How does this calculator work?

The model in brief, with the formulas: the calculation model. Choosing a comparison site: what to look for? Reading your annual statement: what is where?

Assumptions

• All 8,760 hours of a year are calculated with standard profiles. Generation per month comes from PVGIS for your location, orientation and tilt (without a postcode a Dutch average), with the weather per hour as the KNMI measured it in the year of the hourly prices: so generation falls on the hours when electricity was actually cheap or expensive then. Consumption follows a daily profile that depends on how many weekdays someone is at home during the day (0 to 5; the weekend counts as at home). The heat pump runs mainly in winter, air conditioning (cooling) in summer: mostly in the afternoon and on sunny days.
• The annual generation can be determined in two ways. From the panels: power × yield per kWp × what the panels still achieve at their age. The yield per kWp comes from PVGIS (European Commission) for your location, orientation and tilt: the average over almost twenty years of satellite measurements, including the usual losses from the inverter, cables, heat and dirt (14%), without shade. Measured yield: the annual generation of one calendar year, for example from your inverter app, converted to a normal year (the average of the last ten years) using the sunshine the KNMI measured that year at the three nearest weather stations, and to this year using the decline in yield of the panels (by default 0.5% per year). How much sun there is varies per year; that is why it also shows the range within which generation falls in 9 out of 10 years. Generation does not quite keep pace with the sun: 10% more sun gives about 8.5% more generation, because sunny years are warmer (warm panels deliver less) and the KNMI measures on a flat surface.
• Because the calculator works per hour, short peaks disappear, such as a kettle under a cloud. As a result it usually overestimates self-consumption by 2–5 percentage points. With a home battery this makes little difference: the battery absorbs the short peaks.
• Charging on solar surplus is more favourable in the calculator than in reality. The calculator only charges from 1.4 kW of surplus (like a charger on 1 phase; on 3 phases that is 4.1 kW), up to the charger power you enter, but on sunny days the car is not always at home, or is already full. Real self-consumption then usually lies between 'daytime' and 'on solar surplus'.
• How the car charges makes the biggest difference to the result. Choose the option that matches how the car really charges.
• The battery uses the usable share of its capacity that you enter (usually 90%). Some energy is lost when charging and discharging (by default 10%, adjustable), and the battery and inverter always use a little electricity (standby, by default 30 W); that standby consumption counts as household consumption. With ‘smart on hourly prices’ the battery plans the cheapest use for today and tomorrow every day, assuming a perfect forecast. In practice this yields a little less.
• Imbalance trading comes on top of smart control on hourly prices. The amount comes from a table that we calculated once using TenneT's imbalance prices of 2025, per quarter hour, for an example home. The battery only deviates from its plan if the imbalance price is far enough (usually more than € 0.40 per kWh) from the hourly price; below that, the profit is eaten up by energy tax and losses. We assume the trading party responds after about 5 minutes into the quarter hour. The lower bound only responds to the previous quarter hour, the upper bound knows the price in advance. Imbalance prices vary greatly from year to year: treat the amount as an indication.
• A dynamic contract costs the market price plus VAT per kWh, plus the supplier's purchase mark-up, plus energy tax. For feed-in you get the market price plus VAT, plus or minus the supplier's feed-in adjustment.
• Grid costs and the tax reduction per connection are part of your electricity bill, but they are the same for every contract and every choice. They therefore don't count in the differences or in ‘All contracts compared’.
• The result is an estimate, not a quote. After a year with panels, you can read the real figures from the inverter and the smart meter: self-consumption = (generation − feed-in) ÷ generation.

How to read the amounts?

All amounts are per year, including VAT, and cover electricity only(no gas). They apply to the calculation year (2027), without net metering, with this week's supplier rates. Only step 1 recalculates the past year (2025), with the real hourly prices and the rules of that year, so you can put it next to your annual statement. See the amounts as a good indication, not a quote. What says the most is the difference between two choices.

