The solar electric systems associated with the term “solar” are usually simple grid-tied types, with PV modules and an inverter or inverters for converting DC from the modules to AC for running loads. They save their owners money by offsetting utility bills or selling back power to the utility, and that’s as far as they go.
But much of the world is not connected to a grid, or even nowhere near one. In these situations, all electricity has to be generated on-site. These sites can range from remote communities, resorts, farms, and cabins to mines, oil & gas fields and pipelines, national park facilities, traffic control systems, railroad systems, marine platforms, monitoring stations, security installations, maritime navigation systems, remote highway lighting, weather stations, and much, much more.
In these applications, the main reason to “go solar” is not so much going green as it is saving green—in this case, saving the dollars it might take to connect a remote location to a grid. Under the best circumstances with minimal terrain considerations, it can cost a minimum of $25,000 just to run a mile of transmission line for a single home in the developed world—and in less developed places with multiple users or greater energy needs, and with mountains, rivers or forests to contend with, the cost increase maybe hundreds of times that often prohibitive. So are generators, which require expensive maintenance, constant fueling, and produce round-the-clock noise and emissions. Often in these situations, solar is not just the cleanest choice—it may be the only choice.
Anywhere there’s no grid, or a weak or intermittent grid, solar electricity generated on-site must be stored for use when the sun isn’t shining. That’s where Morningstar solar controllers come in. The charge controller is the “heart and brains” of a solar electric system relying on batteries to operate. The controller ensures that the batteries are neither over-charged or under-charged, or drained too deeply, or operated in extreme temperatures since all those conditions can dramatically shorten their life. The controller also controls loads, such as lighting systems connected to solar modules and batteries, for timely operation. If there’s an inverter in the system the controller “partners” with it to ensure optimum battery charging.
This simplified diagram below illustrates the major components of an off-grid system and how it works: