It's important to note that you should never connect a battery directly to a solar panel because you risk damaging both pieces of equipment. There must always be a controller or regulator between the two.
Charge controllers are necessary for solar panel systems, since they regulate the flow of current between the battery and the charging device. Without a charge controller, the voltage in the battery can be excessive and can result in a short life.
Charging a 12V battery isn't as simple as connecting the solar panels to the terminals. Directly charging a 12V battery with photovoltaic panels isn't possible. You'll need the appropriate tools and components to connect the solar panels: 12V battery.
As a rule of thumb, you can connect your solar panels directly to a battery if the output voltage (Vmp) doesn't exceed 35% of the rated battery voltage. That's 16V max. for a 12V battery.
Many installations require a charge controller to help bridge the gap between the PV panels and batteries. This charge controller is a voltage and current regulator designed to prevent your solar batteries from overcharging.
Instead, the charger stops charging the battery when it has reached its desired voltage to keep the lifespan longer. It's not ideal to connect a solar panel directly to a lithium battery.
Depending on the charging capacity, it will take around 4-20 hours to charge a 12V battery with a single 100W solar panel. If you want to charge the battery fast, you can increase the number of solar panels you use for charging.
You need around 310 watts of solar panels to charge a 12V 100Ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller. You need around 380 watts of solar panels to charge a 12V 100Ah lithium battery from 100% depth of discharge in 5 peak sun hours with a PWM charge controller.
Although solar panels can directly charge the batteries, this is only sometimes the case. Solar panels can be used to charge batteries. Typically, a charge controller is required to protect the battery by converting the voltage output from the solar panel to a level appropriate for the battery being charged.
20W and 50W solar panels are good for fast charging small 12V batteries. For example, a 20W solar panel can charge a 20Ah 12V battery in around 17 hours of direct sunlight. A 50W panel can do it in around 8 hours. 80W and 100W solar panels are good for fast charging large 12V and car batteries.
The charge controller is one of the most vital components of the solar panel system. It helps guard the battery against overcharging and improves its lifespan; otherwise, directly connecting the panels to the battery can cause overheating and explosions. You can go for the PWM or the MPPT charge controller.
How to parallel connect solar panels to an inverter. The positive terminal of the solar panel is connected to the positive terminal, and the negative terminal is connected to the negative terminal. This makes it easier to connect the panels in series. This allows for a better connection of all panels together.
You always need a solar charge controller if you are installing an off-grid solar system with batteries. Only the smallest panels — such as 1 or 5-watt trickle chargers — can operate without a controller. You do not need a solar charge controller for grid-tied residential systems.
Solar Regulators: The Bottom Line
Unless your DC to DC charger has an inbuilt one, then yes! You do need a solar regulator. Further, solar regulators are the key to making sure your panels will serve their purpose for a long time. Regulating the power flow prevents the battery bank from being overcharged.
Think of the charge controller as a strict regulator between your solar panels and solar battery. Without a charge controller, solar panels can continue to deliver power to a battery past the point of a full charge, resulting in damage to the battery and a potentially dangerous situation.
If you're using a 12V 100Ah lead acid battery, you can expect the fridge to run for about 30-50 hours because lead acid batteries can only be discharged to 50%.
100Ah battery will run a 400W appliance for 3 hours. 100Ah battery will run a 100W appliance for 12 hours. 100Ah battery will run a 1W appliance for 1,200 hours.
In summary. If you have a 12 volt 100ah battery and you buy a 300w solar panel, it will only take you 4 hours to fully charge it.
You'd have to do a bit of math for this but don't worry, it's very simple to calculate a rough estimate of how much power you need for your panels. All in all, you'd need around 300W of solar panels for pairing with your 120Ah battery.
How Many Batteries Can a 100 Watt Solar Panel Charge? Typically, a 100 watt solar panel at its maximum efficiency can charge a single 100Ah 12V battery in a day. This calls for at least 8 hours of sunlight with no obstructions in between the sun and your solar panel.
Although many existing lead-acid chargers will still charge our Lithium battery, it is generally discouraged to do this. The risk is the lead-acid chargers may wind up in fault code condition at some point, despite the Lithium battery probably having received a full recharge.
The simplest possible solar battery charging circuit is just to connect the positive wire from a solar panel to the positive battery terminal, and the negative solar panel wire to the negative battery terminal. This was the main practice back in the day, and will quite happily charge a battery!