A question we often receive is, “Can I link my solar panels directly to the battery?” Although it is technically possible, we strongly recommend not doing it. A battery is a delicate object, and the strong electrical power from solar panels might easily damage it. A charge controller serves as a safety barrier between solar panels and a battery and should be included in every household solar panel setup. In this article, we will show you how to connect solar panels, a regulator, and a battery.
The charge controller helps protect the battery
What does a controller actually protect?
A charge controller is used for:
• reduces the voltage of panels to match the battery’s level. When the battery is connected directly to panels with a higher voltage, the battery gets hot. It not only makes a battery last less time, but it can also cause it to explode.
• stops charging when full. If you recharge the battery after it’s completely charged, its temperature increases because it tries to take in more electric current than it can handle. Therefore, you experience quicker aging, less ability, and a potential explosion in the most severe situation.
• prevents the use of a battery when it is deeply discharged. Regularly fully discharging a battery reduces the number of times a battery can be charged.
• stops backward flows of electricity. During the night, electricity can go from the battery back to the panels, which can cause the temperature to increase and perhaps result in fires in the PV modules.
• lets you check the condition of the panels and the battery
Solar controllers manage the voltage of panels in various ways. The PWM controller reduces it to the level of the battery. An MPPT controller, however, utilizes the additional voltage from the panels and converts it into electricity.
PWM and MPPT
PWM (Pulse with Modulation) and MPPT (Maximum Power Point Tracking) can be used interchangeably when the voltage of the solar panels is somewhat higher than the voltage of the battery. For instance, you may set up either of them using 30-cell panels and a 12V battery or 60-cell panels and a 24V battery. However, even in these situations, an MPPT controller enables you to collect an additional 20–25% of energy. This kind of solar controller is particularly effective during the winter, when panels reach their highest voltage levels.
OutBack FM80-150VDC 80A FLEXmax MPPT Charge Controller
Battery compatibility Lead acid, 48 VDC Lithium-ion Controller type MPPT Charge Controllers Maximum charging current 80 A Maximum voltage of the solar panels 150 V
Morningstar TriStar TS-45 45A PWM Charge Controller
Battery compatibility Lead acid Controller type PWM Charge Controllers Maximum charging current 45 A Maximum voltage of the solar panels 125V
Schneider Electric Charge Controller Conext XW-MPPT100-600
Battery compatibility Lithium-ion, Lead acid Controller-type MPPT Charge Controllers Maximum charging current: 100 A The maximum voltage of the solar panels is 600 V
Calculation the highest voltage and amperage
To select a charge controller, we have to find the maximum current and make sure it fits our solar power system. The controller’s amperage should be greater than the total power of the solar panels divided by the battery voltage. Calculating the formula looks like:
Current = 1.25 * (PV_power * Num_PV)/ Battery_Voltage
where is: current to charging, PV power, solar panel power. Everything is multiplied by 1,25 (increased for 25%) for safety reasons. The size of a controller must be bigger than the current.
Wirring with batteries
Whether you have a PWM controller or an MPPT regulator, the process of connecting it to the batteries and panels is the same. Usually, a charge controller has three wiring sections: one for panels, one for a battery, and one for DC loads. We’ll use a basic copper wire and connect the black wire to the charge controller’s “minus” terminal and the battery’s “minus” terminal. Next, we’ll use a red wire to connect the charge controller’s positive terminal to the battery’s positive terminal. Next, we will fasten the wires securely into the charging controller.Switch on the charge controller; it should be capable of measuring the battery’s charge. The user handbook of a charge controller should have a wiring schematic that you can refer to if you are unsure.
Connection to solar panels
Once you have linked the charge controller to the battery, it is now secure to connect it to the panels. From the junction box of a panel, there are two cables, one positive and one negative. In certain cases, there are only two wires that directly connect to the controller. Usually, there are MC4 connectors on both ends, with a “male” connector for the positive cable and a “female” connector for the negative one. First, we have to join MC4 connections with a matching set of connectors that have wires on the other ends. If you have two wires going out directly from the junction box, you can skip this step.
Next, we have to connect these wires to the regulator: the positive wire goes into the “+” terminal, and the negative wire goes into the “-” terminal. After we have linked the panels to the controller, it should be able to identify them. See the condition of your array on the charge controller screen. Solar panels begin producing electricity as soon as they are exposed to sunlight.
In aplicatioin SPAC we have five tabs about characteristics of selected solar panel. First tab contain general information. Second tab contain mechanical characteristics. Next two tabs contains electrical characteristic Voltage and Amperage.
Pros and Cons
MPPT
• High efficiency (90%)
• converts extra voltage of panels into current
• manages charging process
•connect via bluetooth to connect to to a laptop or a smartphone
10-15 year lifespan
• more expensive than a PWM-controller
PMV
• 15+ year lifespan
• smaller than MPPT
low efficiency ( about 80%)
• works well only when the voltage of panels is slightly higher than the voltage of a battery
Battery connection combinations
The combination of parallel and series connections easily obtains the desired voltage and power of the Kooja panel required. The total power of the solar system in W remains the same, whether the panels are connected in series or in parallel. When connecting the panels in parallel (depending on the number of panels), a thicker cross-section of the wire used to connect the panels is necessary. Depending on the desired power and selected components, the nominal voltage of the system varies from 12V to 96V and even more for large on-grid systems. Accordingly, and depending on the batteries that you can find on the market as well as your budget, it is necessary to correctly dimension and connect the batteries in order to obtain the desired nominal voltage for your system.
Parallel battery connection
When linking batteries in parallel in a solar system, all positive contacts are connected to one branch, while all negative contacts are linked to another branch. Positive contacts are consistently indicated in red, whereas negative contacts are denoted in black. When batteries are connected in parallel, the voltage of one battery becomes the voltage of the entire battery system. Additionally, all batteries in the parallel system must have the same nominal voltage. Hence, it is impossible to link batteries with voltage ratings of 12V and 6V. Furthermore, when batteries are connected in parallel, the similarity in their Ah rating becomes inconsequential. In a parallel connection, it is feasible to combine batteries from diverse manufacturers with varying Ah ratings, as well as mix new and old batteries. Each battery will consistently deliver its maximum power during discharge and draw precisely the amount of electricity it requires, without any risk of overcharging.
Serrial battery connection
We connect the end plus and end minus to the device. When connecting batteries in series, the voltage of all batteries adds up. We can connect 12V and 6V batteries in series, but only if they have the same number of Ah and are from the same manufacturer. However, this is a rare case since batteries are usually connected in series with the same rated voltage and capacity in Ah, which we will discuss here. When connecting batteries in order, it is very important to note that only batteries must be connected in order. – From the same manufacturer, possibly with the same production date and the same lot, batteries must be of the same capacity and condition.
Conclusion
There are several variants of connecting solar panels and batteries. The charger controller is a necessary intermediary between them because it prevents equipment damage and fire. If in an off-grid solar system the devices work at a voltage of 24 V, we can choose batteries of that type or a smaller voltage of 12 V and then increase their capacity by connecting them in parallel. In all this, take into account how the charge controller fits. The charging voltage should be similar to the battery voltage, except for the MPPT-type charge controller, which can trim the higher voltage. With all this, there may be an increase in the charging current (take into account the thickness of the cables to reduce resistance and the eventual breakdown of the system).
