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200ah batteries are no longer unusual in residential or RV solar systems, as the cost has gone down and it has become an alternative to using several small batteries. But how many solar panels do you need to charge it? And how long will this process take?
Two 300 watt solar panels will charge a 200ah battery in five hours. If it is a lead acid battery discharged at 50%, charge time will take 2 to 3 hours.
How Many Solar Panels Does It Take to Charge a 200ah Battery?
The number of solar panels required depends on its wattage output. The higher the output rating of the panel, the faster it can recharge a 200ah battery.
To find out how many solar panels you need, use this formula:
Battery amp hours x volts = solar panel watts required
If your 200ah battery is 12 volts:
12 x 200 = 2400
To recharge a 200ah battery, the solar panels must produce 2400 watts. There are about 5 hours of sunlight a day on average, so your solar PV system has to produce 2400 watts minimum in 5 hours or less. If your area receives more sunlight hours, you have more flexibility of course.
Solar panels that can charge a 200ah battery under 5 hours:
- 2 x 300W
- 2 x 350W
- 3 x 200W
- 2 x 400W
- 6 x 100W
- 3 x 250W
These solar panels in combination (called arrays ) can produce at least 2400 watts. Some of them can generate more than that if the sky is clear.
300 watts is the standard solar panel size, so we recommend those. You can start with the 300W Solar Kit by Renogy then add another 300 watts.
As much as possible use a solar array that can produce more than 2400 watts. Because weather changes constantly, there will be times when solar panels will not be able to produce high power. Having extra capacity will offset this and allow you to charge the battery without losing too much time.
Solar panel sizes are measured in watts. The higher the wattage the greater the potential output. A large solar array can probably charge the battery in an hour, but it would generate a lot of excess power. If you have a large battery bank or on the grid, this energy can be stored for use later. With a large enough solar panel, you can charge two batteries.
This brings to the next question, how long the charge time will be. And the answer depends on several factors.
What is the Charging Time of a 200ah Battery?
Predicting the charge time for solar batteries is complicated because of the many variables involved. The depth of discharge, sunlight availability in your area, solar panel size all influence the charge time.
Two 400W or 350W solar panels can recharge a 200ah 12V battery in 5 hours or less. Using the other solar panel combinations given above, you can charge the battery in the same time.
To charge the battery in under two hours, you just increase the number of solar panels. Two 300W solar panels produces up to 600W an hour. 600 x 5 = 3100 watts, enough for the battery.
But if you have 6 x 300W solar panels, that is good for 1800 watts an hour. Even a completely discharged 200ah battery will be topped in an hour and half or so.
How Long Does a 200ah Battery Last?
This will be determined by the load and the depth of discharge. The runtime will depend on how many watts the load is consuming per hour. There are many different scenarios possible so let us go over a few of them.
A 200ah battery can run a 40 inch TV, a 1000 watt LED light bulb set and a ceiling fan simultaneously for 6 hours before it is completely drained.
A 12V 200ah lead acid battery has 2400 watts, but if you follow the 50% DOD rule, only 1200 watts can be used. The example with the TV, light bulbs and ceiling fan had the battery being drained completely. If you recharge at 50% its runtime will be cut in half.
Amps Drawn Per Hour
Another way to estimate the battery lifespan is to check how many amps the load draws per hour. The capacity of most solar batteries are based on a draw of 5 amps per 20 hour cycle. If the load draws 5 amps an hour, the battery is good for 20 hours until it is discharged completely.
However this is only for estimates because batteries lose power faster when you draw more amps. So while 5 amps / 20 hours is a good guideline, it does not follow that you get 10 hours with a 10A draw. Most likely the battery will be good for 8 hours or 9.
Because runtime measurements are imprecise, the rule of thumb is to get a larger battery or reduce the load. If the battery capacity is 2400 watts (or 1200 if it is lead acid), you should not fill it to capacity.
Can the battery load at its full capacity? Yes it is possible, but that would put a lot of strain on the system. And there would be no energy left in case of a sudden power surge. Without extra reserve, a jolt of power cold damage whatever load you are running on the battery. Grounding solar panels can also prevent sudden power surges.
The easiest way to figure out how long a 200ah battery will last is to check the watts usage of each appliance. Simply add them up and then you get an idea of how many hours the battery can last. Keep in mind that you need an inverter and a charge controller to complete your solar panel system setup.
Factors That Affect Solar Battery Charge Time
Of course these calculations assume that solar panels perform in optimum conditions. So if your solar array is not producing the power you expect, there are many reasons.
Sunlight availability varies according to location and season. Solar panels naturally perform best during summer and are least effective during the winter, though solar cells may still generate some power.
Solar panel output is at its peak when the sun is high up the horizon, around noontime. As the sun sets, solar power output drops too. So a 300 watt PV module can supply 300 watts at its peak. But that will drop as the afternoon sets in.
In other words do not be surprised if your solar array does not consistently give you that peak number. That is why we suggest that the solar panel size must be greater than what the battery requires.
Solar Panel Efficiency
Solar panel efficiency ratings indicate how well they turn sunlight into direct current (DC). When the sun’s rays strikes the PV module cells, a chemical reaction takes place that converts the energy into electricity.
But only a portion of this is actually converted and usable. The efficiency rating of most solar panels is 18% to 23%. With solar power technology constantly improving, this efficiency rating is only going to get better. For now, anything over 20% is good enough to recharge batteries.
Efficiency is tied in to the number of sunlight hours available. A 300W solar panel with a 23% efficiency rating will produce more power than a similar 300W solar panel with an 18% efficiency rating. The rating becomes even more crucial during overcast days, as higher rated panels can produce more power.
Battery Depth of Discharge
Depth of discharge (DOD) indicates when to recharge a battery. With lead acid batteries, the DOD is 50%. When the power drops to that level, it is time for a recharge. With some lithium the DOD is up to 90% or 100%.
Take a completely discharged 200ah battery and two 300W solar panels. With 5 hours of sunlight, charging time will be:
600W x 5 sun hours = 3000W
Theoretically the two solar panels can produce 2400 watts in four hours, so it might take 4 to 5 hours to fully charge the battery.
If it was an FLA battery and you recharged at 50%, that would mean a 2 to 3 hour charge time. Of course these calculations assume you want the battery filled to 100% capacity, as some like their batteries topped at 85%.
The reason is that topping lead acid batteries at 100% can be as bad as letting it drop to 0%. Doing this a few times will not hurt, but keep repeating it and the life cycle will shorten. Ideally, the charge should be stopped at 85%.
Remember that depth of discharge is only one element. You have to include the other factors mentioned like solar panel efficiency, sunlight hours and the weather.
200ah batteries have become popular for obvious reasons, the low cost, efficiency and the many options available. The key to getting the fastest charge is to do it when the sun is out and not let the battery discharge completely.