fed into the grid. (see figures 2 and 3)

Figure 1. Monthly average daily values of PV production and household consumption

Figure 2: Monthly values of self-consumption and self-sufficiency

How does the PV system impact on the electricity bill?

Now that we know the energy performance of the system, the main interest is to know what are the real savings we have obtained. For this we will use several assumptions, always using an hourly energy balance. The VAT considered is 21%, an electricity tax of 0.051127% and a monthly meter rental of 0.80€.

The property has contracted the following "me cambio" tariff from Gesternova:

- Contracted power: 4.4 kW

- Energy price: 0.1255 kWh

- Power price: 0.1152 €/kW per day

  • Scenario 1: House without PV installation.

Annual cost: 993€, of which 59% was the cost of energy, 19% the cost of power and the rest taxes.

  • Scenario 2: House with PV installation, with the above conditions, without compensating surpluses.

This is the same as a system with zero discharge, since as soon as you finance it, it makes no difference if you do not produce the energy or if it is not bought from you.

Annual cost: 646.8€, of which 49% was paid for the energy and 29% for the power. This system has managed to save €344.2 in one year, which is 34.6% of the total bill. In this assumption the weight of the bill falls more on the power.

  • Scenario 3: House with PV installation, with the above conditions, but with a surplus compensation.

Annual cost: 535.8€, of which 42% of the bill is due to energy consumption and 35% to the power term. With this system, it has managed to produce annual savings of €457.3, which means an annual saving of 46%.

  • Scenario 4: We simulated what would have happened under the new electricity tariffs.

We return to the cost of the bill without PV installation with the new tariffs.

Gesternova Easy Tariff.


- Peak: 0.089514 €/kW day

- Valley: 0.009382 €/kW day

Energy: Fixed price 24 h: 0.182294 €/kWh

Annual cost: 1137.2 €. Now the percentage of energy is 71% of the bill and only 7% of power. It can be seen that with the new tariffs the power cost has decreased, but the energy costs have increased. The bill has increased by 14.5%.

  • Scenario 5: New tariff with hourly discrimination without PV installation.

Gesternova Hourly Tariff.


- Peak: 0.089514 €/kW day

- Valley: 0.009382 €/kW day


- Peak: 0.247513 €/kWh

- Flat: 0.149839 €/kWh

- Valley: 0.107204 €/kWh

Annual cost: 1,032.8 €. 70.5% would be the cost of energy and 7.2% of the power term. The new tariffs have significantly increased the price of the monthly bill.

  • Scenario 6: A home with a self-consumption PV system with the new electricity tariffs

Gesternova Easy Tariff

The cost of the bill is 547.6€, of which 63% corresponds to energy and 14% to power. This makes an annual saving of € 589.6 compared to not having a PV system. This is a saving of 51.8%.

- Gesternova Hourly Tariff

Here the cost of the bill is € 456.8. 60% corresponds to the energy and 16% to the power. This leads to an annual saving of 576 € compared to what you would pay without a PV system, with the same tariff. A saving of 55.8%.

  • Scenario 7: House with a 5 kWh battery in the PV-system

In this scenario we would have the lowest monthly costs; 338,6€.

Adding a battery saves 118.2€. It should be noted that very high values of self-consumption and self-sufficiency are achieved, but the savings are only 11.5% compared to a system without a battery. In this case the energy surplus is very low.

Table 2. Annual cost of the electricity bill (VAT included) for the different tariffs with and without self-consumption photovoltaic installation.

Table 3. Influence of the battery on system performance


The systems that achieve the greatest savings are those that use tariffs with hourly discrimination and surplus compensation.

In our case we have achieved a saving of 576€ per year on the bill, that is 55.8%.

It is important to emphasise that to be considered a good sized installation, it should produce energy similar to the annual consumption. In this way significant savings can be achieved and the energy we inject into the grid can be compensated for.

A much larger system would mean a very high cost for little increase in savings, as we could end up with surplus energy that cannot be compensated in the bill, as well as greatly increasing the cost of the installation, delaying the moment in which it is amortised.

In a system without a battery, energy savings of between 30% and 50% can be made, depending on the user's habits, percentages that translate very similarly in the bills.

Residential systems make more sense to have a surplus, as without it they can be inefficient systems as they stop producing energy that could be compensated for.

With the new tariffs the annual amount of the bills is higher, but because the energy consumed has gone up, and the power has gone down, it makes domestic PV systems even more profitable. The power term has dropped from €185/year to €74/year, a decrease of 60%, while energy went up by 39%.

In short; self-consumption PV systems are very profitable economically with the current regulations and should lead to significant savings. The installation required depends on the individual situation and specialist companies will determine the appropriate system.

News based on this article and the studies of Mariano Sidrach de Cardona.

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