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a) What kind of a load was used, will these inverters have such a high efficiency with inductive (refrigerators, washing machines) or diode-capacitive one (TV sets, computers, monitors etc) load or they just mean very rare nowadays pure resistive load?
b) Does this efficiency include efficiency of its MPPT or it is just an inverter efficiency?
c) In some cases such a high efficiency is achievable by reducing waveform quality cause the output capacitor takes some energy to recharge 120 times per second and an output coil also has its resistance, what about waveforms quality in the whole range of loads? Such a plain curve in case of Enphase M215-60-2LL (95-96% efficiency in a load range 10-100%) makes me to suspect they have a reduced output filter, but Powercom SLK-1500 looks more (85-96% efficiency with load range 10-100%) realistic - all right, a good output filter reduces efficiency in case of small loads.
d) by the way - who made all these measurements? The problem is that most of contemporary digital voltmeters and ampermeters give wrong results with non-sine voltage and current measurements, so the better filter - the worst efficiency will be shown. In some cases (Tom Bearden's MEG) they ever show "over-unity!"
e) Why the Enphase M215-60-2LL results are actual just for 25-40 Centigrades? What if somebody installs them at the roof, will it have these 25-40 Centigrades?
b) Does this efficiency include efficiency of its MPPT or it is just an inverter efficiency?
c) In some cases such a high efficiency is achievable by reducing waveform quality cause the output capacitor takes some energy to recharge 120 times per second and an output coil also has its resistance, what about waveforms quality in the whole range of loads? Such a plain curve in case of Enphase M215-60-2LL (95-96% efficiency in a load range 10-100%) makes me to suspect they have a reduced output filter, but Powercom SLK-1500 looks more (85-96% efficiency with load range 10-100%) realistic - all right, a good output filter reduces efficiency in case of small loads.
d) by the way - who made all these measurements? The problem is that most of contemporary digital voltmeters and ampermeters give wrong results with non-sine voltage and current measurements, so the better filter - the worst efficiency will be shown. In some cases (Tom Bearden's MEG) they ever show "over-unity!"
e) Why the Enphase M215-60-2LL results are actual just for 25-40 Centigrades? What if somebody installs them at the roof, will it have these 25-40 Centigrades?
Tags: inverter, Micro inverter
Micro Inverters are no the be all end all solution but I feel they do make sense in some smaller applications. For example in small residential systems they do make sense. For a one or 2 module gird tied system micro inverters are likely the only solution. As system size increases above a few kW Micro inverters become too costly.
Another important consideration is the type of installation. In the residential space the roof is typically complex, has obstructions or may be exposed to shading from nearby objects. In these types of scenarios distributed MPPT solutions (micro inverters and DC power optimizers) do make sense. The ability to use different string lengths, different mounting orientations, different size modules, and shade tolerance are all valuable tools in rooftop PV system design. I must disagree with the conclusion that distributed solutions never add energy, and that shading rarely occurs. Shading is common in the residential space and there have been several independent studies that show that where shading occurs distributed technologies add substantial added energy. This makes perfect sense because with distributed MPPT solutions the current of the entire string is not reduced by shading one module in the string.
On the other end of the spectrum are ground mounted utility scale systems. In these types of systems many of the design advantages offered by distributed technologies are of less valuable. String length, module orientation, and module type are all simple inputs to the system design equation. In utility scale system shading is normally not an issue since nearby objects that would create shade are very uncommon. Without shading, the potential for increased energy yield typically comes from module mismatch. With a well matched array the lower efficiency of micros compared to larger inverters makes it difficult to produce additional energy. DC optimizers fare better here since their higher efficiency means that the lost energy recovered from mismatch can be larger than the losses incurred by inserting the optimizers into the system. Well matched is a key phrase since many systems installed during the many "PV booms" around the world are far from well matched.
Another important consideration is the type of installation. In the residential space the roof is typically complex, has obstructions or may be exposed to shading from nearby objects. In these types of scenarios distributed MPPT solutions (micro inverters and DC power optimizers) do make sense. The ability to use different string lengths, different mounting orientations, different size modules, and shade tolerance are all valuable tools in rooftop PV system design. I must disagree with the conclusion that distributed solutions never add energy, and that shading rarely occurs. Shading is common in the residential space and there have been several independent studies that show that where shading occurs distributed technologies add substantial added energy. This makes perfect sense because with distributed MPPT solutions the current of the entire string is not reduced by shading one module in the string.
On the other end of the spectrum are ground mounted utility scale systems. In these types of systems many of the design advantages offered by distributed technologies are of less valuable. String length, module orientation, and module type are all simple inputs to the system design equation. In utility scale system shading is normally not an issue since nearby objects that would create shade are very uncommon. Without shading, the potential for increased energy yield typically comes from module mismatch. With a well matched array the lower efficiency of micros compared to larger inverters makes it difficult to produce additional energy. DC optimizers fare better here since their higher efficiency means that the lost energy recovered from mismatch can be larger than the losses incurred by inserting the optimizers into the system. Well matched is a key phrase since many systems installed during the many "PV booms" around the world are far from well matched.
