5 hard lessons learned from the first wave of mobile BESS

In our last edition of Current Affairs, we left off on a promise and a warning. We shared that mobile battery energy storage systems (BESS) have earned their place into the temporary power sector, including film sets, events, construction, disaster zones — by showing up and delivering reliably under pressure.

Building BESS units that can survive the road, satisfy regulators, integrate with what’s already on site, run quietly, handle unpredictable loads, and still pencil out financially is anything but simple. As political climates change, interest in clean tech is evolving, as does the cost of energy, and these systems are gearing up for a wave of new launches that can speak for itself.

Alex Smith, a solutions architect from California, and the former CTO of Moxion Power, has watched these systems move from a napkin sketch to deployment and identifies five lessons that stood out for him.

1. Mobility is a major constraint

A Mobile BESS should be mobile. That means if you are trying to maximize the freedom of movement, then you also need to take into account regulatory restrictions that impede mobility. In North America, the key driver in the asset class for vehicles which can be towed is the 10 000 pound (4536 kg) weight limit. If you go above that, the driver needs to have a commercial drivers license (CDL). Many equipment rental yards have drivers with CDLs and larger trucks, but those logistics costs add up and cut against the return on investment.

On the surface, it’s a battery problem. Everyone knows batteries are big and heavy, so just use a high energy density chemistry. But then you get to the next obstacle on the road — UL 9540 safety testing that is so aggressive most passenger EVs wouldn’t pass the testing. So, integrators are left with two choices.

Either use a high energy density chemistry to start with and then add additional safety materials, in turn cutting the costs and weight budget, or start with a more stable, lower energy density chemistry and build up a leaner system.

After the battery constraint, the next largest contributor to the mass budget is the inverter.

Here is where the balance of systems can really be won or lost for product differentiation. Typical grid connected inverters are not mass constrained, so they use a transformer for isolation. A typical 50 kVA transformer is the size of a mini fridge and weighs 500 pounds (227 kg). If you are focused on optimizing your weight budget, then the most suitable options are to either design a non-isolated system or to use an isolated DC/DC at about 15 pounds (6.8 kg).

Every pound saved is another pound of content that can go back into your product, either in more energy (kWh), more power (kW), or lower cost structural materials.

2. Not all inverters are created equal

Depending on your starting point, one might be tempted to reach for an automotive, solar, stationary storage, or data centre inverter. These are all commodity items, globally produced, certified for their intended markets, and available off the shelf.

Automotive inverters are designed for three-phase motor control, completely missing the active neutral point which is required for off-grid operation of unbalanced loads. They are highly optimized for a single motor and have full control over the system. A supervisory controller is constantly taking throttle input from the driver, running vehicle dynamics models, and sending a torque request to the inverter. Asking the inverter to operate on-grid/off-grid to unknown loads is a completely different controls problem. These inverters are also thermally designed for short duration max power, not continuous loading near max power. So, while these could work with enough effort and creativity, it is not the problem that OEMs should be solving.

Solar inverters are cheap and readily available with recognised safety certifications. But they only do one thing, connect to the grid and then push solar generation to the grid. The grid manages the voltage and frequency, these solar inverters push current. As soon as the grid drops, these inverters instantly shut-off or “island” to protect line-workers. Many are also now transformerless or non-isolated. They can get away with this because the potential fault current from a solar panel array is substantially smaller than short circuit currents from a battery pack.

Stationary storage inverters are close to meeting the requirements of a mobile BESS as they are designed to operate on-grid and off-grid, galvanically isolating the battery pack. In on-grid mode, they act as a current source, pushing and pulling against a grid. When a power outage occurs, it instantly islands, then there is a multi-second delay to disconnect the system from the grid, then the inverter starts back up in grid forming (voltage/frequency) mode and reacts to loads. Many have limited surge capacity, which is why household installations typically do not include the AC unit because it will overload the inverter and cause another blackout.

Data centre inverters come even closer. They need to provide uninterruptible power to erratic loads, but those loads are known and the system is sized correctly during the design process. Many also solve the uninterruptible part through double online conversion, that is, converting grid power from AC to DC, with the energy storage system on the DC link, then to the eventual DC or AC server load. This works, but it is inefficient with multiple conversion steps. Some more advanced systems might have an online eco mode that passes through the AC portion and can quickly disconnect the grid but most still have a transition time and are not seamless.

