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Photovoltaic micro-inverters: Advantages and challenges for rooftop PV systems

Dr. Praveen Jain is the CEO of Sparq Systems Inc., which is producing a high-durability, lightweight micro-inverter  for the North American market, to be commercially available in the third quarter of 2010.

Dr. Jain is also Canada Research Chair in Power Electronics and Director of the Queen's Centre for Energy and Power Electronics Research (ePOWER), and an internationally-acclaimed researcher with over 400 publications and 40 patents.

The following interview took place at Intersolar North America on July 15, 2010.

Dr. Praveen Jain is the CEO of Sparq Systems Inc.,; Sparq_micro-inverter
Dr. Praveen Jain is the CEO of Sparq Systems Inc.,; Sparq_micro-inverter

Solar Server: Can you tell me a little bit about the product you are planning on launching? I understand it is a form of micro-inverter?

DR. JAIN: Yes, we are about to launch a micro-inverter which is highly reliable. This is the first of its kind in the market that will for the first time meet the same reliability as PV modules. It is a lightweight, high-density design, it is extremely suitable for the integrated AC model panel. Right now, if you look at any PV module, you have DC power coming out. We are about to provide a solution where you will have AC power coming out. We are going to replace the junction boxes with our micro-inverter. And in doing that, we are not using any mechanical support or any mechanical clamps, it will be directly mounted on the panel.

SOLAR SERVER: Can you talk a little more about the advantages of micro-inverters over standard inverters?

20-30% extra energy

DR. JAIN: The biggest advantages of micro-inverters are in the small installations below 10KW. In these applications what happens because most of the applications are on rooftops the very different orientations of PV panels, there is partial shading, there is snow, there is dust. So what happens in the traditional string inverter technology, all of those modules are connected in series, and the maximum power that can be delivered in the system is decided by the weakest module. So let's say the module is trying to produce 250W, but it is under partial shading, it can produce only 50W, and all the panels will be governed by the lowest amount of power. So using the micro-inverter, one can produce almost 20-30% extra energy from the installed system, so that is one of the biggest advantages of micro-inverters.

There are some secondary benefits of micro-inverters, one of them is that in the traditional string inverters you have high-voltage DC distribution. That is a safe voltage, but there are concerns from the home user, they don't want to see high-voltage going on their roofs. And they would prefer traditional AC voltage, they are more comfortable that this is going on their roofs. Then other advantages are in terms of the installation costs, with the integrated AC model panel, you can considerably reduce the installation cost. So these are some of the advantages of micro-inverter technologies.

But in order to achieve these advantages, one of the driving factors for micro-inverters is that micro-inverters should be highly reliable, should match the lifetime of the modules. Otherwise if this micro-inverter fails, you have to replace the whole system, so these inverters must be highly reliable. So this is one of the key requirements for these micro-inverters. The other one is that they must be lightweight, so that they can easily attach to the modules. In our solutions, we offer the lightest weight micro-inverter with the highest reliability in the industry.

Competition with centralized inverters

SOLAR SERVER: That's quite remarkable. So is your product for the 10KW and under market, primarily?

DR. JAIN: As I mentioned to you earlier, it is easy to justify micro-inverters for the 10KW and under market, but when you look at the large farms, solar farms, there are studies which have been done, and those studies have shown that if you use micro-inverters, you can gain maybe 5% additional energy harvesting. So now it is the trade-off between how much energy harvesting you are getting and what is the cost of these micro-inverters. So with time when the cost of these micro-inverters have come down to a level where they can compete with the centralized inverters or the string inverters, then micro-inverters will be equally useful as any other centralized inverter in large installations.

SOLAR SERVER: Do you believe this will happen, and if so in what kind of timeframe?

DR. JAIN: I think in my opinion this will happen in max three to five years time frame.

SOLAR SERVER: You are looking at a big shakeup then.

DR. JAIN: I think it is going to happen. We are getting a lot of push right now from the module manufacturers, that they want to produce integrated AC panels. So if they produce integrated AC panels, there is no place for the large inverters.

SOLAR SERVER: Are you currently producing other products at Sparq?

DR. JAIN: Well, we are going to have the general ability in Q4 of 2010.

SOLAR SERVER: How does it feel to be entering the micro-inverter  field, with some of the other companies that have come that have captured a fair market share, do you see a lot of competition with, say, the industry leaders? Or do you see this as more of a competition with the central inverters?

