Off-grid sites have a problem that grid-connected ones do not: every watt is generated locally, stored locally, and paid for in fuel or panel area. A DC generator removes one of the conversion stages in that chain.
A conventional AC genset produces alternating current, which then has to be rectified to charge a battery bank. Each conversion costs efficiency and adds hardware that can fail. Innotec DC gensets generate direct current at the bus voltage, feeding the battery or the DC load without an inverter in between.
Why variable speed matters off-grid
A fixed-speed AC set runs at 1,500 or 1,800 rpm whether the load is 2 kW or 20 kW, because that is what holds 50 or 60 Hz. Off-grid loads are rarely steady, so a fixed-speed set spends much of its life running fast and lightly loaded — the least efficient way to burn diesel.
A DC genset has no frequency to hold. Engine speed is varied to regulate output voltage, so the engine sits where it is efficient for the load actually present. Peak efficiency is engineered above 93%, and fuel consumption on the standard sets is 240–245 g/kWh.
Charging a battery bank properly
The controller runs a precision PID loop against the charging characteristic rather than simply holding a fixed voltage, which is what extends bank life. Overvoltage, overcurrent, overspeed and overheat protections are built in, along with thermal and short-circuit protection.
Because the alternator is brushless and bearing-less, there are no slip rings, exciters or diodes to service — the failure modes that matter most on a site nobody visits weekly.
Hybrid: solar, battery and genset together
On a hybrid site the genset is a backstop, not the primary source. It should start rarely, run at the load actually required, and charge the bank quickly before shutting down. Variable speed and direct DC output suit that duty far better than a fixed-speed AC set, which is sized for peak and inefficient at everything below it.
See also applications of hybrid DC generators.
Sizing an off-grid set
Three standard DC gensets are published with full specifications:
- 5 kW, 48 V — air-cooled single cylinder, 85 kg, for small remote installations
- 14 kW, 24 V or 48 V — turbocharged 3 cylinder, liquid cooled
- 25 kW, 48 V — the largest standard set, for continuous duty
Fuel tanks are available integrated at 200, 400 or 600 litres, or the set can be supplied open-frame to mount on an existing tank. Gas sets are built to order where a gas supply exists.
Other DC generator applications
The DC generator range also covers battery charging systems, military and defence equipment, marine, and mobile and off-highway equipment.