inverter. Several banks could also be split up on individual
timers so they are powered on sequentially for a charge
session. Even finicky lithium-ion (Li-Ion) batteries can be
charged in this fashion (Figure 3).
Powering wall warts with solar panels will also help
to recoup some of the inherent inefficiencies of less
expensive power inverters. Cheaper inverter models will
often have a significant idle power draw, consuming up
to 10 watts even when no load is attached. Deploying
these inverters on timers will cut their standby draw on
the batteries to zero, but will still allow you to use them.
Even better is to take the DC output from the panel
and charge batteries directly. By eliminating the inverter,
you can gain some additional efficiency. You still will
need to provide regulation to protect the batteries under
charge. One cheap and dirty way to do this is to use a
mobile multi-voltage power adapter — it is not the most
efficient converter, but it will hold the output voltages
through swings caused by passing clouds and other
weather changes (Figure 4). The balance you are working
for is one between efficiency and convenience. An
elegant setup will provide both convenient access to
your appliances and be energy efficient.
Imagining this probably conjures images of a horrible
DC power octopus in the center of your house — not a
very convenient arrangement. One possible solution is to
create a separate DC power distribution system within your
home. This is actually easier than it sounds. Most homes
have phone systems with at least four pairs of telco wires
— a pair of these could be utilized to distribute low-current
DC throughout your home to charge small devices.
In the old days, the telephone company actually used
a pair of your internal phone wires to power the lights in
your “princess” phones with — you guessed it — an 18
VAC wall wart. With local regulation, a solar panel or
single DC power supply could be set up to provide trickle
charging or efficient lighting power to all of the rooms in
your home though existing telco jacks. Remember that
if you use this approach, telco wire has a very small safe
current carrying capacity of only a few watts.
Still another approach is to convert mission-critical or
negotiable loads into battery charger loads. You can do
this by using a deep-cycle battery to power an inverter
which, in turn, runs these loads. This approach may seem
complex, but it is fairly trivial to implement.
For example, we have a shallow water well and septic
pump in a remote vacation home which we power in this
fashion. When these loads cycle, they are drawing power
from the battery directly, or through a load-sensing AC
inverter. Otherwise, the battery is being charged by a
solar panel. This method is especially effective for loads
that cycle rarely or infrequently but require continuous
Finally, another tactic is to automate power savings.
For example, with a house full of kids you may find it is
cost-effective to replace the light switch in the basement
with an IR (infrared) sensing switch. This type of switch
will turn the lights on when a warm body is in the
room but after a set time interval without warm-body
movement, it will turn the lights off.
This type of switch can also be set up to power
appliances only when people are present. This is great for
rec-room environments where devices like video games,
TVs, and stereos should be off when nobody is using
them. When the kids forget to turn the lights out manually,
an IR switch can also save you energy and money in
the long run.
Saving energy is a personal challenge that collectively
can add up to a significant national effort toward energy
independence. Start with taming the lowly wall wart and
you can make a difference!
Remember to be safe, and have fun whatever you do! NV