The self-consumption rate shows what percentage of the solar power produced you use yourself – directly or via the battery.
The rest is fed into the grid. A high self-consumption rate is usually good for profitability, because solar power you use yourself replaces expensive grid electricity, while power fed into the grid only earns the feed-in tariff.
How the self-consumption rate is calculated
Self-consumption = solar generation − feed-in − battery losses
Self-consumption rate = self-consumption / solar generation × 100 %
Self-consumption therefore covers the solar power used directly (Direct self-consumption) and the solar power charged into the battery – minus the losses when charging and discharging.
autarc calculates all values for every time step of the year – hourly or at the selected Simulation resolution – and then adds them up over the whole year. More in Energy flows.
Example
A solar system produces 8,000 kWh a year. 2,000 kWh of it are used directly and 1,200 kWh are charged into the battery; 4,800 kWh are fed into the grid. 200 kWh are lost when charging and discharging.
Self-consumption = 8,000 − 4,800 − 200 = 3,000 kWh
Self-consumption rate = 3,000 / 8,000 × 100 % = 37.5 %
Why the annual rate isn't an average of the months
The annual rate is the sum of self-consumption over all time steps divided by the sum of solar generation. A simple average of the monthly rates would be wrong: in winter the rate is often high, because little solar power is produced and almost all of it is used directly. In summer it is lower, because much more is produced than used. The sum method weights each month by its actual generation.
What counts towards the self-consumption rate?
Custom producers only if you choose: by default only the solar system counts. If you turn on
Include in KPIsfor a custom producer (e.g. a wind turbine), it counts too: its production is added to the generation, and the part of it used on site counts as self-consumption.Only solar power in the battery: if the battery also charges cheap grid electricity with the control scheme
Tariff arbitrage, that energy doesn't count as self-consumption. Its charging and discharging losses aren't deducted from the rate either.All consumers: solar power used by the household,
Heating system,Wallbox / EV,Air conditioningor custom consumers counts as self-consumption.
What influences the self-consumption rate?
System size relative to consumption: the larger the system compared with consumption, the more is fed in and the lower the rate.
Battery: a battery stores solar power from the day and releases it in the evening and at night. The rate rises.
Additional consumers: a heat pump, wallbox or air conditioning use more solar power themselves.
Timing of consumption: consumption during the day (e.g.
Home Office) raises the rate, consumption mainly in the evening lowers it.Orientation: east-west systems produce more in the morning and evening and often reach a higher rate than purely south-facing systems.
Self-consumption rate and autarky level
The self-consumption rate refers to generation: how much of the solar power do you use yourself?
The autarky level refers to consumption: how much of your electricity demand does the solar system cover?
A very large system therefore often has a high autarky level but a low self-consumption rate.
Please get in touch if you have any requests or feedback.