[LINK] A Clean Energy Revolution -- Now

stephen at melbpc.org.au stephen at melbpc.org.au
Sun Sep 22 04:29:28 AEST 2013

Here's a somewhat simplistic but interesting discussion of solar panel 
inverters. Any linker have more information regarding this technology?  


Micro Inverters and AC Solar Panels. The Future of Solar Power?

In the beginning, there were solar panels which produced electricity as 
Direct Current.

To make that electricity useful for powering appliances or connecting to 
the grid, it was converted to Alternating Current (AC) using a large box of 
electronics called an inverter.

In Grid Connected systems, the solar panels were connected together in 
series (called strings) to create higher voltage DC which is good for 
reducing losses. However, this also created some problems.

Hence the Micro Inverter was invented.

Micro Inverter

A Micro Inverter is simply a miniaturised inverter, sized to suit 
individual solar panels rather than a string of solar panels.

They aren’t new; they first appeared in the late 1990’s but arguably it was 
a bit too early and the technology suffered a bit from reliability issues 
and high price. In the last few years however, they have re-surfaced and 
are starting to really take off.

Around the world there are at least twenty one different brands of Micro 
Inverters. In Australia, about 8 brands of Micro Inverters are approved for 
use with more on the way.

AC Solar Panels

An AC Solar panel is simply a solar panel that has been fitted with a Micro 
Inverter so that it produces Alternating Current instead of Direct Current.

What's good about AC Panels and micro inverters?

There are a number of complexities caused by the traditional way of 
connecting solar panels together (in series) which Micro Inverters can help 
overcome including:

High Voltage DC

High Voltage DC can create a risk of very high temperature arcing and 
potentially fire. Because Micro Inverters convert to AC the potential for 
this to occur is greatly minimised.


High voltage DC requires relatively expensive protective switches and 
fuses. By using AC, switchgear is more commonly available and thus cheaper.

When solar panels are connected together in a series string, shading just 
one of them can dramatically affect the entire array; (kind of like 
standing on a hose).

As an example: Imagine an array of 3 solar panels connected to a 
conventional, central inverter. One of the panels has been pooed on by a 
bird, which could easily reduce its output by 50%. However, it will also 
reduce every other panels' output by the same amount.

But by having a Micro Inverter on each solar panel, the outputs are 
completely independent of each other. So that bird poo is going to only 
affect the soiled panel:

According to the US National Renewable Energy Laboratory, this effect can 
yield as much as 12% more energy.

Solar panel mismatch

When solar panels are made they each have slightly different electrical 
characteristics due to imperfect manufacturing tolerances. When you connect 
them together in series string, this effect is called "mismatch". Micro 
Inverters can adapt to the individual characteristics of each panel, 
avoiding mismatch.

Maximum Power Point Tracking

Like the effect of mismatch, different electrical characteristics also 
create different Maximum Power Points for each solar panel. The maximum 
Power Point is the perfect point for extracting maximum power from a solar 
panel and Micro Inverters attached to individual solar panels can therefore 
target this point better.

Monitoring and fault finding

Almost all inverters have some level of monitoring and fault finding 
however; it can only see the combined output from every solar panel in the 
series string. A Micro Inverter however, can monitor each solar panel 
individually, allowing you to easily identify exactly what's happening more 
quickly and easily. 

Factory fitted

Assembling and connecting components in a factory environment is inevitably 
a more controlled environment and can potentially save time and money. A 
number of solar panel manufacturers now factory assemble Micro Inverters to 
produce AC Panels.


If your series string inverter develops a fault, your entire solar array 
stops producing power until it is fixed. If a Micro Inverter develops a 
fault, the remaining Micro Inverters can continue to operate, so you should 
have a more reliable system.


Series string inverters can only accept specific number of solar panels per 
inverter so it's not always possible to simply add a few more panels at a 
later date. AC Solar Panels however, can be added much more easily because 
they are independent of each other.


In a series string, all your solar panels need to be connected in the same 
orientation so they are combining to produce the right voltage at the same 
time to fire up the inverter. Because they operate independently, AC Solar 
Panels can be oriented in any direction and will not affect the operation 
of other solar panels.

What's bad about AC panels and micro inverters?

Nothing is perfect however, and Micro Inverters do have some downsides 

On the roof

If your Micro Inverter develops a fault, someone has to get up on the roof 
and disconnect it from under your solar panel. This can add time and cost, 
compared to simply taking a series string inverter off the wall.