Your electricity bill in 2027

What you can expect to pay in total for electricity: the fixed supply costs, plus the electricity you take from the grid, minus what you get back for feed-in (or plus what you pay in feed-in costs). The grid costs are added, and the fixed tax reduction per home is deducted. You can compare this amount with the electricity part of your annual statement. The monthly amount is the annual amount divided by twelve. If you get back more than you pay, it says ‘back’: ‘you get € 128 back per year’.

The past year next to the calculation year

Step 2 shows your bill for 2025, as you confirmed it in step 1, next to the one for 2027. The Net metering line is what net metering took off your bill that year. The difference between the two years comes mainly from the end of net metering, and further from other prices and older panels.

A home battery saves

How much lower your electricity bill per year becomes with the battery, compared with the same home without a battery. With a fixed contract it is only about self-consumption: solar power you would otherwise feed back, you use yourself in the evening. With a dynamic contract, smart control and possibly imbalance trading are added, if you choose them. If you have not (yet) entered a battery, the calculator uses the size with the fastest payback (green in the table per battery size), and 10 kWh until that is known. If it shows a plus (+€ …), the battery earns nothing and you only pay for the losses and standby consumption.

Payback time

The purchase price divided by the saving per year. The price is a market range (from cheap to expensive), so the payback time is too; if you enter the price from your quote, it uses that price. Ranges exist for a home battery, a charging point and solar panels (€ 0.60–1.00 per watt-peak, fully installed, 0% VAT). For a fixed battery that is steered smartly with a dynamic contract, it uses the price excluding VAT (see the question about VAT below). Subsidies are not included. Interest, maintenance and replacing the inverter are not included. If the payback time is longer than the battery's lifetime, it does not pay for itself.

Solar panels save

How much lower your bill per year is thanks to the panels, compared with the same home without panels (calculated without a battery).

Charging on solar surplus saves

What you save per year at most by charging the car on solar surplus instead of in the evening (or during the day). It is an upper limit: the calculator charges from 1.4 kW of surplus (on 3 phases without phase switching 4.1 kW) up to the charger's power, but on sunny days the car is not always at home.

All contracts compared

Per contract the electricity costs per year: fixed costs plus consumption, minus feed-in. Grid costs and the tax reduction are not included here, because they are the same for every contract. These amounts are therefore lower than your electricity bill, but the differences between the contracts are correct. A minus for feed-in means you get money back, a plus that you pay.

Besides the dynamic contracts, it includes fixed contracts from suppliers, with their feed-in costs per kWh or in a tiered scale (an amount per month, depending on how much you feed back per year). There are not many yet; the list is being expanded. We compare the model contract with a one-year fixed rate: every supplier must publish it, so it can be compared fairly. That is why those contracts only show the supplier, with a V (fixed); the dynamic ones have a D. Welcome bonuses, cashback and other temporary promotions are not included by default: they differ by moment and by customer and usually only apply in the first year. If you want to include them anyway, enter the welcome bonus or gift of the new contract yourself (with the comparison or the option Other contract) and the termination fee of your current contract (with your contract). They count once in the bill for the year you switch, and only if the comparison's contract differs from your current one.

A model contract is a standard contract whose terms are set by the regulator ACM. Every supplier must offer two: one with variable rates for an indefinite period and one with a 1-year fixed rate. The terms are the same everywhere, so only the price differs. It is usually not a supplier's cheapest offer, but it is the most comparable one. More information at ACM ConsuWijzer (in Dutch).

Note: a regular offer with a welcome bonus is often better value than the model contract. In October 2026, the regular one-year fixed offer was nowhere more expensive at the suppliers in our list: 0 to 4 cents per kWh cheaper, often less than € 100 a year. The welcome bonus was usually larger: € 50 to € 160 for electricity only, € 150 to € 400 for electricity and gas. You usually receive the bonus only at the end of the contract, only in the first year, and it differs per comparison site. The feed-in costs of such an offer are often not listed; with solar panels they can make the difference smaller. To check an offer, enter its rates and the welcome bonus under Other contract.

