Inverters for solar panels are perhaps the most essential part of your system. They allow your solar panels to power your electronic devices by converting DC (Direct Current) electricity into clean AC (Alternating Current). Similar to the electricity from your utility company.
What are different types of inverters for solar panels?
There are three types of inverters:
- Micro-inverters (Grid-tie)
- String inverters (Grid-tie)
- Hybrid inverters (Off-grid)
In this article, we will describe the different types of inverters for solar panels and help you to understand which one is best according to your needs and budget.
Lastly, we will give our general recommendation to size your inverter in both grid-tied and off-grid configurations.
What Are The Different Types Of Inverters For Solar Panels?
First of all, inverters for solar panels are slightly different from DC to AC inverters that you could directly use with 12V batteries or plug into the cigarette lighter of your car.
The output power of a solar panel is constantly fluctuating over the course of the day and is strongly correlated to the weather (passing-by clouds, rain, full sun, etc).
Because of these fluctuations, all inverters for solar panels include a MPPT solar charge controller that will optimize the solar production.
That said, the working principle of a solar inverter is similar to a regular pure sine wave inverter as described in our recent article.
All solar inverters are:
- Robust to operate in all kinds of climates
- Reliable for continuous operation (Always-On mode)
- Powerful enough to absorb your solar production and cover your power needs
- Efficient to convert DC to AC (above 90%)
What Are Micro-inverters For Solar Panels?
A micro-inverter, as it’s name suggests, is a tiny version of an inverter. The device is roughly the size of a WIFI router and is installed below the solar panel. It will handle the power of one to two solar panels and deliver AC electricity (120/230V, 60Hz) to your house and will be transferable to the utility grid.
Multiple micro-inverters are connected in parallel to increase the total power output of the solar system.
Micro-inverters are connected to the utility grid (grid-tied) and to your home’s electrical system. In addition, they can be coupled to an Energy Storage System (ESS) that accepts AC power, like the Tesla Powerwall 2.
What Are String Inverters For Solar Panels?
Grid-tied string inverters are the most popular type of inverter.
They are designed to deliver clean AC power from a string of solar panels to the electricity grid. They also allow self-consumption of your solar electricity during the day.
They look like a large shoe box, and are wall mounted inside your house. The DC production of the solar array is transferred to the central inverter to be converted into AC electricity. The inverter is connected to the utility grid and to the house power circuit.
Similar to micro-inverters, string inverters can also be coupled to an AC battery.
What Are Hybrid Inverters For Solar Panels?
Hybrid inverters, also called Off-grid inverters, are specially designed to deliver AC power at any time in the absence of grid electricity.
Therefore, they include a battery charger for electricity storage.
They are also called “Smart Inverters” as they automatically regulate the charge/discharge current of the battery in function of the electric load and the solar production.
DC electricity from the solar panels is converted into AC, similar to a grid-tied inverter. In addition, DC power is also fed into the battery during charging. If the sun is not enough, the inverter will get DC electricity from the battery and converts into AC.
Most models also allow an external AC source (fuel generator) to take over in case of a power shortage from the batteries and solar panels.
What Type Of Inverter Do I Need For My Solar Panel System?
In this part, we will describe the main features of each solar inverter and give you our recommendation.
In a solar system, you can count as many micro-inverters as the number of solar panels. Therefore, each panel is individually monitored and controlled.
Average price: 0.3USD/Watt
- Limit the power loss from shading
- Optimize the solar production of each solar panel
- More efficient (+25%) and durable than a string inverter (15 to 25 years)
- Easier to add extra panels to your system
- Smart monitoring with mobile phone app
- Hard to perform maintenance (below the solar panel)
Should you use a micro-inverter?
In the end, we would recommend micro inverters for domestic solar production only. We appreciate their high durability and efficiency, resulting in cost saving over time.
Unlike micro-inverters, you only need one string inverter to control your solar array. Usually, a string of solar panels in series produces high DC voltage (from 120V to 500V DC) to the string inverter which converts it into AC (110V/220V).