When you hear about the suitability of a particular inverter technology for a particular project, it comes from the perspective of this hard-earned experience. To the best of my knowledge, no peer reviewed paper has demonstrated a performance advantage for micro inverters in commercial applications -- let alone an LCOE advantage (taking into account the considerable difference in price points for string or central inverters compared to micro inverters). Perhaps you can show me otherwise?
I have seen recent work presented by NREL which demonstrates the performance advantage of the micro-inverter architecture for shaded conditions. This analysis appears to be well done and we appreciate the rigorous approach. Again, though, I wonder if the performance advantage (3.7% in the case of light shading) can overcome the price premium for the microinverter system.
So we tend to think that other factors are at work in the inverter market. The perceived ease of use of micro inverters shouldn't be discounted, for example. In the fast-growing North American market there are many new entrants so this factor is important. We are excited to be launching our SB 240 micro inverter system this year and look forward to serving the needs of these new entrants to the market and those companies who have built their businesses around the characteristics of microinverter technology. We have a few tricks up our sleeves and are optimistic about our chances to compete in this segment. After all, our track record is pretty good.
However our firm opinion is that over time even these new entrants might seek ways to improve returns and move towards more established technologies with proven gains in LCOE or ROI.
BTW, this might also explain your comment about "integrators turning to micro inverters for large-scale projects." I wonder if you can point to (for example) any of the Top 15 commercial systems integrators who are using microinverter technology for large-scale projects? If one supposes that these large, sophisticated integrators might be using global best practices, then it might be important to note that these companies rely on central inverters or decentralized string inverter architectures to deliver leading returns to PV investors.
I have seen recent work presented by NREL which demonstrates the performance advantage of the micro-inverter architecture for shaded conditions. This analysis appears to be well done and we appreciate the rigorous approach. Again, though, I wonder if the performance advantage (3.7% in the case of light shading) can overcome the price premium for the microinverter system.
So we tend to think that other factors are at work in the inverter market. The perceived ease of use of micro inverters shouldn't be discounted, for example. In the fast-growing North American market there are many new entrants so this factor is important. We are excited to be launching our SB 240 micro inverter system this year and look forward to serving the needs of these new entrants to the market and those companies who have built their businesses around the characteristics of microinverter technology. We have a few tricks up our sleeves and are optimistic about our chances to compete in this segment. After all, our track record is pretty good.
However our firm opinion is that over time even these new entrants might seek ways to improve returns and move towards more established technologies with proven gains in LCOE or ROI.
BTW, this might also explain your comment about "integrators turning to micro inverters for large-scale projects." I wonder if you can point to (for example) any of the Top 15 commercial systems integrators who are using microinverter technology for large-scale projects? If one supposes that these large, sophisticated integrators might be using global best practices, then it might be important to note that these companies rely on central inverters or decentralized string inverter architectures to deliver leading returns to PV investors.
Claiming that today's micro-inverters---which use mixed-signal ASIC technology to operate at 96% efficiency and deliver utility interactive and wireless networking capabilities---is anything like the microinverters of the 1980's is absurd.
The rate of evolution in microinverters is faster than string inverters in every dimension (from performance and reliability to cost and features), which is the whole point of why end-customers are so interested.
I would hope that the rate of micro evolution is progressing as they have a ways to go to catch up with string inverters. They aren't as reliable, they aren't as efficient and they aren't as cost effective as string inverters for larger installations. It baffles me to hear about 600kW to 2MW micro installs. I find it hard to believe that those LCOE/ROI works out in favor of the customers, and I have yet to be proven wrong. I would be happy to sell people 4000 SB240's, but I feel compelled to warn against it for multiple reasons, mainly, because it doesn't make sense. Micros just aren't there- yet.
Also, I think you need to reread the article as he never tried to compare micros from 30 years ago to the ones today. He only mentioned that they have been around a long time.
The rate of evolution in microinverters is faster than string inverters in every dimension (from performance and reliability to cost and features), which is the whole point of why end-customers are so interested.
I would hope that the rate of micro evolution is progressing as they have a ways to go to catch up with string inverters. They aren't as reliable, they aren't as efficient and they aren't as cost effective as string inverters for larger installations. It baffles me to hear about 600kW to 2MW micro installs. I find it hard to believe that those LCOE/ROI works out in favor of the customers, and I have yet to be proven wrong. I would be happy to sell people 4000 SB240's, but I feel compelled to warn against it for multiple reasons, mainly, because it doesn't make sense. Micros just aren't there- yet.
Also, I think you need to reread the article as he never tried to compare micros from 30 years ago to the ones today. He only mentioned that they have been around a long time.