Solar PV Battery Charge Controller (Voltage Regulator)
Solar PV Charge Controller / Battery Voltage Regulator
A charge controller (aka voltage regulator, charge regulator or battery regulator) regulates the electrical charge going from a solar panel array to a battery bank, protecting the battery cells from being overcharged when they battery become full.
The voltage regulator also stops reverse current flowing from the batteries to the solar panels, which would otherwise happen at night when the panels aren’t producing current.
Charge controllers are an essential part of any solar PV battery system. Other components include:
- Solar panel(s)
- DC/AC inverter
- Battery bank
Types of Charge Controllers
A Constant Voltage Regulator can either take a variable input DC voltage and convert it to a stable output voltage which can, depending on the converter, be higher or lower DC voltage than the input DC voltage.
Diversion (Dump) Load Controllers: have the capability of being either a solar charge controller, a DC load controller, or a diversion load controller.
The Low Voltage Disconnect (LVD) feature allows you to connect a DC electrical load that is the same voltage as your battery bank and have it turn off when the voltage of the battery bank is low. This protects the batteries from being drained (also known as deep discharging) which damages the battery cells and reduces their lifespan.
Types of charge controller
There are 2 types of solar charge controller:
- Maximum Power Point Tracking (MPPT) Solar Charge Controllers
- Pulse Wave Modulation (PWM) solar charge controllers
Both charge controllers adjust the charging rate based on the battery’s charge level to try and allow charging close to the battery’s optimum capacity, as well as monitoring temperature to prevent the battery from overheating.
PWM vs MPPT Solar Charge Controllers
The charge controller is a key component of a solar power battery storage system.
Comparing MPPT and PWM
If maximizing charging capacity were the only factor considered when specifying a solar controller, everyone would use a MPPT controller. But the two technologies are different, each with it’s own advantages. The decision depends on site conditions, system components, size of array and load, and finally the cost for a particular solar power system.
A maximum power point tracking (MPPT) controller performs well in colder conditions such as Scotland. As the solar panel’s operating temperature goes down, the Vmp1 increases – operating at a peak of around 17V at their peak power point at Standard Testing Conditions (STC is 25C°) – contrast this to the battery voltage of about 13.5V. The MPPT controller captures this excess module voltage to charge the battery. A MPPT controller can produce up to 20 – 25% more charging than a PWM controller in cool conditions.
a MPPT controller in cool conditions can produce up to 20 – 25% more charging than a PWM controller.
In comparison, a PWM controller is unable to capture excess voltage because the pulse width modulation technology charges at the same voltage as the battery. However, when solar panels are deployed in warm or hot climates, their Vmp decreases, and the peak power point operates at a voltage that is closer to the voltage of a 12V battery.
There is no excess voltage to be transferred to the battery making the MPPT controller unnecessary and negating the advantage of an MPPT over a PWM.
Array to Load Ratio
In a situation where the solar panel array is large, but the power draw from the load on the batteries is small, the batteries will remain close to a full state of charge. A PWM controller would be capable of efficiently maintaining this system without the extra expense of an advanced MPPT controller.
► Size of the System
Low power systems are better suited to a PWM controller because:
A PWM controller operates at a relatively constant harvesting efficiency regardless of the size of the array
A PWM controller is less expensive that a MPPT, so is a more economical choice for a small system
A MPPT controller is much less efficient in low power applications. Systems 170W or higher tickle the MPPT’s sweet spot
► Type of Solar Module
Stand-alone off-grid solar modules are typically 36-cell modules and are compatible with both PWM and MPPT technologies. Some grid-tie solar modules on the market today are not the traditional 36-cells modules that are used for off-grid power systems. For example, the voltage from a 60-cell 250W panel is too high for 12-Volt battery charging, and too low for 24-Volt battery charging. MPPT technology tracks the maximum power point (thus MPPT) of these less expensive grid-tie modules in order to charge the batteries, whereas PWM does not.
MPPT controllers are typically more expensive than PWM’s but are more efficient under certain conditions, so they can produce more power with the same number of solar modules than a PWM controller. One must then analyze the site to verify that the MPPT can indeed perform more efficiently when used in that system’s given set of conditions.
When specifying one technology over the other, the cost of the controller becomes less important than the total cost of the system. To specify a controller technology simply based of cost, be sure to perform a close analysis of realized efficiencies, system operation, load and site conditions.
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