What Is A Solar Inverter, and How Does It Work?

Technology is advancing so rapidly it’s hard to keep up. With every new breakthrough, there comes an entirely new vocabulary that can sometimes make things even more confusing. That is why we would like to take a second to explain the true backbone of solar: solar power inverters.

What Is a solar inverter?

If solar panels are the heart of a system, then inverters are the brain. Solar inverters efficiently absorb the direct current (DC) electricity from solar panels and convert this current into the standard 120 or 240-volt alternating current (AC) electricity, which is the form of electricity used by most household devices and appliances. Without solar inverters, the energy produced by solar panels, which is in DC form, would be unsuitable for typical home or office use.

The solar inverter in a solar power system essentially tricks the transformer into treating the DC power as AC electricity by making it behave like alternating current. It does this through a process that involves transistors that switch on and off rapidly, subsequently supplying the transformed current to the various sides of the transformer. This conversion is essential because most devices and appliances operate on AC power, not DC. DC electricity maintains a constant voltage in one direction, whereas AC electricity changes direction and voltage periodically.

Now, certain inverters now enable monitoring so we can see how your solar power system is performing. We at Sunrun use a monitoring system that helps us guarantee your solar panels will produce 95% of the estimated power needed when you lease your system.

What is AC/DC power?

AC stands for Alternating Current, and DC stands for Direct Current. They’re two different types of electrical power. A direct current (DC) is generated when solar rays interact with the panels in the solar energy system and force electrons to flow freely from atomic structures. Solar inverters convert this DC energy into an alternating current (AC). It is much easier to transport and convert AC power into different energy strengths than DC energy. That is why AC is the standardized form of energy we all utilize in our homes.

How does an inverter save you money?

One of the primary ways a solar inverter saves money is by increasing the efficiency of its solar energy system. The efficiency of the solar inverter is crucial, as it determines the amount of electricity that can be converted to useful power. The more efficient the inverter, the more electricity can be converted, reducing waste and increasing the system's output​​.

Back in 1956, solar systems were only 6% efficient and cost a staggering $300 per watt.¹ Now, with advancements in solar panel technology and more efficient solar inverters, the average solar system operates at 14 to 18 percent efficiency, costing as low as $3 per watt​​. This dramatic increase in efficiency and reduction in cost is a key factor in how solar inverters save money.

The use of a more efficient solar inverter in a solar panel system not only increases the system's output but also helps in saving on electricity bills in the long run. This is particularly important considering the energy output of a 1 KW solar energy unit, which is approximately equivalent to the burning of 170 pounds of coal and releasing 300 pounds of carbon dioxide into the atmosphere​​.

The right inverter for the job

Not all inverters are created equal. Some are more efficient than others, and this affects your entire system's output and potential savings. There are many different kinds of solar panel inverters for homes, from string inverters to DC optimizers:

1. String Inverters: This is the most common type of solar inverter and is named for their setup, where a “string” of multiple solar panels is connected to the inverter. String inverters are suitable for smaller-scale installations like home solar systems. One string inverter can handle one or a few strings of photovoltaic (PV) modules. 

The performance of string inverters can be affected by shading, however, as it converts the aggregate power generated by each string. To mitigate this, string inverters can be paired with power optimizers, which condition DC electricity before it reaches the inverter, which increases the string inverters’ overall efficiency​​.

2. Central Inverters: Similar to string inverters but on a much larger scale, central inverters can support more strings in a solar panel system and are used for very large installations like solar power stations. In these systems, strings of panels are connected in a combiner box, which then sends the DC power to the central inverter for conversion to AC. 

Central inverters are often placed on the ground in a protected area. They are suitable for consistent production across a large PV array but depend on the power grid and will stop working during an outage​​.

3. Micro Inverters are small inverters that are placed on the back of each solar panel. Installing individual inverters allows each solar panel to perform independently. This method distributes the workload so that the system can have a lower standing energy capacity making micro inverters safer for firefighters and repair/installers.

4. Hybrid Inverters: These inverters are versatile, functioning in both grid-tied and off-grid solar power systems. They can connect solar panels to a solar battery and AC appliances as well as the grid. Hybrid inverters can store excess AC electricity in a solar battery or draw power from it during outages. They are particularly favored for mobile homes and buildings that are both grid-connected and not grid-connected​​.

5. Grid-Tie Inverters: These inverters are used in systems that are connected to the grid. A grid-tie inverter converts the DC electricity generated by solar panels into AC electricity that synchronizes with the grid's AC electricity. This allows for the direct use or sale of electricity back to the grid. 

These inverters can significantly reduce electricity bills by allowing excess electricity to be fed back into the grid. However, they depend on the grid's stability and will not work during grid outages, which can be problematic in areas with frequent power interruptions​​​​.

DC Optimizers, like microinverters, are devices that go on the backside of each panel. However, instead of converting the DC energy to AC, optimizers “condition” the DC energy and send the power to a central inverter. This creates a hybrid system that combines the best of both traditional inverters and micro inverters. 

<sup>Sources:
1. “Introduction to Grid‑Forming Inverters – A Key to Transforming our Power Grid”</sup>

^{2. “Solar Integration: Inverters and Grid Services Basics”}