The case of micro-inverters in rooftop solar – pv magazine India
pv review: The slow adoption of rooftop solar power in India is itself a challenge for solution providers. Why has rooftop solar power not taken off in a big way in India?
Sunil Thamaran: The number one problem that we have seen in India is the change in policy from time to time and the lack of awareness of the changes. For example, earlier we had a net metering policy. We now have a gross count policy. Changes have been proposed back and forth at various times in different states. And when this happens, training and awareness is lacking at the level of the implementer, like Discoms or even the installer.
To give you an example, in Bengaluru we faced many challenges when we went to the rural areas. We had to involve Discom, give them advice or share experiences to make sure they understood what they were doing and approved of the systems.
The second problem is the lack of financing because solar is a very capital intensive market. The unavailability of financing at a lower interest rate has been a problem for clients.
Finally, a majority of the roofing market is actually supplied by low-cost players who cannot ensure long-term reliability. This is either a five-year warranty or a maximum of ten years for inverters. This poses a problem because customers have to factor in the costs of replacing a product.
pv magazine: Inverters play a crucial role in the performance of a solar installation. What inverter solutions are available for rooftop solar power?
There are generally two types of inverters used for rooftop installations. String inverters capture the majority of the market. In string inverters, many panels are connected in a string on the roof, and that string is then connected to an inverter box, a large box placed somewhere in the building.
The other solution we offer is module-level power electronics (MPLE), which is what microinverters or power optimizers stand for. Here an inverter is connected just behind each panel, and then at that roof level, the outputs of all these inverters are combined into a single cable that runs down to the meter box. Thus, microinverters can be used safely as DC to AC conversion occurs at the panel level and no high voltage power is flowing through your system.
pv magazine: How do microinverters compare to string inverters in terms of performance? How does roof size and shading affect inverter selection?
The choice of the inverter depends on the overall production and the total cost of ownership, or energy cost.
When it comes to settings, the first thing people should look at is the production efficiency of the system. As a rule, string inverters are efficient from 95%. There are some that are 96% or 97% effective. So they all play at this level.
On the other hand, microinverters offer an efficiency of 98% and more. To explain it to you, it’s a “one inverter, one panel” solution. This means that for a building with ten panels, you will have ten inverters. So if one inverter fails for some reason, the other nine will continue to operate and you will still have power in the building. In other words, it’s not the complete loss of power with microinverters.
On the other hand, with string inverters, there will be one inverter for all ten panels. So if this inverter fails, the whole system is failed until you replace or repair the inverter.
In addition, since each panel is connected to an inverter, the conversion is optimized at the panel level. This maximizes the overall conversion efficiency. You could say that microinverters will be more efficient even if there was a problem with some panels.
This is where the shadow element comes into play.
In a system using string inverters, even if a panel has problems such as shade, dust, or bird droppings, it will limit the performance of the entire string. On the other hand, with the microinverter, only the panels under the shading will produce less, and the rest will continue to produce at a high level.
Microinverters are not only profitable in the first or second year because they are priced higher, but their overall benefits in 20 years will be much greater than with string inverters.
The installation is pretty straightforward. The microinverter is a very small device, weighing just about 1 kg. It’s a plug-and-play type of system where the cable plugs in like a USB drive, and there aren’t many screws.
pv magazine: You mentioned panel failure and the resulting impact on the performance of microinverters and string inverters. How is the failure of the microinverters themselves handled?
In India, you can buy up to 25 years warranty for Enphase microinverters.
We have a continuous monitoring system which is available on the mobile app and also on the web. Each inverter communicates with the cloud via the Internet of Things (IoT). So every customer, including the service provider, can connect and access it. We provide login access to the customer as well as the service provider. We can monitor each system in the field from our office.
pv review: There are not many players in microinverters. What is the main reason?
Enphase is today the world leader in microinverter solutions. In the American market, we hold nearly 50% of the market share. But, there were small players from China. I would say the number one reason is the ability to provide a 25 year long term warranty since microinverters are an expensive solution. It takes a lot of engineering, a lot of quality-conscious design to provide that kind of a solution.
pv review: What are the main design challenges for microinverter companies and what are they working on?
One is obviously the price, as each customer will compare the [microinverter] price with string inverters. This is a huge challenge for us because microinverters are two to three times more expensive.
The second challenge is to be able to catch up with the technological roadmap of the modules. Solar panels continue to evolve, from 400W to 500W, and now even higher powers. We need to improve the performance or the mechanism of our microinverters accordingly so that they can be paired with higher wattage panels. This means that in general the design has to change, the power output has to change, and so on. But it is only a vector that we are driving.
We are investing heavily in the activation of microinverters for high power panels. We offer an IQ8 inverter, which can be combined with 450-500W panels.
In terms of application areas, the residential roofing sector is the main focus because the microinverter is a small system. But, an adjacent market is the small commercial segment. For commercial sector applications, the cost difference will be huge when using microinverters. We meet this challenge by offering a dual solution to couple two panels with one inverter. This will reduce the price per watt because you can couple, say, two 400W panels or meet the 800W requirement with one fixture.
pv review: What are your projects in India?
We also manufacture microinverters in India. We have three manufacturing plants in the world, one in China, the second in Mexico and the third in Chennai, India. Our plant in India can scale up to a million units per quarter, but we have manufactured around 400,000 units per quarter. It started operating in October of last year. This is an export unit from which the units are shipped to the US market. We are also applying for BIS certification. Once this is satisfied, we can also supply the Indian market.
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