The Inverter you choose is one of the key decisions you will have to make when deciding on what type of Photovoltaic system you want. The Inverters convert direct current (DC) electricity generated by solar panels into alternating current (AC) electricity that your home runs on. More important than the photovoltaic panels you select, the inverter(s) are the heart of the system and you want to get this right to maximize power production vs cost.
The three main inverter options available for residential and commercial solar installations are string inverters, micro-inverters, and power optimizer systems. The string inverter is the least expensive option but least flexible in dealing with shading issues. Micro-inverters and power optimizer systems are typically more expensive than string inverters but offer a lot of flexibility in dealing with shade and maximizing power output.
What to read more?
Shading on part of or all a solar panel has the consequence of reducing the total system’s overall power production when using a string inverter. Roof gables, trees, neighbors’ taller house, multiple roof faces for the solar panels, or angle to the sun, can all be factors that reduce production with string inverters. However much of these negative design aspects can be mitigated by using Micro-inverters and Power optimizers.
So why would you want to use a string inverter? They are the most cost-effective inverter option available in the U.S. If your roof is not shaded at any point during the day and does not face in multiple directions, requiring solar panels being placed on roof sections facing different directions, then a string inverter could be your best choice. However, in recent years due to new electrical safety code requirements called “rapid shut-down” the string inverter cost advantage has been reduced somewhat.
The basics about how String Inverters work is that your solar panels are arranged into groups called strings. These strings connect to the inverter and function as a unit. Anything affecting a panel on a string affects the entire string. Thus, a string of solar panels will only produce as much electricity as its least productive panel in the string. If one or more of your solar panel(s) is shaded during any part of the day, the power output from that entire string would be reduced to that lower level.
What to read more about Micro-inverters?
Micro-inverters are more expensive than string inverters or power optimizers, but some of their upfront costs are offset over time by high productivity and electrical output.
Micro-inverters are installed under each individual panel in a solar array. The individual micro-inverters convert the DC electricity from your solar panels into AC electricity right on your roof sending AC power directly to your electrical system. In some cases, Photovoltaic panel manufacturer integrates a micro-inverter into the solar panel itself, further simplifying the installation but complicating repair warranty work down the road.
One of the major advantages of micro-inverters is that partial or complete shading of one panel will not cause the entire string’s output to be reduced. Since each panel is now operating as an independent production device the shading losses are confined to just the panel(s) being shaded. So, the choice to spend the extra dollars for micro-inverters is straight forward if the installation is where one or more panels may be shaded at various times of the day or year, or where panels are facing different directions.
Plus, Micro-inverters also allows you to monitor the performance of individual solar panels rather than just the system total as is the case with string inverters.
The downside to Micro-inverters is the higher failure rate and need to get on the roof and under solar panels when doing corrective work. Some believe the failure rate is increased due to all the sophisticated electronics of an inverter in the harsh weather environment of extreme heat and cold experienced on the roof, but other claims that it is just newer technology teething pains.
Want to learn more about Power optimizers?
Power optimizers offer many of the same benefits as micro-inverters but tend to be slightly less expensive. Power optimizers are often considered a compromise between more expensive micro-inverters and the standard string inverter.
Like micro-inverters, power optimizers are located under each panel or sometimes integrated into the panels themselves. However, the solar panels are still wired in strings and the system will still have a central inverter mounted on a wall in a garage or easily accessible location. The big difference is instead of converting the DC electricity to AC electricity at the panels, the optimizers’ electronics adjust the DC electricity voltage to minimize the negative effects of shading on the string and send adjusted DC power to the inverter. This approach results in higher system efficiency than a string inverter alone and less complexity up under the roof than micro-inverters.
Similar to micro-inverters, power optimizers reduce the impact of panel shading on system performance, and also offer individual panel performance monitoring. Systems that use optimizers are typically more expensive than standard string inverters and slightly more affordable than micro-inverters.
What to read more about Micro-inverters vs Power optimizers?
Micro-inverters and power Optimizers are very comparable and are collectively referred to as “Module-Level Power Electronics,” or MLPEs. They both offer:
-Monitors the performance of individual solar panels.
-Improves performance of solar panels on multi-faced roofs, or roofs that experience shading
Power optimizers have an edge over micro-inverters when it comes to the cost of an increasing size system. With micros, the greater number of Photovoltaic panels, the greater number of inverted needed and thus overall price stays flat. With optimized systems, one can increase the size of a system with the same inverter thus reducing the price per watt installed as the system size increases. One still has to buy additional optimizers and perhaps scale up to a larger inverter, but scalability still works in the optimizers advantage
While both micro-inverters and power optimizers typically have 25-year warranties, that is not the full picture. The optimizers up on the roof are warrantied for 25 years but the central inverter part mounted on the wall may only be warranted between for 12 years. If the 12-year warranty is a concern, many manufacturers offer extended warranties for their inverters for an additional cost.
While Micro-inverter’s warrantees cover 100% of the inverter system for 25 years, that is just materials warranty, the labor warranty to replace roof components is often only 5 years so it can be costly to replace failed micros in the future even if they are covered under warranty.