Getting the right inverter for your PV system is a critical aspect of design and function, and when selecting the right inverter that is matched to your power requirements, there are a few elements that require consideration.
For most home and portable PV systems, you will only need one inverter if you are using either a string inverter or power optimizers for the solar array; if you use micro-inverters, you won’t require a standalone inverter all as they convert DC to AC at the panel.
To understand why you only need one inverter as well as when you could utilize two or more, we need to consider the following :
- The different types of inverters available and how they work
- How to determine what size inverter you would need for your system
- When could you use two inverters, and how you would connect them
Power inverters are essential in a PV system for converting DC-generated power to AC usable power. Since they can be expensive, read on to see which inverter you need and size it correctly.
How Many Inverters Would I Need For My System?
There are three types of inverters available: the string inverter, the power optimizer, and the micro-inverter. You would only need one inverter when using string or power optimizers, but using micro-inverters doesn’t require a standalone one.
What Is The String Inverter?
String inverters are standalone and usually mounted close to the ground for easy access, and the panels grouped in ‘strings’ are connected to the inverter.
As one of the most common and cheapest inverters, you would only need one of these for your PV system. The string inverter then converts the DC-generated power to AC which your household appliance can use.
Most inverters are connected to the battery bank, as unless you are running a very small PV setup that doesn’t use batteries for storage, the inverter will be drawing power from the storage units and not the panels directly.
This type of inverter is reliable and robust, but it can only provide you with performance analysis on the whole system and not give you data on individual panels.
Also, because the solar panels are connected to the inverter in groups or strings, the string inverter only delivers the aggregated overall power.
So if a string of panels are in the shade and their output is lower, the string inverter will deliver this level of power to the home affecting the supply piped into the house.
What Are Power Optimizer Inverters?
Power optimizers also require a central inverter, but they are placed at each panel, and they are designed to condition and maximize the output from the solar panels.
Being connected to each panel, power optimizers enable each panel to become ‘smart’ and relay performance information on both the full array and individual panels for analysis.
Using power optimizers will also require using a string inverter to convert the DC to AC, but power optimizers deliver greater overall performance by optimizing the voltage from each panel before transmission to the central inverter.
You would need one power optimizer inverter for each panel, plus the string inverter for the AC conversion. These are the hybrids between micro-inverters and string inverters.
What Are Micro-Inverters?
Micro-inverters are a super-smart technology that converts DC to AC at the panel itself and then distributes that for usage in the home. They are the most expensive, but you don’t need a central string inverter for this system.
Micro-inverters connect each panel and deliver converted AC directly, rather than sending it to a central string inverter like power-optimizers. Micro-inverters provide accurate panel and system performance data and are not affected if certain panel strings underperform.
You would need one micro-inverter per panel, but you would save money as you don’t require the standalone string inverter.
Micro-inverters are also the most efficient available and are often between 22% and 30% more effective in producing maximum voltage than power optimizers or string inverters and are about the size of an internet router.
This is because the panels using micro-inverters are not set up in strings or groups, and so each panel can deliver its ‘best performance’ without being compromised by panels in shade or directional limitations.
What Size Inverter Would You Need?
You would need to purchase an inverter that matches the output of your solar array, so if you have a 6000W (6kW) system, your inverter would need to a rated at 6000W.
You also need to consider the two different wattages involved here as there is a continuous and surge voltage. Continuous voltage is calculated by adding up the total wattage of all the appliances and devices in the home that would require power.
Surge wattage is the amount of power needed for a short time as motors startup devices, typically 1,5-3 times the rated continuous wattage.
For example, an air-conditioner may have a rated wattage of 2000W, but the startup wattage maybe 3000W, so when looking at the size of the inverter, make sure you take the surge wattage into account and ensure that the inverter you choose can handle the total surge capacity.
You can find the surge wattage on the appliance tag, and totaling both the surge and continuous power will give you a good idea of what size inverter you need.
Could You Use Two Inverters?
You can connect inverters in parallel to double the wattage (power) or in series to increase the voltage. You could do this if you have several smaller inverters that you want to connect to achieve greater voltage or power.
You can connect inverters, but it is not a DIY job and requires technical skill and knowledge. You wouldn’t need to do this in most cases and would only need one inverter for your PV system.
If you need more power from your existing inverters, you can either buy a bigger one or connect them according to your power requirements. While this scenario would be uncommon, you could utilize more than one inverter to increase power or voltage.
In most cases, when installing or upgrading a PV system, you would only require the installation of either a string inverter by itself or in conjunction with power optimizers, or use the micro-inverters only and eliminate the string inverter.