Photovoltaic Batteries at Earthaven Ecovillage
Mattox, Fayetteville State University, JMattox@uncfsu.edu
Earthaven Ecovillage near Black
Mountain, NC features approximately 50 people living deliberately without the national electrical power
grid.Most households utilize solar electric power. Due to
lack of power, the lead-acid batteries in many of the systems there cannot be
We report on studies of consequent battery degradation due to sulphation,
and on possibilities for battery rejuvenation through corrective
equalization using supplemental power.
The “Hexagon Hut” at Earthaven. Two photovoltaic
panels are apparent on the roof.
Two Trojan T-105 golf cart batteries ready
for off-grid residential use. Capacity 200 amp hours at
Earthaven batteries that have
lost capacity due to sulphation.
Switch which selects one pair of batteries
to charge while another pair discharges.
Testing at the Fayetteville State University
inside of a used T-105 battery.
timed discharge in progress.
A discharge curve for one 6 volt
battery. Trickle charge ends at T=0. Discharge at
2 amperes began at 1500 seconds,
and ended automatically at 151,000 seconds
upon reaching a voltage threshold of 11.8 volts
for two 6 volt batteries.
Charge/discharge cycling in the Fayetteville
State Battery Lab (with full charge for each cycle) resulted
in improved battery capacity for Earthaven batteries that were reduced in
capacity due to sulphation. Battery capacity was ascertained
by the length of the discharge as described at the left.
A simultaneous increase in the specific gravity of the sulfuric acid
electrolyte was also noted, indicating desulphation had taken
place. It was found that desulfation could also be achieved
in a single “corrective equalization” with the application of ~300 amp-hours
beyond a full charge, restoring~8 year old batteries from approximately 30%
of new capacity to approximately 60% of new capacity.
Battery capacity degradation at Earthaven
due to sulphation could be eliminated with the availability
of additional power, either by using larger solar panels, or through the use
of auxiliary power for battery maintenance. A generator
powered by biomethane or ethanol could be a sustainable
source of power for community battery maintenance.