Although they are most common in remote locations without utility grid service, off-grid solar power systems can work anywhere. These systems operate independently from the grid to provide all of a household's electricity. That means no electric bills or blackouts—at least none caused by grid failures.
People choose to live off-grid for a variety of reasons, including the prohibitive cost of bringing utility lines to remote home sites, the appeal of an independent lifestyle, or the general reliability a solar power system provides. Those who choose to live off-grid often need to make adjustments to when and how they use electricity, so they can live within the limitations of the system's design. This doesn't necessarily imply doing without, but rather is a shift to a more conscientious use of electricity.
ILLUSTRATED BELOW
gives you complete independence from the grid.
- Solar panel array
- Mounting racks
- Combiner/Array disconnect
- Charge controller
- DC breaker box
- Inverter
- AC breaker Box
- Battery Bank
- Optional: System Meter
- Optional: backup generator
Solar electric panels—a.k.a solar modules, photovoltaic (PV) panels.
Pointed towards the sun, solar panels capture the energy in sunlight and convert it directly to DC electricity. There are three general families of solar panels on the market today—single crystal silicon, polycrystalline silicon, and thin film.
PV modules are very durable and, because there are no moving parts, long-lasting. Most carry 25 year warranties. Solar panels are assigned a rating in watts based on the maximum power they can produce under ideal sun and temperature conditions. You can use the rated output to help determine how many panels you need. Multiple modules mounted together are called an array.
Array Mounting Rack—a.k.a. mount, racks, trackers.
Mounting racks provide a secure platform to keep your panels fixed in place and oriented correctly. Panels can be mounted on your roof, atop a steel pole set in concrete, or at ground level. The type of rack you choose will vary considerably depending on your budget, climate, building codes, and personal preferences. In areas where it snows a lot, you may want to be able to sweep the snow off periodically.
Array Combiner/DC Disconnect
The DC disconnect is used to safely interrupt the flow of electricity from the array of solar panels. It is an essential component when system maintenance or troubleshooting is necessary. The disconnect enclosure houses an electrical switch rated for use in DC circuits. It also may integrate either circuit breakers or fuses, to combine the electricity of multiple sub arrays of solar panels.
DC Breaker Box
All DC goes into this and all DC goes out of it. It is where you ground your system. It has input DC breakers for solar and output DC breakers for the inverter(s) for DC loads. It can also have an input breaker for a windmill or hydro turbine.
The Charge Controller built into a the Outback Power Center pictured at right uses maximum power point tracking (MPPT) to optimize the array's output, increasing the energy it produces. The controller operates the array at its maximum efficiency and feeds the electricity into the inverter after your battery bank is filled to capacity.
A charge controller will also protect your battery bank from overcharging. It monitors the battery bank. When the bank is fully charged, the controller interrupts the flow of electricity from the PV panels. Batteries are expensive and lose potency when under or over-charged, so the controller extends the life of your batteries.
Battery Bank
The battery bank stores energy from your solar arrays. Electricity leaves the batteries in DC (direct current) form and must be converted to AC before powering your appliances.
System Status Meter
System meters measure and display several different aspects of your solar system's performance. They can track how full your battery bank is, how much electricity your solar panels are producing or have produced, and how much electricity is in use. Operating your solar electric system without metering is like running your car without any gauges. It's possible, but you won't know when you're about to run out of juice.
Main DC Disconnect
In battery-based systems, a disconnect between the batteries and inverter is required. The disconnect allows the inverter to be quickly disconnected from the batteries for service, and to protect against electrical fires. We always flipped the disconnect during heavy-duty lightening storms!
Inverter
Inverters transform the solar-produced DC electricity into the alternating current (AC) electricity commonly used in most homes for powering lights and appliances. Grid-tied inverters synchronize the electricity they produce with the grid's "utility-grade" AC electricity, allowing the system to feed solar-made electricity to your home or to the utility grid.
Battery-based inverters for off-grid or grid-tie use often include a battery charger, which is capable of charging a battery bank from either the grid or a backup generator during cloudy weather.
All grid-intertie inverters can be installed outdoors (ideally, in the shade).
AC Breaker Box.
Includes main AC breakers and inverter bypass/disconnect breakers, and breakers for generator input into the system.
Optional Backup Generator
Off-grid systems can be sized to provide electricity during cloudy periods when the sun doesn't shine. Sizing a system to cover a worst-case scenario, like several cloudy weeks during the winter, can result in a very large, expensive system that will rarely get used to its capacity. To spare the pocketbook, some folks include a backup generator.
You can buy generators which are fueled with biodiesel, petroleum diesel, gasoline, or propane. These produce AC electricity that a battery charger, built into the inverter, converts to DC energy, which is stored in the batteries. Like most internal combustion engines, generators tend to be loud and messy and necessitate hauling fuel in to your site.
