Types Of Solar Inverters (String – Power – Micro)

Many people want to do the right things to counter the effects of global warming and human-induced climate change, but the technicalities of solar systems can boggle the mind.

The heart of a solar power system is the solar panels, as they convert the sun’s energy into electrical power. The power is not in a usable format for use in our houses by most appliances as it needs to be converted from direct current (DC) to alternating current (DC) via a solar inverter.

The role of an inverter is to turn the DC from solar panel arrays or batteries into usable AC. There are three main types of solar inverters used in solar installations today:

  1. String inverters
  2. Power optimizers/inverters
  3. Mico-inverters

Let’s look at each type of inverter and the pros and cons.

Solar Inverters For A Solar Farm
Solar Inverters For A Solar Farm

What Does A Solar Inverter Do?

Solar Inverters change the direct current (DC) power generated by the photovoltaic cells of the solar panels into alternating current (AC) that can be used to power most devices and appliances in modern households.

The inverter chops the direct current into strings and inverts every alternate string into a wave. The successive alternating waves change polarity during each cycle at a frequency of 60 Hz (60 times per second).

The inverter blends the alternating half waves into a continuous pure sine-wave of alternating current. This format can be useful in powering electrical AC motors or heating elements as found in our household appliances.

Surplus AC power generated during the peak sunlight hours of 9 am to 3 pm can be fed into the national power grid and used by other users linked to the grid. Without solar inverters, we will not power most electrical appliances or feed power into the grid.

What Are String Inverters and When Are They Used?

String inverters are the oldest and most common type of inverters in use. They are used when arrays of solar panels are connected in series to the solar inverter responsible for converting the solar DC power to AC power of the correct voltage and frequency.

String inverters are also called central inverters and have the sole task of converting all the solar-generated direct current into a useable alternating current output. They are simple and reliable devices and the most commonly used inverter type.

  • String inverters are ideally mounted close to the solar array to effectively convert the DC to AC for transmission to the house distribution system to points of use. They are thus highly visible and can be easily monitored and repaired or replaced.

As the oldest and least complex of all converter types, string type inverters are unfortunately the least efficient at converting and optimizing the available DC to AC. They are connected to the entire solar array, but the weakest generating solar panel limits them.

When one panel is partially or completely obstructed by shade, the performance of the entire string is adversely affected. The solar array’s performance can only be measured as a collective and not by the individual panel.

This lack of visibility of individual solar panel performance requires that each solar panel be tested to discover the under-performing panel.

These central or string-type solar inverters were commonly used in older solar installations, but the advancement of solar panel and inverter technology has made them less popular.

What Are Power Optimizer/Inverters, And Where Are They Used?

Power optimizers have been integrated into the solar panel and work in conjunction with string inverters to convert the DC to AC. The power optimizer conditions the DC power for more efficient conversion to AC.

The DC power is conditioned by each solar panel, thus eliminating the impact of momentarily shaded panels and thus underperforming.

In conjunction with the individual solar panel-based power optimizers, the string inverter can eliminate the total system inefficiency due to individual underperforming panels.

One defective or underperforming panel will not degrade the output of the entire array.

In conjunction with the string inverter, the panel optimizers will allow for identifying individual panel operating performance, making the diagnosis of problematic panels easier.

The solar panel performance can be monitored and eliminated at an individual panel level, making the entire system more efficient and more transparent to fault diagnosis. The power optimizers and integration with the string inverter make the system more expensive.

As the power optimizers are located on each panel, they are located on the solar array on a ground mount or roof mount and thus not easily accessible for servicing.

Power optimizes were added to conventional string inverters but have been surpassed in efficiency and performance.

What Are Micro Inverters And How Are They Used

Micro Inverters represent the highest state of the art in converting solar power DC into AC. Micro Inverters are an improvement on power optimizers in that they are installed on individual solar panels and eliminate the need for a string inverter.

The DC power generated is converted by the micro inverter on each panel to AC and is fed to the join up with the AC power from the other solar panels in the array. This eliminates the effect of temporary shading of individual panels.

Micro inverters are easily scalable to all the solar array panels, or future expansion of the solar panel array is easily integrated. Micro inverters allow for accurate single panel performance monitoring and fault finding.

Although they are more expensive than string and power-optimized string inverter systems, the payback in the benefits easily offset the cost. Power optimizers are panel-specific and require service and repairs to be done on the roof or the ground-based system.

What Type Of Solar Inverter Should I Use?

The best type of individual component to use on solar systems always seems to come down to getting the best payback for your money spent. My answer is always to use the most expensive option you can afford.

The financial payback on investing in solar-powered systems has dropped to below five years with system lifecycles of thirty years. If this were a stock on the exchange, you would not hesitate to invest in the best state-of-the-art system that your current budget can get you.

If you spend some more upfront and your payback reduces from five to six years but with a far greater degree of convenience and efficiency, then invest in the best technology you can afford. Consult with an expert to identify your current and future power demand.

Don’t rely on your limited knowledge to make decisions that will impact you for the next thirty years.

References:

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