Solar Inverter Sizing
How to choose the right solar inverter size for your solar power system.
Solar inverters convert the low voltage DC electricity created by your solar panels to the 120 volts AC electricity used by household appliances.
Sizing a solar inverter is an important part of any solar installation, big or small. Since your solar energy system is going to be producing and sending DC electricity to your inverter, you're going to need to have an inverter size that can handle the load and convert it to AC power. This requires knowing how to size an inverter properly.
How To Size an Inverter
If you're going to understand how to size an inverter you must first understand how inverters are rated.
How Inverters Are Rated
The first way inverters are rated is in Watts (or Continuous Watts).
1. Continuous watts is the total amount of watts the inverter can support indefinitely. A 2000 watt inverter can power up to 2000 watts continuously. A bigger inverter size could handle more.
For your inverter to be right for your system, it's watts rating must be approximately equal to your solar system's watts rating. This is the correct way to size an inverter.
Therefore, if your solar system is rated at 2000 watts, you'll need a solar inverter with about 2000 watts, maybe a little bit more. But not too much more or the efficiency will drop. You can learn more about watts by clicking here to go to the Electrical Fundamentals section of our website.
If you want to run multiple appliances at the same time and want to make sure your inverter can handle the load, just add up all the Continuous Watt ratings of all the appliances that may be running simultaneously.
Depending on the total continuous watts you get, you can determine if you're inverter can handle it. This is also an important part of inverter sizing (how to size an inverter).
So if the total continuous watts of all the appliances that may run at the same time is 3000, it's too much, you'll have to run less appliances at the same time.
The second way solar inverters are rated is in Surge Watts.
Surge watts is the amount of power the inverter can support for a very short time, usually momentary. A 2000 watt inverter rated at 4000 surge watts can handle up to 4000 watts momentarily while starting things like motors - which usually require more power than normal to get started.
For your inverter to be right for your system, it's surge watts rating must be approximately equal to (or greater than) the potential surge watts of each appliance.
You can find this out by looking at the sticker on the back of all of the appliances you will be using with your solar system and checking the potential surge watts of each appliance. By doing this you can determine the minimum surge wattage you'll need your inverter to be rated for. Usually, you'll need about 1.5 to 2 times as much surge watts as continuous watts for a good measure of surge protection (more, if powering heavy duty equipment).
Therefore, if the highest surge watt rating on any of the appliances you plan to use with your solar system is 4000, you'll need a solar inverter with a little over 4000 surge watts.
Input Voltage - Should I get a 12v 24v or 48v inverter.
The next rating you have to look at when sizing an inverter is the input voltage.
For correct solar system sizing... your solar panels, inverter and battery bank all need to use the same voltage.
So the input voltage of your inverter will depend on the inverter's power or watt rating. For inverters with a relatively small amount of power like 100 watts, the voltage will be 12V, 24V and 48V. For higher powered inverters, the input voltage will likely be more. You can learn more about volts by clicking here to go to the Electrical Fundamentals section of our website.
Length of Wire & Solar Inverter Performance
One of the factors that can affect your inverter's performance is the distance between your solar panel array and your battery bank. The longer the wire used here, the lower your inverter's voltage should be to perform optimally, because with long wires voltage drops and current increases.
The higher the voltage and the lower the current, the shorter length wires you can use. With longer wires, you would need to use thicker wires. This is covered in the Solar Wire Types section.
Inverter Stacking (Using Multiple Inverters)
Sometimes people connect more than one inverter together to "stack" up more power. This would typically be done if you have many smaller inverters and want to join them together to form a bigger one.
If your inverter demands increase in time (because you added more solar panels) you can either buy a bigger solar inverter or wire multiple inverters together.
When you install and wire two inverters together, it's called inverter stacking and it can provide either more power or higher voltage.
If two compatible inverters are wired together in series, you can double the output voltage. This inverter stacking technique would be used if you only had two smaller inverters and had to provide 120/240 volts AC.
However, if you were to wire them in parallel, you would double your power (watts). This solar inverter stacking technique would be used if you had two smaller inverters but also had a solar system that was rated at much higher watts (power) than what a single inverter could handle. If you wired two 2000 watt inverters together in parallel, they would be able to handle 4000 watts (4KW) of power.
Inverter Performance With Less Sunlight
By correctly matching your solar panel's, your battery bank's and your inverter's rated capacities, you can improve the performance of grid-connected solar systems.
However, when the sun is not at it's brightest and the system isn't producing at close to full capacity the inverter will be operating at partial load and it's efficiency will drop.
Energy loss also occurs when an inverter is too small to operate in conditions of overload. Another important thing to consider in pv inverter sizing.
Solar Inverter Price
An average quality Modified Sine Wave solar inverter can cost anywhere from $400 - $1000. These low to medium quality range inverters can operate with small to medium sized systems and relatively speaking provide good performance, reliability and consistency.
Obviously, unlike more expensive inverters (True Sine Wave inverters)there is typically a moderate amount of energy or performance loss, but not if your appliances aren't too high tech and your solar application isn't too demanding.
If you want to get a good quality inverter for a pretty big system, it would probably cost you about $900 to $1500 for a 2000 to 3000 watt Modified Sine Wave solar power inverter.
If you want to be able to run basically anything plus have all the automatic features, you would likely have to pay about an extra $500-$1000 for a True Sine Wave solar power inverter.
These higher quality Sine Wave inverters are computer compatible and computer controlled which will add automation and true convenience to monitoring and protecting your solar power system. Never forget to factor in convenience and practicality when doing your solar inverter sizing.
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