Options and the difference

Each option in step 3 shows what it saves per year; step 4 shows the difference with the chosen options together, next to your situation without options. These differences are usually more reliable than the amounts themselves, because the same assumptions apply to both sides.

How accurate is a comparison?

The difference between two situations is more reliable than the amount itself. A deviation in what you enter or in the assumptions is in both situations and largely cancels out in the difference.

If the current situation in the calculator almost matches your real annual statement, you can use the comparisons well. Take the difference and add it to your real bill: that is the best estimate for that situation. A deviation in the calculator is then in both situations and largely cancels out.

Note: with net metering the bill depends mainly on consumption minus generation. A matching bill for the past year therefore shows that those totals were entered correctly, but not yet whether the calculator estimates well how much solar power you use yourself and how much you feed in. So also check consumption and feed-in separately, with your annual statement or smart meter. How reliable a comparison then is, is shown below per topic.

If you enter the amount of your annual statement in step 1, the calculator scales the electricity part (supply and feed-in) of the results to your real bill. Grid costs, the tax reduction and the differences between the options do not change.

The calculator uses a model of 25 parameters. Your consumption depends on six of them: annual consumption, days at home, shifting, weeks away, the daytime share and the night-time share. When calibrating, it adjusts three of them, the annual consumption, the daytime share and the night-time share, so that the simulation of various scenarios starts from your own situation.

With solar panels you can also, in step 2, calibrate to the kWh on your annual statement. The calculator then adjusts two things: household consumption, so the total matches, and how much of it falls in the sunny hours, so the feed-in matches. A different daily rhythm or a car that is away during the day is thus included automatically, for the past year, the calculation year and the comparisons. By default the calculator assumes 4 weeks away from home: 2 in summer (July and August), 1 in May and 1 in February (only standby consumption, and the car does not charge); annual consumption stays the same. That is how the Dutch go on holiday on average (CBS). If you go away at other times, enter 0 to 4 weeks per month next to the kWh of your statement.

Is something running day and night (ventilation, the underfloor heating pump, a boiling-water tap, a server)? Then enter the base loadin watts, below the electricity consumption. It runs around the clock, also on holiday; the calculator spreads the rest of the consumption with the standard pattern. This matters most for a home battery: a high night load can be covered by the battery from daytime sun.

If your statement also shows how many kWh you took from the grid at the off-peak rate (low rate), enter it. The off-peak rate applies on workdays from 23:00 to 7:00 and all weekend. The calculator then adjusts how much of your consumption falls at night. That way it sees whether you charge or run the dishwasher at night, even without solar panels.

If your contract started later in the year, your annual bill also starts later. In step 2, choose the month it starts: the calculator then compares the kWh and the amount from that month to the end of December, and also calibrates on that part. Fixed costs, grid charges and the tax reduction are prorated for that part.

How accurate is the result?

The calculator gives an estimate, not a quote. In short:

• Comparisons: the difference between two situations is more reliable than the amount itself.
• Fixed contract, with net metering (the past year): fairly accurate.
• Fixed contract, without net metering (the calculation year): good, if consumption from and feed-in to the grid match your annual statement.
• Dynamic contract: an indication. Which dynamic contract is cheapest is correct.
• Solar panels: accurate with the measured generation; the weather makes a difference of about 5 to 8% per year.
• Home battery: reasonable for self-consumption only; smart control and imbalance trading are an indication, rather too high.
• Charging on solar surplus and shifting consumption: rather too favourable.

