Solar power in recent years has become completely modular and that is great news for potential system owners. In the olden days, it was necessary to buy not only solar modules but batteries as well. This dramatically increased the cost of your basic system. In 1991 SMA Solar Technology (the world’s largest solar equipment company) produced the first solar “grid-tied inverter.” Solar inverters remain key to all solar projects.
The grid-tied inverter is the piece of equipment which makes it possible to install a solar system on your home without the added cost and complexity of batteries. It is “grid-tied” rather than “battery based” which means it seamlessly connects to the electrical grid your home is already using for power. The “inverter” takes the electricity produced by the solar modules on your roof and makes it directly usable in your home.
The “Microinverter” Changes the Game
Fast forward to 2008, Enphase Energy releases the first “microinverter” into the solar market and changes the game. The “microinverter” is exactly what it sounds like, it is a much smaller inverter. It works essentially the same way as its larger forefathers but has made it so you can have a workingsolar system with just one solar module and one microinverter. Each microinverter attaches directly under each solar module in the array (i.e. if you have 5 solar modules you will have 5 microinverters). Before the microinverter you would have had to buy many solar modules and one larger “central” inverter.
The microinverter has made solar power systems completely modular, not just in their installation and operation but also in their monitoring. As a system owner you want to make sure that your system is operating the way you expect and producing as much electricity from the sun as possible. Enphase has developed a very user-friendly monitoring system that allows you to view the production of every module on your roof on an individual basis. As a system owner you are provided with access to your system’s real-time production information online as well as through an app on your smartphone. This allows you to show friends and colleagues your solar production whether you are at home or a world away.
Enphase Enlighten Monitoring Portal and App
Central Inverters vs. Microinverters
As a result of these two different solar inverter options, the question becomes “Which inverter is right for my system?” It all depends on what type of system you want. Professional solar installers are able to help you make the right choice given your system location and size, as well as the goals you want to achieve with your solar installation. Central inverters and microinverters both have their strengths and there is no absolute winner in the contest.
The easiest factor that can help you decide is the system size. If you want to install a very large solar system, it will be more cost effective for you to buy a central inverter. Buying a central inverter for a system with many modules is analogous to buying your inverter power “in bulk.” Similarly, if you only want a few modules on your roof to try solar power before committing to a larger system you would want to buy microinverters. The nice thing about the microinverter is it allows you to easily add onto your existing solar system in the future. You could install 10 solar modules with 10 microinverters this year and next year add 5 more modules and microinverters to have a 15 module solar system. Adding solar modules onto a system with a central inverter is not impossible, but it is more difficult and is not often done in practice.
Benefits of a Central (String) Inverter
The central inverter (also sometimes referred to as a “string” inverter) is tried and true. The central inverter has been the workhorse of the solar industry for many years and is still going strong. In the areas of utility scale (1MW+) and commercial solar (50kW-1MW) central inverters hold 99.9% of the market since they are so much more cost effective on the large scale. In the residential space microinverters have captured a large part of the market, but there is an inflection point where it becomes cheaper to use a central inverter. Here is a rough cost analysis showing the inflection point where a central inverter becomes more cost effective.
The chart shows after 24 modules it is more cost effective to buy a central inverter. A 24 modulesolar system is equivalent to about 6 kilowatts of power and is on the larger side of residential systems. Although these are rough numbers it is a useful rule of thumb when considering the basic system size you want. If you are looking at a larger system on your home a central inverter is probably the right choice for you.
Central (String) Inverter Pros:
- More cost effective for systems over 6kW
- Proven technology with robust performance
- One convenient inverter location
Benefits of Microinverters
Microinverters have many benefits on smaller (less than 6kW) size systems in addition to being more cost effective. Microinverters provide for a simpler installation as well as mitigating design concerns such as orientation and shading. With microinverters you are able to install modules at multiple orientations without experiencing dramatic losses in efficiency.
If shading is a concern at your site, microinverters are great due to their ability to optimize each module individually. Largely the considerations of system design are not the responsibility of the homeowner and a professional solar installer will help you design the right system for you at a price you can afford.
- More cost effective under 6kW
- Mitigates shading and orientation losses
- Modular and Expandable in the future
- Individual module optimization and monitoring
Bill Ehrlich is a Mosaic blog contributor who works in the electrical industry. After graduating from Notre Dame with a degree in Finance he worked on a cattle ranch in Wyoming and then taught English in China. Returning home to the States he worked at Inovateus Solar, a solar integrator in South Bend, Indiana. Originally from Minnesota, he is currently getting his hands dirty doing electrical construction in the city of Chicago. Outside of work Bill enjoys investing, solar power, and most of all, investing in solar power!
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