Data center · Battery storage
Battery storage in the data center
A data center draws almost the same power day and night. So why a battery? Because German grid charges are not billed on kilowatt hours alone but also on the highest quarter hour of the year. Because rooftop solar arrives at noon. And because a battery can take over part of the supply during a grid outage. This page explains what storage does in a data center, what it does not, and how to size it.
Four jobs for a battery
Shave peaks
When a training run starts or cooling ramps up, the load rises. The battery supplies the peak and the grid sees a flatter curve. That lowers the annual peak demand on which the demand charge is based.
Buffer solar power
When the PV system produces more than the data center needs at that moment, the battery charges and releases the energy in the evening. With a round-the-clock load this is often only needed on sunny middays.
Relieve the grid connection
If the IT load grows faster than the connection, the battery can cover short peaks above the agreed capacity. It does not replace more capacity on a permanent basis.
Support backup power
With a backup function the battery supplies cooling and building services after a switchover pause. The UPS stays in front of the servers, see UPS and backup power.
Battery storage and UPS: two different devices
Both contain batteries, but they solve different problems. The UPS sits directly in front of the IT and takes over without interruption during an outage, for minutes. A commercial battery sits at the grid connection, works on the grid in normal operation and, according to manufacturer data, needs about 5 to 20 seconds to switch to island mode. Servers without a UPS would be down by then.
In a data center the two complement each other: the UPS protects the servers, the battery works on grid charges and solar every day and can carry cooling and building services for a limited time during an outage.
| Feature | UPS | Battery at the grid connection |
|---|---|---|
| Location | directly in front of the IT | at the grid connection or main distribution |
| Grid outage | takes over without interruption (online UPS) | with backup function after approx. 5–20 s |
| Normal operation | waits for the outage | shaves peaks, buffers solar power |
| Duration | minutes until the generator takes over | depends on capacity and load, often hours |
Note: the switchover time is a manufacturer figure (INTILION planning guide), not a value from a standard. Some storage systems are designed for UPS operation; their data sheet then applies.
Grid charges: the highest quarter hour counts
Under § 17(2) StromNEV, the German grid charge consists of an annual demand price in euros per kilowatt and an energy price in cents per kilowatt hour. The demand charge is the product of the annual demand price and the annual peak demand. A single high quarter hour therefore sets the demand component for the whole year. A data center uses more than 100,000 kWh a year and is therefore metered in quarter hours under § 55 MsbG; every peak shows up.
AI clusters in particular change their power draw quickly, for example when a training run starts or cooling adjusts. A battery that covers exactly these quarter hours lowers the billed annual peak. How to calculate the limit and the energy needed is explained on the peak shaving page.
Limit: customers drawing up to 100,000 kWh a year from the low-voltage grid pay only an energy price under § 17(6) StromNEV. There, peak shaving does nothing for grid charges. A data center is almost always above that.
Baseload: hours of use under § 19 StromNEV
For customers with a very steady load, § 19(2) StromNEV provides for an individual grid charge. The condition is that a connection point reaches at least 7,000 hours of use per year and consumes more than 10 GWh per calendar year. The charge may then not be lower than 20, 15 or 10 percent of the published charge, staggered at 7,000, 7,500 and 8,000 hours of use.
Under § 2 no. 3 StromNEV, hours of use are the energy drawn in a year divided by that year’s highest load. A data center with a steady load comes close to these values. Every peak lowers the hours of use. If a battery shaves the peaks, they rise. A worked example with assumed values:
- 11.4 GWh
- annual consumption at an average load of 1,300 kW around the clock (assumption)
- ≈ 7,120 h
- hours of use at an annual peak of 1,600 kW: 11,388 MWh ÷ 1.6 MW
- ≈ 7,850 h
- hours of use if the battery limits the peak to 1,450 kW: 11,388 MWh ÷ 1.45 MW
Note: the example is hypothetical, not a reference project. Whether an individual grid charge applies, and at what level, we check with the load profile and the grid operator case by case. According to the Federal Network Agency, StromNEV expires on 31 December 2028; under the draft successor rules (AgNes), the baseload rule is to continue for existing customers until 31 December 2031. This is planned, not adopted.
Atypical grid use: moving load out of the peak window
Under § 19(2) sentence 1 StromNEV, the grid operator must offer an individual grid charge of at least 20 percent of the published charge if a customer’s contribution to peak load deviates predictably and significantly from the simultaneous annual peak of the grid. In practice, grid operators publish peak-load time windows for this.
A data center with a steady load is usually just as high in these windows as at any other time. A battery can take over the load during the peak windows and recharge outside them. Whether that works with the battery size and the length of the windows only becomes clear when calculated with the load profile.
Note: under the Federal Network Agency’s concept for the period from 2029, atypical grid use is not to be extended in general. Anyone planning today should not count on it beyond 2028.
Solar power with a round-the-clock load
According to the European Commission’s PVGIS simulation, a PV system in Berlin produces about 954 kWh per kilowatt per year when mounted flat facing south and about 1,061 kWh at the optimal tilt. In a data center that needs power around the clock, much of it is used immediately. Storage pays off for solar mainly when PV output exceeds the load at midday, for example with large roof or ground areas next to a small server room.
For electricity tax, PV power from systems up to 2 MW that is consumed on site within the spatial context is exempt under § 9(1) no. 3 StromStG; under § 12b(3) StromStV the spatial context extends to 4.5 km. Under § 12b(1) StromStV, storage does not count as a system for this purpose. Data centers are usually not classed as manufacturing industry and therefore pay the full electricity tax on grid power; we check this case by case.
