Main components of small off grid systems
For most DC-coupled off-grid systems it really comes down to four main components – solar panels, charger controller, inverter (if needed) and the battery bank.
Photovoltaic means 'voltage from light' and refers to a solid-state semiconductor device, aka solar cell, that produces a potential difference (voltage) and current of electrons (electricity) when exposed to light. PV solar panels, or modules, are solar cells assembled between protective layers of glass and plastic and typically framed in aluminum.
Using solar power is all about timing. Solar panels produce electricity when sunlight is shining on them, usually between 11 am to 4 pm. They provide more power when the sunlight is more intense and not reduced by cloud cover. They will produce some on a cloudy day, too, but typically less than 10% of what they would on a sunny day. And of course, they don't produce at night.
The solar PV modules are available in a range of brands, sizes, and output capacity in some ways, the easiest part to source. Look for modules with all the necessary approvals (UL, CE, or CSA labeled) and a 25-year warranty on their power output.
Typically made in aluminum, solar panel racks are mounting systems used to secure the modules.
The primary function of a charge controller is to regulate the flow of electric current from the array of solar modules to the batteries. This ensures the batteries are correctly charged and prevents damage from over-charging. Charge controllers come in a range of capacities based on the voltage and current they can handle. A great feature to look for is high-voltage maximum power point tracking (MPPT). An MPPT charge controller can accept the input from the solar modules at high voltage and charge the batteries at an appropriate lower voltage, using an optimization algorithm to maximize the amount of power going to the battery bank.
The two common types available are deep-cycle lead-acid batteries and lithium-ion batteries. Both types of batteries work well and provide dependable energy storage for off-grid solar power systems.
Lead-acid batteries have been used for well over a century. They're relatively affordable and can provide plenty of electric currents. Lead-acid batteries last approximately ten years, or 1,500 cycles, providing they are well-maintained and used as directed. They are large, heavy, and require periodic maintenance, such as refilling water in the cells. They contain a mix of a recycled and new lead, a toxic metal that must be recycled properly.
Lithium-ion batteries are lighter and smaller than lead-acid batteries. They are significantly higher in price to purchase than lead-acid batteries but require less maintenance, withstand deeper discharges, and last about 13 or more years, or 2000 cycles. Lithium-ion batteries are made from a mix of recycled and new lithium, a rare and reactive metal that must be recycled properly.
It converts direct current (DC) to alternating current (AC) suitable for home appliances
PV modules and batteries produce electricity in the form of direct current (DC). This can charge devices that use DC, like phones, tablets, and battery maintenance chargers. You can get DC lighting and appliances for your off-grid place, especially at motorhomes and sailing boat shops. But the most commonly available and affordable appliances run on alternating current (AC), and the wiring for AC in a building is more standard for electricians. A highly efficient device called an inverter can convert DC from your batteries to AC for your house wiring. For home use, there are two basic kinds of inverters: micro-inverters and string inverters.
-- Illustrations by Crystal Chen