The microturbine is a reliable technology for providing localized sources of combined heat and power. Introduced to the consumer market a little more than a decade ago, the technology has steadily picked up steam through increasing efficiencies and the broadening product diversity. The microturbine equipment we know today represents the evolution of research and development that began in the automotive industry in the 1950s. The design of large engine turbochargers laid the groundwork for the development of the inner components.
The technology reemerged in the 1990s, but since consolidated to product lines offered by only a few companies. Originally offered in 35 kilowatt (kW) capacity (think about that in terms of powering a small office building), microturbines are now available in 30 – 330 kW units.
Larger applications where more power is needed require a slightly heavier-handed approach. Microturbine models, such as Capstone’s C200, can be assembled together to provide higher capacities. For example, by connecting five C200s into a single modular unit, Capstone is able to supply a building the size of a skyscraper with up to one megawatt (1000 kW) of combined heat and power. The construction of the individual units makes them an ideal match for projects of this nature.
As the name itself suggests, the technology leverages a small turbine that uses a combustion process to burn natural gas or other fossil fuels. The thermodynamic cycle used by the microturbine is called the Brayton Cycle, which is similarly applied in larger applications like jet engines. The core of the microturbine is the turbogenerator, which includes a compressor, recuperator, combustor, turbine, and permanent magnet generator.
The permanent magnetic generator is the only moving part in the engine assembly. The use of a magnetic generator eliminates the need for liquid lubricants, meaning that no oil changes are needed over the life of the equipment.
The recuperator recycles a portion of the exhaust gases and transfers that energy for heating purposes. The recycled heat energy can be used to pre-heat boilers for domestic hot water and space heating. Recycling the waste heat is a defining characteristic of the equipment. For a unit such as Capstone’s C65, heat recovery efficiencies can reach as high as 82%.
Based on the efficiencies, microturbines are often eligible for federal and utility rebates. There is a federal 10% investment tax credit that may be taken as an upfront grant. Many states offer rebate and incentive programs to stimulate the purchase of clean, efficient generation solutions. When you combine the incentive credits with the returns from energy savings, the projects often make practical sense.
Since their conception, microturbines have met tough utility requirements in place especially for those who want their equipment connected to the main electrical grid. Some areas of the world limit grid connection because of power anomalies affecting the quality of the current being fed back into the already stressed electrical grid. Another advantage of the microturbine is the built-in controls package, which includes protective functions, requiring minimal or no additional equipment for grid connection. These integrated controls have given way to the acceptance of grid-tied microturbines by regulating bodies.
New York City established its microturbine code in 2007 after a pilot project at Astor Wine & Spirits experienced unexpected delays from city code officials who had little to no experience with the technology. The project was designed with a four-year payback period to the owner, and hit a snag when the Fire Department delayed the final inspection by a few months until a city review board ruled in favor of the project moving ahead as planned. Soon after, Mayor Michael R. Bloomberg formed the Cogeneration Task Force led by buildings commissioner Patricia Lancaster and fire commissioner Nicholas Scoppetta to develop new standards for the safe use and installation of microturbine systems in residential and commercial buildings.
Mayor Bloomberg acknowledged the positive impact microturbines could have on the city’s congested infrastructure along with the potential reduction in building emissions. Recycling waste heat that would otherwise be exhausted into the atmosphere allows microturbines to capitalize on the usable energy produced by fossil fuels to reduce carbon emissions and provide building owners with a new type of investment based on energy savings. Later that year Mayor Bloomberg signed the rule, setting the country’s first Microturbine Standards.
The rule deems “any installation of microturbine systems shall be in accordance with all applicable requirements of the New York City Building Code, the New York City Electrical Code, and Reference Standards.” The building code is enforced by New York City’s Department of Buildings with additional oversight by the Department of Environmental Protection. The National Fire Prevention Association (NFPA) 37 standard also applies, except in municipalities where the code is more restrictive. NFPA 37 is enforced by Fire Department of New York (FDNY) and required a Certificate of Fitness prior to approval.
Having a system in place to inspect and approve these projects has been crucial to the carbon reduction goals of the city. Since the signing of the rule in 2007, there have been more than 160 microturbine installations in Manhattan alone, changing the tide for the microturbine market and giving way to a diverse landscape for sources of on-site combined heat and power.