Subject: [Cob] battery banks

[Barbara Roemer & Glenn Miller]

Mary Lou,

There are so many variables to consider in researching your question. You
might start with this site below to think about what you power needs are
(not necessarily what you're currently using on grid, but what you can
conservatively live with), how many days you have solar energy to collect in
your climate and latitude, how many days of backup energy you want to store,
and what level of batteries you decide you can afford (there is a great
range in quality/price).  Your use has less to do with your square footage
than with efficiency of design, thermal mass, insulation, and solar
exposure.  We have several kill switches so we do not have phantom loading,
and we are very conservative with power use.  We have sunny days every four
days in winter, and we are just about to install our solar array, but we
won't have much winter collection as our site is heavily forested.  We have
run on 12 Trojan L-16's for several years, and we live in a little cottage
of 750 sq ft, but we also have a guest cottage that's perennially occupied,
and we run our shop off the batteries presently.  The Trojans were about
$230 each three years ago, and the cheapest you'd find them for now ranges
from $260-$290 per.  The Hups work out to about 30% more, but one needs
fewer units, and they are warranted for ten years (part of it pro-rated, of
course, and with certain constraints to protect the distributor against
haphazard battery management).

We are ready for our second set of batteries in three years, but we know how
we fried them: insufficient metering and experience, and letting them run
too low repeatedly.  Almost everyone we know off-grid has fried their first
and often second sets of batteries, so you could take a page from their/our
books and buy cheaper batteries until you become adept at managing your
power use, your charging, and conserving.  Or you could go into it with
proper monitoring and lots of information, and be really diligent about
managing the charging and discharging.  The site below will help you sort it
out, but of course the web owner has a vested interest in your buying HuP
batteries, so it isn't quite a disinterested third party!  Nonetheless, it's
a pretty good system, and we are considering HuP batteries for our second
set of batteries (along with proper metering and an autostart generator for
backup to our solar).

Here's the HuP site:

<http://www.hupsolarone.com/faq.htm>

Barbara