Dynamic energy contracts and a home battery
A dynamic contract lets you charge when power is cheap and use it when it is expensive. Whether that earns anything depends on your battery's round-trip efficiency: at 95% the price gap has to be at least 5.3% before you break even. We publish that figure for 235 models.
The efficiency figures on this page come from our own catalogue: 235 active models for which the manufacturer states a round-trip efficiency. They also appear on the product pages themselves, so you can check them per model. We sell home batteries and not energy contracts, so we name no suppliers and receive no payment from any of them.
Is a dynamic contract worth it with a home battery?
It depends on a number almost nobody quotes: your battery's round-trip efficiency. A battery does not return what you put in. To get 1 kWh out at 95% efficiency you have to put 1.053 kWh in. So the evening price has to beat the night price by 5.3% before you break even on the energy alone, and only above that do you earn anything. On a battery with 90% efficiency that threshold is 11.1%, and at 80% it rises to 25.0%. That threshold applies to the total price per kilowatt hour including energy tax, not to the wholesale component alone, because the tax is the same in every hour. Across the 235 models in our catalogue that state an efficiency, the median is 95%, ranging from 80% to 99%. The same dynamic contract is therefore profitable on one battery and not on another, and that difference sits on the datasheet rather than in the contract.
How does a dynamic contract work with storage?
On a dynamic contract you pay the hourly wholesale price for each hour, plus taxes and your supplier's margin. Those hourly prices vary a lot: at night and in the middle of the day, when there is plenty of sun and wind, the price is low, and around the evening peak it is high. Without a battery you barely benefit, because you consume when you are at home. With a battery you can decouple the two: charge in a cheap hour, discharge in an expensive one.
That requires an energy management system that knows the hourly prices in advance and decides for itself when to charge. So this is not every battery: a model that only buffers your own solar output does not look at prices and cannot take part. The product page states per model whether an EMS is included and which one. Where the link to your inverter goes wrong is covered in which inverter works with which home battery.
The number that decides the calculation
Round-trip efficiency is the share of the energy you get back out. The rest is lost as heat in the cells, in the battery management system and in converting direct current to alternating current. The table below is pure arithmetic: at an efficiency of e percent, the high price has to beat the low price by 100/e minus 1 to break even.
| Round-trip efficiency | Needed to deliver 1 kWh | Price gap to break even |
|---|---|---|
| 99% | 1.010 kWh | 1.0% |
| 96% | 1.042 kWh | 4.2% |
| 95% | 1.053 kWh | 5.3% |
| 90% | 1.111 kWh | 11.1% |
| 85% | 1.176 kWh | 17.6% |
| 80% | 1.250 kWh | 25.0% |
The gap between 99% and 80% sounds like a detail of a few percentage points, but in the threshold you have to clear it is a multiple: 25.0% against 1.0%. In the narrow price gaps of a quiet week, that is exactly the difference between trading and not.
| Brand | Models stating an efficiency | Median efficiency |
|---|---|---|
| BYD | 54 | 95% |
| Felicity Solar | 24 | 95% |
| Dyness | 23 | 95% |
| Pylontech | 19 | 95% |
| Deye | 19 | 90% |
| SolarEdge | 15 | 94.5% |
| FOX ESS | 11 | 95% |
| Regitec | 10 | 90% |
An important caveat on these figures: these are manufacturer statements and they almost always apply to the battery itself, not to the whole system. The inverter has its own losses on top. So the efficiency you actually achieve at home is lower than what is shown here. We reproduce the figure as the manufacturer states it and say what it excludes, rather than turning it into a system efficiency we have not measured.
What comes off the return
The price gap is the ceiling on what you can earn, not the earnings. At least four things come off it, and naming them is more honest than presenting a payback time that leaves them out.
- Round-trip efficiency, as above: at 95% you keep 0.95 of every kWh you buy.
- Inverter losses, which the manufacturer's figure does not yet include.
- Wear. Trading on price gaps means more full cycles a year than simply buffering solar output. Most batteries in our catalogue are rated for 6,000 cycles or more, but the warranty term in years runs regardless and is often the binding limit rather than the cycle count.
- Taxes and margins. You also pay energy tax and your supplier's margin on every kWh you buy. The relevant gap is therefore the gap in your final hourly price, not in the raw wholesale price, and that gap is smaller.
