An off-grid solar power system is one that
gets most or all of its electricity from the sun using solar
panels (photovoltaic panels) and none from a power utility such as
a hydroelectric dam, nuclear, coal or natural gas fired plant, ...
The grid, which the system is "off" of,
refers to the complex network of power lines that connect the
utilities to the numerous buildings that use the power. Since in many
locations there may be clouds for days or weeks at a time, off-grid
systems usually have a back-up generator as well. In addition they
may have wind turbines, microhydro and other small electricity
The following is a simplfied diagram of an off-grid system.
The various parts are:
- solar panels - These take the
solar energy from the sun and turn it
into electrical energy, electricity.
- batteries - Since the sun doesn't
always shine, the electrical energy has to be stored somewhere
for use in the meantime. We store it in batteries.
- charge controller - This controls
charging of the batteries, similar to how as a cell phone charger
controls charging of a cell phone.
- service box - This part you should be
familiar with since you already have one of these. This is your
breaker panel with all your breakers in it for in case there is
an electrical short somewhere.
- loads/appliances - Your lights, fridge,
fans, clocks, ...
- generator - A diesel, propane or
natural gas generator for generating power in case there hasn't
been sun for a long time and the batteries are dead. This will
provide elecricity when that happens.
- inverter - Takes the power in the
batteries and converts it into a form suitable for your
loads/appliances. It also takes power from the generator and
passes some through to your loads/appliances and uses some to
charge the batteries.
Here's another diagram with more of the parts filled in.
The added parts are as follows:
- solar array - If there are multiple
solar panels in a system then they're collectively referred to
as a solar array.
- battery bank - Multiple batteries in a
system are referred to as a battery bank.
- disconnect switches - Throughout
the system there are switches that are normally closed but
are in place in case a part needs to be isolated for repairs
and to prevent a short circuit in the system from damaging parts.
For example, the charge controller has disconnect switches
to either side of it.
- inverter bypass switch - If the solar
system can longer supply power to the loads then this allows
the generator to take over while the solar system is repaired.
- lightning arresters - Lightning
arresters are on any wires that may bring damaging electrical
current into the system from lightning. For example, if lightning
strikes the solar panels then the panels will be damaged but
the lightning arrester at the charge controller should protect
- combiner box - Depending on the number
of solar panels and how they're wired up, it may make sense to
have a box near the panels that combines many of the wires coming
from them into just a few wires for the long distance to the
- display and control unit - Some systems
allow networking of their components so that they can be controlled
and monitored from a single box, usually with an LED display.
For example, OutBack's MATE and Magnum Energy's Remote Control.
- shunt - Part needed if you're going
to be using an amp hour meter or battery monitor of some sort.
Allows for monitoring of current going into and coming out of
the battery bank.
amp hour meter page for more details.
- amp hour meter - A device that monitors
the battery's state of charge (SOC) by measuring the electrical
current going in or out of the battery bank. Also referred to
as a battery monitor.
amp hour meter page for more details.
- automatic generator starter - If the
batteries are low and there is no sun then the generator is
run to top up the batteries and take over supplying power to the
loads. This can either be done manually or be done automatically
as a feature of the inverter, charge controller, display and
control unit (e.g. OutBack's products) or a standalone automatic
generator starter box (e.g. Magnum Energy's Auto Generator Start
Additional components not shown above are those needed for
powering pumps using solar which you can
learn about on the solar pumping page,
including pump sizing.
And of course you need wires that are appropriate sizes both
for safety reasons and to make sure you get the required performance.
For the latter, see the
page about sizing wires to maintain the necessary voltage over long
distances such as from the solar array to the charge controller
calculating the voltage drop.
Designing/sizing an off-grid solar power system
A number of online calculators have been developed and made available
here to help you design your off-grid system. They are very detailed
and will require real time and focus to complete. This is an
iterative process in that results from one calculator may make
you go back and redo calculations in other calculators. Each will open
in its own window/tab and clicking on links in the body section of
those pages will also open new windows/tabs so that you don't lose
Maintaining an off-grid solar power system
And off-grid system is not plug-and-play. The solar panels need to
be kept clean, the generator needs to be kept fueled and to have
its oil changed periodically, and the batteries needs all sorts of
maintenance to keep them working well and to have a long life.
See these pages
on battery maintenance for details on that.
Detailed video tour of an off-grid system