Per topic:

Solar panels

• Measured generation (a full year, from your inverter's app) is the most accurate. The calculator converts it to an average year using the weather the KNMI measured that year.
• Estimated generation (number of panels × the PVGIS yield for your location) assumes panels without shade. If you have shade from trees, a chimney or a dormer, set the yield lower.
• The weather varies per year: in 9 out of 10 years, generation is usually about 5 to 8% higher or lower than in an average year. The range for your location is shown under Solar panels.
• Calculating per hour: short peaks disappear, such as a kettle under a cloud. As a result, without a home battery the calculator usually estimates self-consumption 2–5 percentage points too high, and your bill is more likely to come out a little higher than lower. With a battery this makes little difference: the battery absorbs the short peaks.

Your consumption

• The total per year is correct if you take it from your annual statement.
• When you use electricity, the calculator does not know exactly: it uses a standard pattern, adjusted to what you enter (at home during the day, shifting consumption). A heat pump runs mainly in winter, an air conditioner in summer. Whether that is right for you, you can see from consumption and feed-in.
• Shift consumption and at home during the day yield rather too much in the calculator: it knows in advance when it is favourable. By hand, or with a timer, you usually achieve a bit less.

Heat pump and air conditioning: estimate from your home

If you don't know the consumption, the calculator estimates it from your home. It is a starting value you can change, not a heat-loss calculation; an installer makes that to choose the right heat pump.

• Gas consumption: floor area times the gas per m² that matches the energy label: from 3 m³ (A++++) via 9 m³ (C) to 13 m³ (G), for heating, hot water and cooking. Without a label, by construction year: from 12 m³ (before 1945) to 3.5 m³ (2021 or later). That is actual consumption, lower than the label suggests for older homes (TU Delft), matched to the average household of just over 1,000 m³ (Milieu Centraal).
• Heat pump: from that gas to electricity as in 'Calculate from your gas consumption'. The capacity is the heat for space heating (without hot water) divided by 1,500 full-load hours; a hybrid can be smaller.
• Air conditioning: 50 W per m² you cool in a well-insulated home (label A+ or better, or from 2015), 70 W on average and 90 W for label D–G (or before 1992). Consumption: 400 hours at full capacity per summer, with an efficiency (SEER) of 5.5.

Electric car

• How the car charges makes the most difference to the result. If it charges at a fixed time(in the evening), the result is reliable.
• Charging on solar surplus is more favourable in the calculator than in reality: the calculator charges from 1.4 kW of surplus (like a charger on 1 phase; on 3 phases without phase switching 4.1 kW), but on sunny days the car is sometimes away or already full. What it yields is therefore an upper limit.
• Charging in the cheapest hours (smart charging on the hourly price, with a dynamic contract) picks the hours with the lowest price; they are known a day ahead. If the car is away during the day, only in the evening and at night; this also applies to weekends if you indicate that the car is away during the day then. The calculator charges in sessions of about 20 kWh (with few kilometres once every few days, at most a week), in the cheapest hours of those days together: a smart charger usually charges a lot in one go, mostly from the grid. A session does not cross a month boundary: each month the car charges in proportion to the days at home. With a fixed contract it charges at night.
• Charging controlled by the supplier (the supplier controls the charger or car, often for a payment) spreads each session evenly over the cheapest half of the hours the car is plugged in, with at most a third of the charging power. The car then charges steadily through the night, as we saw on the meter of a home with such a scheme. That is slightly more expensive than charging only in the cheapest hours; you enter the payment separately. Some suppliers also charge the kWh they control at a lower price than the hourly price. That does not appear as a separate amount on the invoice, only as a lower average rate. For a home we compared with its invoices, it saved about as much as the payment itself in 2025. The calculator does not include it, so controlled charging often works out slightly better in reality.
• Charging costs in an app (from the charge point, the car or the supplier) often show only the hourly price. On your bill, energy tax, the supplier’s purchase surcharge and VAT are added per kWh. The calculator includes everything, so charging looks cheaper in the app.
• What makes charging cheaper only counts if you fill it in: a charger with MID meter(ERE payment) and a payment for smart charging from your supplier.
• Not every supplier can smart-charge every charge point or car. The calculator does not take this into account yet: with ‘In the cheapest hours’ it assumes this works with every dynamic contract. Check with the supplier which charge points and cars it supports. We favour no supplier: every supplier is calculated with the same rules.

