Clarify your self-consumption goal before sizing the solar installation
Distinguish self-consumption with or without surplus resale
Before choosing the power rating, decide whether you're aiming for "pure" self-consumption or self-consumption with resale. Without resale, you're mainly seeking to cover your daytime usage and limit the paperwork. With surplus resale, you monetise the electricity you don't consume via a purchase contract, which can make sizing a bit more comfortable. Set a clear goal from the start.
Estimate a realistic self-consumption rate based on usage (day/night, remote work, pool)
The self-consumption rate depends on your usage profile. Remote work, a daytime water heater, a pool pump or air conditioning all increase the share consumed "as the sun shines." Conversely, a household mostly present in the evening self-consumes less, unless appliances are controlled or storage is added. Aim for a realistic order of magnitude before oversizing.
Identify site constraints that change the picture (shading, orientation, roof space)
A tree, a chimney, a dormer or an unfavourable orientation can significantly cut output. Available space, the condition of the roof covering and cable routing also matter. A site visit and an output simulation avoid surprises and help size the solar installation as precisely as possible, with no "wasted" watts.
Measure the consumption to cover: the basis of reliable sizing
Analyse bills and the consumption profile (subscribed power, seasonality)
Start from 12 months of bills. Identify the kWh consumed, the subscribed power (in kVA) and the periods when it spikes. A home heated by electricity doesn't have the same profile as one with gas heating and a few electrical uses. Also note the peak and off-peak hours, as they influence the consumption pattern.
Rely on precise readings: smart meter, sub-meters, readings over 7 to 30 days
The load curves from smart meter data give a detailed view, day by day, sometimes hour by hour depending on service access. For a project, a short reading period is often more telling than an annual average. Measure over 7 to 30 days, including both weekday and weekend. If needed, fit a sub-meter on a large load to isolate its share.
Translate usage into kWh: water heater, heating, air conditioning, EV, appliances
Convert each use into kWh. The rule is simple: power (kW) x duration (h). Make a list by load.
- Water heater: heating cycles and hours
- Heating and air conditioning: weather-dependent
- EV charging: kWh per session and frequency
- Appliances: hob, oven, washing machine
- Standby and IT equipment: baseline consumption
This gives you a daily profile. It's the basis for sizing a solar project around self-consumption, without oversizing.
Calculate the right solar power rating: rule of thumb + step-by-step method
Understand local output: irradiation, tilt, orientation and solar obstructions
Start by estimating your roof's yield in kWh per kWp. Local irradiation, a tilt often close to 30 to 35°, orientation and shading (trees, chimneys, buildings) all cause output to vary. A simulator such as PVGIS gives a baseline, then you refine it with a site visit and a survey of solar obstructions. To go further, also see how the impact of a tree or a chimney can hurt output.
Size in kWp based on daytime consumption: avoid oversizing
In self-consumption, you size the system first based on what you use while the sun is out. A simple method:
- Gather your smart meter data (30-minute curve) or your meter readings.
- Calculate the kWh consumed between 9am and 5pm over the year.
- Estimate the local output, often 900 to 1,400 kWh/kWp/year depending on the zone.
- Target solar power: kWp = annual daytime consumption / output.
This avoids exporting too much, especially if your usage isn't set to change (heat pump, electric vehicle).
Choose the right equipment: modules, micro-inverters or a central inverter, cable cross-section
A simple, lightly shaded roof: a central inverter is often the right choice. A roof with multiple planes or shading: micro-inverters limit the loss. On the cabling side, aim for a low voltage drop and comply with the NFC 15-100 and UTE C 15-712-1 rules. An RGE QualiPV installer secures the choice and the installation without surprises.
Optimise self-consumption on the ground: load control and technical options
Schedule consumption at the right time: water heater, EV, pumps, air conditioning
With solar, the gain mainly comes from shifting usage. Schedule the water heater for the middle of the day via a contactor or relay. Start EV charging when output exceeds a threshold. For a pool pump, mechanical ventilation, air conditioning or irrigation, aim for solar hours and plan for an automatic stop if output drops.
Assess the value of a battery in 2026: cases where it makes sense and its limits
In 2026, a battery is mainly a lever in specific cases: high evening consumption, few controllable loads during the day, need for continuity (off-grid site, brief outages). Limits: investment cost, efficiency, ageing. Without load control, it charges poorly and profitability stretches out. To go further, also see storing solar electricity.
Think about overall sizing: heat-pump water heater, heat pump, home automation, load shedder
Check the proper sizing of the production-usage pairing. A controllable heat-pump water heater or heat pump absorbs the midday peaks. Add home automation, a load shedder and real-time monitoring to avoid exceeding the subscribed power and keep the installation stable.
Secure compliance and profitability of the project in 2026: points for tradespeople to watch
Check the procedures: Enedis, Consuel, connection, self-consumption agreement
Before installing a single solar module, lock down the paperwork. Enedis connection request, choice of whether to export or not, and signature of the appropriate self-consumption agreement. On the safety side, the Consuel certificate is prepared from the design stage. Diagrams, protections, labelling and enclosures all need to be consistent. Keep a well-documented file.
Frame the grants and the sale: purchase tariff, EDF OA, possible CEE depending on context
Clearly state what falls under the Obligation to Purchase contract for the surplus. Since the order of 5 June 2026, there is no longer an investment premium: support is limited to a single feed-in tariff of €0.011/kWh (P+Q ≤ 100 kWp), indexed by 2% a year. The rates can change, so base your figures on the rate in force at the date of the connection request. CEE doesn't fund solar, but other trades on the job may qualify depending on the context. Set an unambiguous framework.
Formalise the costing: assumptions, scenarios, warranties, maintenance and output monitoring
A good costing means a realistic estimated output and simple scenarios. Self-consumption rate, price per kWh, shading, panel ageing. Specify warranties (modules, inverter), maintenance, and output monitoring. This secures profitability over the long term. To help your clients decide, you can also clarify the choice between full resale vs self-consumption based on their profile.
Key figures
1,000–1,400 kWh/kWp/year
Average output in France
5–7 m²
Surface area per kWp
30–50%
Target self-consumption rate
Frequently asked questions
At minimum, expect a prior declaration at the town hall, then a connection request with Enedis including a Self-Consumption with Export Agreement (CACSI) and, if you're selling, a purchase contract (often via EDF OA). Timeframes vary by local office, but generally allow 4 to 10 weeks between the connection request and commissioning. Also plan for the Consuel certificate if Enedis requires it for the given configuration.
Louis Airy
COO of Argile
