12 Volt Batteries And Solar Panels: All You Need To Know

When it comes to solar power, 12-volt batteries and solar panels are both common items in any arsenal. While some users may use 6v, 24v, or even 48v battery setups, 12v batteries are certainly the most common, and the easiest to set up and manage, especially for smaller solar setups.

But what about different sized 12v batteries? Can you use any solar panel with a 12v battery?

Solar panels of any size can be used with a 12v battery, but, the panels must have a 12v rating too, and you must use a charge controller.

In this article, we’ll be covering the following:

  • The size of solar panels required for a 12v battery
  • Different 12v battery sizes
  • Solar panel trickle chargers
  • How long do 12v batteries last

If you’ve been wondering about 12v batteries and the right solar panels to use for them, you’ve come to the right place! In the following article, we’ll be diving deep into all you need to know about 12v batteries and solar panels.

Let’s get started!

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What size solar panel will charge a 12v battery?

Technically, all you need to charge a 12v battery is a solar panel with a 12v rating. This can be any sized solar panel, although the bigger it is the quicker your battery will charge.

Anything under 5–10 watts is not enough, though, as these will only “trickle charge” your battery very slowly. In general, 12v panels are only available up to a rating of around 200-watts, though, and from there up they are usually 24v or 48v.

There are various sizes of 12v batteries available, 100ah being the most common. For this reason, the amp hour rating of the 12v battery you have and how quickly you want it to fully charge will determine what size solar panel you need.

How big of a solar panel do I need to charge a 12v battery?

For a 12v battery, you’ll ideally need a panel of 200-watts to charge a 100ah battery — the most common 12v battery size.

Given that a 200-watt panel can produce around 60 amp-hours per day — on a sunny day under ideal conditions — you should be able to fully charge a 100ah battery with a 200-watt panel in 5–8 hours.

Solar Panel Optimal Operating Temperatures

Solar panels are rated and tested at 77°F – which is the industry standard. Although, solar panels operate between 60°F and 95°F. So the following calculations are based on the optimal environment – variations will occur.

These optimal temperatures will be used to calculate the following charge times and the ah/watt current charge.

Seasons and shadowing will reduce the currents and charge times, so it’s best to get more panels or higher-rated panels to overcompensate, so you maximize the potential.

How many solar panels are needed to charge a 12v battery?

A single 200-watt panel should charge a 12v, 100ah battery in a day. Alternatively, two 100-watt panels or four 50-watt panels will do the same.

It is possible to use smaller solar panels — a single 100-watt panel for example — but this will just increase the time it takes for your battery to charge.

If you’re using your battery as a backup or using much less than a full battery charge in a day, a 100-watt panel is certainly large enough to get the job done.

How long does it take to charge a 12v battery with a solar panel?

Typically, a 100-watt panel produces around 6ah per hour under ideal conditions or roughly 30ah–40ah per day. If you’re charging a 100ah battery from a flat, it will take about two days to fully charge the battery.

It’s important to note that proper battery maintenance and care requires that your 12v battery never goes under 50%.

This is usually maintained by a charge controller, and so you’ll technically only need a panel that can produce 50ah per day to keep your battery fully charged.

How long does a 12-volt solar battery last?

How long a 12v battery lasts depends on a variety of factors; its amp-hour rating, the size of the solar panel that is charging it, and what load you’re putting on it.

Let’s take a 100ah 12v battery as an example.

Let’s say you’re using a 200-watt panel to charge your battery. This means that you’ll be able to charge your battery fully in less than a day under ideal conditions.

A 100ah battery technically has 50ah of power available before recharging is required (to avoid damage), and so if you are putting a heavy load on it you can expect it to last a day or so.

If you are using the battery for lighter loads; charging mobile phones, just using it for backups, or running a few LED lights, you can get away with using a smaller solar panel as the battery won’t go dead in a day.

Can you connect a solar panel directly to a 12v battery?

Technically, you can connect a solar panel directly to a 12v battery as long as it’s not more than 5-watts, but connecting any higher-rated panels is not a good idea.

