Micro-Grid Operations
“The PRO-Verter™ is the missing link in this industry… it is the key to unlocking the full potential of solar & wind power in portable Micro-Grid applications.”
When operating equipment using portable power generators, systems function along a continuum of efficiency, from very low to very high, depending on how they are configured.
- Brian Bosley (Chief Technology Officer)
Portable Power Generators, Micro-Grids, & Efficiency
When operating equipment using portable power generators, systems function along a continuum of efficiency, from very low to very high, depending on how they are configured.A typical portable power model can be characterized as a “closed circuit” or “micro-grid.” They are both defined as a small power system that typically includes self-contained generation, transmission, distribution, sensors, energy storage, and power management software. It may be integrated with other power systems, but can operate independently from them.
Equipment consuming electricity in a closed circuit often does so dynamically. That is, they consume power at varying rates, depending on their state of operation. Communications devices, medical equipment, lighting, and refrigerators are just a few of examples of equipment that operate in this fashion.
When a portable fuel-driven power generator (gas or diesel) is the primary source of power in a closed circuit, it must operate continuously in order to provide any electricity, even if the load requirements of connected equipment are minimal or intermittent. This results in very low efficiency operations.
When the primary source of power in a closed circuit is battery-based (stored) power, then the connected equipment receives power only as needed. This results in a very high level of overall efficiency.
In a true micro-grid, multiple sources of power generation can be used simultaneously to provide equipment with uninterrupted power. The key to successful integration of multiple power sources is proper power management.
With any portable power configuration, there are limitations that often prohibit full dependency on a sole power source. For example, fuel-driven power generators (including Fuel Cells) require fuel to operate, which may or may not be available. Renewable energy power generators that rely on solar or wind generation may not keep up with maximum power demands due to environmental conditions.
The Logical Solution - The “Hybrid” System
Use of a battery-based Hybrid system comprised of solar, wind, and traditional fuel generators provides the operator with maximum autonomy and flexibility (based on the environmental conditions) and ensures that traditional fuel-driven generators are used only as necessary. In this model, the renewable power generators become the primary power generators, and the fuel-driven generators become the secondary source.
A Hybrid power generator configuration mitigates the risk of dependency on only one power source, while simultaneously increasing operating efficiency dramatically. Additionally, the “open architecture” of a Hybrid configuration allows for the addition of other power generating sources into the circuit as needed.
The Solar Stik™ PRO-Verter™ - Managing a Hybrid System
The Solar Stik™ approach to solving the portable power challenge is to use a device called a P.R.O. Verter (Portable Remote Operation Inverter/Charger, or PRO-Verter™). The PRO-Verter™ acts as the hub through which all power in a micro-grid or closed circuit is channeled. The PRO-Verter™ manages multiple power sources, providing operators with one Uninterruptible Power Supply (UPS) for their applications.
To the maximum extent possible, the PRO-Verter™ relies on a connected battery source for power. If the batteries are unable to supply power based on low voltage, it will shift the load to a supplemental power source, such as a fuel-driven generator.
Cost/Benefit Analysis
When a fuel-driven generator is continually operated as a primary power source in a closed circuit (continuous operation), the logistics of fuel supply become the largest single factor in determining the actual operational costs. The Project Manager for DoD Mobile Electric Power Systems (PM-MEP) has concluded, partially based on research conducted at the National Renewable Energy Laboratory (NREL), that significant cost savings can be realized if a fuel-driven generator can be turned off for periods of time.
In a Hybrid configuration, the primary power generators (solar/wind) harness “free” electricity, while fossil fuel-driven generators operate only as necessary. This may result in significant savings in fuel and generator wear & tear (and longer mean times between failure).
Using a PRO-Verter™ with a Conventional Fuel-Driven Generator
The PRO-Verter™ is connected between the Solar Stik™ Power Pak and an AC power source, such as a fuel-driven generator, with all system loads (equipment) connected to the PRO-Verter™.
The PRO-Verter™ distributes power from the Solar Stik™ Power Pak batteries as demanded by the appliances, until a user-determined voltage set point is reached. At this point, the generator is activated (manually or automatically, see below) and assumes the appliance load. Simultaneously, additional AC power produced by the generator to is then used by the PRO-Verter™ to charge the Power Pak batteries. This process ensures that the generator is run under a “consistent load” condition and that all fuel consumed by the generator is used to produce power for storage.
PRO-Verter™ in “Manual” Mode
The Hybrid Configuration can work with any attached fuel generator in the manual mode. In this mode, the operator can simply monitor the state of charge of the battery bank and start the generator when the batteries are low, turning the generator off when the batteries are fully charged. The disadvantage of this approach is the need for hands-on operation and close monitoring of the system’s performance. Its significant advantage, however, is that the manual mode can be used with any attached fuel generator with an AC output, even small pull-start models without an electronic ignition. The PRO-Verter™ used in the manual mode can be quite compact, making it very suitable for missions requiring maximum portability.
PRO-Verter™ in “Automatic” Mode (APM / AGS only)
In the automatic mode, the PRO-Verter™ will automatically start and stop an attached generator when the attached batteries reach a pre-set voltage level, eliminating the need for hands-on operation and close monitoring of the battery voltage. This will work, in principle, with any generator that has an electric start feature.
PRO-Verter™ in “UPS” Mode
The Hybrid configuration can also be used in place of a traditional UPS (uninterruptable power supply). In UPS mode, the fuel-driven generator or grid power (if available) is used as the primary power source with solar & wind power generation as secondary sources. Unlike traditional UPS systems, using a solar/wind power generation system as a backup yields extended run times with the fully charged batteries ready to assume critical loads during times of generator or shore power interruptions.
Conclusion
In the context of a Cooperative Research and Development Agreement (CRADA) with PM-MEP, Solar Stik™ Inc. has built an automatic version of the PRO-Verter™, called the PRO-Verter™ Advanced Power Management (APM) version. At PM-MEP’s request, the first version of the PRO-Verter™ APM has been optimized to work with the 3kW Tactical Quiet Generator (MEP-831A/MEP-832A).
A Hybrid configuration consisting of Solar Stik™ Inc.’s solar and wind generators with the 3kW TQG was first demonstrated at PM-MEP’s Annual User’s Conference in Orlando in May 2010. Since then, it has served successfully at 6 official military exercises for data collection. The project is currently in the hands of PM-MEP and US Army RDECOM/CERDEC for formal testing.
For further information about the Hybrid configuration or any other solutions offered by Solar Stik™ Inc, please contact Al Zaccor (COL, USA-Ret), Military and Government Business Development, at 703.835.0217 or azaccor@solarstik.com.
