Hybrid Cycling with PV and Genset: Hybrid Test Bench Results

Michael M.D. Ross
RER Renewable Energy Research

Acknowledgements:

Research conducted on behalf of the Photovoltaics and Hybrid Systems Program at the CETC-Varennes (Natural Resources Canada) with partial funding from the Panel on Energy Research and Development (PERD).

Citation:

Ross, Michael M. D. Hybrid Cycling with PV and Genset: Hybrid Test Bench Results. Report to CETC-Varennes (Natural Resources Canada). Montreal, Qc: RER Renewable Energy Research, 2004.

Summary:

This document reports on a five-week test run on the hybrid system test bench of the Photovoltaic and Hybrid Systems Group at the CANMET Energy Technology Centre—Varennes. During the test, a photovoltaic array and a genset provided power to a DC load, with energy surpluses and deficits being accommodated by a battery.

The PV hybrid system functioned exceptionally well over the course of this test. Losses were generally very low. The dispatch strategy kept the battery at a high state-of-charge while minimizing rejected solar energy. The data acquisition systems for both the meteorological station and the hybrid test bench collected a relatively unbroken record of the test.

System losses were caused by (in order, with most significant losses first): non-ideal photovoltaic array characteristics and operation conditions, including lack of maximum power point tracking; losses in the battery; rejected energy during charge regulation; resistance of the long cables connecting array and test bench; conversion of the AC genset output to DC; and array blocking diodes.

A simple dispatch strategy was formulated on the basis of several observations from this test:

• The voltage thresholds typically used by commercial dispatch controllers to terminate genset operation return a highly variable amount of charge to the battery, which can be avoided by instead using the charge returned to the battery.
• While a genset dispatch strategy should, in general, endeavour to avoid charging the battery just prior to a sunny period, it should also, at times, do precisely the opposite: in order to equalize the battery, the dispatch strategy should bulk charge the battery to a point where sunlight can effectively fully charge the battery over the course of a sunny day, minimizing wasteful and damaging part load operation of the genset. This is especially attractive given the low losses seen during charge regulation in this test.
• If a voltage threshold is used to start the genset, and then a certain amount of charge is returned to the battery, the voltage at the end of genset run is an indication of the state of the battery. If it is low, the battery probably does not need equalisation. If it is high, equalisation is necessary.

Because this was the first test run on the hybrid test bench with a PV array and charge controller, much time was spent scrutinizing all monitored data to ensure that instruments and systems were functioning acceptably. While most equipment performed admirably, serious problems with the photovoltaic array and meteorological station were identified.

Created 2007/03/06   Updated 2007/03/06     ©2007 RER Renewable Energy Research