Cat Microgrid Technology Suite
Remote locations with no access to grid power are often forced to rely on fossil fuel to keep their generators running. Secluded regions are difficult to reach, making fuel delivery costly. Caterpillar now offers a microgrid solution that reduces the fuel requirements, allowing renewable energy sources to provide most, if not all, of the electrical needs for off-grid sites. Even locations with grid access can benefit from this technology as the microgrid can be connected to the regional grid, providing backup power and peak shaving to increase reliability and reduce electricity costs.
Renewable energy and storage capacity both increase the purchase price of a hybrid microgrid, but lower operating expenditures more than compensate for the one-time capital expense, which decreases the total cost of ownership. The integrated suite reduces design, installation, and inspection time, which in turn lowers the initial price tag.
Image courtesy of Caterpillar
Size and Capacity
Caterpillar's microgrids can be sized anywhere between 10 kW and 100 MW. They sell a variety of off-the-shelf packages and offer custom-designed solutions as well. The modular design is scalable, so customers can start small and purchase more as needed.
Caterpillar has an off-grid testing facility in Tucson, AZ which had been powered by 1200 kW worth of diesel generators; the company recently added a 500 kW photovoltaic (PV) array with a 500 kW hybrid energy storage system consisting of batteries and supercapacitors. The addition of solar and storage will decrease fuel consumption by 33%. That's less money spent on fuel and less CO2 being pumped into the atmosphere.
CdTe Solar Panels
In 2015, Caterpillar signed an agreement with First Solar, giving the PV manufacturer a contract to provide solar panels for the Cat microgrids. First Solar is the leading manufacturer of thin-film cadmium telluride (CdTe) PV modules. Cadmium telluride panels offer several advantages over silicon PV: they work better under cloudy conditions, they're much less expensive to manufacture, and they have a lower temperature coefficient, so they maintain their output even when the cell temperature is extremely warm. CdTe panels also have the lowest carbon footprint for manufacturing.
Image courtesy of First Solar
On the other hand, CdTe panels are less efficient than silicon, with commercially available panels in the 15% range (compared to 20% for silicon). Also, while cadmium is relatively abundant, tellurium is a rare element, which limits the number of CdTe panels that can be produced from this material. Most concerning, however, is the fact that cadmium is a highly toxic substance. When these panels reach the end of their lives, it will take some effort to recycle the materials without releasing cadmium into the environment.
Energy Storage System
There is no universal energy storage system that's suitable for every application, so Caterpillar provides a range of technologies. Lead-acid and lithium-ion batteries are well-established components in the Caterpillar Microgrid's arsenal. More adventurous customers may want to experiment with Caterpillar's rechargeable zinc-air batteries, which are less expensive and less prone to overheating than Li-ion. Zinc-air batteries can operate over a wider range of temperatures, allowing them to work in harsh environments without the need for costly (and energy-using) environmental controls. Finally, zinc-air batteries deliver the deepest discharge capabilities - up to 95% without a significant degradation in performance.
Image courtesy of Caterpillar
A battery's high energy density provides long-term storage, but its lower power density makes it slow to respond to quick fluctuations in power needs. Supercapacitors and flywheels are the complementary technology, delivering short bursts of energy when loads increase, and absorbing energy spikes when supply exceeds demand. Above you see Caterpillar's 1200 kVA (960 kW) flywheel unit, which operates with a 97% round trip efficiency.
Software Control
Coordinating the storage and delivery of energy requires a sophisticated software algorithm. A microgrid control system performs a continuous feat of choreography, ensuring that voltage and frequency remain stable in the face of varying inputs, loads, and power factor. Caterpillar's Master Microgrid Controller (MMC) handles these duties and has the ability to integrate the microgrid with the larger regional grid, allowing the microgrid to operate in both stand-alone and grid-tied modes.
Off-the-Shelf = Lower Cost
A 2013 report by the National Renewable Energy Laboratory (NREL) offered several suggestions for reducing the cost of solar energy. Much of the report focused on the "soft costs," which currently account for about 75% of the total price of a PV system. These costs include design, permitting, and installation, all of which can be drastically reduced by using more off-the-shelf integrated systems. The same concept applies to microgrids: a system whose components are designed to work together is easier to install and can be pre-approved by authorities having jurisdiction (AHJ).
While remote locations are the primary customer-base for Cat microgrids, businesses, campuses, and military bases are also adopting the microgrid concept. We can expect to see more companies selling "microgrid-in-a-box" packages. It's good for the grid, good for the ecosystem, and good for businesses - the triple crown!
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