What Size Inverter For a 100W Solar Panel?

Mention the word inverter and we think of those devices that allow AC devices to run off solar panels. Mostly they are used in large solar arrays, but can you use an inverter with a 100 watt solar panel? Do you even need one? The answer to both questions is yes.

A 12V 100W solar panel needs a 12V 200W inverter to run AC powered appliances, and at least a 100ah battery to store energy. A 12V 5A PWM or MPPT charge controller is required to keep the battery from overcharging. With this system you can draw 100W from the inverter for 3 to 4 hours or 200W for 1 and half hours.

How to Calculate Solar Inverter Size

Calculating inverter sizes is the same no matter what the solar panel output is. Before you can figure out what inverter capacity to use, you must know how many watts a day your solar panel produces.

Suppose you have a 12V 100W solar panel and your location receives 6 hours of sunlight. Your 100W solar panel produces the following power a day.

100 x 6 = 600 watts

Accounting for energy fluctuations during those six hours, the output may be 500W to 550W. We are using 600 watts for simplicity but keep variation in mind when crunching your own numbers.

Now we calculate the battery, because this is where solar power goes. This is also where the inverter will draw power to operate your AC devices.

Around 15% or so of energy may be lost when a solar panel charges a battery Assuming the panel is 85% efficient:

600 x .85 = 510 watts

510 watts goes into the battery. If you have a lead acid battery with a 50% discharge rate, the 510 watts is used to top the battery. 510 x 2 = 1020 watts.

Now we convert 1020 watts into amp hours. If you have a 12V battery the conversion is:

1020 / 12 volts = 85 ah

You need an 85ah battery capacity. 100ah 12V batteries are more common than 85ah so that is what you should get.

Now that you know the battery size, you can figure out what inverter to get. The rule of thumb with inverters is the capacity should be at least 25% to 50% greater than the total wattage required.

If you are going to draw the maximum output of 100 watts an hour, the inverter has to be at least 125 or 150 watts. Others suggest doubling the wattage, and since 200W inverters are more common, that is what we recommend you use. We recommend the BMLK 200W Car Power Inverter, as it works with 12V and 120V systems and should be able to handle your needs.

If you are going to connect several 100W solar panels in a series or parallel, you will need a bigger inverter. Use this guide to find the ideal inverter for your system. You don’t want to get one that is too large, but if you plan to expand your solar panels, a bigger inverter will be needed.

Your will not be risking your system buying a larger inverter. Of course it does not make financial sense, but nothing bad will happen to your module. However, you must never use an under powered inverter because it will cause damage to the battery and whatever device you connect to it.

Important Reminders on the Calculations

The sunlight hours will vary depending on your location, season and solar panel efficiency. If you live in the Midwest you will get more sun hours compared to someone who is the Pacific Northwest.

Also, a PV module with a 23% efficiency rating like the LENSUN 12V solar panel will convert more solar power than a lower rated module. Even if they are in the same location with the same sun hours available, the higher rated panel will win out.

The battery capacity and discharge rate will differ depending on what type you use. With lead acid batteries it is almost always 50%. Some of the newer AGM batteries have a 60% discharge rate, but most are still at 50%.

Lithium ion batteries have different discharge rates too. The best ones are rated 100%, meaning you can drain it completely. Most lithium batteries though have a discharge rate of at least 70%.

Inverters incur energy losses too. The acceptable level is 85%, though newer and more powerful systems are now 95% efficient. The more effective the inverter, the more solar power you will be able to use.

Why do all these stats matter? Because it is going to determine how much power you can use with your 100W solar panel and inverter. The conversion formulas are simple, but because of these variables, the result will vary depending on the situation and various factors.

Do You Need a Solar Inverter?

Inverters are almost always mentioned alongside solar panels so that some people may think they are essential. However there are instances wherein you may not even need one.

Solar panels produce DC power which an inverter transforms into AC. If your device runs on DC, there is no need for an inverter. You only require one if you want to run electronics that use AC power.

Cell phones run on DC power, as well as some flat screen TVs, motors, electric cars and laptops. You can connect these onto a solar power system without using an inverter. They can run off the solar panel or the battery. Most home appliances however, run on AC. Toasters, dishwashers and refrigerators use AC.

You don’t have to worry about large appliances if you are using a 100W solar panel. You will only be using this to power small electronic devices like lights, a laptop, maybe a small TV and some potable kitchen appliances.

There are also those who might say that 100 watts is too small to use an inverter. After all most of these are in the 3kwh to 4kwh range, so 100W is very small. However there are portable inverters in the 200W range available. If you need to use one for a portable solar panel, there are options available.

Can I Connect Several 100W Solar Panels to an Inverter?

If you want to build a solar array you need more than 100 watts. Fortunately you can connect several of these to gain more power. But make sure the inverter has enough capacity for what you need.

The number of solar panels you can connect to inverter depends on its capacity. If the inverter is 200W, you can only use 2 x 100W solar panels maximum. If you want the inverter to have reserve power – and you should – you can only use one 100W solar panel.

This is why planning is important. Right now you may only need 100 watts, but what about the future? If you see at any point a need to upgrade, buy a larger now. With a 500W system for instance, you can install powerful solar panels and run several devices at once.

Tips For Using an Inverter with Solar Panels

The following tips are for 100W solar panels, but many of them also apply to larger PV modules. Always keep these in mind before you buy and install an inverter.

• The inverter will use the battery to power whatever you connect o it. However the battery obtains its energy from the solar panel. The charge controller meanwhile, must be the right size and make certain the optimum amount of power goes into the battery. All of them must match for the system to work.

• The more watts you draw per hour, the faster the battery will drain. It is not as simple as 100 watts is good for an hour, 50 watts for 2 hours etc. The more current is drawn, the faster the battery depletes.

• The inverter capacity is limited by the amount of watts going into the battery. In our example we assume the panel draws 600 watts with six hours of sunlight. But if the sky is overcast, production will go down. So will the capacity of the inverter.

• The wires and cables you use make a big difference. The thicker the cable, the better. It will cost more yes, but energy loss is reduced. With 100 watt modules however, the losses will be quite small unless you wire these into an array.

Conclusion

In the end, how you intend to use your 100W solar panel will determine what inverter to buy. In some cases as shown here you may not even have to use an inverter. If you do require one, take into account your future plans and if a larger system will be needed.