String or Micro: Which Inverter is Right for Me?

What is an inverter and why do I need one?

When solar panels generate energy, it is created in the form of DC (Direct Current) electricity. As it is, this electricity is not usable for our homes. All the equipment in a house needs to be converted to AC (Alternating Current) electricity. An inverter’s job is to convert DC electricity to AC so we may use it in a compatible form. There are two primary technologies for converting DC to AC known as string inverters and microinverters. Both types of equipment have advantages and disadvantages that we will discuss.

String inverter

String inverters turn the DC power of several groupings of solar panels, each known as a string, to AC. The inverter is typically placed at an accessible location and near the point of interconnection to the home’s power meter.

This is for accessibility and maintenance purposes. A side effect of a string inverter system is that there are risks for inefficiencies and underproduction of the system. A string inverter system is wired in series. This can be thought of like a dogsled. Just as the sled can not go faster than the slowest dog, the system cannot produce more power than the worst performing panel.

There is a benefit to this, however. In a series circuit, the voltage is equal to the sum of each panel and can therefore be higher than that of a parallel circuit. A higher voltage can be useful for when you have a ground mounted system that is far away from the home, and a phenomenon called “voltage drop” is an issue. Higher voltages will generally experience lower voltage drops over long distances.

A counter to some of the downsides of string inverters would be adding Module-Level Power Electronics (MLPE) devices called Power Optimizers. These take the DC power from a solar panel and convert that to the most efficient voltage and current for the Inverter. One power optimizer is installed for each panel in the system. This offers a few benefits that are comparable to that of microinverters such as panel level monitoring and maximized potential for individual panels, but these too, come with drawbacks. If an optimizer goes down, you will still suffer the problems of losing quite a bit of energy production as the whole string of panels will be affected. Optimizers generally have a 25-year warranty, but the inverter will not. If the inverter is not rated for the same lifetime as the rest of the system, then the cost of replacing a string inverter should be factored into the cost analysis. Each optimizer also provides an additional point of failure. While Nova Solar stands behind our workmanship with a 20-year end to end warranty, we can recognize that things happen, and human errors occur. In general, the fewer connections the better.

Microinverter

A second type of MLPE are microinverters. Microinverters do the same job as string inverters, but rather than servicing groups of solar panels, they convert DC to AC for one single panel. This means that for each solar panel in an array, there is an equal number of microinverters. Cost is the primary disadvantage to this technology, but microinverters come with tremendous advantages.

One of the largest benefits to a microinverter system, is that the performance of each panel is independent of the others. Suppose a panel in an array that receives full sun in the afternoon, receives some shading early in the morning from a vent on the roof. With a traditional string inverter system, this would cause the whole array to suffer. However, if we were to use microinverters, we could allow that one instance of shading early in the morning and not have to worry about whether the rest of the system is subject to reduced production. This same affect can be observed when you have a system with an east facing array and a west facing array where one will always produce more than the other depending on the time of day.

Having an inverter underneath each panel means that you have the option to use monitoring software for your system as you can see the performance of each individual panel. In addition to this being great for people who enjoy the fine details of their energy production, it is also a great tool for installers troubleshooting an issue. In general, when something fails in a solar system, it will be the inverter. If one microinverter goes down, only one panel goes down, rather than the whole system. It should also be noted that the top manufacturers in the industry offer 25-year warranties on their microinverters so it should not be expected to have any issues with these.

Inverter Box on side of house

Another positive note about microinverters is the aesthetics they can offer. There is no bulky box that needs to be mounted on the side of the house. Micros can instead be hidden underneath the array. Usually only homeowners’ associations are concerned with this type of detail, but for those individuals that prefer a more sleek, premium look, then microinverters are the technology they should seek.

Check out our blog post here if you are interested in learning more about solar system aesthetics.

Our view is that microinverters are a superior technology with a better warranty, but there are advantages to string inverters when used for ground mounted systems. We generally like to stay away from power optimizers since the added cost does not offer much value when compared to microinverter systems. If you are interested in getting a free estimate for a solar system for your home, please visit our quote page!

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