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A 400 watt solar panel system combined with an inverter and charge controller can run several devices and appliances in your RV. To get maximum mileage you have to know not just the watts but also how many amps your system produces.
A 400 watt solar panel can produce a maximum of 33 amps an hour or 165 amps a day with 5 hours of sunlight. Due to temperature, weather and other factors, the average output will be 26 amps an hour or 120 to 128 amps per day.
How to Calculate Amps in a 400 Watt Solar Panel
Converting amps, watts and volts is easy, but you have to make some adjustments on the results because of the way solar power works. But you can still get a good estimate of the amps in question.
- Watts / volts = amps
- Amps x volts = watts
- Watts / amps = volts
However, a 12 volt system actually operates at 15 volts, so in our example:
400 watts / 15 volts = 26.6 amps
A 400 watt solar panel can produce 26.6 amps an hour. There are many available, but we like the Renogy 400W Solar Panel Kit as it has a high efficiency rate. This is the maximum output possible in this configuration. However you can use this calculation for any solar panel size.
Most calculations use 12V and technically it is correct. However since it actually goes up to 15 volts, instead of 33 amps (400W / 12V) you get 26.6 (400W / 15V). The higher the voltage the lower the amps.
You can use these conversions even with higher voltage systems. A lot of solar systems are still using 12 volts, but 24V systems are becoming more common. The ACOPOWER 500W 24V solar panel kit, for instance, can be used for high powered appliances in RVs, boats and oter applications.
What Charge Controller Should I Use For 400 Watt Solar Panels
A 40A PWM charge controller can be used for 400W solar panels as long as it is 12 volts. An MPPT charge controller should be used for solar systems larger than 400 watts and running at 24V.
To find out what charge controller size is required, divide watts by volts and add 20% to the result.
400 watts / 12 volts = 33.3 amps + 20% = 39.9 amps
So a 40A charge controller will run a 400W solar system. Charge controllers are rated or sized by their amps, 10A, 20A, 30A and so on. Most PWM charge controllers have a maximum limit of 60A. An MPPT charge controller such as the Renogy 30A 12V/24V Controller can handle higher voltage systems.
There are many reasons why an MPPT controller is better than PWM, but the most important is its ability to handle different voltages. If you are going to use a PWM charge controller, the solar panel and battery voltage has to match. if the battery is 12V, the solar panels have to be 12V.
With an MPPT controller, you do not have to worry about matching voltages. The controller will assess the voltage of the PV modules ad batteries and adjust the current for the best results. It will optimize both panels and battery so your system runs smoothly.
PWM charge controllers are best used for smaller solar arrays under 4000 watts. If you need more power, it is best to go with a device like the Renogy 40A MPPT controller because they are more efficient. PWM charge controllers also need longer, thicker wires, which can be expensive. But if you plan to stick with 400 watts, a PWM controller will be enough.
Why is My 400 Watt Solar Panel Producing Low Amps?
So your calculations show that this solar panel is good for up to 26 amps an hour. But when you check the data you are getting lower amps, around the low 20s. What is wrong?
Some reasons why your solar system is not generating enough amps:
Cloudy Skies. Even if there is no rain, clouds that pass by and cover the sun will affect the solar panels. Even it is just for a few moments, you will notice a drop in the charge rate.
Shading. Solar cells are sensitive to any type of shading. Foliage, dirt, etc. even a small amount can affect the output. Solar panels need to be cleaned every now and then to prevent dirt buildup.
PWM Charge Controller. As we explained earlier, a PWM controller is limited to 14.4V, whereas an MPPT controller can run a 400W solar array at maximum power.
Low Solar Panel Efficiency. An efficiency rating of less than 20% is not enough for a solar system of this size. The more efficient the solar panel, the higher the amps the system can supply.
There is nothing wrong with your solar panels. The 26.6 amp output is simply the highest possible under this setup. In perfect weather with at least 5 hours of sunlight you can expect up to 128 amps a day.
But if the weather turns south, the sky gets cloudy or drizzles, the solar panel production will drop. From 26.6 amps it could go down to the low 20s. If the rain turns into a downpour the output will halt or slow to a crawl.
You can expect 24 to 26 amps an hour from a 400 watt solar panel during summer. But the amps will be lower during spring, fall and winter. As the watts drop so do the amps.
The point is solar power production will vary. It will be highest during summer and lower during the other seasons. That should not be a problem if you are on a grid tied system since you can access the main grid. If you are off the grid you can use place the extra energy in a battery bank.
What Can I Power with a 400 Watt Solar?
What you get out of this solar panel system depends on the charge controller you have, the weather, your living area and the type of devices you use.
With an MPPT charge controller, a 400 watt solar panel can run a mini fridge , power an inverter to watch TV, some LED lights, a fan and an RV roof vent. You could also have some watts in reserve if you are energy efficient.
All of this depends on how the panels are used. Most average sized RVs will get by with 400W, and it is enough for a couple or a family of three. It is probably too much for a single person, unless you run a lot of high powered appliances.
A 400 watt soar array is enough for boondocking and camping. This is also enough power for a camping trip in spring or early fall. You can run the entire electrical system of an RV on this system, but you have to b careful about how much power you consume.
A 400W solar panel is not enough to run an off the grid house, but you can use it to power several appliances. A TV, laptop, Blu-ray player, console, lights, fans, and a printer are within its capacity. However, toasters, microwaves, hair dryers, washing machines and other large appliances are out of the question.
How Many Batteries Do I Need For a 400 Watt Solar Panel?
It depends on how much power you need to use when the sun goes down. If you are off the grid or on a mobile home, your backup power supply should be enough to cover up for the solar panel in case of cloudy or rainy days.
A 100ah 12V battery is equal to 1200 watts. Even if the battery is lead acid with a depth discharge of 50%, that is still 600 watts. A fully charged 100ah battery can cover up for your 400W solar system in case of a cloudy day.
Ideally you should let the solar panels charge the battery all day. Run your appliances from the battery , and since it is being charged, it will not run out of power. At sunset you still have a full powered battery available for use.
If a 400 watt solar panel system is sufficient for you during the day, it will be too for the night as well. So a 100ah battery should be good enough for a typical RV.
Keep in mind that most RV solar setups have additional power sources such as a generator or offshore power. If you have one, you don’t need to rely solely on the battery. However it is still a good idea to have at least as much power as the solar panels in case of emergency needs.
Now that you know how many amps a 400 watt solar system can provide, it is easy to determine if it is the right size for your camper. And equipped with an inverter and a charge controller you should have no problems running all the appliances and devices you need.