Micro inverters or optimizers, How do they work?

Solar Questions and Comments
1

I’m trying to wrap my head around the technology, so please tell me if I’ve understood correctly.

Micro-inverters work 1 per panel to make a parallel array of panels so if 1 fails the rest of the system keeps working. In theory, then, only 1 panel could be functioning and you would get at least 1 little power generated.

Power optimizers, I’m not so sure how they are working. One per panel, but its still a series array? Does that mean there is a mimimum amount of power needed to pass through the system in order for it to work? If I read the technical specs more carefully, will that tell me what the minimum is?

Also, being in series, I’m going to assume then that for monitoring purposes, power optimzers work more like non-ugraded string inverters and you can only monitor whole system performance where on a micro-inverter system you can monitor each individual panel? (Ok, yes I assumed… actually, I think this is more like an educated guess).

I never by my Christmas lights made with serial wiring; when does the superior performance finally outweigh the additional cost in solar energy systems?

Using something I learned in a 1979 5th grade science class! Finally! (I think).

2

Hi petiteviolon,

Yes you have roughly described the workings of micro-inverters and Solaredge optimisers.

Micro-inverters are fitted to every panel and are the best options for rooftops with multiple aspects and small/difficult mounting locations. As you mentioned a big advantage is that if one micro stops working it does not effect the other panels. Yes you can have only 1 or 2 panels with micro inverters if you like.

SolarEdge power optimisers are very different and work together to deliver the optimum voltage (380V) to the SolarEdge inverter. Generally this works very well but you need a minimum of 7 or 8 (unshaded) panels to reach this required voltage.

What type of rooftop do you have? Is space and shading a problem?

3

Its partially shaded on the north and west sides in the late afternoon. It would probably affect only 2-3 panels if they needed to go over that far at all.

Is the optomization of space or allowing the system to work in partial shade the only reasons to consider the added cost?

4

If you only have small shading issues as described, you could ask to quote a normal string solar inverter and just add a few Tigo optimisers on the effected panels. This is the cheapest option.

If you can afford the bit extra for Enphase micro-inverters or a SolarEdge system then it is a great choice.

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5

Hi petiteviolon,

As CER says you have the basic idea regarding the difference in how the two types of systems work, however, the gains in power output using Enphase micro-inverters actually make them the best choice for ANY roof configuration and, especially if you have multiple angles and shading issues. All the studies I have read, and our own experience in the real world (comparing string systems and string systems with optimisers, directly with Enphase micro-inverters) on systems we have in operation show micro-inverters produce more power on average than string inverters. You will get a higher peak power performance from string inverters but, over the course of a day, a week, a month, or a year, the micros will produce substantially more power. Just to be clear we install systems on the coast of Yucatan, Mexico and as such none of our systems have shading issues and the micros always outperform string inverters.

Due to the great weather we enjoy, and our installation methods, we average between 2 and 2.25 kilowatts per panel per day using 375watt panels and enphase IQ7+ micro-inverters.

2 years ago we were looking at using string inverters with tigo optimisers because the Enphase M250 micros have a maximum power through put of 250watts. However, now that the IQ 7+ has a throughput of 290 - 295 watts we do not even consider string inverters at all.

One of the many things to consider regarding panels, is their lack of performance to their peak listed wattage. Panels almost never hit their rated output. A 380 watt panel may hit this level for a brief period during the day when all conditions are correct but, for most of the day the panel is not even close to full power output. The sun is not hitting the panel in the right position the panel is in a fixed position, heat reduces panel efficiency, dirt debris and shading all reduce panel efficiency as does the string inverter and the length and gauge of cables used to connect the system. This is why the recommendation for a micro-inverter is to over size the panel compared to micro-inverter output. By oversizing the panel, the micro-inverter is able to get to maximum output for the inverter sooner, and hold that level of output longer. This is the main way that micro-inverters outperform string inverters.

One other factor to consider - aging of the system. As your panels age, their performance declines. This will be noticeable with a string inverter system as this type of system depends on peak efficiency to boost overall performance. As this peak power declines so does the overall production. In 10 years your system could be producing as little as 90% of the power when new.

On the other hand a micro-inverter system does not depend on peak power to get maximum results, therefore, you should see about the same overall production from a micro-inverter system in ten years, as you do when it is new.

Hope this has helped in your decision.

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