Solar Inverter Buying Guide
What’s the definition of solar inverter?
Solar inverters is an electronic system that operates the photovoltaic(PV) modules in a manner that allows the modules to produce all the power they are capable of. The solar mate charge controller is a microprocessor-based system designed to implement the MPPT. It can increase charge current up to 30% or more compared to traditional charge controllers.
This is a multi-function inverter/charger, combining functions of inverter, solar charger and battery charger to offer uninterruptible power support with portable size. Its comprehensive LCD display offers user-configurable and easy-accessible button operation such as battery charging current, AC/solar charger priority, and acceptable input voltage based on different applications.
How many types of solar inverter?
Solar inverters may be classified into three broad types:
Stand-alone inverters, used in isolated systems where the inverter draws its DC energy from batteries charged by photovoltaic arrays. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available. Normally these do not interface in any way with the utility grid, and as such, are not required to have anti-islanding protection.
Grid-tie inverters, which match phase with a utility-supplied sine wave. Grid-tie inverters are designed to shut down automatically upon loss of utility supply, for safety reasons. They do not provide backup power during utility outages.
Battery backup inverters, are special inverters which are designed to draw energy from a battery, manage the battery charge via an onboard charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during a utility outage, and are required to have anti-islanding protection.
What size should I buy?
There is often some confusion around this question.
In general, as a minimum, the inverter needs to be able to handle the maximum power that your solar power system can generate. That usually means they if you want a 5kW solar system, you get 5kW of panels and a 5kW inverter to suit. Simple eh? Actually it can get a little more complicated than that. Let me explain.
Because of system losses in the panels, your solar inverter can actually be rated at up to 25% less (in AC kW) than your panel array - in some situations. Confused? So are a number of installers! The Clean Energy Council guidelines for inverter sizing recently changed, and I provide a detailed explanation of when 'undersized' inverters are allowed here.
A final word of caution: Be aware that inverters are rated in "DC input" and "AC output" terms. Make sure your inverter is also rated to suit the output of your panels in DC! (The previous link explains how to check this)
What about the physical size of the inverter?
Grid connected inverters come in a variety of shapes, sizes and weight. The smallest inverters are around the size of a large briefcase. The larger inverters are around the size of a small travel case.
They are generally located as near as practicable to your electricity meter and should always be located in the shade for best performance. The best advice is to have a look at the inverter (or check out it's specification sheet) and see whether it will fit near your electricity meter and what it will look like.
Does solar inverter have a Warranty?
Typically, grid connected inverters have a life span ranging form 10 to 20 years. You should expect most inverters to last 10 years minimum.
Grid connected inverters have warranties ranging from 5 to 10 years with an increasing number of manufacturers offering pay for service warranty extension. Most retailers are now offering 8 to 10 years warranty. Obviously, the longer the warranty the more protection you have.
So check out the Warranty on your inverter and balance this against other features of your system to help you make an informed decision.
Is the inverter expandable?
This is an important consideration if you are intending to expand your solar system in future.
The best solution at present would be to consider a multiple MPPT (Maximum Power Point Tracking) inverter. These inverters have multiple MPPT trackers allowing you to add additional solar PV arrays at a later date or install solar PV arrays at different orientations. This will enable you to readily add a new string of panels (even if the panels are not exactly the same as the original panels) to your current system.
In future, individual solar PV panels may have a small MPPT inverter attached to the rear of the solar PV panel, typically called micro inverters. This would potentially enable different models of solar panel to incorporated in the same solar power system, would overcome shading issues and make individual solar PV panel monitoring possible.
How efficient is a grid connected inverter?
Inverter Efficiency is a measure of how well the grid connected inverter converts the power it receives from the solar panels into power available to your home or to the grid. Most grid connected transformer based inverters have an efficiency of around 93% or better, transformerless are typically around 95% or better.
Efficiency would only be a factor if two similar inverters had significantly different efficiency.