Generators and Charge Controllers for
Standalone PV Systems
Generators can provide backup power for a standalone PV system if battery
voltage recedes below a number of different programmable minimum set levels.
Set levels may include voltage settings, current draw settings, or time settings at or
under a specific condition.
Most standalone PV power systems of any real size (over 1,000 DC watts)
have standby generators. These generators are gas or diesel powered. They deliver
energy during long-term dark days as in winter or when the battery discharge
reaches a set level. Standby generators should comply with NEC Article 230 for
Electrical Service Requirements, Article 250 for General Grounding Require-
ments, Article 445 for Generator Installation Requirements, and Article 700 for
Emergency Power System Safety Installation and Maintenance Requirements.
You will get more power out of your system, and have greater control over the
batteries, energy, and the information about how your system is working if you
use a more sophisticated charge controller, such as one with MPPT. When you
compare the additional performance of a properly designed system with a cheap,
bare-bones product, the cost is going to favor the better controller.
The purpose of the charge controller is to charge the battery from the power
produced by the PV array. The charge controller, when sized and programmed
properly, extends the life of the battery while maximizing the energy storage
capacity of the battery. It helps ensure that the PV system operates efficiently. Bat-
teries are complex and sensitive. They are easily overcharged and over-discharged.
Read the charge controller manuals cautiously, thoughtfully, and thoroughly. It is
easy to damage the battery and controller during installation.
Charge controllers have many functions, such as:
Properly charging the battery
Shielding the battery from overcharging
Limiting the charging voltage
Stopping reverse current to the PV array during the night
Protecting circuits from overloading
Compensation for changes in battery temperature to coincide with
Safeguarding against lightning
There are several types of charge controllers—series, shunt, deep discharge
protection, and MPPT.
122 ADVANCED PHOTOVOLTAIC INSTALLATIONS