Solar string inverters, micro-inverters and power optimizers. Whatâ€™s the best choice? Finn offers his point of view in this video (transcript included).
Transcript begins :-
There are three main components in a solar PV system â€“ the panels, the racking/mounting, and the inverter. This video focuses on the inverter, whose job it is to convert the DC electricity generated by the panels into AC electricity that is used by your home.
Now, youâ€™ve got three choices when it comes to inverters.
If youâ€™ve got a short attention span, hereâ€™s my hot take. Microinverters and optimizer based systems are more expensive than simple string inverters, but they have a variety of benefits that make them worth considering; especially if you have a shaded roof.
Now, letâ€™s go into details.
String inverters are roughly the size of a briefcase and they are mounted on a wall. All of the panels connect into them. For residential sized systems, youâ€™ll only need one string inverter per solar system. They operate at high DC voltages, but theyâ€™re perfectly safe when installed by a competent licensed solar electrician.
Microinverters on the other hand are the size of small paperback books and theyâ€™re installed on the back of each individual panel. So, for say a 6.6 kilowatt system made up of 20 panels, youâ€™ll have 20 micro-inverters along with them.
Microinverters convert DC to AC at the source, meaning thereâ€™s no high voltage DC running through your roof at any point in time. Itâ€™s all much safer AC electricity instead, and this is why I use microinverters for my own home. Parts of my home are made out of straw bales â€“ seriously â€“ and I didnâ€™t like the idea of high voltage DC running through those straw bales.
In Australia in 2020 as far as Iâ€™m concerned, the only game in town when it comes to microinverters is Enphase. (Disclosure: Finn holds Enphase shares).
One core advantage of microinverters over string inverters is that it makes every panel independent of each other. So when one panel is shaded, it only affects that panel. In a string system, when one panel is shaded, the whole string of panels can go down â€“ kind of like when you stand on a hose.
Because micro-inverters have this panel level optimization, youâ€™ll also find that you can get as much as 12% more energy out of a microinverter system over a year compared to a string system. This also means that you can have panels facing every possible direction; whereas with string inverters, you can only choose two, sometimes three directions per inverter.
Now letâ€™s talk about optimizer-based systems, which as I said, are sort of a hybrid between string and microinverters.
In a system that uses optimizers, you have both the big string inverter on the wall as well as individual optimizers on each panel. So, you get essentially most of the same benefits as a microinverter based system, but with a slightly different technology.
Now, for many years SolarEdge was the only real optimizer based system on the market. But, there have been two big entrants to the market that have been challenging SolarEdgeâ€™s dominance. They are Tigo optimisers and Maxim integrated panels.
Tigo optimisers work with any inverter; whereas with SolarEdge you have to use a SolarEdge string inverter with the SolarEdge optimizers. And, with Tigo, you donâ€™t need to optimize the entire system like you do with SolarEdge. So if only two of your panels are shaded by say an aerial, then you only need to put a Tigo optimiser on those two panels.
That brings significant cost savings compared to SolarEdge, but bringing even more significant cost savings to the market are Maxim integrated panels. At the time of filming, early 2020, the only brand of Maxim integrated panel that is sold in Australia to the best of my knowledge are the Seraphim MX panels.
Maxim integrated panels have three tiny chips embedded in the solar panel itself; compared to Tigo or SolarEdge optimisers that are bolted onto the back of the panel. And, these Maxim optimisers bring most of the benefits of other optimisers at a fraction of the cost.
Now, do you need this panel level optimization (PLO) at all, or to rephrase, do you need to spend extra money on panel level optimization?
If you have a simple roof with no shading issues, then in my opinion, itâ€™s much harder to justify the extra cost of panel level optimization, but itâ€™s up to you whether itâ€™s worth a few grand. If you have a complicated roof with lots of different faces with or without shading, then PLO is well worth it.
If you have a simple roof with small shading issues, Tigo optimizers will give you the best results for the lowest cost.
Microinverters and Tigo/SolarEdge, but not Maxim, also offer panel level monitoring. Trust me, this gets boring fast, but a small percentage of owners canâ€™t get enough of it â€“ so it may be worth considering being able to monitor the power of each panel individually.
For a deeper dive intoÂ panel level optimisation â€“ see this post. For everything you need to know about choosing a solar power system and an installer in Australia, check out Finnâ€™s book, The Good Solar Guide, which is free to read in its entirety online.