Welfare units, mobile workshops and site-support vehicles spend their working day parked with the engine off, running heating, kettles, lighting, tools and charging points. That is an off-grid power problem, and solar is often part of the answer, but only part. A dependable system comes from sizing the whole chain to the real daily load, not from bolting a panel to the roof and hoping.
Start from the daily energy budget
The first job is not choosing hardware, it is adding up the load. For each item, take its power and the hours per day it runs, and work in watt-hours or amp-hours. A welfare vehicle’s heater, urn, lighting and device charging over a shift add up quickly, and site tools on a mobile workshop can dwarf everything else.
The daily energy figure drives every other decision: battery size, charging capacity and inverter rating all follow from it. Guessing here is where off-grid systems fail.
Size the battery on usable capacity
The battery bank has to carry the vehicle through the working day, and often overnight, without engine running. Size it on usable capacity:
- Lithium (LiFePO4) gives 80-90% usable depth of discharge, far more energy per Ah installed, and much lower weight, well suited to a vehicle that cycles hard every day. Respect its low-temperature charging limits on vehicles stored cold.
- Lead-acid/AGM is limited to around 50% usable depth of discharge and is heavier, but cheaper up front and more tolerant of cold charging.
For a daily-cycling welfare or workshop vehicle, lithium’s usable capacity and cycle life usually justify the higher price.
Plan more than one charging source
Solar alone rarely covers a working welfare vehicle, especially in a UK winter. Design the charging as a combination:
- Solar: useful, free daytime energy that extends runtime and offsets the load, but variable and seasonal. Size it as a contributor, not the sole source.
- DC-DC charging from the vehicle: a converter charges the auxiliary bank whenever the vehicle drives between sites, with the correct profile for the battery chemistry.
- Mains hook-up: where the vehicle returns to a depot or has site power, a mains charger refills the bank overnight, the most reliable source of all.
The dependable design treats solar as a bonus on top of DC-DC and mains charging, not as the thing everything depends on.
Inverter for the 230V loads
Kettles, heaters, power tools and chargers need 230V, so the system needs an inverter sized to the largest combination of AC loads running at once, and remember motor and heating loads have high start-up surge. Match the inverter type to the equipment, and size it against realistic simultaneous use rather than the sum of everything on board.
Manage and protect the system
Off-grid systems live or die on how well the battery is protected and the loads are managed:
- Battery protection. A Battery Guard isolates non-essential loads before the bank is exhausted, and protects any engine-start battery on split systems, so the vehicle still starts at the end of a hard day.
- Load management. A programmable controller lets you prioritise loads and shed the low-priority ones as reserves fall, keeping essential welfare functions running longest. Driving loads through CAN switching such as iConnex keeps the wiring simple and diagnosable.
- Monitoring. Give the crew a clear state-of-charge readout so they can manage usage rather than discover the problem when the kettle dies.
Putting it together
- Add up the daily energy budget honestly.
- Size the battery on usable capacity for that budget.
- Combine solar with DC-DC and mains charging.
- Size the inverter to realistic simultaneous AC load.
- Protect the battery and manage the loads by priority.
- Give the crew visibility of the state of charge.
Do that and the vehicle supports a full shift off-grid, with solar cutting the charging burden rather than carrying it. Intellitec’s Battery Guards, DC-DC converters, inverters and control systems are UK manufactured.