Energy and Human Ambitions on a Finite Planet, 2021a

13 Solar <strong>Energy</strong> 213
Cars have a similar problem: a top area around 10 m 2 equipped with
the most expensive PV money can buy would get 5 kW, or less than
7 horsepower. That’s about 20 times less powerful than typical cars,
so again: light <strong>and</strong> slow.
13.6 Residential Solar Considerations
Despite these drawbacks, it can still make a lot of sense 73 to invest in
solar photovoltaics for the home. We’ll explore sizing <strong>and</strong> cost in this
section.
73: The author runs most of his house from
an off-grid PV system he built: a solar enthusiast
when it comes down to it.
13.6.1 Configurations
A typical household uses much or most of its energy when the sun
is not shining: lighting, cooking, evening entertainment, charging an
electric vehicle, etc. To get around this, the system would need to have
local storage, 74 or be tied to the regional electrical grid so that excess
production can be exported in the daytime <strong>and</strong> electricity produced
by the utility used at night or when household dem<strong>and</strong> exceeds solar
production. The overwhelming majority of solar installations in the U.S.
are grid tied, <strong>and</strong> very few mess with batteries, which can double the
cost of a system <strong>and</strong> need replacement before the system has paid for
itself in electricity bill savings.
74: . . . batteries: expensive, require maintenance,
<strong>and</strong> periodic replacement
Box 13.4: Disappointing Dependence
A disappointing surprise to many who “go solar” is that their house
has no power when the electrical service to the house is disrupted—
even in the light of day. A grid tied system needs the grid to operate.
Safety concerns prohibit PV systems from continuing to energize a
disabled grid.
Only “off-grid” battery systems continue to work in these scenarios,
but then the disappointment shifts to the price tag, maintenance, <strong>and</strong>
replacement of worn-out batteries after a few thous<strong>and</strong> cycles.
While a description of the components <strong>and</strong> practical workings are beyond
the scope of this book, students might be interested in an article the
author wrote after first getting started tinkering with PV systems [90].
[90]: Murphy (2008), “Home photovoltaic
systems for physicists”
13.6.2 Sizing <strong>and</strong> Cost
How large does an installation need to be? If the goal is to cover annual
or monthly electricity use in a grid-tied system, the only two pieces
of information needed are the typical electricity consumption in the
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.