How Long Does It Take For Solar Batteries To Charge? How Long Will It Last!

It takes 18 hours to fully charge a solar battery with a capacity of 200 amps with a 200-watt solar panel. The time it takes for solar batteries to charge depends primarily on the capacity of the battery and the power rating of the solar panel. Available sunlight is also a factor.

To illustrate let’s look at a simple example. Using a battery with a capacity of 200 amps and a solar panel rated at 200 watts here is what you would do step by step:

  1. Convert the watt rating of the solar panel into amps.
  2. Divide the capacity of the battery by the amps produced by the solar panel.

200 watts / 18 volts x 75% = 8.3 amps.

To get the energy produced by our solar panel in amps, we simply divide the watts, in this case, 200 watts by the voltage, in this case, we used 18 volts. We also need to account for inefficiencies that will reduce the solar panels’ output.

Under lab conditions in which solar panels are tested, they produce close to their rated output. In real-world conditions, they produce up to 75% of their rated output. This means instead of the solar panel producing 11.1 amps as its rating suggests, it will produce around 8 amps per hour of peak sunlight.

Peak sunlight hours are the hours when the sun gives off maximum solar energy. These are the hours close to midday. Early morning and late afternoon produce less solar energy so peak sun hours are used to estimate solar production.

Having converted watts to amps you can calculate how many hours your battery would need to get fully charged.

200 amps / 8.3 amps = 24 hours

This formula can be used to estimate the charge time of any size battery with any size solar panel.

Battery Size, Solar Panel SIze and Charge Time

Solar batteries extend the use of solar panels beyond just the daytime. Because solar panels do not work at night, they are a necessary component if you want to continue using solar energy at night or if you have an off-grid system.

But how do you incorporate batteries as part of your system? Can you directly connect a battery to a solar panel for example?

Can I Hook A Solar Panel Directly To A Battery?

A solar panel can be connected directly to a battery if it produces less than 5 watts of energy or if the voltage of the solar panel and battery match. If the solar panel is over 5 watts or if the voltage is higher than the battery, then this requires the use of a charge controller between the solar panel and the battery.

Batteries produce a voltage of 12 volts. They also accept a voltage of a maximum of around 14 volts. Solar arrays can produce voltages reaching up to 600 volts depending on how they are configured. A single solar panel can produce up to 23 volts.

If the voltage produced by solar panels is too high for the battery, the battery will overheat and get overcharged. In severe cases, the battery will be permanently damaged. This is where charge controllers come in.

Charge controllers regulate how much voltage and current goes into a battery while it is charging. In this way, charge controllers protect the battery from damage.

Do Solar Panels Drain Batteries At Night?

Solar panels will not drain the batteries overnight. Solar panels are equipped with blocking diodes that prevent reverse current. In most cases, solar systems that have batteries should have a charge controller as well. A charge controller prevents current from flowing in reverse from the batteries to the solar panels.

If there is any battery drain it is likely to be caused by:

  1. A direct connection between the batteries and solar panels.
  2. A malfunctioning diode in the solar panel.
  3. A faulty charge controller.
  4. The battery is damaged from overcharging or consistently being drained to empty.
  5. Parasitic draw from appliances connected to the battery.

Why Won’t My Solar Panel Charge My Battery?

A solar panel will not charge a battery if there is a mismatch in voltages between the two or if the current produced by the battery is too low. While these are the more common reasons it could be also caused by a faulty battery or charge controller or a bad connection.

Current flows from high voltage to low voltage. Thus, the voltage in your solar panel has to be higher or match the voltage of your battery for it to charge. The solar panel also has to produce enough current. Generally, you wouldn’t use a 5-watt solar panel to charge a 100-amp battery because it produces too little current.

The problem may also be with a faulty connection between your components. It may be from using the wrong type or gauge of conductor or even from reversing the polarities in the connection.

Another cause could be a damaged battery or charge controller. In this case, the battery might not accept or hold a charge. There is also the possibility the fault could be with the solar panel. It might be it’s not getting direct sunlight or if it is and it’s still not charging, it might be defective.

There are several points at which a solar system can fail. To work out where the failure is, you have to check each point.

How Long Does A Solar Panel Battery Last?

A solar battery has a lifespan of between 3 to 15 years. The lifespan is determined firstly by what type of battery it is, with lithium batteries having a longer lifespan. Secondly, and just as crucially, the conditions under which the battery is used will influence its lifespan.

There are three main types of batteries commonly used in solar systems. These are lithium, flooded lead acid, and sealed lead acid batteries. Lithium batteries can last up to 10 years. Flooded lead acid batteries last between 3 to 5 years. Sealed lead acid batteries last between 5 to 7 years.

Aside from its chemistry, the main determinant of how long a battery lasts is its maintenance. Batteries have a depth of discharge. This is the recommended amount of energy you can use before you recharge it. Exceeding the depth of discharge will reduce its capacity and shorten its lifespan.

The depth of discharge for lithium is 80%, while lead acid batteries have a depth of discharge of 50%.

Watson Tanganyika

(Solar + DIY Enthusiast) - I got into renewable energy after seeing someone power their home with solar panels. Before that, I thought electricity was something you could only get from your utility. Every day I learn something new about renewable technology and I'm amazed by its vast untapped potential. I genuinely believe it can transform our lives and writing about it is my small way of contributing to the revolution.

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