In a nutshell, each of these inverters works well for the intended application but falls short of what temporary power systems need. The inverter with enough active neutral current to support 100% imbalance loads, black-start a microgrid, operate seamlessly between solo operation and AC coupled to other devices, and take whatever load shows up that day.

3. Microgrids are efficient

The electrical grid is the largest, most complex machine ever built. To keep it running, we need months to years of planning for any changes. We also have decades of historical power usage trends, to then optimize down to the hour level forecast of how much power will be used, and how much capacity is needed to support that. The wiggle room in between is absorbed in the sheer scale of the system that has megatons of spinning steel inertia on what is relatively a slow moving system. Even with hundreds of thousands of uncorrelated loads, they all average into a smooth, predictable demand curve.

California Independent System Operator (CAISO) shows what’s going on at any moment of the day and what is about to happen next.

A mobile BESS has none of those advantages of predictability – it is flying blind. The loads may be from a welder, air compressor, HVAC unit, stage lights, or any combination of those all hitting at the same time. There is no rotating mass, there is no historical data usage for that exact job, just some loose estimates. The inverter then gets to make or break the job, with the expectation that it runs as flawlessly as the grid.

Industry wide this is solved with oversizing, providing additional power capacity to handle unexpected load peaks. Mobile BESS cannot avoid that entirely, but this is exactly where it shines.

Diesel generators with the same oversizing, are frequently running slightly above idle to simply keep someone’s ham sandwich cold in the refrigerator. As soon as that generator is on, it is burning fuel to keep the mechanical assembly rotating at a fixed RPM at 1% load factor or 100% load factor, and at these low loading conditions, it is really inefficient. It can create wet stacking issues and increase the calendar frequency of maintenance intervals from engine hours.

Batteries, on the other hand, do not care if they sit idle all day, and inverters don’t really care either. Technically speaking, they are not immune to low load efficiency losses, switching losses still exist, but the order of magnitude makes them negligible.

4. Interoperability is asset utilization rate

An equipment rental operator has a fleet of assets and their entire business model hinges on asset utilization rate, or the amount of time it is rented versus sitting in the yard. Anything that cuts against that is an impediment to deployment. What that means for mobile BESS in practice is that it needs to work well with every piece of equipment in the yard and support the most potential number of jobs possible. The fleet operator does not want to guess whether that piece of equipment can run 480 V three-phase, 208 V three-phase, or 240 V single-phase power. It needs to do all of them. It also means that if they want to pair the mobile BESS with additional units to add power or energy, or with a hybrid with generators in their fleet, they need to be able to mix and match equipment to function together with their job.

A basic stationary storage inverter will operate as grid forming or grid following, but it would not coordinate with multiple units easily. Simplistic on/off grid inverters typically use a vendor locked proprietary communication protocol to talk amongst themselves to coordinate together, which prevents it from scaling the solution.

Approaching the problem from first-principles thinking, the real solution is more physics based and how our grids actually work.

If the inverter can follow the voltage/frequency as the primary control signal, then no external communication is needed. This is similar to how a grid-tie inverter works. But then how does the inverter know how much current to inject? That answer lies in what is called AC droop control. The inverter has a configurable virtual impedance, as the frequency changes it reacts to add active power (P) and as the voltage changes it reacts to adjust reactive power (Q). The concept is elegant, the implementation is non-trivial in taking multiple variables and compressing them into a PWM signal that is updating every 25 microseconds.

5. Mobile BESS needs seamless transitions

Imagine this, your Mobile BESS is silently powering a big budget film shoot. It is loaded up with multiple 18K stage lights simulating the power of the sun, so that the director can get that perfect shot. But the inverter needs to switch between grid forming or grid following mode and has a power blip. Do you want to take the risk of a lighting brownout there? We don’t think so.

That is the space temporary power lives in and why gapless or seamless transitions are the right solution to be able to ride through those transitions.

In a hybrid generator configuration, the generator coming online and offline as an additional source is not a rare event, it is happening daily. The easy solution is double online conversion, but you have doubled up the inverter cost and efficiency losses without adding more power to the end user. Power is your most critical metric. It is what the entire rental industry bases pricing rates on and not the place to give ground on your return on investment (ROI) model.

