Diesel generators have long been a reliable source of energy for various off-grid applications.

Peak load demand and inrush current are key considerations for sizing a conventional generator. High power is needed during short peaks at start-up or during operation as loads get turned-on or off. Non-linear loads such as uninterruptable power supply (UPS), variable frequency drives (VFD) and large load demands such as HVAC and water heaters can present a challenge and can impact power quality under all operating conditions. In some instances the large inrush currents can stall a genset and create an unexpected power outage.

To address the peaks, a typical generator is significantly oversized relative to the average demand. This results in the generator running in less than desirable efficiency range, resulting in higher fuel costs and emissions. In addition, this under loading contributes to fouling, slobbering, wet-stacking and visible emissions… All of these lead to premature service and unnecessary downtime and maintenance costs.

Conventional generators run at specific speeds to develop an AC frequency (i.e. 1500 RPM for 50Hz, or 1800 RPM for 60Hz). If you want to run it slower to conserve fuel, unlike taking your foot off the pedal in a car, the generator cannot reduce its speed as the output frequency becomes unsuitable for your equipment. In conclusion, most generators are oversized, run at a constant speed, and are under-loaded for a majority of the applications. While doing this, they consume unnecessary amounts of fuel, output higher than necessary noise and air pollutants. This is not ideal.

Enter BluVert Technology, a technology company from Vancouver Canada who developed a serial-hybrid generator to address all of these issues. The system consists of a diesel engine used intelligently as a variable speed genset where only the required energy is produced by the diesel genset and a right-sized amount of energy storage (super-capacitors) handles peak shaving. Peak shaving is a technique used to reduce the amount of energy required by the diesel generator by supplementing it with additional capacity from the ultra-capacitors to meet the peak demand.

Ultra-capacitors, also known as super-capacitors, store electrical energy. They’re in-between a capacitor and battery, and offer the best of both. Unlike batteries, capacitors are ideally suited for many rapid charge/discharge cycles and exhibit a longer life than conventional batteries ( x 1,000 cycle life). They exhibit an extremely high power density, operate in broad temperature ranges (-30/+50C) and don’t contain hazardous chemicals like batteries do.

The ultra-capacitors in the BluVert system provide a few functions:

• Provide fill in power when the inrush current of large inertia loads exceeds the capacity of the genset.
• Store energy when excess capacity is available from the genset
• Store energy when regenerative power is available in the system, i.e. the process of recovering kinetic energy created by a motor during stopping or braking and converting that energy to electricity (hoists, cranes, downhill conveyers, etc)
• Provide intermittent power while genset is started-up and brought online
• Help stabilize voltage grid and frequency. Renewable energy like wind and photo-voltaic (PV) exhibit fluctuating supply due to gusting or cloud, ultra–capacitors can buffer this effect within milliseconds.

The BluVert system is based on a DC-bus architecture. This means that the power is distributed using DC-Voltage, and converted to AC when required. BluVert uses a variable speed generator to produce the DC voltage, and since DC voltage doesn’t depend on frequency like AC power does, changing the engine RPM to find the “sweet spot” or most efficient fuel economy, doesn’t impact the power quality. The brake specific fuel consumption (BSFC, or the amount of fuel used per kW of power produced) improves with a smaller load at a lower speed. This is where the system differs from a battery based alternative. Rather than generating power, for it to be stored (which comes with inherent efficiency losses), we only generate the minimum power necessary, and use minimal storage. All the while operating the generator at the most optimal speed-to-power zone. Depending on the application this can result in up to 60% reduction in annual operating costs.

This architecture lends itself to complement a renewable micro-grid (i.e. wind and solar). A typical challenge for renewable energy output is how to deal with the intermittent interrupts and grid stability. Changes in weather (change in wind speed, or cloud formations) can alter the voltage output of a renewable energy source. BluVert maintains micro-grid stability by providing a base output using the variable speed generator, and varying the generator RPM and ultra-capacitors charge/discharge rate to maintain a stable grid. Running a variable speed generator in conjunction with the renewable energy source, results in you being able to utilize up to 20% more of the renewable energy (referred to as a higher renewable penetration).

Without the diesel backup or expensive battery storage, the micro-grid would black-out whenever the sun disappears behind the clouds, or the wind dies down. The BluVert system provides a quick response and fills in the required dips with either the capacitor (short) or diesel (longer periods).