From an analysis
by Roger Andrews, of a
Tesla/Solar City system
installed on the island
of Ta’u.
The island is in
American Samoa,
near the equator.
It received a grant
for solar panels,
plus 3-day battery
backup, to provide
electricity for
the tiny island.
Any outages longer
than 3 days would be
handled by a diesel
generator.
Adding just a 3-day battery
backup, more than doubled
the cost of the solar panels.
That cost does NOT
include at least one set
of replacement batteries,
likely to be needed
during the lifetime
of the system.
On Ta’u, which is
near the equator,
even with the
diesel power backup,
the solar system was
designed to produce
40% more power than
the island's average
daily needs for
electricity.
Other areas, not near the
equator, are likely to need
even more surplus
solar energy capacity.