Solar panels will produce varying voltage outputs depending on the amount of sun hitting them, and this dipping and spiking of the voltage can quickly damage your battery.

Solar panels can generate up to 20v, which is much higher than the 12v required by a 12v battery. This can lead to overcharging, permanently damaging your battery.

The best course of action is to use a charge controller or regulator between the panel and battery, as this regulates the charge current and keeps your battery healthy.

What are solar panel trickle chargers for 12v batteries?

Solar panel trickle chargers are mainly used to charge 12v car batteries. These chargers charge your battery at a rate equal to the self-discharge rate of the battery, which helps keep your battery charged at the desired level.

These panels are usually no more than 4–10 watts, and simply keep your battery from going dead from the small amount of power consumed by small clocks, alarms, or indicators in your car while it’s not in use for long periods.

As long as your battery is over 20ah or so capacity, these trickle chargers will not overcharge your battery.

Solar panels and amp-hour charging times

Depending on the ah rating of your 12v battery, you may be wondering what size solar panel is best to pair it with, as well as how long it’s likely to last. As mentioned earlier, it’s difficult to estimate how long a particular size battery will last as it depends on what you use it for.

In general, amp hours refer to how long you can draw 1-amp from a battery before it will go flat. For example, a 10ah battery will produce 1-amp per hour for 10 hours before it dies.

To make this easier, you can look at it from a wattage point of view. So, 1 watt-hour is defined as 1 watt of power expended for 1 hour, the same as 1 amp hour is defined as 1 amp of current expended for 1 hour.

If you’re using an appliance that uses 100-watts with a 12v battery, it will be drawing roughly 0.8 amps per hour. Because of the 12v to 120v conversion needed for most normal electrical appliances, you need to multiply the current you need to generate by a factor of 10, giving you 8-amps per hour of power.

So, a 100ah battery being drawn at 100-watts through a 120v inverter will supply you with roughly 12.5 hours of use.

In the examples below, we’ll stick with our example of 100-watts of expended power, and the panel you’d need to fully charge your battery from flat in one day.

These examples are using an average of 6-8 hours of sunlight per day, just to be safe. As mentioned earlier, if you are not using your battery every day, you can successfully use a smaller panel than the examples below.

Amp Hours (12v battery)Solar Panel SizeEstimated Usage
12ah30 watts (1.6 amps per hour)1.5 hours
15ah40 watts (2.4 amps per hour)1.9 hours
20ah50 watts (2.9 amps per hour)2.5 hours
35ah80 watts (5 amps per hour)4.3 hours
50ah100 watts (6 amps per hour)6.2 hours
60ah100 watts (6 amps per hour)7.5 hours
80ah120 watts (7 amps per hour)10 hours
100ah120 watts (7 amps per hour)12.5 hours
125ah150 watts (8.5 amps per hour)15.6 hours
200ah200 watts (10–12 amps per hour)25 hours
300ah350 watts (25–30 amps per hour)37.5 hours
400ah400 watts (33-35 amps per hour)50 hours

How long does it take to charge a 12v battery?

Again, the length of time it takes to charge a 12v battery will depend on both the size of the solar panel, plus the amp hour rating of the battery.

Let’s use 100ah and 50ah batteries as an example, to see how long most standard solar panel sizes will take to charge it.

How long does it take a 5w solar panel to charge a 12V battery?

A 5-watt solar panel produces roughly 0.28ah of current under ideal conditions, and so it would take around 360 hours to fully charge a 100ah battery, or 180 hours for a 50ah battery (typical for most cars).

A panel of this size is suited only for trickle charging, or for charging very small batteries (5ah).

How long does it take a 7w solar panel to charge a 12V battery?

A 7-watt solar panel produces roughly 0.58ah of current under ideal conditions, and so it would take around 172 hours to fully charge a 100ah battery, or 86 hours for a 50ah battery. Again, this is best for trickle charging only.

How long does it take a 10w solar panel to charge a 12V battery?

