Spain · potencia contratada
How much contracted power do you actually need?
Potencia is a fixed part of the bill. Reducing genuine excess can save money, but reducing it by guesswork can create avoidable interruptions and later reconnection costs.
Contracted power is not annual energy use. Energy measures how many kilowatt-hours the home consumes over time; power measures how much electrical load can be used at once. A low-consumption home can still need high power for short periods.
1. Find the current contracted levels
Copy the kW shown for every power period on the bill. Domestic access arrangements can permit different contracted values for peak and off-peak power periods. Record the annual cost attached to each, not just the kW figure.
Then find recorded maximum demand. The bill, the CNMC “Entiende tu factura” view or the distributor’s customer portal may show maximum demand and interval consumption. Use a long enough history to include the household’s demanding seasons.
2. Build a simultaneous-load picture
List appliances likely to run together: induction hob, oven, electric water heater, air conditioning, pool pump, heat pump, tumble dryer, vehicle charger and battery inverter. Their nameplate ratings are not always their continuous draw, but the exercise identifies combinations that create peaks.
Do not add every appliance in the house. Ask what realistically overlaps. A timer can prevent the water heater and EV charger from running during dinner. Smart chargers, home-energy systems and battery schedules can reduce simultaneous demand without changing comfort.
Illustrative overlap — not a recommendation
Why timing matters more than the appliance list
- Cooking load
- 2.4 kW at that moment
- Water heating
- 1.5 kW
- Background load
- 0.5 kW
- Combined example
- 4.4 kW
Scheduling the water heater outside the cooking period changes the peak without changing the day’s energy consumption.
3. Use measured peaks, not one average
Monthly kWh divided by hours gives an average that hides short peaks. Contracted power decisions need interval data or maximum-demand history. Review at least a representative year where possible, including the hottest or coldest period and unusual occupancy.
A single exceptional spike deserves investigation. It may be a real simultaneous load, an event that will recur, or a configuration that can be managed. The aim is not to set power exactly equal to the highest observed number; it is to understand what caused that number and retain a sensible operating margin.
4. Account for solar, batteries and EVs correctly
Solar can reduce grid demand during daylight, but evening peaks can remain unchanged. Cloud movement can also reduce generation while loads continue. A battery may support household demand, yet its discharge power, reserve setting, state of charge and backup configuration limit what it can cover.
EV charging is often the largest flexible load. Reducing charge current or scheduling it for a low-demand period can be more effective than paying for high power all day. If future electrification is planned, compare the saving from lower power now with the likely cost and process of increasing it later.
5. Test the saving before requesting a change
Calculate the annual power cost at the current and proposed levels using the contract’s power prices and applicable regulated treatment. Include any one-off cost associated with the modification. A tiny annual saving may not justify operating close to the limit.
| Evidence | What it answers |
|---|---|
| 12 months of maximum demand | Has the current level been approached? |
| Interval consumption | When do the peaks occur? |
| Appliance schedule | Can loads be separated? |
| Future equipment plan | Will demand soon increase? |
| Annual cost difference | Is the saving material? |
6. Request the change through the supplier
The supplier normally manages a requested power change with the distributor. Have the bill, CUPS, holder details and requested values ready. Ask for the total one-off cost, the expected effective date and written confirmation of the new levels.
CNMC consumer guidance notes that changing contracted power can involve cost, particularly when increasing it, and that distributor data can help the consumer assess maximum demand. Rules and permitted frequency can change, so confirm the current conditions before submitting the request.
7. Check the first complete bill afterward
Confirm that the new power values and prices are correct and that the effective date is reflected. Monitor interruptions and maximum demand. If normal living now requires frequent manual load management, the reduction may have been too aggressive.
Official sources
- CNMC — electricity supply, bill information and power-saving guidance
- CNMC — “Entiende tu factura” and demanded power
- CNMC — modifying supply-contract conditions
Reviewed 28 August 2026. Confirm current charges and procedures with the supplier before changing power.