Formula and meaning
Annual vehicle energy demand is compared with available PV surplus to determine the remaining grid energy.
E₍charge₎ = km · consumption / 100 / η · PV share = min(PV surplus, E₍charge₎)
E-mobility · photovoltaics
PV Surplus Charging Calculator
Calculate solar share, grid energy and annual charging cost when charging an EV with PV surplus.
EVAC/DC
02
Results
ƒ(x)
Set the inputs and run the calculation.
Context
At 15,000 km/year, 18 kWh/100 km, 2,000 kWh PV surplus, and €0.35/kWh, about 67% of charging demand is covered.
PV surplus is treated as an annual energy budget. Hourly matching, storage, seasonal yield, and smart charging control are not simulated.
Inputs and method
Estimate PV surplus charging
Compare annual vehicle charging demand with available solar surplus.
Inputs
Annual distance, vehicle consumption, charging efficiency, PV surplus and grid price.
PV surplus is useful only when car and charger are available at the same time. An annual value can therefore show a high theoretical PV share while winter or night charging still needs grid energy.
Calculation
Charging demand = km·consumption/100/η; PV share = min(surplus, demand); remainder comes from the grid.
Example
15,000 km, 18 kWh/100 km and 2,000 kWh surplus cover about two thirds of demand at 90% efficiency.
Sources and limits: Annual energy balance; hourly coincidence and storage operation are not simulated.
Estimate PV surplus charging in detail
Compare annual vehicle charging demand with available solar surplus.
What does this quantity describe?
Energy calculators balance quantities over time and separate useful energy, losses and grid import. This matters because power is instantaneous while energy is its time integral.
Formula and variables
Charging demand = km·consumption/100/η; PV share = min(surplus, demand); remainder comes from the grid.
Choose the inputs correctly
Annual distance, vehicle consumption, charging efficiency, PV surplus and grid price. PV surplus is useful only when car and charger are available at the same time. An annual value can therefore show a high theoretical PV share while winter or night charging still needs grid energy.
How to use the calculator
Enter annual distance, vehicle consumption, charging efficiency and the annual PV surplus actually available for charging. Surplus is the PV yield remaining after subtracting the rest of the household's consumption.
Worked example
15,000 km, 18 kWh/100 km and 2,000 kWh surplus cover about two thirds of demand at 90% efficiency.
Understand the result and units
PV surplus is useful only when car and charger are available at the same time. An annual value can therefore show a high theoretical PV share while winter or night charging still needs grid energy. An annual value describes a scenario, not a guarantee for every day. Efficiency, coincidence, temperature, driving profile and tariff assumptions can change practical results more than rounding.
Distance in kilometres per year, consumption in kWh/100 km, energy in kWh per year, prices in euros per kWh.
Typical applications
Estimating what share of annual charging demand can be covered by existing PV surplus, and comparing remaining grid cost with and without PV use.
Assumptions, limits and common mistakes
Annual energy balance; hourly coincidence and storage operation are not simulated.
Common mistake: Don't confuse annual PV surplus with total PV yield – only the share left over after household consumption is available for charging. A high calculated PV share does not mean every single charging day has enough surplus; the annual balance hides seasonal and daily variation.
Frequently asked questions
Where do I get the PV surplus input value from?
Estimate it as PV yield minus the rest of household consumption, for example with the PV self-consumption calculator, or read it directly from an existing PV system's meter data.
Why is grid power still needed if the PV share is high?
The calculation is an annual balance. In winter, or when the car isn't at the charging point during the day, PV surplus is often unavailable at the right time even though enough energy was generated over the year.
Does the result change if I charge during the day instead of at night?
Yes, but not directly in this model, which only balances annual energy totals. Charging during the day raises the practically usable PV share because generation and consumption coincide in time.
Dynamic tariff? Find the cheapest charging window with the electricity charging planner →