28 essential terms to understand solar energy, batteries and the energy transition.
28 terms
The orientation angle of panels relative to south. An azimuth of 0 degrees = due south (optimal). A 45-degree deviation (south-east or south-west) reduces output by only 5-8%.
Battery Management System. The control electronics built into a battery that manage charging, discharging, temperature, and cell balancing. The guarantor of safety and longevity.
One cycle = a full discharge followed by a recharge. LiFePO4 batteries withstand 3000-6000 cycles before losing 20% of capacity. NMC Li-ion: 500-2000 cycles.
Ratio between actual output and maximum theoretical output of a solar panel. In France: 11-14% depending on the region (about 1000-1400 kWh/year per installed kWp).
Total cost of the solar electricity produced over the installation's lifetime, divided by total output. Usually 0.05-0.10 EUR/kWh, well below the grid rate.
Energy Saving Certificates (Certificats d'Économie d'Énergie). A bonus paid by energy suppliers for energy renovation work. The amount varies by project and geographic area.
Percentage of total capacity used before recharging. An 80% DoD means 80% of the battery is used. A moderate DoD significantly extends lifespan.
Ratio between useful energy and total energy. A solar panel's efficiency is 18-22%. An inverter's efficiency is 95-98%. Every conversion causes losses.
Estimate of the annual electricity output of a solar installation, in kWh/year. Depends on peak power, solar irradiation, orientation, and tilt.
A device that converts the direct current (DC) produced by solar panels into alternating current (AC) usable by household appliances. The heart of a solar installation.
Kilowatt-hour. Unit of energy. 1 kWh = the energy used by a 1,000 W appliance running for 1 hour. It is the billing unit for electricity and the capacity unit for batteries.
Kilowatt-peak. Maximum power of a solar panel under standard test conditions (STC: 1000 W/m2, 25 degrees C). A 400 Wp panel produces 400 W under ideal conditions.
A battery using lithium-ion (Li-ion) or lithium iron phosphate (LiFePO4) technology. LiFePO4 cells are preferred for solar storage: 6000+ cycles, high safety, 10+ years lifespan.
Levelized Cost of Energy. The discounted cost of energy over an installation's full lifetime. Accounts for investment, maintenance, replacement, and production.
Enedis's smart electricity meter (France). Required for self-consumption with surplus resale. Enables two-way metering (production and consumption) at no extra cost.
Lithium Iron Phosphate. The preferred battery chemistry for solar storage and portable power stations. Advantages: 3000-6000 cycles, excellent thermal safety, no cobalt, falling cost.
A small inverter installed under each individual solar panel. Advantages: better yield with partial shading, per-panel monitoring, and greater safety.
French government grant for energy renovation. For solar: up to 4,000 EUR depending on household income. Can be combined with the CEE bonus and reduced VAT.
A tariff option offering a reduced kWh price during off-peak hours (usually at night). Ideal for charging an EV or home battery at lower cost.
The tilt angle of panels relative to horizontal to maximize annual output. In France: about 30-35 degrees. Due south is the best orientation.
Maximum power of a solar panel or installation under standard test conditions. Used as a reference to compare panels with one another.
VAT at 10% (instead of 20%) for solar installations under 3 kWp on a home more than 2 years old. A significant saving on installation cost.
Directly consuming the electricity produced by your solar panels instead of feeding it into the grid. Reduces your electricity bill by 30 to 70% depending on the installation.
Selling surplus solar electricity to EDF OA (purchase obligation) in France. Rate guaranteed for 20 years. In 2026: about 0.13 EUR/kWh for surplus on an installation under 9 kWp.
Amount of solar energy received per unit area. Measured in kWh/m2/year. Ranges from 1100 kWh/m2 (northern France) to 1800 kWh/m2 (south). A key factor in energy yield.
A battery's state of charge expressed as a percentage (0-100%). To preserve lifespan, it is recommended to keep the SoC between 20% and 80% day to day.
French network usage tariff (Tarif d'Utilisation des Réseaux Publics d'Électricité). A charge paid by all consumers for the upkeep and expansion of the power grid. Represents about 30% of the bill.
Watt-peak. Peak power of a solar panel. 1 kWp = 1000 Wp. A typical residential panel is between 300 and 500 Wp in 2026.
