Components for your PV (Solar Electric) System

Charge Controller

C40 Charge Controller

Every solar electric system with batteries should have a charge controller. A charge controller regulates the amount of current the PV modules feed into a battery bank. Their main function is to prevent overcharging of the batteries, but charge controllers also block battery bank current from leaking back into the photovoltaic array at night or on cloudy days, draining the battery bank. The two main types are PWM (Pulse Width Modulated) and MPPT (Maximum Power Point Tracking). PWM technology is older and more commonly used on smaller solar arrays. Choose a PWM charge controller that is the same nominal voltage as your solar array and battery bank. The controller must also have enough capacity (in rated Amps) to handle the total current of the solar array safely. MPPT charge controllers can track the maximum power point of a solar array and deliver 10-25% more power than a PWM controller could do for the same array. They do this by converting excess voltage into usable current. Another feature of MPPT charge controllers is their ability to accept higher voltage from the solar array for output to a lower voltage battery bank. Charge controllers typically cost between $50 and $750 depending on size, type and features.

Batteries

Deep Cycle Battery

Batteries chemically store electrical energy in renewable energy systems. They come in several voltages, but the most common varieties are 6 Volt and 12 Volt. The three types of batteries that are most common to RE systems are Flooded Lead-Acid (FLA), Sealed Absorbed Glass Mat (AGM), and Sealed Gel Cell. Flooded lead-acid batteries are the most cost-effective variety. They require maintenance that involves monitoring voltage, adding water, and occasional equalization charging. Additionally, FLA batteries vent hydrogen under heavy charging so they must be stored in a ventilated enclosure. Because of the maintenance issues of FLAs, some people prefer sealed batteries, which don’t require maintenance. Since they are sealed, they do not require watering, nor do they typically vent any gasses. AGM batteries cost more and are more sensitive to overcharging than FLAs.  Gel Cell batteries are similar to AGMs in that they are also sealed and therefore do not require maintenance, but tend to be the most expensive of the three types. The useful life of all battery types is measured in charge cycles rather than units of time. Depth of discharge is directly related to number of charge cycles possible: the deeper you drain batteries each time you use them, the fewer charge cycles you will get from them. Sealed batteries tend not to last as long as flooded batteries. Well-maintained FLAs can last as long as ten years, with sealed batteries lasting closer to five years. Other factors to keep in mind are that some of these batteries weigh over 200 pounds and, depending upon capacity,  can cost anywhere from $20 to $1200 each. So, given the maintenance issues, weight and expense, consider your energy storage needs very carefully. Planning for five days of battery storage for your system may not be your best option!