Can a Solar Panel Charge a Car Battery?

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Solar panels are now used to power everything from appliances, well pumps to mobile devices. But can solar panels charge a car battery? And how many solar panels will it take? It’s an interesting question given how popular renewable energy is today.

Any 12V solar panel can charge a car battery. A 300 watt solar panel that generates 9 amps can recharge a 70ah car battery in 8 hours.

How Many Solar Panels Do I Need to Charge a Car Battery?

Solar panels can charge car batteries because they are similar to deep cycle batteries used in solar systems. Both are 12 volts and capacity is in amp hours (ah). Any solar panel, regardless of size, will work, but the larger the panel is going ot charge fater.

Battery capacity x volts = number of solar panels needed

Most cars today have a battery capacity of 70 to 100 ah. If you have a 12V 70ah battery and it is completely drained, how many solar panels will you need?

70 x 12 =840

You need 840 watts of solar power. In this case we recommend the Dokio 300W Portable Solar Panel Kit as it is lightweight and has a high efficiency rating. The Dokio is an 18V panel, but a charge controller ensures only the right amount of current goes into the battery.

if you have a 100ah battery you will need more solar panels. But the calculation steps are similar to the one given above. We have to point out that solar panel wattage output is based on ideal conditions. A 300 watt solar panel is rated as such because that is what it can generate under the best conditions.

In less than ideal weather the output will drop. So a solar panel might give you 300 watts an hour at midday during summer and drop to 280 or lower in the afternoon. This determines the charging time, but is only one factor as we explain in the following.

How Long Does it Take to Charge a Car Battery with Solar Panels?

Sunlight is not the only factor that determines how many solar panels you need. The state of the battery is another. In the example above, we assume the battery is fully discharged, which is why it takes several hours and so many solar panels.

To calculate the time:, use this: solar panel maximum power point current x sun hours = car battery charge time

The maximum power point current (lmmp is the current or amperage the solar panel produces. This is what is shown in a high quality MPPT charge controller like the Victron 50A SmartSolar. This is tells you how many amps are going into the car battery.

A 300 watt solar might produce 9 amps at maximum power, so it will take 8 hours to recharge a fully discharged 70ah car battery.

8 x 9 – 72

This assumes there are 8 sun hours available. if there are only 5 hours charging time can take two days. The amps produced by a solar panel also fluctuates depending on how much solar energy it can convert.

In certain conditions the solar panel might charge up to 32 volts and generate 9 amps. if conditions change the voltage might drop and the amp increases.

The charge controller ensures only the proper voltage goes into the battery. So even if the solar panel reaches 32 volts, only 13.6 volts or less goes into the car battery.

Once you know how to convert watts and amp hours, it’s easy to figure how many solar panels you will need to charge a battery. Converting is only half the equation though. You also need to consider how depleted the battery is. No matter how powerful a solar panel is for example, it will be difficult to recharge a dead battery.

The most important factor is the sun hours. Solar panels need sunlight to convert into direct current, so wi8thout it the panels will not work. There must be a sufficient amount of sunlight, and there needs to be enough hours as well.

How many hours is ideal depends on the battery size. We all want our batteries to charge as fast as possible, but if the skies are overcast it will take longer than usual.

How to Charge a Car Battery with Solar Panels

You need four things: a car battery, a voltmeter, solar panel and a charge controller. Connect one end of the charge controller to the solar panel, and the other end to the car battery. With a voltmeter, you will be able to tell if the battery is charging. All 12V car batteries is actually 12.7-14V. When the voltmeter goes up to14V, then the solar panel has fully charged the battery.

You may have heard some stating it is all right to connect a solar panel directly to a car battery. That is dangerous and could lead to overloading or overheating. and damage the battery. That is where a charge controller becomes critical. It regulates how power flows into the battery so there is no overheating.

if you connect directly to the battery, the charge will start at 13.5V. That will not harm the battery, but that number will go up. As more solar energy goes into the battery, the voltage level increases. If it goes beyond 14V the battery will start overloading. With a charge controller it will not happen, and your battery is safe.

The only time it is safe to directly connect a solar panel to a car battery is if it has a built in charge controller. If you have a dedicated solar car battery charger, a direct connection is acceptable.

Can a Solar Panel Recharge a Dead Car Battery?

it is very difficult, if not impossible. Solar chargers can charge a depleted battery, but it might not be able to produce enough power to jump start a 100% dead battery. Even under ideal weather, there probably won’t be enough charge available. Reviving a dead battery with standard chargers is difficult enough, and those generate more power than a typical solar panel.

Can You Overcharge a Battery with Solar Power?

We have covered that topic here, but in summary is yes, it is possible to overcharge without a charge controller. That is why we emphasized that a charge controller be used. It is the most effective way to safeguard your battery in case a lot of current comes in.

Which is Better, Solar Battery Chargers vs. Regular Battery Chargers?

Solar [panels have come a long way, but they are not yet as powerful as regular car battery chargers. The biggest drawback of solar chargers is the lack of power. It can charge a battery yes, but not at the same speed as a standard charger.

Regular battery chargers come with multiple amperage settings, while solar chargers produce a limited amount of current. You could increase the power by using several solar panels, but it becomes expensive and difficult to set up.

The good news is solar panels are improving all the time. Cars are also becoming more receptive to solar technology. With electric cars now being produced, we can expect more vehicles to rely on renewable energy sources.

Can a Solar Panel Resume Charging if it Stops?

if you are charging a car battery and a cloud passes by, can you restart the charge? Will the solar panel resume where it left off or do you have to go back to zero?

It will depends on the sola panel design. Most of the time, when a cloud passes it is temporary. The charge will slow down but will not stop. When the cloud has disappeared, the panel will pick up where it left off. With enough sunlight your car battery will be fully charged.

If you’re not sure, check the manual that came with your solar panel. That provides all the information you need if it can resume charging or not.

Conclusion

The increasing popularity of electric cars have had people wondering if they can use solar panels with regular vehicles. As has been shown here, it is very possible. As solar panel technology continues to improve, expect it to be more widely used to charge not just cars but other vehicles.