How big a battery do you need for an event without diesel?

For most events the battery does not have to carry the whole day. It carries the peaks and the quiet hours, while a small grid connection or a generator at a good load delivers the average. Built that way, a one-day event with a 51 kW peak needs about 30 to 40 kWh of battery, not 310. The battery itself is built like a fixed business battery: cells with a battery management system, an inverter and a controller. The sizing logic is the same as for a site battery on a building site, where a crane plays the part of the stage.

You organise a festival, a market, a company day or a club weekend on a field or a square. The only power is a generator the rental company sized "to be safe". It runs from the first sound check to the last fridge at night, mostly for a few coolers and some lights. The neighbours hear it, the catering smells it, and somebody has to refuel it on Saturday evening.

What you do not see is how badly that generator works. A generator sized for the headline act spends most of the day at a fraction of its power, and that is exactly where it burns the most diesel per kWh. A battery does not fix that by being big. It fixes it by being sized on the right two numbers.

Running a business site without the grid is what we do on permanent sites. In Zele, Special Renting Van Zele, a rental company for electric lifting gear, runs its warehouse, offices and machines without a grid connection. It uses 30 kWp of solar panels, a battery, and a generator for about 5% of the yearly need. An event is shorter, but the question is the same: what must the battery deliver, and what charges it?

Why does a festival generator burn so much diesel for so little power?

Because it is sized on the peak and runs on the average. A generator works best between about 40 and 80% of its power. When the load drops to about 30%, the diesel burnt per kWh starts to rise. Below 10%, it can waste 60% or more of its diesel per kWh.

Those figures come from the energy monitoring at Glastonbury Festival. The same study found that a large share of the generators were significantly oversized. The reason is simple: the need is calculated from peak values, not from what really runs. Add a margin "to be safe", and the generator idles through the morning, the changeovers and the night.

The volumes are large. UK festivals alone use more than 12 million litres of diesel a year, according to research by A Greener Future and Powerful Thinking quoted by the BBC. In Belgium, the innovation cluster Flux50 ran four sessions in 2025 with ten companies to help event organisers bring storage into their power supply.

The hidden costs pile up: fuel and refuelling, a generator that runs all night for the coolers, noise near the stage and the neighbours, and exhaust near the food. And a bigger generator "to be safe" makes the problem worse, because it runs at an even lower share of its power.

How big must a battery be for a festival or event?

Big enough for two numbers: the highest power at one moment (kW) and the total energy over the event (kWh). The first sets the inverter, the second sets the battery. Then add a reserve of 20 to 30% on the energy, and check how the battery recharges.

A large battery with a small inverter cannot start the fryers. A small battery with a large inverter runs empty before the headliner. Both numbers matter.

For scale: a coffee van with two espresso machines, grinders, fridges and lights used 14.6 kWh over a nine-hour shift, according to the UK supplier NXTGEN. A full stage is another order of magnitude. That is why measured values from an earlier edition are worth more than any rule of thumb.

Worked example: which battery does a one-day event need?

In this example a one-day event uses about 248 kWh with a peak of 51 kW. On a battery alone that means about 310 kWh of usable capacity. With a small connection or generator doing the average, 30 to 40 kWh is enough. The figures are illustrative.

The event runs from 10:00 to midnight: a bar, lighting, toilets and backstage all day, four food trucks at lunch and dinner, and a stage in the evening.

Three ways to power the same day:

• Battery only, charged before the event. 248 kWh plus a 25% reserve is about 310 kWh usable, with an inverter of at least 60 kW for the 51 kW peak and motor starts. That is a large unit to transport, place and recharge.
• Generator of about 30 kVA with a battery. The generator runs from noon to midnight near its best load and charges the battery when the site is quiet. The battery runs the morning alone (about 12 kWh) and adds up to about 27 kW when the stage and the fryers peak together. About 40 kWh usable and an inverter of about 30 kW is enough.
• Temporary connection of 25 kVA with a battery. The connection covers the average all day, the battery only the peaks above it. About 30 kWh usable and an inverter of about 30 kW.

Compare that with a single 60 kVA generator for the whole day. In the morning it would run at about an eighth of its power, right in the zone where it burns the most diesel per kWh. The battery lets the generator shrink to the average, or disappear behind a small connection.

Battery only, battery with a generator, or battery on a temporary connection?

Choose by what is available on site and how long the event lasts. A battery alone suits short, quiet events. A hybrid of generator and battery suits remote sites over several days. A small connection with a battery suits sites near the grid.

