Off-grid commercial sites are often designed around current requirements, with some allowance for future growth. That approach works, until operations change.

Workshops expand. Equipment becomes more power-hungry. Load profiles shift.
And suddenly, a system that once felt comfortably sized starts hitting its limits.

This is a common challenge for rural and off-grid businesses, particularly those relying on three-phase power where grid reinforcement is not an option.

This case study looks at how an off-grid aviation site increased available power without scrapping its existing system, and more importantly, the design principles that made that possible.

The Site Context

Based in the heart of rural Somerset, Historic Helicopters operates a fully off-grid facility dedicated to the restoration and preservation of historic aircraft.

The work carried out on site includes heavy mechanical equipment, specialist tooling, and controlled environments for sensitive avionics; all of which place real demands on electrical infrastructure.

Several years ago, Historic Helicopters moved to an off-grid system featuring a 10kVA per phase three-phase setup. At the time, this was an appropriate and robust solution.

As restoration projects became more ambitious and operational demand increased, that original capacity began to feel restrictive, not because the system was failing, but because the site had grown.

Why Off-Grid Systems Hit a Ceiling

When an off-grid system reaches its limit, the constraint is usually not “lack of batteries” in isolation. In practice, ceilings tend to appear in one or more of the following areas:

• Inverter throughput
  Inverters ultimately limit how much power can be delivered at any given moment, regardless of stored energy.
• Three-phase balance and scaling limits
  Many three-phase systems perform well until one phase becomes the bottleneck.
• System architecture
  Some systems are inherently modular; others require replacement to increase capacity.

In many traditional designs, hitting the inverter ceiling triggers a costly assumption: everything must be replaced. That assumption is not always correct.

The Key Design Question: Can the System Scale?

Before deciding whether replacement is necessary, there are four questions that matter more than brand choice or battery size:

1. Is the inverter architecture modular or monolithic?
   If inverters can be paralleled per phase, capacity can often be increased additively.
2. Is the DC infrastructure already capable of higher throughput?
   Busbars, protection devices, and cabling often determine the true ceiling.
3. Can monitoring and control remain unified after expansion?
   Scaling without coherent control introduces new reliability risks.
4. Is the growth driven by sustained load or short-term peaks?
   This distinction determines whether more kVA, more kWh, or both are required.

If the answers to most of these are favourable, expansion without replacement is usually achievable.

The Approach Taken at Historic Helicopters

At Historic Helicopters, the original system architecture allowed for modular expansion.

Rather than removing the existing equipment, capacity was increased by adding inverter capacity symmetrically across all three phases, doubling available output from 10 kVA per phase to 20 kVA per phase.

This was achieved by installing six Victron 10 kVA Quattro inverters, configured as two units per phase, operating in parallel with the original system.

To support the higher sustained load:

• Battery storage was expanded to 108 kWh using PYTES V12 lithium battery modules, designed for demanding environments and year-round operation.
• On-site generation was increased with 40 kW of roof-mounted solar PV, ensuring the expanded inverter capacity could be effectively utilised rather than simply shifting the bottleneck.

Crucially, the original system remained in service throughout, forming part of the expanded architecture rather than being displaced.

What This Achieved

This approach delivered several practical benefits:

• No wasted capital
  Equipment installed years earlier continues to operate as part of the current system.
• Minimal operational disruption
  Expansion was carried out without extended downtime, allowing restoration work to continue.
• A scalable foundation
  The system is now fully monitored and designed with further expansion in mind, should site demand continue to grow.

Today, the site operates with the power headroom required to run heavy workshop equipment, maintain controlled environments, and support future projects - all while remaining fully energy independent.

Why This Approach Might Not Apply

Adding more equipment is not always the best solution. Full replacement is often needed when the original system was not designed to be modular.

The key is to identify what part of the system is limiting growth and then decide whether it is possible for the existing system can be expanded or must be replaced.

In Conclusion

Before asking “How much more power do we need?”, the more important question is:

“Which part of our off-grid system limits growth, and can it be expanded, or only replaced?”

Answering that correctly is often the difference between a targeted upgrade and an unnecessary rebuild.