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									   The Effective of DC to AC Inverter Based on a Vanadium Redox
     Flow Battery System with Low Cost but High Performance

                                   Wachirasak Phisitsangkhakool
                         King Mongkut’s University of Technology Thonburi
                        The Joint Graduate School of Energy and Environment
                                         91 Pracha-Uthit Rd.
                                         Bangmod, Tungkru
                                          Bangkok, 10140


Renewable energy system based on Photovoltaic (PV) arrays requires a mean for storing energy so that
the supply can better tally with demand. Vanadium redox flow battery (VRFB), which has many
advantages over any other kinds of secondary batteries, is the new-model highly efficiently secondary
battery for stationary energy storage. The Cellennium Company Limited is the sole licensee of Squirrel
Holdings Limited to commercialize a numbers of new inventions associated with vanadium fuel cells
in Thailand. A study is reported of an entirely new method of obtaining alternating current from a flow
battery using an inductionless electronic power switching circuit instead of the conventional inverter
with an inductive motor and alternator. This method was patented by Spaziante, Kamapanatsayakorn,
and Zocchi in 2001. It is extremely simple, low in cost, and highly efficient. It cannot be used with
other types of battery, such as lead-acid and nickel-cadmium batteries. The stack of vanadium fuel cells
in the battery has voltage taps along its length so that when the output is connected to the taps in
succession at equal intervals of time the result is a sinusoidal wave form. A frequency of 50Hz is easily
obtained due to the very rapid response of the vanadium fuel battery to change in the loads at the taps.
The output is practically free from unwanted harmonics, and the efficiency is 98%. The cost of the
inverter will be only a few percent of the price of conventional inverters.
Besides providing an alternating current output, the method can be used to control the manner which
variable electrical inputs are fed into the battery so as to maximize the storage efficiency.
Applications of the method will include:
                            Maximum power point tracking of the inputs from solar photovoltaic arrays.
                            Acceptance of alternating current from wind turbines running at variable
              rotation frequencies depending on wind strengths.
                            Acceptance of alternating current from diesel generator sets running at
              variable speeds adjusted to suit average loads.
                            Connection of renewable sources of energy (solar and wind) to the electrical
              power grid.
This paper gives details of the technical requirements of a system with a 1.2kW output, and analyses
the economics of the system in comparison with other traditional systems.

Keywords: Vanadium redox flow batteries; DC to AC inverter; grid connected renewable energy
systems; wind power and solar photovoltaics; Inductionless inverter

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