In a hybrid set-up the controller starts the generator when the battery runs low or the load rises, and stops it again when the battery is full. How that works is explained in our article on a generator with a battery. The diagram below shows the idea.

Large festivals already work this way. At Danish festivals, Greener used batteries to boost existing grid connections: NorthSide ran on 2 x 422 kWh next to connections of 230 A and 280 A, and saved 2,400 litres of diesel and 145 generator hours, according to Greener. At Lollapalooza in Chicago the 2024 main stage ran on a hybrid battery system, with a 67% cut in fuel use reported by Billboard. In Belgium, Sfinks Mixed runs two of its stages on solar power with large batteries, in a pilot with Bolt, according to the festival.

Can you get a temporary grid connection for an event in Belgium?

Yes, in all three regions, and it is often the cheapest way to cut diesel. In Flanders, a temporary connection for a building site or an event below 25 kVA follows the quick procedure of the technical regulation (TRDE). In Wallonia, ORES offers event connections with one or more sockets up to 125 A.

In Flanders the maximum terms for a temporary connection below 25 kVA add up to about five weeks, as long as you answer at once. From 25 kVA the grid operator first makes a study. On 3 x 400 V, 25 kVA is about 36 A per phase. That is rarely enough for a whole festival, but often enough for the average of a small event, with a battery for the peaks. Our article on what to do when a site connection comes too late explains the terms, the study line and what to prepare.

In Wallonia, ORES has a simple formula for fairs, community festivals, annual club events and other cultural, musical or sports events: one or more sockets up to 125 A, and the price is shown when you book online. You apply, pay the offer, do any preparatory works, and ORES connects. If ORES can deliver 125 A where your event takes place, you may not need a battery at all.

Which rules apply to generators and batteries at events in Belgium?

The Belgian electrical code (AREI) applies to every temporary installation, and in Flanders a generator at an event counts for its full power under the environmental rules. Local rules on noise and opening hours come on top.

Inspection (AREI). A temporary installation built from separate parts (generators, distribution boards, cables) is inspected before each use. For non-household installations the AREI allows an exception for use of at most 48 hours, under the full responsibility of the operator and with all measures taken to avoid danger. A set with a fixed composition, such as a generator on a trailer or a battery unit that stays one whole, is inspected before its first use. Mobile and temporary installations also get an inspection visit every year.

Environment (VLAREM, Flanders). According to the Departement Omgeving, generators at temporary events are not stationary motors. They fall only under heading 12.1 (electricity production), and their full power counts, because an event generator is not an emergency generator. Ask your municipality what that means for your event.

Noise and nuisance. For activities that are not classified under VLAREM, local rules can apply, such as a municipal or police regulation. A battery that runs the quiet hours takes the generator out of the night.

Safety of the battery. A battery near the public needs a sound enclosure, a battery management system and a place agreed with the organiser and, where needed, the fire service. What to check is in our article on business battery safety.

Rent a battery for one event, or invest for a site that hosts events every year?

For a single event, renting is usually the sensible choice. For a ground, venue or farm that hosts events every year, a battery system of your own pays off. It works for the events and for the rest of the year too.

A one-off festival uses a battery for a few days. A site that hosts markets, club weekends and a summer festival uses it much more, and the same battery can store solar power, cut peaks on the connection, or keep coolers running between events. That is where a fixed or semi-fixed system with solar panels and a controller makes sense. Our article on powering weekend and seasonal sites shows the same logic for campsites and retreats.

Maybe the site has a small connection that cannot carry the peak? Then a semi-off-grid system lets the battery do the heavy lifting and uses the connection only to charge it. In Maasmechelen, a customer who already had a generator for emergencies can now choose the street connection or the generator to charge his own off-grid system: 24 kVA of charging power and 30.8 kWh of battery.

Recurring events also give you data. After one edition with monitoring you know the real peak and the real energy per day, and the next battery is sized on facts, not on a margin.

What happens when you ask us to look at your event site?

We start with what must run on the site and when, not with a device. Then we design and install a battery system for your business that fits the ground and the events it hosts.

1. Step 1: Analysis and sizing. We list the zones, the loads per zone and the hours, and work out the peak in kW and the energy per day in kWh. Measurements from an earlier edition help a lot.
2. Step 2: Technical design. We choose the inverter power, the battery and the charging source: the grid connection, a generator, solar panels or a mix.
3. Step 3: Installation and commissioning.
4. Step 4: Monitoring and support. You follow the system remotely, see how full the battery is, and learn from each event for the next.

Not the right fit? For a single event far from any site you own, a rental generator or rental battery from an event supplier is usually the better deal.