Written by Robert Collins, lead Solarcraft Engineer
When we think of a generator, we think of something burning fuel to create our standard 60 Hertz AC voltage. For remote power applications this may not be the most efficient choice. This is especially true when the equipment we are trying to power requires low voltage DC power.
The old standard for AC generators is an engine running at a fixed RPM (speed) in order to create the fixed frequency of 60 Hertz AC power. If the back-up power required is small when compared to generator’s capability, excess fuel is consumed… because of the fixed RPM of the engine. These types of generators achieve peak efficiency when powering a large, constant, AC load.
AC vs DC
A new type of AC generator is gaining popularity, the “inverter” type. In this type, the native AC output of the generator is first converted (rectified) to DC, and then back to AC again electronically, by an inverter. Because the inverter creates the fixed 60 Hertz frequency electronically, the engine no longer needs to run at a fixed RPM. This allows the engine to run at lower speeds when loads are light, thus saving fuel and wear. At the present time, this technology is limited to generators of 10 kW or less. Regardless, these “inverter” type generators offer dramatic improvements in fuel consumption.
Here lies the problem. In many remote applications the loads do not strictly require AC power. In fact, unless motors or lighting are involved, the AC output of the inverter will have to be converted back to DC, again, to power the loads. The DC generator solves this issue.
The DC generator is essentially the same as the inverter type, minus the inverter. It also runs at varying speeds depending on the load, achieving the same reductions in fuel consumption. The DC generator realizes additional increases in efficiency because the losses in the inverter are avoided.
DC generators are actually commonplace; there’s one under the hood of your car. And like your car, the real magic of a DC generator lies in the fact that it can charge batteries directly, without the wasted energy and the added complexity of an AC to DC battery charger. The addition of batteries to a DC generator system provides for the most dramatic improvement in efficiency yet; the ability the shut the generator off.
Consider a system with a 300 Watt, 24 Volt DC load:
Batteries can be mated to 3,000 Watt DC generator such that 24 Volt DC power can be supplied continuously. The generator will start only when the batteries are depleted, and will only run until the batteries are charged. Ignoring battery efficiency for the moment, this 3000 Watt will only run 10% of the time to power the 300 Watt load… now we’re talking!
More Subtle Advantages
Because the DC generator is dedicated to battery charging, it can be programmed to run at its peak efficiency… its sweet spot. Because other alternative energy sources store their power in batteries, the DC generator can also be added directly to these technologies with minimal complexity. The DC generator can augment, or replace entirely, the alternative energy source. Where solar or wind power is impractical or impossible, this may be the only option.
Learn more about our Solarcraft DC Generator.
Or, CONTACT US directly so we can assist with any more questions you may have.