164 Week 5: Resistance
This internal resistance will quite naturally cap the power and current the battery can provide as
one cranks up the load on it. It still doesn’t indicate the way voltage and current depend on things
like temperature, the degree to which the battery is discharged already, and how old the battery is –
allof these things and more affectrealbatteries, dynamos (electric generators), solar cells, and any
other method we have of turning (potential) energy into electricalpower. But we will do quite well
with our idealized battery, and even better with our idealized battery with an internal resistance –
the rest is a mix of more advanced physics and associated engineering and doesn’t change the idea,
only the details.
5.1.1: Batteries and Renewable Energy
Before we move on to resistance, it is worth pointing out that battery physics and engineering are
importantin our society, and becomingmore importantas we move in the direction of renewable
energy sources, hybrid or flat-out electric cars, rechargable electronic devices galore and more.
One of the biggest obstacles to the widespread adoption of solar orwind generated power is the
difficulty of storing power that is generated when the sun is high and bright or when the wind blows
strongly for use at night or on calm days. With fuel-generated energy, as long as one provides the
fuel one can produce the energy! This is not possible with sunlight, and parts of the Earth get no
sunshine at all for months at a time (as well as sunshine 24 hours a day other months at a time).
Similarly, even “windy” locations can have calm weather for days or even weeks at a time.
It requires hundreds of pounds of lead-acid batteriesper personjust to store the average power
needed for a single day (say) generated from solar energy or wind energy collected in intervals
during that same day. Lithium batteries that store the same amount of energy are much smaller
and lighter, but lithium is an alkali metal and burns when exposed to air, making it more difficult to
safely engineer high-capacity batteries. Alternative battery technologies (say, zinc-oxide batteries,
lithium batteries, and more with very different chemistry, both wet and dry) are constantly being
explored, driven by the need to store at least a few days’ worth ofpower from intermittant sources
to bridge those times when the source is not available, as well as to make it possible for our laptops,
tablets, and phones to run for days on a single charge and for electrical cars to travel long distances
on a charge and recharge quickly.
The inventor(s) of a really, really compact and efficient way of storing energy would both make a
well-deserved fortune from the idea and would enable any number ofbeneficial changes to our energy
hungry society. In the meantime, rechargable batteries have andare likely to continue to have many
problems: They are (so far) bulky and massive, they get hot while operating at high power levels
(due to their internal resistance!), they are often made with toxicor comparatively scarce materials,
they are consequently difficult to safely dispose of, they (so far) wear out and can store much less
energy after a few hundred or at most a few thousand charges, they can explode or catch on fire if
overdriven (making them very nearly a munition in the hands of the unscrupulous or violent). Put
all of this together and so far, batteries arevery expensive, both in direct dollar cost per unit of
energy stored and in terms of environmental cost and risk! Yet there is little doubt that within the
decade, batteries will be running many if not most of our homes and cars in addition to all of the
things that they are used for now.
If this topic interests you you can learn a great deal about rechargable/secondary battery technol-
ogy (which is very much a moving target, where the costs per unit ofenergy stored by a rechargable
battery have decreased by some 60 to 80% over the last ten or fifteen years) by visiting:
Wikipedia: http://www.wikipedia.org/wiki/Rechargable Battery
To summarize: at this point (with this paragraph being written in 2017) large capacity, high
density, long lifetime rechargable batteries for capable of running a“typical” U.S. household (that
uses, say, around 30 kilowatt-hours of energy a day) costs less than $5000 at full retail to an individual