[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?
http://www.solarquotes.com.au/inverters/micro/
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 arent new; they first appeared in the late 1990s 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.
Switchgear
High voltage DC requires relatively expensive protective switches and
fuses. By using AC, switchgear is more commonly available and thus cheaper.
Shading
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.
Redundancy
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.
Modularity
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.
Orientation
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
including:
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.
Efficiency
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.
Price
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
technology.
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.
http://www.enecsys.co.uk/
http://enphase.com/
http://solarbridgetech.com/
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
yet.
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
Inverters.
http://www.tindosolar.com.au/
http://acsolarwarehouse.com/
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
installer.
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.
--
Cheers,
Stephen
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