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 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 dive deep into all you need to know about 12v batteries and solar panels.
BEST CHOICE SOLAR BATTERIES
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 solar panel, although the bigger it’s, the quicker your battery will charge.
Anything under 5–10 watts is not enough, 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; 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 charge fully 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.
See also: Best Solar Batteries: Top Picks and Comprehensive Buying Guide for 2022
Solar Panel Optimal Operating Temperatures
Solar panels are rated and tested at 77°F – which is the industry standard. However, 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 calculate the following charge times and the ah/watt current charge.
Seasons and shadowing will reduce the currents and charge times, so getting more panels or higher-rated panels to overcompensate to maximize the potential is best.
How many solar panels are needed to charge a 12v battery?
A single 200-watt panel should charge a 12v, 100ah battery daily. Alternatively, two 100-watt panels or four 50-watt panels will do the same.
It’s possible to use smaller solar panels — a single 100-watt panel, for example — but this will increase the time your battery takes 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 charging a 12v battery with a solar panel takes?
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 charge the battery fully.
It’s important to note that proper battery maintenance and care requires that your 12v battery never goes under 50%.
A charge controller usually maintains this, 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 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 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 (to avoid damage), so if you put 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 die 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, much higher than the 12v required by a 12v battery. This can lead to overcharging, permanently damaging your battery.
The best action is using a charge controller or regulator between the panel and battery, which 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 wonder what size solar panel is best to pair it with and how long it’s likely to last. As mentioned earlier, it’s difficult to estimate how long a particular size battery will last, depending 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, and 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 draw 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 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 use 6-8 hours of sunlight daily to be safe. As mentioned earlier, if you are not using your battery daily, you can successfully use a smaller panel than the examples below.
Solar Panel Battery Amp Hours, Solar Panel Size and Usage Chart
| Amp Hours (12v battery) | Solar Panel Size | Estimated Usage |
| 12ah | 30 watts (1.6 amps per hour) | 1.5 hours |
| 15ah | 40 watts (2.4 amps per hour) | 1.9 hours |
| 20ah | 50 watts (2.9 amps per hour) | 2.5 hours |
| 35ah | 80 watts (5 amps per hour) | 4.3 hours |
| 50ah | 100 watts (6 amps per hour) | 6.2 hours |
| 60ah | 100 watts (6 amps per hour) | 7.5 hours |
| 80ah | 120 watts (7 amps per hour) | 10 hours |
| 100ah | 120 watts (7 amps per hour) | 12.5 hours |
| 125ah | 150 watts (8.5 amps per hour) | 15.6 hours |
| 200ah | 200 watts (10–12 amps per hour) | 25 hours |
| 300ah | 350 watts (25–30 amps per hour) | 37.5 hours |
| 400ah | 400 watts (33-35 amps per hour) | 50 hours |
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.
They don’t last as long as other types that 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. These batteries are extremely expensive and out of the price range for most small solar setups.
12v Solar Panel Battery FAQs
How Long Does It Take To Charge A 12v 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 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?
How Long Does A 10w Solar Panel Charge A 12V Battery Take?
How Long Does It Take A 25w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 50w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 60w Solar Panel To Charge A 12V Battery?
How Long Does It Take An 80w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 100w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 120w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 180w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 200w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 300w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 400w Solar Panel To Charge A 12V Battery?
How Long Does It Take A 500w Solar Panel To Charge A 12V Battery?
Conclusion
With the correct pairing of solar panels and a 12v battery, you can easily ensure 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.
