The mine has used the BH10H AC in its original form, and now in phase II of Joy's development of the machine.

"In Phase II, the BH10H AC machine was placed back into service in the same mine application as in the benchmark Phase I period in order to achieve an apples-to-apples comparison and data retrieval process," Battery Hauler product manager Donnie Evans said.

The Mid-West mine undertaking the comparison was no easy pick for Joy to demonstrate its hauler's performance.

"This mine has some fairly adverse conditions. Unlike most coal operations in the Illinois Basin, this Midwestern mine produces a compliance product.

"However, seam conditions are often less than desirable; the seam pitches and rolls. In fact, the mine actually has hills underground, something that is uncommon to most of the other underground mines in the Midwest, and it's relatively shallow, with less than 150 feet (45 metres) of overburden in places," he said.

A room and pillar operation, the coal seam varies widely in thickness and elevation and has partings, making it unsuitable for longwall mining.

The seam's variability also precludes continuous haulage as a serious consideration.

The mine operates with four walk through super sections, each with two continuous miners, four battery powered haulage vehicles, two dual-boom roof bolters, as well as a Joy Stamler feeder breaker.

"Historically, rubber-tired haulage has proved best for the mine currently operating the BHAC machine," Evans said.

"Here, the BHAC has been operating along with other Joy Stamler battery haulers in one of the walking super sections. With the rolls and undulations in the mine, as well as the occasional soft bottom, this mine has offered a good proving ground for battery haulers in general," he said.

According to Evans, with the introduction in Phase II of ejector hydraulics and electronic controls, battery life of the mid-seam BH10H AC battery hauler operating on an extended super section at the mine was increased 10%.

This nearly duplicated the 10-12% improvement in per discharge cycle gained in the Phase I implementation period (September 2006 to March 2007), as compared to similar model machines with DC motors and electrical drive packages.

"Since implementation of Phase II at the Midwest coal mine, they are realizing 9 to 9.5 hours of operation per discharge cycle with the original battery design and 10.5 to 11 hours of continuous operation per discharge cycle with the larger amp hour capacity battery," Evans said.

Evans also noted there is no trailing cable with the hauler, an advantage to the mine operator with far more flexible haulage routing.

"Obviously, diesel powered haulage would provide the same cable-less flexibility," Evans said.

"However, with battery powered haulers there is no requirement for any additional face ventilation and these machines operate much cooler than diesel's."

The hauler also offers "vertical articulation" terrain compensation feature - a boon in undulating bottoms inherent with rolling seams.