How to select an inverter - type and size
There are plenty of options available when it comes to selecting an inverter. Inverters vary in size, efficiency, performance, and capabilities. So what’s the best solution for you? The key questions you have to answer are the following:
- Do you have a single phase or three-phase electricity supply?
- Do you want back-up power from a battery?
- What is the size of your solar panel array?
- How much power are your appliances using?
What is an inverter?
An inverter converts the Direct Current (DC) electricity generated by solar into Alternating Current (AC) electricity so that you can use it in your home.
3 phase / single phase inverters
Most inverters can work with three-phase systems. The Solar PV inverter Fronius Symo is an example of a three-phase inverter, designed for 3-phase electricity only. Other inverters, like e.g. the Victron Quattro, can only work with a three-phase supply if three inverters are installed, one for each phase.
Type of inverters
When selecting an inverter, the first thing to consider is the type of inverter. In order to keep this article simple, we are describing only the main types of inverters below, and there are two types:
- Hybrid inverter
- Solar PV inverter
A common misconception about installing solar is that you always have power during load shedding. In most cases, this is not true: Solar PV inverters automatically shut off during outages for safety purposes. If you want to keep your property running on backup solar power during an outage, you need a hybrid inverters, as well as batteries. This type of inverter combines a solar inverter and a battery charger into one. As many people want to keep the lights on during load shedding in South Africa, this inverter is common in SA’s residential solar PV systems.
A hybrid inverter is also known as:
- (hybrid) grid-tied inverter
- battery (-based) inverter
- off-grid inverter
Many people choose to install a hybrid inverter in anticipation of adding batteries later to their system, however some hybrid inverters need at least a small battery to function properly.
Some hybrid inverters are integrated with MPPT charge controllers (click here for examples), otherwise, charge controllers will have to be added separately.
You can find SunStore’s hybrid inverters by clicking here.
Solar PV inverter
This type of inverter is also called:
- Grid-tied inverter
- PV inverter
- Grid inverter
- Solar inverter
They convert the DC power directly into AC power, which you can use in your home, but they do not have the possibility of charging a battery.
Some solar inverters, like SunStore’s Fronius grid inverters, are designed to work together with a Victron hybrid system (also called “AC-coupled” systems). The solar inverter will convert a large part of the PV power during the day into AC power, while the hybrid inverter can be used at night together with the battery.
You can find SunStore’s solar PV inverters by clicking here.
What size of inverter do I need?
As a very rough rule of thumb - same as your solar panel system; for a 6 kilo Watt peak (kWp) solar panel system, you would need a 6 kW inverter.
A more precise answer:
The size of your inverter will play an important role in overall electricity production. Inverters come in all different sizes.
Similar to solar panels, the size of an inverter can be rated in Watts (W), kilo-Watts (kW) or kilo Volt-Amperes (kVA). kVA is apparent power, and as a rule of thumb, the kW power is around 80% of kVA. Therefore, an inverter rated at 10 kVA is equal to a 8 kW inverter. In general, inverters are able to handle a peak Wattage of a very limited duration for about 1.8 times the size of the inverter.
When it comes to inverter sizing, installers will take two primary factors into account: the size of your solar panel system and your electricity usage.
The right size inverter for your specific applications depends on how much wattage your devices require. This information is usually printed somewhere on electronic devices, although it may show voltage and amperage ratings instead. Look at the biggest appliances that you want to connect simultaneously to your solar system in terms of Wattage, e.g. water heaters, electric grills, air conditioners, Jacuzzi, etc.
Your inverter should be able to handle the peak Wattages that these appliances require when running at the same time.
If it is going to be too expensive, you can decide to not connect these particular appliances to the solar power / backup system. You can ask your installer to only connect your ‘essential loads’ to the solar system.
Your solar panel system
The size of your solar panels is the most important factor in determining the appropriate size for your inverter. Because your inverter converts DC electricity coming from the panels, it needs to have the capacity to handle all the power the array produces. If you are installing a 5-kilowatt peak (kWp) system, you can expect the proposed inverter to be around 5,000 W, plus or minus a small percentage.
The array-to-inverter ratio of a solar panel system is the W rating of your solar panels divided by the maximum output of your inverter. For example, if your array is 6 kW with a 6000 W inverter, the array-to-inverter ratio is 1. If you install the same sized array with a 5000 inverter, the ratio is 1.2. The majority of installations will have a ratio between 1.15 to 1.25; inverter manufacturers and solar system designers typically do not recommend a ratio higher than 1.55.
Many inverters can be connected in parallel. This means that two inverters, e.g. two 5 kVA inverters in parallel, operate as if it was one inverter of 10 kVA.
There are many ways to describe inverters, and there are some other types of inverters like e.g. micro-inverters, which will be described in separate articles.
Have a look at all of SunStore's Inverters: Click Here
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Source: adapted from energysage.com