The Ecological impact shows how much CO₂ the planned system avoids compared with the current state. It lets you show your customers the environmental benefit of their new heat pump or solar system at a glance.
You find the values in every scenario of the simulation below the Cost comparison, and as a slide in the proposal presentation.
What is shown?
Avoided CO₂: the amount of CO₂ the planned system saves.Avoided car kilometers: how many kilometres an average car would have to drive to emit this amount of CO₂.Planted trees: how many oak trees it would take to absorb this amount of CO₂.
In the simulation you switch between 1 Year and 20 Years at the top right. CO₂ and car kilometres are scaled up accordingly. The number of trees stays the same, because the same trees keep absorbing CO₂ year after year.
Carbon footprint comparison
The Carbon footprint comparison shows the yearly CO₂ emissions in Current and in the scenario as bars. If you compare two scenarios via Compare with:, a third bar is added. The difference between Current and the scenario is the avoided CO₂.
How the values are calculated
The avoided CO₂ is made up of two parts:
Solar power: every kWh of solar power doesn't have to come from the grid. This saves the CO₂ that grid electricity causes in the project's country, e.g. 0.217 kg CO₂/kWh in the UK. autarc deducts 0.05 kg CO₂/kWh from this – the CO₂ per kWh caused by manufacturing, transporting and installing the PV system including the battery.
Old heating system: if the planned system replaces the old heating system, its emissions no longer occur: the average yearly consumption of the last 3 years × the emission factor of the old heating system.
Avoided CO₂ = PV yield × (grid CO₂ factor − 0.05) + consumption of old heating × emission factor Avoided car kilometres = avoided CO₂ / 0.246 kg CO₂ per km Planted trees = avoided CO₂ / 18.9 kg CO₂ per oak tree and year
For the Current bar, autarc multiplies grid consumption and solar power by the grid CO₂ factor and adds the emissions of the old heating system. The scenario bar is the Current value minus the avoided CO₂.
Emission factors of the old heating system
Heating system | kg CO₂/kWh |
Oil, condensing oil | 0.266 |
Gas, condensing gas | 0.201 |
LPG | 0.234 |
Pellets | 0.036 |
Wood | 0.027 |
District heating, other | 0.25 |
Electric heating, existing heat pump | grid CO₂ factor |
Grid CO₂ factor
Country | kg CO₂/kWh |
United Kingdom | 0.217 |
Germany | 0.332 |
Austria | 0.114 |
Switzerland | 0.033 |
Italy | 0.285 |
France | 0.042 |
Sources: grid electricity from Our World in Data / Ember (2025), each over the full life cycle. PV system from the German Environment Agency (Umweltbundesamt).
Where do I find the values in the project?
PV yield: from the linked PV planning (see How is the PV yield calculated?).
Old heating system: the
Heating systemand theØ Gas consumption last 3 years (kWh/year), or the value for your fuel. You can enter both in theHeatpump-Check, in theTechnical feasibilityor directly in the simulation by clicking theHeating systeminCurrent.
Frequently asked questions
Why is the avoided CO₂ 0?
Usually the scenario has no PV system switched on and doesn't replace the old heating system. Or the Heating system or the yearly consumption of the last 3 years is missing.
Why does the number of trees stay the same over 20 years?
An oak tree absorbs about 18.9 kg of CO₂ every year. To offset the CO₂ avoided each year, you therefore need the same trees every year, not new ones.