Average price: 0.2USD/Watt
- Easy to install
- Only one inverter to maintain
- Cheaper than multiple micro-inverters
- More efficient at converting DC to AC
- Low power output during shading
- Less durable (10 years)
- Less modular (solar capacity and power output are fixed)
- Needs extra space for installation
Should you use a string-inverter?
Central string inverters are convenient to install and to maintain but they suffer from low efficiency if local shading occurs (up to 25% loss). In most cases, solar panels are connected in series to the inverter. Therefore, if one solar panel is shaded, the whole string of panels is affected and so is the power output. That said, we still recommend central inverters for domestic solar systems especially because they are affordable and easy to maintain.
Hybrid Off-grid inverters
Hybrid inverters are string inverters that include a battery charger and a smart energy management system. They are very versatile and can be installed even if you have access to grid electricity.
Average price: 0.25USD/Watt
- Easy to set-up
- Self-consume at any time or dispatch your solar electricity to the grid
- Smart energy management system with remote monitoring
- Easily connect any type and size of solar batteries
- Versatile systems
- Limited power output
- Needs a dedicated room for installation
- Can be noisy (cooling fans, humming sound)
Should you use a hybrid inverter?
Off-grid hybrid inverters are the most versatile inverters. They give you the ability to run your own power station without the need of external grid power. We recommend them for all situations in which the grid is missing, like camping, RV’s, boat and off-grid houses, in combination with lithium batteries. Some brands already offer integrated systems including off-grid inverters and batteries in a plug-and-play solution called an Energy Storage System (ESS).
What Size Of Inverter Do I Need For My Solar Panel System?
In this section, we will explain how to size your inverter in grid-tied and off-grid configurations.
What Size Of Inverter Do I Need In A Grid-tied Configuration?
When connected to the utility grid, have no fear of running out of power: if your solar production is not enough, the grid will supply your power. In that case, the size of your inverter is related to your solar arrays total peak power.
We recommend to oversize your inverter capacity by 30% compared to the total solar panel peak power.
Inverter size = TotalPV Peak Power * 1.3
For example, if you are looking to install six solar panels of 400W each (2400W), select an inverter of at least 3000W.
Keep in mind that a larger string inverter allows you to add extra solar panels later on.
What Size Of Inverter Do I Need In an Off-grid Configuration?
In an off-grid system (boat, RV’s, camping, cabin…), there is no grid back-up in case of power shortage.
We recommend to oversize your inverter by 40 to 50% compared to your peak power needs. Mainly because some appliances (refrigerator, water pump, power tools…) are reactive loads that require a higher amount of power to start and operate than their rated power. Other types of appliances are resistive loads that will only need their rated power (TV, computers, lights…)
Inverter size = Total Appliances Power*1.5
To give you an idea, we have summarized different appliances that you could run simultaneously with a 500W, 1000W, 1500W and 3000W hybrid inverter:
|LED TV (100W)||Electric Fan (60W)||Laptop (150W)||Refrigerator/freezer (100W)||Vaccum cleaner (700W)||Led lights (6*5W)||Electronics (phone, tablets, 25W)||Water pump (1kW)|
Final Thoughts From Koos Mulder
According to Koos:
Micro inverters could be a good choice for AC coupled systems (grid-tied) thanks to their high efficiency, however he rose our attention on two issues:
- Safety, as the back of a solar panel can be very hot (+60°C) and the more inverters you have (one per panel) the higher the risk of an electric fire
- Maintenance, although you might not need to perform maintenance for years, when you eventually do, it might be complicated to figure out where the defective micro-inverter is.
He still favors central hybrids inverters as they are much easier to install, control and ultimately, they are cheaper. They might be slightly less efficient (-5%) but it is balanced by all the previous advantages.
In the end, the main trend is now geared towards energy storage at home, with smart inverters and solar batteries: the Energy Storage Systems (ESS).
Electricity consumers will turn into prosumers, to sell their excess electricity to the grid when prices are high.
By doing this, we could achieve a higher amount of renewable energies in our global electricity production.