The Cost comparison shows what your energy costs today and what it will cost with the planned system. The difference is your savings.

In Current, the section is called Current costs and shows the costs without a new system, broken down by component.

How the costs are calculated

For each variant, autarc simulates a full year – hourly by default, or in 30-, 15- or 1-minute steps if you prefer. You set the resolution in Current under Simulation resolution (see System simulation overview).

In every time step, autarc determines how much energy each component needs and where it comes from (see Energy flows). This gives the costs per component:

Electricity from the grid: kWh drawn × the consumer's electricity price, plus the base price. This applies to all consumers, e.g. household, heat pump, wallbox (at the Price at home) and custom consumers.
Self-produced electricity from the PV system, custom producers or the battery has no running costs. The purchase of these systems is not part of the cost comparison but of the investment (see Profitability).
Fuel for heating: consumption of the old heating system (e.g. gas, oil, pellets) × fuel price. If it keeps running alongside a heat pump, it appears in the list as Backup heating.
Fuel for cars: mileage × consumption × fuel price for combustion cars, and for the fuel share of plug-in hybrids.
Charging away from home: kWh charged away from home × Price away from home.
Feed-in tariff: kWh fed in from the PV system and custom producers × feed-in tariff. It is deducted as a negative cost.

Costs = sum of the costs of all components − feed-in tariff  Savings = current costs (Current) − new costs (scenario)

Setting energy prices

Click a component in the component list to edit its energy prices. Every electricity consumer – household, heat pump, wallbox and custom consumers – offers three tariff types: Flat rate, Time-of-use and Flexible tariff. The heat pump, wallbox and custom consumers can also simply use the household tariff. Every tariff has a Base price (EUR/month). You also set:

Fossil heating: the current fuel price, e.g. Gas price (EUR/kWh).
Mobility: the fuel price, Price at home and Price away from home, set per vehicle in the wallbox planning.
Feed-in tariff: Feed-in tariff (EUR/kWh). With Time-of-use you can set a separate feed-in tariff for each Time-of-use windows entry.

Current costs in Current

In Current you see what the property costs today:

Key figure Current costs (EUR/month): the average costs per month in the selected period.
Chart: the costs per month, stacked by component.
List: the costs of each component in the selected period with the monthly average, e.g. Household 1,350 € (Ø 112.50 € monthly) for one year. Components without costs are not shown.

Current has no investment. Plannings you switch on in Current count as already existing, with an investment of 0 €.

Cost comparison in a scenario

In a scenario, autarc compares the new costs with Current:

Current costs (EUR/month): the costs in Current.
New costs (EUR/month): the costs with the planned system, with the savings per month below.
Total savings (EUR/year): the difference over one year or over all years of the analysis period.

The chart shows one bar for Current and one for the scenario for each month (or year). If you compare two scenarios via Compare with:, a third bar is added and the key figures show the difference in percent.

Below the chart, each bar has a list with the costs per component and the Total costs (EUR/year). This shows exactly where the savings come from.

1 year or analysis period

In Current and in every scenario, you switch between two views at the top right:

1 Year: the costs in the first year, month by month.
Analysis period (e.g. 20 Years): the costs year by year over the analysis period, including price increases. Electricity rises with the Yearly energy cost increase, heating fuel and car fuel with the Yearly fossil cost increase. Recurring costs such as maintenance or insurance appear here as a separate row.

You set the assumptions under Settings > Financial settings: Yearly energy cost increase, Yearly fossil cost increase and the analysis period. Current and each scenario have their own values, so you can play through, for example, a cautious and an optimistic price development.

For the savings, autarc always calculates Current and the scenario with the assumptions of the scenario, so that both sides are comparable.

Mobility: comparing combustion cars and EVs

You record the vehicles the household already has in the wallbox planning under Existing cars. They apply to every wallbox planning and every simulation of the project.

In Current: a combustion car appears with its fuel costs, an EV with its charging costs.
In a scenario: if a planned EV replaces an existing car (Replaces), that car's fuel costs drop out. Instead, charging at home is added, with solar power where possible, plus charging away from home.
Cars that are not replaced cost the same in Current and in the scenario.

Frequently asked questions

Why are the savings negative?

Usually a new consumer is added in the scenario that has no counterpart in Current, e.g. a heat pump without an old heating system, or an EV that doesn't replace a combustion car. The comparison then only shows the additional electricity costs. Model in Current what actually exists today. More in Profitability.

Is the investment included in the cost comparison?

No, the Cost comparison only shows running costs. How investment and savings compare is shown in Profitability and the internal rate of return.

Why are heating costs so high in winter?

Winter is when most heating happens. With a heat pump the increase is steeper, because it needs more electricity per kWh of heat when it's cold. A gas, oil or pellet heating system works at roughly the same efficiency all year and is therefore spread more evenly, with a base demand for hot water in summer.

Why is the scenario more expensive than Current in summer?

Check whether consumers are switched on in the scenario that are missing in Current, e.g. Air conditioning. A fair comparison needs the same consumers in Current and in the scenario.

Why aren't the savings over the analysis period simply the yearly savings times the number of years?

Because prices rise every year: each kWh saved is worth more in later years. On top of that come the Recurring costs, which only appear in this view. If they are higher in the scenario than in Current, they reduce the savings.

Cost comparison: How are costs and savings calculated?