We deliberately put no example figure here. We do not maintain verified Dutch tariff data, and a worked example built on an invented price gap is precisely what this page sets out to avoid. What the hardware costs, and how we do calculate with that, is in what does a home battery cost.
A dynamic contract is also a tax condition
This is why the dynamic-contract question and the VAT-recovery question belong together, and almost no page makes the connection. Among its conditions for reclaiming VAT on a home battery, the Dutch tax authority requires that you hold "a dynamic energy contract so you can trade electricity" and that the battery "has an Energy Management System (EMS) so it can trade electricity".
Without a dynamic contract you therefore do not meet the conditions and there is nothing to reclaim. But note the other side: if you do meet them and reclaim the VAT, you become a VAT entrepreneur for that battery and then pay VAT on your supplier's payments and on your private use, with the bookkeeping that comes with it. All seven conditions are set out verbatim in subsidy and VAT on a home battery.
What changes on 1 January 2027
Dutch net metering ends on 1 January 2027. Until then you may offset exported power against imported power, which makes a kilowatt hour you export worth as much as one you import. While that holds, storing your own solar output earns almost nothing: you are saving something that already counts at full value.
From 1 January 2027 that stops. From then on, every kilowatt hour you use yourself instead of exporting is worth the gap between your import price and your feed-in payment. That is why demand for home batteries rises towards that date, and it is also why a dynamic contract only really matters from then: you will have two sources of spread to steer on, your own generation and the hourly price. What that means for your consumption is in which home battery do I need.
Does it work with a plug-and-play battery?
Partly. A plug-and-play home battery has the inverter built in and its own app that can respond to hourly prices, so in principle it is suitable for price trading and needs no installer. The limit is power: a wall socket holds discharge power to around 800 watts. That is enough to carry your base load through the evening peak, but not a dishwasher, tumble dryer or heat pump. How much you can shift per evening is therefore capped by power rather than capacity, which flattens the daily return.
What to look at if you want to trade on price
- Round-trip efficiency. Compare the stated percentage across models and work with the threshold from the table above, not with the percentage itself.
- An EMS that knows hourly prices. Without price control you are only buffering your own generation and the contract does nothing for you.
- Charge and discharge power in kW. This sets how much you can shift within the few expensive hours. A large battery with little power cannot exploit a short peak.
- Cycle warranty and warranty term in years. Trading costs cycles; check which of the two expires first.
- A released combination with your inverter. See the compatibility guide: an unreleased combination costs you the warranty regardless of how good the arithmetic is.
If you are steering mainly on point 1, these are the highest efficiencies among the models up to 30 kWh that carry a price on the product page, one model per brand. Where the efficiency ties, the cheapest per kilowatt hour comes first. The 99% at the top of the range above sits on a model outside those bounds.
See all home batteries, with capacity, power and the stated efficiency on each product page.
Frequently asked questions
Do I need a dynamic contract for a home battery?
No, a battery also works on a fixed contract, buffering your own solar output. A dynamic contract adds a second way to earn, namely the gap between cheap and expensive hours. For VAT recovery, however, a dynamic contract is a hard requirement from the tax authority.
How big does the price gap need to be before storage earns anything?
At the median 95% efficiency in our catalogue, the high price has to be 5.3% above the low price to break even on the energy. At 90% that is 11.1% and at 80% it is 25.0%. Inverter losses, wear and taxes come on top.
What is round-trip efficiency?
The share of the energy you get back out of the battery after charging it. At 95% you get 0.95 back out of every 1 kWh you put in. The rest is lost as heat and in conversion.
Does the stated efficiency cover the whole system?
Usually not. Manufacturers state the efficiency of the battery, excluding the inverter. The system efficiency you achieve at home is therefore lower than the datasheet figure.
Does trading on prices wear my battery out faster?
Yes, because you complete more full cycles a year than when you only buffer solar output. Most models in our catalogue are rated for 6,000 cycles or more, but the warranty in years runs regardless and is often the binding limit.
Can I trade hourly prices with a plug-and-play battery?
In principle yes, but discharge power stays around 800 watts because the unit plugs into an ordinary socket. You shift your base load with it, not heavy appliances.