How to Select a Solar Inverter? Easy Calculation

By Matthew Joseph Nandirio •  Updated: 09/27/21 •  8 min read

If you have decided to meet your energy needs with solar energy, you must be wondering about a solar inverter. A solar inverter changes the energy generated by your solar device into a usable form. Hence, it is a vital part of the solar energy system. It is designed to work for at least 15 years. However, it has parts that can make it prey to failure before that. Thus, you must keep a lot of things in mind before buying a solar inverter.

How Do I Choose A Solar Inverter?

When buying a solar inverter, you should first select the right size. Also, you should be clear about what type of solar inverter you would like. Another important parameter to consider is efficiency. You can also compare various features different solar inverters offer. In addition to this, you must ensure that your inverter can stand the weather conditions in your area.

How Big Should My Solar Inverter Be?

The ideal size of your solar inverter depends on a host of factors. One important factor is the panels on your device which form an array. More specifically, it depends on how much electricity your array produces. The amount of electricity produced per unit of incident light primarily depends on the size of your array.

If you are looking for a solar inverter for 100w solar panel, then try this dedicated article. It has more details on the topic. Or else, let’s continue to our article

Further, it also depends on the design of your solar panels. This is because the design directly impacts how sunlight hits. Thus, it impacts how much sunlight is trapped. Moreover, you also have to consider environmental factors. For example, if your device is in shade half the time or does not face the sun directly, it may not get a lot of sunlight. Hence, it may not generate as much electricity as it could with its size.

You must factor in your location as well. It means your latitude and longitude. These also determine how much irradiance your device is getting from the sun. Again, in this case, even large devices may not produce the expected amount of electricity. Generally, if a device does not produce a lot of electricity, it only requires a small solar inverter. Therefore, factors that reduce the sunlight incident on your panels will contribute to reducing the size of your inverter. This is true corresponding to the size of your array.

That said, you can also fix a microinverter for your solar device. As the name suggests, microinverters have a lower size than ordinary inverters. It is because a microinverter depends on the size of an individual solar panel instead of an entire array. They change electricity at the panel level.

How Do I Calculate What Size Inverter I Need?

The size of your inverter is related to its rating. It shows how much power an inverter can supply. For example, a 1000 Watt device can supply 1000 watts of power. Generally, your inverter should have a similar rating to your solar device. For example, if your array is 5500 watts, then your inverter must also be near 5500 watts. If your inverter has a rating of exactly 5500 watts, then the ratio of array/inverter is 1. Generally, this ratio goes up to 1.55.

A large ratio means that the inverter is much larger than your inverter. Thus, the amount of electricity you receive in your home would depend on the size of your inverter. If your solar panels produce more electricity than your solar inverter can handle, it will clip the power. Hence, it will result in losses.

For example, your panel produces 7000 watts of electricity. But the capacity of your inverter is only 5500 watts. Then, you will lose the additional energy generated by your device. Thus, you must go for a high ratio only if your array gets less sunlight due to environmental factors or the way it is placed. Also, the size of your array must not be 30% higher than that of your solar inverter. If you are on a tight budget, you can get a slightly smaller solar inverter.

On the contrary, you can also have an inverter that is too big for your solar energy system. An inverter can handle a low output. However, it may not be optimal. It will not be efficient. Also, it will produce lower amounts of electricity than an inverter which is just the right size. So you should get an inverter that is larger than your needs only if you want to increase the coverage of your solar array.

Solar Inverter Size Chart

You know the range of ratings within which you should buy your inverter. Now, you should consider a list of devices that need a minimum amount of power from your inverter.

DeviceMinimum Power Needed (Watts)
Cell phone25
Personal Laptop100
Bulb100
Fridge100
TV175
Iron1000
Fan1100
Chain Saw1250
Toaster1200

So, you must add the minimum power needed by each device you want to connect to your inverter. Then you must keep another 20% of the total as additional power.

Inverter Size Calculator

You need not calculate the size of your inverter all by yourself. You can also use several online tools to help you with the same. They will ask you for the inputs and directly tell you the power of the inverter you need.

Inverter Battery Size Chart

In addition to inverter size, you should also have a battery backup. This will help in case of a power failure. The size of the battery depends on how much energy you use. If you use too small a battery, then you risk running out of power.

On the other hand, if you use too big a battery, you just end up spending too much. Unless you plan to or foresee an increase in your energy consumption, you must not invest in a battery that is too large for your use.

Therefore, to calculate the size of your battery, you should first estimate the amount of energy you would need. This is the product of the amount of power your devices use and the time they use it for. Thus, it is in kilowatt-hours. For example, say you use your fridge for 5 hours a day.

The energy you would use = 100 * 5 = 0.5kWh

Once you have done this, you can calculate the size of your battery. This depends on 3 main factors:

  • Type of battery – There are mainly two types of batteries. They are lead-acid batteries and lithium-based ones.
  • Depth of discharge – This is the amount of battery that will be discharged compared to its capacity in terms of percentage.
  • Multiplication factor – This is based on the inefficiency of the battery

You can follow this simple table to help you with your calculations.

Battery typeFormulaSize (kWh)
Lead Acidenergy*2*1.2240
Lithium(energy*1.2*105)/100126

Note that these values have been calculated by keeping in mind that the energy you would use is exactly 100 kWh.

Inverter Rating List

Your inverter will have a continuous rating. This is the power it supplies on a continuous basis. Your devices use this power a few moments after they have turned on. This is different from the power your inverter supplies during a surge. Usually, during a surge, your devices would need extra power to start. Your inverter supplies this power for a very short period of time. So, when you choose an inverter, you should pick one that can take care of the surges.

Here is a list of top-performing inverters with their ratings

CompanyInverterRating
Darfon AmericaH7 Hybrid Inverter7.6kW
GoodWe USAA-ES Series9.6kW
CPS AmericaCPS 250/275kW String Inverter250/275kW
JEMA EnergyFX6 Central, Bidirectional Smart Inverter, and Power Station1MW – 3MW

Inverter Sizing For PV System

Thus, sizing an inverter for a solar energy system takes a few steps.

  1. Determine the type of inverter – You should first know whether you want an interactive inverter or a standalone one. The former will support the loads. On the other hand, the latter stores energy and is for a specific need.
  2. Once you have done this, you must know the energy output based on your array and weather conditions.
  3. Finally, you should analyze the costs involved.

Other Features

While size is a vital parameter when selecting an inverter, you should also make sure you choose the one with the best efficiency. You can also look for add-ons and other features that different companies may offer. Further, make sure your inverter can handle the weather. Sometimes, some inverters seem great. But people often forget to check if they can stand tough weather. Therefore, you should see if the electrical components are well protected.

Also, you must check if your inverter has a working cooling system in place. One of the most common reasons why inverters fail is because their cooling systems do not work properly. Moreover, you should always check for any manufacturing defects.

Conclusion

Choosing the right inverter for your solar energy system is not an easy task. However, it can save you a lot of maintenance time if you do it right. Once you have decided on an inverter, be sure to ask for a warranty. This will help you get a replacement without any hassles, in case there is an issue.

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Matthew Joseph Nandirio

Matthew Joseph Nandirio is the Founder of walkingsolar. After graduating from the University of Houston in 2002, matt started working as an electrical and electronic engineer for several multi-national solar energy companies. He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research. He now shares his 20 years of expertise through his articles on the walkingsolar website. Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.