The calculations are greatly simplified and do not consider additional heat losses. In most cases, more energy is needed and the cost considerably higher in real-life situations. It must also be kept in mind that home consumers also have to pay the transmission and renewable energy fees and the excise duty on electricity. VAT is also added to the price of electricity.

Q: I want to boil some pasta for dinner. How much will it set me back?

A: Dinner for two requires boiling roughly 1.5 liters of water. If we estimate the tap water temperature at 13 degrees, this alone requires 545.7 kilojoules of energy. At best, a 2,000 megawatt stove top can do it in 4.5 minutes using 0.15 kilowatt-hours of electrical energy. At the price point of €1,000/MWh, the cost comes to around 15 cents.

Because boiling pasta usually takes at least another seven minutes, whereas the stove top might be left at its highest setting, the cost could grow to 38 cents. The average price of electricity on Tuesday of €469/MWh would put the total cost at a more reasonable 18 cents.

Q: It has been a long time since I've visited my town apartment of approximately 30 square meters. I want to heat it using electricity and achieve a cozy temperature. How much would that cost me?

A: Provided the apartment has not been heated for some time, the temperature could have dropped as low as five degrees. Women prefer an average temperature of at least 23 degrees. A ceiling height of 2.5 meters would require approximately 97 kilograms of air to be heated. This requires 1,700 kilojoules of energy.

It would take approximately ten minutes using a 3,000 MW radiator. The cost at the peak price of €1,000/MWh is 50 cents, while it is 23 cents at the average price point. However, heating up the walls and furniture would require more energy, with the actual price of heating the apartment considerably higher.

This calculation also demonstrates why it is not sensible to keep such a radiator switched on all night. It would consume 24 kWh of energy over eight hours that would add €11 to the bill even at the €469/MWh average price point.

Q: I usually spend about five minutes in the shower and prefer warm water. What is the cost there?

A: Let us once again presume that the water temperature is 13 degrees when it reaches the boiler. A warm shower would require the temperature to exceed that of the human body, for example, at 38 degrees. Let us also presume the showerhead spews eight liters of water every minute for a total of 40 liters used.

In that case, it would take 4,181 kilojoules of energy to heat the water. This would take a 2,000 watt boiler approximately 35 minutes and require 1.2 kWh of electrical energy. The price would be €1.2 during the morning rush hour and 56 cents at the Tuesday average price point.

Q: I have an average-sized fridge. Should I unplug it this week?

A: It is difficult to evaluate energy consumption without knowing the exact model and its energy class. Typically, an E or F-class fridge would consume 200-250 kWh of energy per year, while A+ and better fridges use fewer than 100 kWh. The Tuesday average price (€469/MWh) would put the cost at 25-32 cents or under 13 cents depending on the type of fridge. Opening the fridge door often adds to the cost.

Q: I have an approximately 2 m³ bathroom, and I usually switch on the floor heating when using the sauna. How much is that?

A: Without knowing the material the floor is made of, let us take the average density (2,400 kg/m³) and thermal capacity (1,000 J · kg)-1 of concrete. Another great simplification is that we will be raising the temperature of the entire floor that is 7 centimetres thick by 10 degrees. This means raising the temperature of 336 kilograms of concrete. A lower thermal capacity means we need to use just 3,360 kilojoules of energy.

Presuming the floor heating system has a power of 125 watts per square meter, this would take approximately four hours. Without factoring in additional heat loss, this would require roughly 1 kWh of electrical energy – a cost of under 50 cents at Tuesday average price.

Q: I saw that the price is cheaper at night, while I want to get my washing done sooner. Does it make sense to wait?

A: When doing laundry, typically, over 90 percent of energy is spent on heating the water. Therefore, it is sensible to prefer a lower washing temperature. Using 10 liters of water heated to 30 degrees, a typical wash cycle uses 710 kilojoules of energy. The power of modern, energy efficiency washing machines is between 500 and 750 watts. Heating the water to the desired temperature takes 15-25 minutes.

That corresponds to 0.2-0.25 kWh of energy. Doing a load of laundry at 30 degrees would cost 20-25 cents at the Tuesday average price.

The amount of energy that needs to be expended rises to 1,965 kilojoules if the water temperature needs to be 60 degrees. This would cost over 80 cents during the peak price period (€1,000/MWh).

A kilowatt-hour of energy costs "just" €200/MWh around midnight, with a single load costing under €20 cents even at 60 degrees.

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