Home battery

A matching bill for the past year says almost nothing about the battery. With net metering, electricity you feed in is worth as much as electricity from the grid, so a battery yields nothing; because of losses and standby consumption it even costs a little. The savings without net metering depend on how much solar power you have left over during the day and how much you use in the evening and at night (you check that with consumption and feed-in), on the difference between the price of electricity and the feed-in compensation, and on the battery itself: you enter the losses (manufacturers often state 5–10%, in practice usually 10–15%) and the standby consumption yourself.

Do you already have a battery? Then look in the battery's app at how many kWh it discharged in a year, and compare that with ‘Via the battery (discharged)’ under ‘What happens to your solar power?’. If they roughly match, the savings are fairly correct too. Note: that block calculates with the battery for self-consumption only. If your battery also charges from the grid (smart control), it discharges more in reality.

Contract: fixed or dynamic

• With a fixed contract the calculator uses your own rates; those are certain. Comparing another fixed contract is therefore reliable: only the rates change. The price increase per year does not count here.
• With a dynamic contract the bill depends on when you use electricity, and the calculator does not know your consumption per hour. That is the biggest uncertainty here; how large in euros, we have not yet tested against real annual statements. The result is more accurate if your daily rhythm is regular and you fill it in well, and if large consumers run at a fixed time.
• Which dynamic contract is cheapest, is reliable: all suppliers use the same hourly prices and the same consumption; they differ only in mark-up, fixed costs and feed-in rules.
• The hourly prices are those of the past year (2025), adjusted by the price change per year (by default -1.7% per year: the expected wholesale price from PBL plus inflation according to CPB; without PBL inflation alone, without both 10%). A fixed rate does not change with it. The pattern (cheap afternoons, expensive evenings) doesn't change quickly, so the effect of shifting is fairly reliable. How high prices will be in the calculation year, and how big the gap between cheap and expensive hours becomes, is uncertain.
• Per quarter hour or per hour: the power market has a price per quarter hour. The calculator works per hour, using the average of the four quarter-hour prices; many suppliers bill the same way. If your supplier bills per quarter hour, it makes little difference to the bill; a battery or car that is controlled on quarter-hour prices can earn a little more than the calculator shows.
• Switching from fixed to dynamic is therefore an indication. If you already have a dynamic contract, step 1 is the best check: there the calculator uses the real hourly prices of the past year, so you can put the result next to your annual statement; only the markup and the energy tax are current.

Net metering and the calculation year

• With net metering (the past year) the result is fairly accurate: the bill then depends mainly on consumption minus generation, and you enter those yourself.
• Without net metering (the calculation year) the result is more sensitive: what matters is how much solar power you use yourself and how much you feed in. In a test with a real home over a full year, the calculator estimated 60.4% feed-in; in reality it was 61.1%. If your consumption and feed-in match, the comparison with and without net metering is reliable as well.
• The calculation year: only the age of the panels changes for certain; the prices are an assumption.

Gas and petrol: outside the electricity bill

A heat pump or an electric car raises the electricity bill, but you buy less gas or petrol. The calculator only includes that if you switch it on, with the heat pump or the car (in your situation or with the pencil on an option). It is then shown separately, under Outside the electricity bill: the electricity bill itself does not change.