DR. JAIN: Let me first comment first on the other micro-inverters. I am very excited to enter into this market, because myself, from an academic background, I have been in power electronics for the last 30 years, in a number of applications, and I know that one of the drawbacks of micro-inverters is the reliability. If you don't have high reliability, then we are not doing a good job from that point of view. So we are very confident that our products offer the highest reliability in the market. So sure, we are just a startup company and coming into the market right now, but we are very confident in the future we are going to be very tough competition to all existing micro-inverter  companies.

Eliminating electrolytic capacitors

SOLAR SERVER: Now, in terms of reliability, can you talk about some of your innovations that are leading towards a more reliable micro-inverter

DR. JAIN: Yes, in our micro-inverter, we have eliminated the use of electrolytic capacitors. Electrolytic capacitors are the most unreliable component in any power supply design or any power converter design. So we have eliminated them, and while achieving this elimination, we have reduced the number of power conversion stages. So we have reduced the number of power conversion stages, and we have eliminated the unreliable component which is the electrolytic capacitors. So our developed material is lower than others, and we don't have any unreliable components, and in doing that, we have used the most advanced control technology.

25 years warranty

SOLAR SERVER: That's something that people have been talking about here at Intersolar in terms of systems. I've heard people mention again and again that the inverters don't have the lifespan that the panels do. Do you have an expected lifespan for your micro-inverters?

DR. JAIN: We are giving a warranty of 25 years.

SOLAR SERVER: That's very impressive. So other than the electrolytic capacitors, what can account for this increased lifespan?

DR. JAIN: I think the lifespan is due to eliminating electrolytic capacitors, and to reduce the amount the amount of other active elements in the inverter.

SOLAR SERVER: So you've streamlined it, essentially?

DR. JAIN: Yes.

Entering the North American market, followed by the European market

SOLAR SERVER: What markets are you looking at launching in, geographically?

DR. JAIN: Geographically, I think first we are going to go into the North American market, and then we plan to go to the European market six months after our first launch in North America. The other benefit of our micro-inverter  is that it is universal, so it can be used as it is in North America, Europe or Asia. It can configure itself for a 50HZ system, a 60HZ system, 208 volt system, 220 volt system, it can self-configure. So you can use the same product anywhere. So the only difficulty we have to enter the European market is to apply for the additional certifications from European agencies.

SOLAR SERVER: That's a typical delay. And you say the North American market – are you targeting California, Ontario, New Jersey, or all of the above?

DR. JAIN: I think we are targeting everything.

SOLAR SERVER: How are you going to deal with the locally produced requirement for systems in Ontario?

DR. JAIN: Right now, our initial production will be based in Ontario. So we are going to produce these inverters in Ontario, we have established relationships with a contract manufacturing company. They are a 6-sigma quality control company, so our objective is to use the most reliable, high-quality parts.

SOLAR SERVER: Any other comments about the micro-inverter market or about your product?

DR. JAIN: In my opinion, right now the micro-inverter market is almost non-existent. It is a very small market, compared to the growth that we see. We see a very, very explosive growth in max three years, five years. So right now micro-inverters might be generating in the area of hundreds of millions of dollars, but we could be reaching several billion dollars in the next three, four years time.

Micro-inverters versus power harvesting systems

SOLAR SERVER: Another question, I've noted that some of the power harvesting systems made by SolarEdge and some of the other companies also note that they have avoided some of the serial losses through their harvesting systems. How do you feel about micro-inverters versus power harvesting systems?

DR. JAIN: That's a very good question. The other architecture which was evolving say two years ago before micro-inverters became popular in these applications was that you have a maximum power tracker using a DC-DC converter that can be mounted in the junction box. So from there you can do the individual maximum power tracking. And you can have the same system advantages in terms of the higher energy harvesting as the micro-inverter. But one of the drawbacks of such architecture is the cost. What is happening is that you have the cost of the string inverter, or central inverters, and then your additional cost of this maximum power tracker. Another factor is the efficiency. Now you have an extra stage of conversion. So you have lower efficiency, higher cost, and in my opinion, lower reliability. Because you still have one central inverter that can fail. I think that architecture won't be very competitive.

SOLAR SERVER: Any other comments?

DR. JAIN: No, that's all right. It is a very exciting time and we look forward to seeing how our technology comes to the market.

SOLAR SERVER: Thank you very much.