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Solar panels produce DC power, which most appliances cannot use since they run on AC electricity. To convert DC to AC, you will need an inverter. This guide will explain what inverter size is needed for a 200W solar panel and also what battery and charge controller sizes you have to get.
The inverter size should be 25% greater than the largest power load you will need. If you are going to use a 200 watt solar panel, you have to get a 250W inverter. A 100ah battery is also required if you want to store the solar power for use at night.
How to Calculate Inverter Size for Solar Panels
A 200W inverter is not enough for a 200W solar panel because they are not 100% efficient. When an inverter runs and converts DC to AC, some power is lost.
Inverter efficiency ratings range from 85-95%, so you have to add 10-25% when calculating what size you need for solar panels. If you do not compensate for the inefficiency, the inverter will not be enough.
Inverter efficiency is calculated as:
Inverter size x efficiency rating = inverter load capacity
You have a solar panel like the Renogy 200W Solar Panel Kit and decided to buy a 200W inverter. Its efficiency rating is 85%. Using the formula given here:
200W x 85% = 170
A 200W inverter with an 85% efficiency rating has a maximum load capacity of 170 watts. It is also not a good idea to run a full load on an inverter so you will end up with less than 170 watts. You might also want to check how many amps the inverter draws.
Even assuming your solar panel does not produce the maximum output of 200 watts, a 200W inverter with an 85% efficiency is too small.
If the inverter is 95% efficient, it still is not enough:
200 x 95% = 190
The maximum load is 190 watts. If your solar panel produces 200 watts an hour, it will overload the inverter. Depending on your location the solar panel might generate around 190 watts or less. But even then you would be running the inverter at full capacity, which should be avoided.
Until we get 100% efficient inverters, you should always add 10-25% to the size you will need. This way you can rest easy knowing the inverter is capable of handling the maximum output your solar panel can generate.
More Solar Panel Inverter Calculations
To make up for the inefficiency, your inverter has to be 10-25% larger than the power load. This also applies for larger systems, for instance, if you want to run a fridge on 400W solar panels .
The formula is:
Solar panel size + 25% (you can use other figures, but it cannot be less than 10%)
So if you have a 200W solar panel, a 250W inverter is the minimum required:
200W + 25% = 250
A 250 watt inverter for a 200 watt solar panel makes a lot of sense for many reasons. Even if the inverter is only 85% efficient, it can still run the solar panel with maximum output:
200 x 85% = 212W
Most high quality inverters have a 90% or higher efficiency rating, so there is more than enough capacity available. If your inverter has no AC output however, it will not work.
A 200 watt solar panel will not always generate 200 watts. Most of the time it will probably be less than that. But having a 250W inverter provides insurance that in case the panel does produce maximum output, your system can handle it.
You can use this same formula for all kinds of solar panels and inverters. You simply replace the watt size and inverter efficiency rating with your own figures.
Calculate Inverter Size for Batteries and Solar Panels
A solar inverter system also requires a battery. Since solar panels cannot run at night, you need a battery to store solar power. When night – or rain – comes, you can use the battery to run your appliances off the inverter.
A 200W solar panel can produce up to 1000 watts with 5 hours of sunlight. You need a 100ah battery to store this energy. The inverter size will depend on how much of that power you want to run per hour. A good option is the Banshee 100ah as it is optimized for inverters.
First we have to determine how much power your solar panel produces in a day. Next, we have to calculate how much battery power you will use per hour. This will tell you what inverter size to get.
To calculate the battery size for your solar panel:
Solar panel wattage x peak sun hours = total power output per day in watts
Watts / battery voltage = battery capacity
If your region receives 5 hours of peak sun a day:
200 watts x 5 hours = 1000
Your 200 watt solar panel can produce up to 1000 watts a day. If the conditions are not ideal or you get less than 5 sun hours daily, replace the number above. For this example we will use 1000 watts.
Now we need to convert watts into amp hours (ah) because that is how battery capacity is measured.
Watts / battery voltage = amp hours
If you are going to use a 12V battery:
1000 watts / 12 volts = 83.3
1000 watts is equal to 83. 3 amp hours or 83.3 ah. The closest battery size available is a 12V 100ah, so that is what you should get. When shopping for deep cycle batteries, make sure the wire size is correct.
How Long Can an Inverter Run a 200W Solar Panel?
An inverter will keep running as long as it has a power source. If it is connected to a battery, the inverter will operate continuously until the battery is out of energy.
To continue with our example, we will use a 200W solar panel and a 100ah battery. If the solar panel puts 1000 watts into the battery per day, what inverter size will you need?
The inverter size depends on how much power load you will use per hour. The formula is:
Power usage per hour + inverter efficiency rating = inverter size
Your solar panel produces 1000 watts a day, all of which goes into a 100ah battery. If you are going to use 200 watts an hour, you will need a 250W inverter with at least 85% efficiency.
If you are going to use 500 watts an hour, you will need a 550W or 600W inverter. You must always add 10-25% to the total and choose the next largest size available. So if the numbers show you need a 550W inverter and you cannot find one, go for 600W.
It is always better to overestimate the amount of inverter power you need. This is also true for batteries especially if you are running a large system.
What Charge Controller Does Your Inverter Need?
A 200W solar panel running on a 250W inverter and 12V battery requires a 20A charge controller. For the best results, you should use an MPPT charge controller.
To calculate the charge controller size, divide the total solar panel watts by the battery voltage.
Watts / volts = charge controller size in amp hours (ah)
In our example we have a 200W solar panel and a 100ah 12V battery.
200 / 12 = 16.6
The charge controller has to be at least 16.6 amps. The closest size available is 20A, so you should get a 20A charge controller.
The most common charge controller sizes are 10A, 20A, 30A, 40A, 60A, and 100A. Use the same formula – watts / volts = amps – and choose the next largest charge controller size. Just like with inverters, you should make allowances for the size.
Charge controllers are either PWM or MPPT. MPPT controllers do a better job of maximizing solar power output and battery charging. If you are going to use several 200W solar panels together, an MPPT charge controller will be ideal.