Weather effects

Because Micro Inverters are on the roof (albeit under the solar panels) 
they do suffer from more extremes of weather including heat, cold and 
moisture. This means they have to be really carefully built and in many 
cases, use electronic components that are more robust than would otherwise 
be required. As a general rule, extremes of temperature reduce the 
efficiency of electronic devices and shorten their life.


Although they are getting close, Micro Inverters have not yet reached the 
same efficiency levels of series string inverters, so they can't convert as 
much solar energy into electrical energy.


Again, they are getting close, but Micro Inverters remain about forty to 
fifty percent more expensive than high quality series string inverters and 
almost three times the price of low cost series string inverters.

When is an AC Solar Panel or Micro Inverter a better choice?

As you can see, there are a number of advantages to AC Solar Panels using 
Micro Inverters. The most common reason people choose them is because they 
have shading or they need to use different orientations on their roof to 
generate the power they require.

An increasing number of people are also choosing them because they are 
prepared to pay a premium to avoid mismatch, increase their redundancy and 
allow for future expansion. The other benefits described tend to strengthen 
the case and some people just love the idea of having the latest/newest 

Clearly, if you have shading or sub optimal orientation Micro Inverters are 
an ideal choice and could end up being cheaper in the long run because they 
will produce more energy.

Beyond this, Micro Inverters become a personal choice about how much you 
are prepared to pay balanced against the extra features and advantages.

How popular are they?

A few years ago there were virtually no Micro Inverters or AC Panels 
installed around the world. However, in California it is estimated that 
around 40% of all inverters installed in 2012 were Micro Inverters, so they 
taking market share rapidly, particularly in the US. They are growing in 
other countries too, but are best suited to Residential markets where the 
price difference is less noticeable.

The Australian solar market is around 98% residential, so it is logical 
that we will see pretty strong growth here too. In fact, we know that in 
the last 6 months from a base of effectively zero, more than 10,000 Micro 
Inverters have been sold and we have only just started. Although this 
represents a small fraction of the market, within a couple of years it's 
quite reasonable to predict that around 20% of the market or more, could be 
utilising Micro Inverters.

Who sells AC Solar Panels and Micro Inverters?

We know of twenty one Micro Inverter manufacturers around the world 
including: Enecsys, Apparent, Sparq, Kaco, Power One, Tigo, Array 
Converter, Solar Bridge, , GreenRay Solar, Azuray Technologies, Petra 
Solar, Direct Grid, Accurate Solar, OKE/SMA, Exeltech, National 
Semiconductor, Larankelo, Enphase, APS, SWEA & Plug & Power.

Enecsys and Enphase are undoubtedly the market leaders with APS not far 
behind however SMA and Power One (both huge Inverter manufacturers) are 
sure to shake things up a bit once they get going. A new kid on the 
(Australian) block is Solarbridge who, instead of selling the inverters 
individually, team up with solar panel manufacturers to sell the AC panel 
as a complete, factory assembled unit.


There is a growing list of big name PV companies around the world who have 
partnered with Micro Inverter companies to produce and sell AC Solar panels 
including Westinghouse Solar, BenQ, Canadian Solar, Suntech, SunPower, 
NESL, Hanwha SolarOne, Sharp and probably more that we haven't heard of 

In Australia, we have (at the time of writing) one company producing AC 
Solar Panels. Adelaide's Tindo Solar manufacturer solar panels and use the 
SolarBridge Micro Inverter providing our only true, locally made AC Solar 
Module. AC Solar Warehouse based in QLD also sell a good range of Micro 


Beyond these two companies, a growing number of Distributors and Dealers 
can access Micro Inverters and fit them to pretty much any solar panel you 
like with APS the biggest selling Micro Inverter to date.

The last word

A few readers have asked if AC inverters represent a "Do-It-Yourself" 
option and the short answer is no, although it is tantalisingly close. 
Because you are dealing with 240V AC power, a licenced electrician is still 
required to connect them and for rebates or FIT's you'll need an accredited 

Just how much of the market Micro Inverter equipped AC Solar Panels take 
remains to be seen but one thing is for sure; they do solve some hairy 
problems and have a big future.

If they can get the cost down just a little bit more, then they may well 
become the dominant solar inverter technology.



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