There are two types of inverters in the solar power industry, namely String Inverters and Micro Inverters. String inverters are similar to Uninterrupted Power Supply (UPS) battery type inverters used to maintain AC when the grid power goes down. Micro inverters are integrated into modern solar panels to convert the solar-generated DC to AC at the solar panel.
Solar panels are designed to last twenty-five to thirty years, and the micro inverters built into each panel should also last between twenty and thirty years. String type and UPS type inverters are sized to generate much higher power outputs and typically last between ten and fifteen years.
The durability of inverters is linked to their proper use and maintenance. We will consider the use of:
- UPS Inverters (ten to fifteen years)
- String Inverters (ten to fifteen years)
- Micro Inverters (twenty to thirty years)
Let’s look at why these inverter types exist and how they are correctly deployed.
How Long Do Different Inverter Types Last?
As micro-inverters are integrated to the solar panels they are designed to last for the same lifespan as the solar panel (twenty to thirty years). Sting inverters and power inverters are designed to last ten to fifteen years as they are used with varying amounts of power input and power draw.
Regular inverters or Uninterrupted Power Supply inverters were the first types of inverters designed to convert the direct current (DC) supply from a backup battery system into useful alternating current (AC) of the correct voltage (V) and frequency (Hz).
Most household, office, and industrial machines were designed to run on AC as this was the type of power that was easiest to generate and transmit over great distances. The high voltage AC is transmitted to substations from the power plant where the voltage and current are adjusted for local distribution.
When the grid power is interrupted, we need to maintain power to critical electrical installations such as computers and life support systems. Battery backup systems store enough power to keep critical electrical devices running for a few hours.
The DC from the battery bank must be converted to AC (120V and 60Hz in the US; 220V and 50Hz in Europe) to power the AC-powered appliances. This conversion from DC to AC is done via an inverter consisting of a collection of switching components (MOSFETs), and transformers generate the pure sine-wave AC.
The development of solar power panels has created a clean, renewable energy source that we can convert from DC to AC. Solar panels produce DC, and when tied into a solar array in either parallel, series, or a combination of both, they are then connected to the grid via solar string inverters.
The sting inverters convert the DC from the solar panels into AC that can be fed back into the power grid or tied into the electrical distribution panel of a home or business.
These string inverters have to convert variable DC power output into functional AC as the solar exposure varies during the day.
The disadvantages with string inverters are that they can be limited in performance by the solar panel with the weakest output. This may be due to some solar panels being partially in shadow during the day or not functioning optimally. The system is limited by its weakest producing solar panel.
Solar panel designers introduced micro inverters on each panel to overcome these problems. A dedicated micro inverter will convert only the DC of a single solar panel to AC and then feed this AC to a common collection and distribution point.
Micro inverters are designed to convert a fixed maximum load from a single solar panel. They will thus not be exposed to variable operating conditions giving them a much better productive life cycle.
What Causes Inverters To Fail?
Inverters are the most vulnerable components in a grid-tied power backup system or solar-powered system. Voltage fluctuations caused by the grid-supplied power are the leading cause of damage to inverters. Circuit breakers and fuses are installed to protect the inverters from high voltage damage.
Improper ventilation and cooling of inverters are also a leading cause of deterioration of the inverter components and premature failure. Cooling fans can be deployed to draw cool air into the inverter housing to cool down the components.
Selecting and sizing the inverter to match the solar panel array power generation capacity is critical to the longevity of the inverter. The inverter should always be larger than required. A good guideline is to select an inverter with a capacity of 133% of the maximum solar array power output.
Maintenance of the inverter installation will also help prolong the device’s operational life. Ensure that the inverter is installed in a fully shaded, cool, and dry location with sufficient airflow around the device.
Where multiple inverters are installed in parallel, sufficient clearance between the inverters must be provided to allow for proper heat dissipation.
Protecting The Most Expensive Parts Of Your Solar Or UPS
When we consider the cost of a complete solar power supply system or a grid-tied uniform power supply system, the most expensive components will be the batteries, inverter, solar charge controller, followed by the solar panels and the wiring.
The solar panels are designed to be robust and last between twenty-five and thirty years, and a relatively less expensive than other system components. The batteries in the battery bank are costly and have a much shorter useable lifetime.
Flooded batteries are cheaper than Lithium Iron Phosphate batteries but have short useful lifecycles and are cumbersome to maintain. Li-ion technology batteries are costly but will last three to five times as long as flooded lead-acid batteries and are much lighter and virtually maintenance-free.
Solar charge controllers in off-grid systems are used to protect the batteries and the solar panels and control the battery charge rate to exploit the battery lifespan optimally.
Inverters play the same role of protecting the battery bank during charging from grid power and also during DC to AC power inversion when the grid power is off. Investing in the correct sizes of charge controller and inverter is the best way to protect your battery bank from damage.
It never hurts to go bigger when selecting inverter and solar charge converter sizes. The chances are that your power demand will grow in the future, and planning to add capacity in a modular manner is an excellent way to design your system.
Your inverter and charge controller are the sacrificial components of your power supply system, protecting the significant investment in your battery bank. Ensure that you invest in the best protection you can afford when sizing and purchasing an inverter.