Microturbine manoeuvres


For the uninitiated, microturbines are aerospace-derivative turbine engines. The engine or generator package is as small as a beer keg and typically has few moving parts. In the case of Capstone engines, it has just one: a variable-speed shaft with a permanent-magnet generator on one end, an air impeller wheel in the middle, and a palm-sized turbine on the other. Some microturbine designs utilize components including electro-mechanical fluid pumps, gearboxes and radiators. But with a turbine shaft rotational speed of up to 96,000 rpm, the endurance of bearings with viscous lubricants are severely challenged. So Capstone builds its engines without the need for any such fluids, devices or subsystems. Instead, Capstone microturbine engines use air cooling and the company’s patented air bearings to keep the entire system free of any lubricant, coolant or other hazardous fluid needs. It’s a design that has proven itself over the course of more than eight million hours of documented fleet operation, with a number of units still going strong after 30,000 and 40,000 hours of operation.

What is fairly new in CHP is size: instead of tens of megawatts, microturbine generators create tens of kilowatts

When Capstone first began development of the microturbine generator, the goal was to create an engine for hybrid vehicles. In that realm, emissions are the be-all and end-all. So the design goal was to create a microturbine engine with pollutant emissions as close to zero as possible – without any costly exhaust treatment devices or chemicals. The company specification for NOx emissions at full load is less than 9 ppm at 15% O2, or 0.47 pounds (0.21 kg) per MWh. However, independent tests of their equipment, including those performed for and published on the US Environmental Protection Agency (EPA) website, consistently show NOx output well below half that.

While a few dozen microturbines are used in buses and other hybrid vehicles in the US, UK, Japan and elsewhere, Capstone learned early on that delivering clean, daily on-site power and heat to solve energy problems and cut costs at commercial, industrial and public facilities would prove the better, more accessible market.

Challenging the US utility perspective on DG

A new report on the current status of, and prospects for, distributed energy resources in the US was fairly downbeat in its conclusions. But, says Elisa Wood, the report has not told the whole story, and underestimates DG's current and potential position.

If the August 2003 blackout was a wake-up call, it appears many influential players in the US slept through it. Most utilities continue to take a wait-and-see attitude about distributed generation, and policymakers often support their reticence, despite a call for less centralization after the massive grid failure that darkened the North-east.

The Electric Power Research Institute (EPRI), a non-profit research institute set up by utilities, attempts to gauge the US distributed generation market and its possible paths for growth in a new report, ‘Distributed Energy Resources: Current Landscape and a Roadmap for the Future.‘ While the report sees promise in the end-use market, it envisions only an ‘incremental’ increase in the use of distributed energy to fix the country's transmission system. ‘I think the blackout has got people interested in the bigger picture, but it has not really been a driver,’ explains Dan Rastler, the report's author.

The end-user market has at least 30 GW of untapped potential in the US

The report estimates that the US has 30 GW of grid-connected distributed generation capacity, a small percentage of the country's 953 GW of electric capability. In all, the country has an estimated 234 GW of installed DG. But small reciprocating engines, used to supply emergency or standby power, account for about 81%, most of which is not grid-connected. Combustion turbine technology is the second most widely used approach with 7% of the mix, and combined heat and power (CHP) is the second most widely used application at 9%.

The future offers several pathways to growth for distributed energy, depending on how technologies and markets evolve, according to the report. The largest market, now and probably through to 2015, is what Rastler describes as the end-use pathway, where consumers use distributed generation to achieve savings and reliability. The end-user market has at least 30 GW of untapped potential in the US, which EPRI says is likely to be realized as state and federal policies improve. EPRI sees the end-user market emerge in several ways, among them:

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