• Gas: the kWh of the heat pump × the SCOP is the heat it delivers. The same heat from a condensing boiler costs 1 m³ of gas per 8.79 kWh × 90% efficiency. By default € 1.38 per m³, the average price of a fixed contract including energy tax and VAT (CBS).
• Cancelling the gas connection (all-electric, also a tick box): then the fixed supply costs and network charges for gas no longer apply, by default € 361 per year (CBS). Include cooking on induction in your electricity consumption.
• Petrol or diesel: the kWh you charge at home ÷ 0.17 kWh per km is the number of km; × the consumption of your current car (by default 6.5 litres of petrol or 5.5 litres of diesel per 100 km) and the average pump price of the last 30 days (CBS; petrol now € 2.44 per litre). Public charging does not count: those km are not on the electricity bill either.
• Price increase: as with electricity, per energy carrier: gas 2.7% and petrol or diesel 2.7% per year (first PBL, then inflation according to CPB, otherwise 10%).
• Energy costs only. We do not count maintenance, road tax, insurance or the depreciation of the car or the boiler. With the tick box it counts in a second payback period, next to the one on the electricity bill.

How to make the result more accurate

1. Enter your real electricity consumption and, with solar panels, the measured generation of a full year (from your inverter app) instead of an estimate.
2. In step 1, compare the result for the past year (with net metering) with the electricity part of your latest annual statement.
3. Also compare grid consumption and feed-in with your annual statement or smart meter. If they differ, adjust consumption, time at home during the day or when the car charges until they come close.
4. Still not right after that? Let us know with ‘Is this wrong?’ in the results. That helps us improve the calculator.

Saving without investments

Without net metering, solar power you feed back earns little. Electricity you use yourself while the sun is shining, or at an hour when electricity is cheap, is then worth the most. That is often possible without buying anything.

Frequently asked questions

How does energie27 make money?

At the moment, from nothing. No ads, and no payment from suppliers or installers, for a place or for customers. We only issue a licence for the dashboard for advisers to community organisations, such as a local energy advice desk. Companies that sell something themselves don’t get a new licence: that could cast doubt on our independence.

We earn nothing from you as a visitor. Links to suppliers and sources are ordinary links, without referral fees or affiliate codes. This is also how you can assess other comparison sites: what to look for in a comparison site?

Sources

Supplier rates and energy tax: energieprijzen-nl (CC BY 4.0), itself sourced from the websites of the suppliers and the Belastingdienst. The average fixed contract (if you do not enter your own rates): CBS (Statistics Netherlands) (average energy rates for consumers, also via energieprijzen-nl); CBS has no average for the feed-in compensation and feed-in charges, so for those we use the middle value of the fixed contracts in the comparison. Consumption of washing machine, dishwasher and tumble dryer: Milieu Centraal; share of hot water (a quarter): Milieu Centraal. Gas per m² by energy label (estimate from your home): Majcen, Itard and Visscher (TU Delft), matched to the average consumption (Milieu Centraal). Grid charges: the rate sheets of the grid operators; the grid operator for your postcode comes from their open small-consumer data (also via energieprijzen-nl) and is looked up in your browser. Market prices: EnergyZero (day-ahead market). Solar yield: PVGIS © European Union; sunshine per year: KNMI (daily data, global radiation, normal year 2016–2025); postcode: PDOK Locatieserver. Imbalance trading: calculated with the imbalance prices of TenneT (2025), processed into a table.

Outside the electricity bill: gas price, fixed supply costs and network charges for gas from CBS (Statistics Netherlands) (Average energy prices for consumers); pump prices of petrol and diesel from CBS (Statistics Netherlands) (Pump prices of motor fuels), both via energieprijzen-nl.

No guarantee

The results are estimates based on your input, public rates and market prices, without any guarantee of accuracy or completeness. They are not a quote and not personal advice. No rights can be derived from the results.

Are you going to buy something or switch? Then check the rates and conditions with the supplier and ask an installer for a quote.

Energie27 is free. We keep the calculation and the data as accurate as we can, but we are not liable for damage resulting from its use, except in the case of intent or gross negligence. If you spot an error, report it with ‘Is this wrong?’ in the calculator or via contact. What we did with reports is on the page feedback.

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