The single most common reason a solar system 'can't run the machine' is a motor that draws six times its rated current for one second at start-up. The fix is cheap, well-known in industry, and missing from most solar quotes.
Key facts
- Direct-on-line motor start draws 3–6× running current for 1–3 seconds.
- A VFD (variable-frequency drive) ramps the motor up gently, cutting the surge to near running current.
- A high-surge hybrid inverter and battery cover what remains.
- Bonus: gentler starts extend motor and belt life.
The surge, in numbers
A 15 kW three-phase press draws about 22 A running and 90–130 A for a second or two when started direct-on-line. A 25 kW inverter sized for the running load trips on that inrush. Oversizing the inverter to 100 kW to cover the surge costs more than the press.
What the VFD does
The drive controls voltage and frequency so the motor accelerates over several seconds instead of slamming to full speed. Inrush drops to roughly the running current. The inverter can then be sized for the real load plus a modest margin, the battery is not hammered, and the motor runs smoother. The Reblong oil press in Ibadan starts this way every morning on 30–35 kWp of solar.
Where it applies
Oil presses, hammer mills, compressors on cold rooms, borehole pumps, conveyors — any motor above about 5 kW. Cold rooms are the classic case: compressors start dozens of times a day, and at 3 a.m. the battery has to deliver each start.
Have a motor that 'solar can't run'? Send us the nameplate.
Talk to Frontières BayFrequently asked
Does a VFD save energy too?
On variable loads such as pumps and fans, yes — often 20–30%. On a press it mainly protects the system.
Is it included in your quotes?
Always, on every motor over about 5 kW.