Mother Earth News_December_2016_2017

PB MOTHER EARTH NEWS December 2016/January 2017

applications: lights, electronics, and mo-

tors, plus a few other specialized uses. By

matching the best form of energy to its

application, total electricity consumption

can be greatly reduced while enhancing

comfort and convenience. Five common

uses of electricity in conventional grid-

tied homes won’t typically show up on an

off-grid homestead: space heating, water

heating, cooking, clothes drying, and air

conditioning. Each of these consumes too

much energy to be ap-

propriate when the sup-

ply is finite and the task

is best-served by other

forms of energy.

In the early years, PV

modules were much

more expensive than

they are today, and bat-

teries were less expensive.

Early practice was to size

for a week of storage

capacity, but that led to

small arrays and large

battery banks, resulting in chronically in-

adequate charging. Modern systems are

often sized for only two to three days of

storage capacity, as long as the system in-

cludes a backup generator. As budgets al-

low, users add an additional array rather

than increasing battery capacity.

Battery-based systems are gener-

ally wired to 12-volt, 24-volt, or 48-volt

standards. Many folks still assume that

a homestead system will be 12-volt be-

cause that’s all they’ve seen. Twelve volts

is a holdover from the days before reliable

inverters were available. Automotive and

RV products — including lights, TVs, and

unreliable blenders — were all available in

12-volt capacities to serve that industry.

Good inverters have been available since

1987, and systems have progressively

moved toward inverter-based, alternating

current (AC) loads in the years since. With

AC-based systems, 12-volt advantages

have largely disappeared, and the strong

disadvantages of high-current and large-

wire sizes discourage the use of 12-volt

batteries for all but the

smallest cabin homes.

Flooded Lead-

Acid Batteries

The most common

batteries in off-grid resi-

dential systems are flood-

ed lead-acid. Among

flooded lead-acid bat-

teries, there are three

common battery types

from which to choose;

each has its niche. Golf

cart batteries are mass-produced by the

millions and remain the best low-cost

choice for small systems. Seldom do sets

last more than seven years, and typically

they last four to five years. In return, they

stand up to remarkable abuse, including

chronic undercharging and lack of equal-

ization, and still provide adequate service.

For some systems, frequent recycling and

replacement of a set is a reasonable, low-

cost approach. However, golf cart batteries

only work in smaller systems.

The second commonly used flooded

lead-acid battery type is the L16. These

This 24-volt set of high-capacity industrial cells could offer up to 15 or more years of service.

Many assume Many assume Many assume

a homestead a homestead a homestead

system will be system will be system will be

12-volt because 12-volt because 12-volt because

that’s all that’s all that’s all

they’ve seen.they’ve seen.they’ve seen.

http://www.barnlightelectric.comwww.barnlightelectric.com

800-407-8784

BAR N LIGHT ELECTRIC

WHERE VINTAGE

AND MODERN

WHERE VINTAGE

AND MODERN

Collide®

Circle #2; see card pg 97

ALLAN SINDELAR (3)

p 61-64 Battery Power.indd 62 10/13/16 3:09 PM