Alternatively, an inverter system can switch from grid forming to grid following and try to rush through the transition without anyone noticing. This gives the end user the total combined power of the source and the inverter, but at the risk of a brownout or equipment damage during the transition. This is the status quo for most systems today and most OEMs do not find out about it until it is too late.

A seamless transition is where the inverter is always on, never changes modes, and rides through other systems joining or leaving the AC bus. Simply put, you have no transition time if there is a ride through and fast response.

The technology is finally ready

If all of this has existed in theory, why didn’t the first wave of mobile BESS in the market build it?

According to Smith, taking Moxion off the ground, the pieces existed separately and had not yet converged into something you could actually ship, at a weight and a price that worked.

The genuine breakthrough that opened the category was the maturing of LFP battery cells – the energy density, cycle life, safety, and cost that finally made a serious mobile BESS viable. The pioneers read that moment correctly and went to market on the right chemistry at the right time. That half of the problem — the battery — was solved and is only getting even better as new variants of LFP, LMFP, Sodium Ion, Solid-State and others continue to evolve.

The other half of the solution was not ready. The available inverters at the time came with their own version of pick your poison. And the control layer that the field turned out to require, the ability to recharge at full power straight off a generator with no extra boxes, to drop next to any source and share load without commissioning — wasn’t a finished product yet. Worse, that control layer depends on the faster switching that newer silicon provides, so you could not really have perfected it on the old hardware anyway. The hardware enables the controls, the controls justify the hardware. In 2020, you could not have both at once.

There was a market lesson hiding in there too, not just technological.

The first deployments revealed how rental yards actually behave with drop-off and pick-up services. Rental yards like to say they are logistics companies and their business is twice as hard as Amazon because they have to both drop off at a moment’s notice and pick-up. Additionally, on the ready-to-go market, if we aim straight at the diesel-generator market, then we are fighting a known trusted incumbent for a problem nobody felt they had. Address the pain point aiming at a new emerging field — running an electric vehicle fleet off a diesel generator, working under a noise ordinance, rebuilding a neighborhood that would not have a grid for years anyway, and there is no incumbent to dislodge and far less friction to switching cost.

We have the technology and the market

It is easy to see why our team is composed of various engineers and physicists who worked at CERN, home of the large Hadron Collider, and they like a good challenge.

Which brings us to what’s shipping now, and why it looks different. The systems being designed today get to start from the full picture: lighter and quieter because they’re transformerless and built on high frequency switching devices, able to form a grid, follow one, or share a bus with a stubborn old generator using nothing but the physics of AC electricity, engineered from day one for the rodeo the first wave discovered the hard way.

This is the work ADVANTICS has been doing since 2020, when we first shipped variable output-mode control aimed at matching generator capabilities. It is why our release of AC droop control matters here: it is the piece that lets a storage asset couple cleanly into a low-inertia bus and hybridize with generators that were never designed to run in parallel — the capability the field was asking for before the technology could deliver it. In 2026, we started shipping our dual active bridge (DAB) isolated DC/DC converter, making galvanic isolation mobile again.

ADB-PC-GN01

A 90 kVA bidirectional, four-wire inverter that runs on-grid, off-grid, or as part of a microgrid, balancing loads across phases and managing real and reactive power. The four-wire platform is what gives it a true, driven neutral instead of a soft one.

ADB-PC-DC01

A 100 kW bidirectional, isolated DC/DC converter operating up to 1500 V, wide enough for traditional LFP and emerging chemistries like sodium-ion, with galvanic isolation placed where it belongs, at the battery interface. For applications that require isolation — defence among them — this replaces a heavy line-frequency transformer with a fraction of the mass.

ADB-PC-DC02 coming up soon

A high-power, bidirectional, non-isolated DC/DC converter up to 950 V, for the cases where every pound counts and isolation isn’t required.

ADM-PC-BI25

A 50kW bi-directional isolated converter. Keeps high voltage batteries redundantly isolated and prevents short circuit currents from reaching the AC circuits.

ADM-CS-EVCC

An EV charge controller for DC and AC standards, so a depleted unit recharges off the same CCS, NACS, or MCS infrastructure that fuels a passenger EV, and the rental yard becomes a charging depot.

Contact: contact@advantics.fr

Find out more about tailored solutions for your industry: https://advantics.fr/products