The adjustment almost nobody makes after going solar

What contracted power is and what happens when you exceed it

Contracted power is the maximum flow of electricity your home can draw from the grid at any one moment. It does not measure how much energy you use in a month, but how much you can ask for at the same time. If energy were water, contracted power would be the width of the pipe: you can use little water over a year and still need a wide pipe to fill the bath quickly.

When you ask for more than your limit, the power control switch cuts the supply: that classic moment when the lights go out because the oven was switched on with the hob already running. In ordinary domestic supplies the control works exactly like that, by cutting off: there is no maximum-demand meter recording the peak and billing it separately, as happens with larger supplies. Either you fit within your contracted power, or you are left in the dark until you reset the switch.

That power is paid for through the standing charge on your bill, every month, whether you use it or not. Which is why it deserves to be properly tuned, all the more so once the roof is doing part of the work.

Inherited power levels: the figure nobody has reviewed in years

Many homes in the area carry a contracted power that someone decided decades ago. It was set for a house with electric heating, and then gas arrived. A renovation was planned with every conceivable appliance in mind. Or the house was simply bought with the contract in place and nobody touched a thing. In villages like Moixent or Enguera it is common to find homes with power levels sized for a way of life that no longer exists.

The result is a standing charge higher than necessary, month after month, year after year. It is not a scandalous waste on any single bill, which is exactly why it goes unnoticed: it is a silent drip. Some signs that you may have more power than you need:

• Your supply has never cut out even with several large appliances running at once.
• Your contract dates from a time of electric heating or storage heaters that are no longer in the house.
• There are one or two of you and the power was contracted for a large family.
• You moved cooking or hot water to gas and the contracted power was never adjusted.

What changes when the roof starts producing

With panels, a good share of your daytime peaks no longer comes from the grid. The washing machine at midday, the dishwasher after lunch, the air conditioning on a July afternoon: while the sun is working, much of that demand comes off the roof. Around Xàtiva, a well-placed south-facing roof produces around 1,500 kWh per year for each kWp installed, and the usual range in the area sits between 1,350 and 1,500. An east-west layout yields somewhat less, around 0.82-0.85 of what a south-facing roof would give, but it spreads production more evenly across morning and afternoon.

This means the power you need from the grid during the day genuinely falls. The midday peak from the hob is no longer carried by the grid alone: it is carried by the grid and the roof together. That is why, after installing panels, many households discover their contracted power is oversized during daylight hours.

What does not change: at night the grid is still in charge

Here lies the most common mistake. Without a battery, once the sun goes down your home depends entirely on the grid again. And the night has peaks of its own: dinner with the oven on, the air conditioning running through an August night, the water heater warming up. Contracted power has to cover the worst moment of the day, not the best.

That is why adjusting your power after going solar is an exercise in caution: it can be fine-tuned, but by looking at the night, not at midday. Lowering your power based only on what the roof produces at two in the afternoon is the recipe for sitting in the dark at ten. With a battery things change, because it covers night-time peaks too, but that is a different conversation and a different calculation.

The peak exercise: hob, oven and air conditioning at once

Before changing anything, it is worth doing a simple exercise: imagine your home's worst quarter of an hour. Not the monthly consumption, but the moment when the most large appliances are on at the same time. It goes like this:

• List the appliances that demand the most: hob, oven, air conditioning, electric water heater, tumble dryer and car charger if you have one.
• Ask yourself which ones genuinely coincide: in many homes the oven and hob do, but the dryer can be moved to another time.
• Separate day from night: whatever coincides at midday will have help from the roof, whatever coincides at night will not.
• Watch your home for a few weeks: if the switch never trips and you never get close to the limit, there is room to spare.
• Leave a sensible cushion: the aim is to fine-tune, not to live on the edge of a cut-out.

How to request the change from your supplier

A power change is not requested from the distribution company directly: you ask your supplier, the company that bills you each month, and they process it with the local distribution company, which carries out the adjustment on the meter. The usual path is this:

One important detail: regulations limit how often you can modify your contracted power, so this is not an adjustment to keep trying blindly every few weeks. It pays to decide with data, once and properly. If the house changes later on, with an electric car or a new battery, you repeat the exercise and adjust again.

• Review several bills and find your current contracted power and the standing charge you pay for it.
• Decide on the new level with the peak exercise done, looking above all at the night.
• Contact your supplier and request the modification in writing.
• The supplier passes it to the distribution company, which carries out the change; depending on the case there may be a regulated fee.
• Keep the confirmation of the change together with your supply contract.

Contracted power as a saving lever alongside your panels

On a typical domestic bill, network charges and levies account for around 40% of the total. Part of that weight is tied to contracted power: the more power, the higher the standing charge, whatever your roof produces. Adjusting it is one of the few decisions that saves money without installing anything at all.

For context: the average residential installation in Spain is around 5.5 kW according to APPA's 2025 sector data, with a typical payback of 6 to 7 years before deductions. A well-sized power contract accompanies that journey and shortens it a little further. We see it as part of the same job: the panels cover the energy and the contract finishes off the bill. And because we monitor every installation daily, when the consumption pattern of a home in Xàtiva or Canals shifts over the years, it shows, and the contract can be adjusted again with the data in hand.

Inherited three-phase: your power split across three wires

Around the district there are plenty of country houses, ground floors and old workshops with a three-phase supply from another era: it was contracted for a well pump, an irrigation motor or a machine that may no longer exist. Three-phase splits your contracted power across three phases, and that changes the arithmetic completely, because you do not have one big tap but three medium ones.

Here is the detail almost nobody mentions: the meter balances energy across the phases, but power is watched phase by phase. If the air conditioning, the oven and the water heater happen to hang off the same phase, a peak on that one phase can cut your supply even though the total across all three is well within the limit. So on three-phase, how the loads are distributed in the panel matters as much as the figure in the contract, and installing solar is the right moment to review that distribution too.

And switching to single-phase? Sometimes it pays: it simplifies the contract, suits most domestic inverters better and removes the distribution problem. But if a three-phase motor is still in use (the well, to name the obvious one), the conversion stops being trivial. It is a decision to take calmly: an inventory of what is connected, what actually gets used, and only then the numbers.

Two power levels in one contract: peak and off-peak

The domestic 2.0TD tariff lets you contract two different power levels: one for peak and mid hours, and another for off-peak, the night hours and the weekend. Hardly any contract takes advantage of it: most carry the same figure in both slots because nobody has ever touched it.

With panels on the roof, this asymmetry starts to make sense. By day, production covers part of your peaks and the daytime power can be trimmed. At night the grid and your habits are in charge: if you charge an electric car in the small hours, you can raise only the off-peak power, whose network charge is far cheaper than the peak one. It is not a minor trick: regulated charges come to around 40% of a household bill, and the power part is paid every day of the year, whether you use it or not.

A typical profile in Xàtiva: a house with panels, daytime consumption partly covered by the roof, and a car charging while the family sleeps. That contract can take a trimmed peak power and a more generous off-peak one, so you pay for capacity where it is actually used. Each supplier handles the request its own way, but the right to two different power levels comes from the tariff, not from the company.

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