There's 3 types of inverter options available to homeowners today: A central inverter which was the only type of proven inverter readily available to the residential market before 2011. A solar breakthrough was realized around that time when Enphase microinverters came along and offered so many advantages over traditional central inverters. Then a few years ago, a third option started to make some real noise, and I like to call it a 'hybrid' option as it combines the benefits of both central inverters and microinverters. That option is the SolarEdge power optimizer.
So what's the difference between microinverters and power optimizers?
Enphase microinverters (about the size of an iPad) are mounted under each solar panel on the roof and directly converts the solar panel's DC current into AC current. Power Optimizers are similar to microinverters in that they also are mounted under each panel and perform maximum power point tracking, but they do not convert DC electricity into AC on the roof. The SolarEdge power optimizers go a step further, essentially ‘optimizing’ the voltage and current running through the solar panels to harvest the maximum level of power out of each panel and sends that power to a central inverter which does the hard work of converting the optimized DC current into AC electricity.
Both products are similar and offer significant advantages over using a central string inverter:
- 25 year warranty
- Higher efficiency means more power
- Design flexibility enabling the use of multiple roof slopes, tilt angles and azimuths
- Panel-by-panel monitoring
- Both mitigate power loss due to partial shading from trees and obstructions
So which should you choose for your home? Both are great options and I recommend choosing one or the other over using just a central inverter. But I can specifically think of 3 Reasons you should choose Power Optimizers over Microinverters: Reliability. Higher Energy Production. Lower Cost.
One advantage power optimizers have over microinverters is the issue of HEAT. The DC to AC conversion within a microinverter dissipates heat. We all know the hotter anything gets, the less efficient it becomes. Power optimizers have an advantage over microinverters since the heat generated at the conversion process is done at the central inverter which is usually located inside a garage or outside on a wall near your main electrical panel out of the direct sunlight. The inverter part of your solar is the nuts and bolts component, the ‘moving parts’ of your solar system. Having that moving part of your solar system multiplied for every solar panel on your roof I believe makes your solar system less reliable. Power optimizers need only half the amount of 'moving parts' inside a microinverter. Multiple microinverters tasked with DC to AC conversion year after year and more specifically during summer heat waves I think results in a higher risk of failure. Thankfully both the Enphase and SolarEdge product warranties are quite long at 25 years.
A disadvantage with microinverters is their risk of ‘power clipping’. Enphase’s largest sized residential microinverter is its M250 model which refers to its ability to produce a maximum 250w AC output from each solar panel when connected to the microinverter. Unfortunately this limits your choice of brand, type and size of the solar panel you can effectively pair with an Enphase system. Want a 72 cell solar panel? Sorry, not compatible. Choose a solar panel with an output greater than 250w AC, and you run the risk of clipping the top off your solar panel’s production at 250w AC. On the pairing recommendation of Enphase's website it denotes that the M250 can be paired with solar panels with ratings up 310w DC.
(UPDATE 1/5/2017 Enphase now denotes the M250 can be paried with solar panels rated up to 350w. This in my opinion is highly inadvisable)
Unfortunately, this is a bit of an overstatement. I’ve installed a handful of solar systems using Enphase M250’s with solar panels sized between 285w- 300w DC that have been negatively been affected by power clipping.
So far in my career I've installed slightly more Enphase systems than SolarEdge, and both are exceptional upgrades to the stand alone central inverter. I can count on two hands how many SolarEdge systems I’ve had issues with that involved some form of maintenance or replacement. The majority of those involved replacing the inverter only, and had nothing to do with the power optimizers. That’s why I love the extended 25 year warranty SolarEdge provides for its central inverter to mirror its 25 year power optimizer warranty. On the flip side of that coin I’ve had 3 times the amount of service calls involving Enphase, all of which required troubleshooting the Enphase monitoring system or replacing faulty microinverters. And let me tell you, it’s a lot easier to replace a defective wall mounted central inverter at ground level than it is to replace a microinverter on the roof. Why does it seem that every time a microinverter goes out it happens to be smack dab in the middle of the solar array? It’s never a microinverter on the perimeter, so we have to temporarily lift and set aside 4-6 panels just so we can reach the one panel in the middle with the faulty microinverter. Frustrating!
2. HIGHER ENERGY PRODUCTION
Currently, the peak efficiency of an Enphase microinverter is 96.5%. The peak efficiency of SolarEdge power optimizers is 99.5%. Remember though, the SolarEdge system is a hybrid that adds the central inverter component. That central inverter operates at 97.6% efficiency. So with a little math we find that a 99.5% peak power optimizer efficiency multiplied by 97.6% central inverter efficiency equals a peak efficiency of 97.1% with SolarEdge compared to 96.5% with Enphase. That may not seem like a big difference at first glance, but it adds up day by day, year over year. Truth be told, there are those that state Enphase may produce a higher energy yield over SolarEdge, but they’ll never back it up with an accurate apples to apples comparison. Here's a side by side case study that proves just how much SolarEdge Power Optimizers will outproduce Enphase Microinverters.
When a solar panel is shaded from a tree, chimney or a cloud in the sky during the course of a day, its voltage drops. At night, the voltage drops to zero obviously until the sun comes up the next day. To capture power produced by a solar panel, your system is limited by the minimum voltage required by the inverter. The lower the minimum voltage, the greater the amount of energy that can be harvested. A central inverter usually requires a minimum system voltage over of 125v. An Enphase microinverter requires a minimum voltage of 22v. The SolarEdge power optimizers start tracking at only 5v. This means they’ll produce more power in shaded conditions and kick on earlier in the morning thus producing more power as the sun comes up.
3. LOWER COST
I know it’s hard to believe. “So what you’re telling me Mike is that power optimizers are more reliable and produce more power than microinverters but cost less?” In a word: YES. A microinverter system is comprised of sophisticated monitoring parts, components and AC trunk cabling not required by SolarEdge. However there is no central inverter to install like with the SolarEdge system, true. On the surface, adding a central inverter to the system sounds like it should cost so much more but it doesn’t. A microinverter is about 2 ½ to 3 times the cost of a power optimizer, and remember it has twice the amount of ‘moving parts’. It’s pretty much like taking a central inverter and dividing it up into 24 smaller inverters over an entire solar system. That’s not cheap. Although the SolarEdge solution requires adding the cost of a central inverter, when you add up all of the microinverter equipment, cabling, monitoring, warranties and the labor to install the Enphase system, the upfront cost to a homeowner is still about 10% more than SolarEdge.
So there you have it: Better reliability, more energy produced and a lower cost. When it came down to deciding which upgrade I wanted for my home’s solar system, the choice was easy. I have SolarEdge and you should too.