The real numbers on the profitability of solar and battery installations

The result: even with less support, solar power remains an excellent investment, provided you optimize your self-consumption. Production monitoring and equipment management: these levers help maintain return-on-investment times comparable to those of before. Solar power therefore remains as profitable as ever, provided you consume your own energy wisely.

The State is reducing subsidies for solar energy: a negative signal for the energy transition

Since March 28, 2025, the S21 tariff order – which governs the conditions for purchasing photovoltaic electricity in France – has been amended, resulting in a significant reduction in aid for solar installations. Specifically:

• The self-consumption bonus has gone from €160 to €80/kWp.
• The surplus buyback rate falls from 12,7 cents to 4 cents/kWh.

This is a bad signal for the energy transition, as the adoption of solar energy gives individuals access to affordable electricity, thus accelerating the installation of heat pumps and the use of electric vehicles.

But should we therefore give up investing in solar energy? No. And here's why.

Falling panel prices and high electricity prices: two levers favouring the profitability of solar energy

• The price of electricity remains historically high and is expected to rise again in 2026 with the end of ARENH[1].
• Photovoltaic panels are becoming less and less expensive: prices have dropped by 30% in one year. In 2025, with a competitive installer like Hello Watt, which benefits from good prices for equipment and passes them on in its quotes, you should expect to pay approximately:
  • €7.000 for a 3 kWc installation
  • €11.000 for 6 kWc
  • €14.500 for 9 kWc

The average lifespan of photovoltaic solar panels is around 30 years.

Hello Watt conducted a study on three typical homes in Nantes

Hello Watt analyzed the profitability of three typical installations (3, 3 and 6 kWc[9,5]) according to three electricity consumption profiles (2, 3.000 and 6.000 kWh/year). Result: even with a reduction in subsidies, solar remains profitable, provided that self-consumption is optimized:

• Before March 28, 2025, it took an average of 10 years to make an installation profitable;
• With the amendment of the decree, the average profitability increases to 12 years;

It is necessary to improve its self-consumption rate by around 20% to return to the profitability of before March 28.

How to easily improve your self-consumption?

1. Monitor your production and consumption to shift certain uses: +10% self-consumption

On average, solar panel owners self-consume 40% of their production.

Among users of the Hello Watt application, the average self-consumption rate rises to 49% (with a strong variability between 30% and 70%).

The self-consumption rate depends on several factors: solar production (itself linked to the size of the installation), the household's electricity consumption (its shape and level) and whether or not usage is shifted towards sunny hours. Logically, a small installation (3 kWp) achieves a better rate, but between 6 and 9 kWp, if the sizing is appropriate, the gain in self-consumption is limited.

How do they do it?

Thanks to the Hello Watt app, they can:

• View their solar production, consumption, grid injection and self-consumption rate hour by hour.
• Adapt their habits: for example, running household appliances, delaying the water heater or charging the car when the panels are producing.

Already more than 40.000 people use the Hello Watt app to track and evaluate their solar production, a figure that has more than doubled in one year.

2. Control your equipment (water heater, IRVE terminal, etc.): +10%

To prioritize your solar electricity consumption, the ideal is to automatically synchronize the operation of certain devices with production peaks.

Thanks to intelligent control solutions, it is possible to trigger equipment at the right time, based on real-time production. For example:

• Water heater: automatic activation when the panels produce the most, thanks to a dry contact (a small electrical relay that acts like a smart switch) or via an energy manager (a connected box that controls the devices according to the available production).
• Electric vehicle charging: Some charging station models can adjust charging power or wait for sufficient sunlight before starting charging. This allows you to charge directly using your solar power, without drawing electricity from the grid.
• Washing machine, dryer, dishwasher: control possible via connected sockets, or delayed programming based on times of high solar production.

Some home automation solutions allow this type of automated control, without manual intervention.

Result: you consume more free electricity, and significantly reduce your dependence on the grid.

3. Install your solar panels on two roof sections

To maximize self-consumption, it may be wise to install the panels on two differently oriented roof sections (for example: southwest and southeast). This configuration allows electricity production to be spread over a wider time range: from the morning with the east-facing panels, and until the end of the day with those facing west.

Result: more regular production throughout the day, better aligned with household consumption peaks (waking up, meals, returning home), which reduces energy losses and optimizes the direct use of your solar electricity.

Is adding a battery to my photovoltaic installation profitable?

If you wish to install a physical battery on your installation, there is an additional cost.

For a solar project of 4,5 to 7,5 kWp, Hello Watt offers a 7 kWh battery for an additional €5.800 including tax. For more powerful installations, it is possible to increase the capacity by adding 7 kWh modules (€3.000 including tax per module), up to a total of 21 kWh.

On average, with a battery, you increase your self-consumption rate by 20 to 30%.

A solar project with battery represents a larger initial investment that does not improve but does not extend or only slightly extend the return on investment time.

Its cost is offset by the additional savings you make by consuming more of your own production.

It is a good lever to gain autonomy and protect yourself against future increases in the price of electricity.

In conclusion

Solar energy remains an excellent solution for reducing your electricity bill, provided you monitor your production and manage your equipment.

But each situation is unique: consumption, hours of presence, electrical equipment, roof surface area... To find out the most cost-effective solution for you, run a free simulation on Hello Watt, then speak with a solar expert who will suggest the most suitable sizing for your profile.

For Sylvain Le Falher, co-founder of Hello Watt: "The reductions in subsidies are a bad signal, but they don't call into question the profitability of solar energy. Solar energy becomes all the more attractive when we know how to manage it intelligently. New installations will no longer be a standalone photovoltaic system, but rather one coupled with a tech solution like the Hello Watt app, which allows us to maximize self-consumption."

[1] https://www.quechoisir.org/action-ufc-que-choisir-electricite-la-nouvelle-regulation-fera-flamber-la-facture-des-consommateurs-n149512/

[2] The choice of 9,5 kWc rather than 9 kWc is not insignificant: beyond 9 kWc, installations benefit from a higher self-consumption bonus. It is therefore often more financially advantageous to slightly exceed this threshold.

Illustrative image of the article via Depositphotos.com.