More on PV on the company site: Commercial and industrial PV. Storage combined with PV: Storage and PV.
Energy Efficiency Act: power from renewable sources
Under the German Energy Efficiency Act (EnEfG), a data center has a non-redundant rated connection capacity of 300 kW or more (§ 3 no. 24 EnEfG). Under § 11(5) EnEfG its consumption must be covered on balance by renewable energy at 50 percent from 1 January 2024 and 100 percent from 1 January 2027.
A battery does not make power green. It helps to use more solar power from the own site instead of feeding it into the grid. The rest is usually covered by a green power supply contract. Under the government draft amending the act, the 100 percent obligation would only apply from 2030; this has not been adopted.
What matters when sizing
- Load profile – the basis is a full year of quarter-hour values from interval metering. Only these show how high, how long and how often the peaks are.
- Power and capacity – two separate figures. Power determines how much peak the battery covers, capacity how long. Commercial batteries are usually designed for 0.5 C, delivering their full capacity in about two hours; one example is the Huawei LUNA2000-215 with 215 kWh and a maximum of 0.5 CP according to its data sheet.
- Reserve for outages – if the battery is also meant to provide backup, part of the capacity stays free and is not available for peaks and solar in normal operation.
- Charging strategy – recharging must not create a new peak. The battery charges from solar or in quarter hours well below the limit.
- Cycles and ageing – manufacturer figures only apply under their conditions. One example: Deye states at least 6,000 cycles for a commercial battery at 25 °C, 0.5 C and 70 % remaining capacity.
- Registration – the battery is registered with the grid operator, under VDE-AR-N 4110 at medium voltage and VDE-AR-N 4105 at low voltage.
Metering concept with PV and EEG payments
If the PV system feeds surplus power into the grid with an EEG feed-in tariff or market premium and power from the battery is also to be paid for, a suitable metering concept is needed. Under § 19(3a) EEG the entitlement for stored power remains if the battery uses exclusively renewable power during the calendar year. The battery must then not charge from the grid.
If it is also to charge from the grid, for example for peak shaving, mixed operation under the delimitation option is required. Since 21 October 2026 it has been applicable through the Federal Network Agency’s MiSpeL determination, only under direct marketing with a separate balancing group and quarter-hour metering, and until 30 September 2027 only with the consent of the grid operator and the metering point operator; there is no right to that consent. We decide which option fits with the metering concept before the battery is ordered.
How we proceed
01
Analyse the load profile
Quarter-hour values for a year, peaks by height, duration and cause: IT, cooling, building services.
02
Set the goal
Demand charge, hours of use, solar, backup or a combination. Power, capacity and reserve follow from that.
03
Calculate the individual case
Economics only with your load profile, your grid charges and your supply contract. We do not quote flat payback periods.
04
Metering concept and registration
Coordination with the grid operator and metering point operator, registration of the battery, and an application for an individual grid charge where relevant.
05
Build and operate
Installation, commissioning, control and monitoring in ongoing operation.
Frequently asked questions about battery storage in data centers
Is battery storage worthwhile for a data center?
Only a calculation for the individual case can show that. What matters are the peaks in the quarter-hour load profile, the grid operator’s demand price, whether an individual grid charge under § 19 StromNEV is within reach, the size of the PV system and whether the battery should also provide backup.
Can battery storage replace the UPS in a data center?
A typical commercial battery cannot. According to manufacturer data it needs about 5 to 20 seconds to switch to island mode, while servers need supply without interruption. The UPS therefore stays in front of the IT; the battery complements it.
Why peak shaving if a data center draws a steady load?
Even a steady load has peaks, for example when training runs start, at full cooling on hot days or during tests. The demand charge is based on the highest quarter hour of the year, so a single peak can set the demand component for the whole year.
What does a battery do for the baseload rule under § 19 StromNEV?
The baseload rule requires at least 7,000 hours of use and more than 10 GWh per year. Hours of use are annual energy divided by annual peak load. If the battery shaves the peak, the hours of use rise. Whether that reaches a threshold in the individual case is shown by the calculation with the load profile.
How large does a battery in a data center need to be?
That depends on the job. For peak shaving, the height and duration of the peaks count; for solar, the midday surplus; for backup, load times bridging time. Power and capacity are sized separately; commercial batteries are usually two-hour systems.
Does a battery help with the Energy Efficiency Act obligations?
Indirectly. Data centers of 300 kW and more must cover their consumption on balance with 100 percent renewable energy from 2027 under § 11(5) EnEfG. A battery does not generate green power, but it helps to use more solar power from the own site.
May the battery charge from the grid?
Technically yes. But if power from the battery is fed in with an EEG tariff or market premium, under the exclusivity option of § 19(3a) EEG it may only charge renewable power. Mixed operation falls under the delimitation option: only under direct marketing, with a separate balancing group and, until 30 September 2027, only with the consent of the grid and metering point operators.
Can a battery avoid the need for a larger grid connection?
It can cover short peaks above the agreed capacity. If the data center needs more power permanently, it does not replace the larger connection, because it has to recharge the energy it delivers from the grid or the PV system.
Read more
Data center on your own site: On-prem AI data center. Protection against outages: UPS and backup power. Calculating peaks: Peak shaving. Commercial storage in general: Commercial battery storage. Larger connections: AI data center power.
Considering a battery for your data center? Let’s talk for 15 minutes about your load profile.