Alternative Energy Storage Surprises

by Linnea Brush
June 4, 2001

This year's 41st Marconi Power Conference delved beyond the usual telecom powering issues to look at utility energy reliability and alternative energy solutions. Of particular interest (to me, at least) was a roundtable discussion led by Marconi. The panel session was called "Alternative DC Power Topologies," and it consisted of individuals from companies making micro turbines, flywheels and lithium-metal polymer batteries.

I've written a lot about secondary batteries for portable applications, such as nickel-cadmium, nickel-metal hydride, lithium-ion and lithium-polymer. Although used in similar applications, often interchangeably, these chemistries have very different power and energy densities. Everyone looks at size, weight, and cost - which are important - but power density and energy density are also critical parameters when comparing battery technologies. It's always been a given to look at these parameters when assessing portable, rechargeable battery packs. But has anyone ever done such a comparison of alternative energy storage solutions?

Well, Marconi did and the results raise questions about what really matters when comparing these products. The discussion focused around various "new" choices in technologies, most of which were less than 50kW. Currently, most problems with backup power will most likely occur at remote sites, such as digital loop carriers (DLCs) and cell sites.

There are many alternative energy solutions available, often with several choices in each category. These include advanced batteries, flywheels, flywheel generators, flywheel UPS/engines, fuel cells, gas turbines, micro turbines, combined heat and power turbines, hybrid high inertia turbines, solar energy and wind power. The discussion specifically addressed lithium-metal polymer batteries (LMP), engine generators, turbines, composite flywheels, fuel cells and high inertia turbines (HIT), and compared them with a "denser" VRLA battery in terms of power density and energy density.

Power density was measured in comparative Watts per cubic feet, with the results given as a multiple of VRLA battery power density. Power density is an important metric for indoor applications, due to space considerations. Relative to the VRLA, the LMP, engine generator and turbine came out higher in terms of power density, with turbines being the "best." The composite flywheel, fuel cell and HIT came out lower, with the composite flywheel being the lowest.

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