PV String Sizing and MicroFIT 2.0

MicroFIT 2.0 defines the 'nameplate capacity' as the larger of inverter size or array size. in other words, both your inverter and your PV array must be less than or equal to 10kW (=10,000W). Unfortunately, and strangely, this decision seems to have been made without the benefit of PV design experience.

Most contractors and system designers will be trying to hit exactly 10kW of array size (for systems unconstrained by roof area). This looks good on paper, but may result in poor system performance over the system's lifetime.

Common PV module sizing includes 250W modules, so 40 x 250W = 10kW quite nicely. Arrays with 40 modules (regardless of module size) will be designed in 4 strings of 10 modules. However, for most grid-tied inverters strings of 10 will result in poor hot weather performance, a problem that will get worse as the modules age. Such a system could spend a significant portion of each hot day not producing at all, as the array cannot sufficiently drive the inverter. (Just think of this past July: hot and sunny.)

Strings of 11, 12, or 13 are a much better design and that's what we use in our designs. So a system based on 44 x 225W modules = 9.9kW is a more robust design than 40 x 250W = 10kW. Similarly, 39 x 250W = 9.75kW is more robust than 40 x 250W, even though it's 250W smaller. In fact, strings of 13 represent the best design, maximizing system efficiency and prolonging inverter life.

String sizing issues can be eliminated all together by using micro-inverters. Whether or not micro-inverters are worth their premium price will depend on your site details.

Overall preferred system design will be based on your site. Call us to set up a site assessment and we can recommend a system design for you!

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It has been a great pleasure working with you, the project has gone very smoothly. We are very pleased and we look forward to continuing our relationship with you over the next 20 years as we generate power.
I was a great relief to find Generation Solar, after having numerous unpleasant dealings with my initial installer. Their responsiveness and professionalism were top notch. They represented me in dealings with my equipment manufacturer over a warranty issue and produced results that I don't feel I could have on my own. Most importantly, they did what they said they would and kept me informed every step of the way. I would not hesitate recommending Generation Solar and look forward to a continued relationship with them.
I just wanted to let you know how pleased we are with the system you and your team installed. Things have been running great. Checking the inverter for the daily output has been part of my routine, and I enjoy counting the kW. Thanks so much for all the work, professionalism and guidance on this project. You and your team are great.
Wanted you to know that Jackson and Geordie were Amazing and very helpful, hard working in the heat. They did an Awesome job and were very tidy, a hot weather bonus is probably in order though they did say they love working for you.

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