If you own a 12V battery, you might be wondering about the compatibility and size of a solar panel to charge it. Connecting a solar panel to a battery requires careful planning to prevent overcharging and ensure efficiency. In this blog, we will learn how to connect an 18V solar panel to charge a 12V battery and maintain its efficiency
What Size Solar Panel to Charge a 12V Battery?
When selecting PV solar panels for 12V battery ensure compatibility with a range of power outputs. The panel specifications must be matched with battery amp-hours, wattage, battery composition, voltage requirements, and energy consumption.
To find the required solar panel size, first convert the amp hours of the battery to determine the total wattage: Amp-hours (Ah) × Volts (V) =Watts (Wh)
100Ah × 12V = 1200 Wh
To charge in 10 hours, calculate using the formula: Total wattage (Wh) / recharge time in peak sun hours (h) = watts for panel
1200Wh/ 10h = 120 watts
As a result, a minimum of a 120-watt panel is required to charge your 12V battery in ten hours. Lithium-ion batteries demand more wattage than lead-acid batteries. Moreover, the choice of a charge controller is crucial for efficiency, regulating electricity flow, and preventing overcharging. Additionally, a power inverter is required to convert DC to AC for appliances.
How to Connect 18V Solar Panel to Charge 12V Battery
Understanding the voltage difference is critical when connecting an 18V solar panel to charge 12V battery. An 18V solar panel is intended to deliver approximately 18 volts, whereas a 12V battery is intended to be charged at approximately 12 volts. Because of the higher solar panel voltage, connecting them directly risks irreparable battery damage. Moreover, if the battery voltage exceeds the open-circuit voltage of the panel, it may not produce enough electricity.
Alternative methods are recommended to avoid potential disasters due to voltage mismatches. To increase efficiency, choose components and connections accordingly.
1. Use a Charge Controller
In off-grid solar setups with batteries, the charge controller is critical for controlling the current and voltage sent to loads. It is recommended to use a solar charge controller that effectively reduces the solar panel’s 18 volts to 12 volts for battery recharge. There are two kinds of charge controllers: PWM and MPPT.
A. PWM Charge Controller
A PWM (Pulse Width Modulation) charge controller acts as a switch that connects the battery and solar panels. During bulk charging, the switch remains turned on, ensuring constant amps while lowering the higher voltage from the solar cells to match the battery voltage.
For example, an 18V 100W solar panel generates 25V (open circuit voltage) and supplies 4.1 amps. The PWM controller reduces the voltage to 12 volts while keeping the amps constant, yielding a 50-watt output. However, this process reduces efficiency and causes power loss.
B. MPPT Charge Controller
An MPPT (Maximum Power Point Tracking) charge controller ensures that the battery receives the maximum current for utilization. It regulates voltage to maximize power delivery to loads while minimizing losses. Its internal mechanism adjusts the voltage output of the solar panels based on the voltage of the battery while increasing amps, making them 30% more efficient than PWM charge controllers. An MPPT controller is recommended when charging a 12-volt battery with an 18-volt, 24-volt, or even 48-volt solar panel.
Also See: 6 Best 30 Amp MPPT Solar Charge Controller
2. Use Converter (DC-DC)
A DC-DC converter is a cost-effective alternative to a charge controller that reduces the high voltage from solar panels to 12 volts for charging a 12-volt battery. Despite creating power losses, especially with larger solar panels, the impact on smaller panels such as 20W or 50W remains negligible.
Therefore, before connecting 18V solar panel to charge 12V battery, keep in mind the 12V battery input voltage limits, which range from 12V to 14V. Use a charge controller or DC-DC converter to mitigate the risks associated with incompatible voltage levels. This is critical, especially when more than six cells are shaded, as it can generate 16 to 18 volts. For this purpose, an MPPT charge controller is more efficient than a PWM. Various devices can be used to ensure safe and compatible charging practices.
You can also use a DC motor to charge a 12V battery with your solar panel.
Also, check out How to Connect Solar Panel to Battery Without Charge Controller
Can I Use 24V Solar Panel to Charge 12V Battery?
Now that you’ve learned about whether you can use an 18V solar panel to charge a 12V battery, let’s explore the compatibility of a 24V panel with a 12V battery. Yes, it is technically possible to use 24V solar panel to charge 12V battery, although it is not the most efficient method. The primary source of concern is the voltage difference between the typical open-circuit voltage of a 12V panel (around 22V) and that of a 24V panel (ranging from 36V to 44V). Because of variations in cell configurations, some panels labeled as 24V may have an output closer to 30V-40V.
These panels are intended to produce at least 30% more power than the batteries they are designed to charge. When connecting a 24V solar panel to a 12V battery, the higher voltage of the panel is reduced to match that of the battery. However, due to the lower voltage, this process is inherently inefficient, resulting in a suboptimal use of power.
To address this inefficiency, it is recommended to use an MPPT charge controller that functions as an auto-adjusting DC-to-DC converter. This controller optimizes the solar panel’s output at its power peak and then down-converts the voltage to charge the 12V battery at full wattage.
Must Read: How to Disconnect Solar Panels
Ultimately, utilizing an 18V solar panel for 12V battery is feasible but may lack efficiency. To establish a reliable connection, it’s crucial to understand voltage variations and choose appropriate components for your battery and solar panel setup. Adhering to these guidelines improves efficiency and safety, ensuring a consistently charged 12V battery.