A 10-watt solar panel produces roughly 0.83ah of current under ideal conditions, and so it would take around 120 hours to fully charge a 100ah battery or 60 hours for a 50ah battery. Again, this is best for trickle charging only.

How long does it take a 25w solar panel to charge a 12V battery?

A 25-watt solar panel produces roughly 1.5ah of current under ideal conditions, and so it would take around 66 hours to fully charge a 100ah battery or 30 hours for a 50ah battery.

How long does it take a 50w solar panel to charge a 12V battery?

A 50-watt solar panel produces roughly 2.9ah of current under ideal conditions, and so it would take around 34 hours to fully charge a 100ah battery or 16 hours for a 50ah battery.

How long does it take a 60w solar panel to charge a 12V battery?

A 60-watt solar panel produces roughly 3.5ah of current under ideal conditions, and so it would take around 28 hours to fully charge a 100ah battery or 14 hours for a 50ah battery.

How long does it take an 80w solar panel to charge a 12V battery?

An 80-watt solar panel produces roughly 5ah of current under ideal conditions, and so it would take around 25 hours to fully charge a 100ah battery or 12 hours for a 50ah battery.

How long does it take a 100w solar panel to charge a 12V battery?

A 100-watt solar panel produces roughly 6ah of current under ideal conditions, and so it would take around 16 hours to fully charge a 100ah battery or 8 hours for a 50ah battery.

How long does it take a 120w solar panel to charge a 12V battery?

A 120-watt solar panel produces roughly 7ah of current under ideal conditions, and so it would take around 14 hours to fully charge a 100ah battery or 7 hours for a 50ah battery.

How long does it take a 180w solar panel to charge a 12V battery?

A 180-watt solar panel produces roughly 9ah of current under ideal conditions, and so it would take around 11 hours to fully charge a 100ah battery, r 5.5 hours for a 50ah battery.

How long does it take a 200w solar panel to charge a 12V battery?

A 200-watt solar panel produces roughly 10ah of current under ideal conditions, and so it would take around 10 hours to fully charge a 100ah battery or 5 hours for a 50ah battery.

How long does it take a 300w solar panel to charge a 12V battery?

A 300-watt solar panel produces roughly 25ah of current under ideal conditions, and so it would take around 4 hours to fully charge a 100ah battery or 2 hours for a 50ah battery.

How long does it take a 400w solar panel to charge a 12V battery?

A 400-watt solar panel produces roughly 33ah of current under ideal conditions, and so it would take around 3 hours to fully charge a 100ah battery or 1.5 hours for a 50ah battery.

How long does it take a 500w solar panel to charge a 12V battery?

A 500-watt solar panel produces roughly 40ah of current under ideal conditions, and so it would take around 2.5 hours to fully charge a 100ah battery or 1.25 hours for a 50ah battery.

What are the best types of 12v batteries for solar panels?

There are generally 3 types of batteries commonly used for solar:

  • Flooded lead-acid (FLA)
  • Sealed lead-acid (SLA)
  • Lithium-ion

FLA batteries are the most common batteries used in solar setups, as they are readily available, inexpensive, and 99% recyclable, making them a great choice if you’re looking for something more affordable.

That said, they don’t last as long as other types need ventilation and regular maintenance.

SLA batteries are non-spill, maintenance-free, and don’t discharge as fast as FLA batteries, plus last a few years longer. These are great if you have a little more to spend on your system and cannot maintain batteries.

Lithium-ion batteries are arguably the best batteries for solar.

They are maintenance-free, more efficient, have a far deeper discharge capability, and don’t need ventilation, making them the ideal choice. That said, these batteries are extremely expensive, and out of the price range for most small solar setups.

Conclusion

With the correct pairing of solar panels and a 12v battery, you can easily make sure you have enough power for your needs!

A solar panel that can charge your 12v battery in a day or less, and a battery that has more than enough capacity for your needs is the ideal combination and will ensure that you never, or very rarely, run out of power.

Solar Panel Batteries FAQ

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