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Mittwoch, 2. August 2017
MWT Panels: A Dotty Idea For Improving Efficiency
A Dotty Idea For Improving Efficiency
by Ronald Brakels
want a solar cell to produce electricity then it’s important to let the sunshine in. Specifically, into the solar cell. Not letting the
sunshine in is a bad idea. Despite how very important this is, most
solar cell manufacturers place a fine metal wire grid on top of
their cells that blocks around 5% to 6% of sunlight falling on
them, for no other reason than they don’t work without it. It
appears the metal grid is necessary to make electrical contacts
required for current to flow.
to reduce the amount of light blocked by the electrical contacts on
the surface of cells is to use Metal Wrap Through technology, or
MWT for short. Instead of having wires run across the surface, a “laser” is
used to cut holes into cells for electrical contacts and very fine
wires called “fingers” radiate across the cell from them. Compared
to using a grid, this method halves the amount of light blocked.
MWT cells have been made since at
least 2010 and panels since at
least 2013, they have never really caught on. I’ve never seen one
in Australia. But this may be about to change. Phono Solar
introduced its new MWT panel
at the Tokyo solar conference in
March this year①and it should be arriving in Australia in the near
MWT provides an efficiency advantage at a price that appears to be
cost effective, more manufacturers may follow Phono Solar’s
lead and provide MWT panels in the future. While I don’t know if
this technology has legs, I can say it definitely has
Solar Cells Work
When light hits a suitable piece of silicon or other
semi-conductor②it can cause electrons to be knocked out of the atoms
they were hanging around. This is apparently very thrilling for
them, because after it occurs they are called “excited electrons”.
By adding tiny amounts of right elements to the top and bottom
sides of a silicon wafer, a junction can be formed that stops
electrons that are knocked below it from going back to the atoms
they came from because of magic — I mean physics.
a metal conductor is attached to the top and bottom of a solar
cell, electrons can travel along it from the top to the bottom to
where they can then do it all over again if they like. On the way,
as they are traveling through the conductive wire, they can be made
to do work, such as powering an LED light, charging a laptop, or
passing through a solar inverter that will change their direct
current (DC) to the alternating current (AC) the
Solar Cells Work
The metal conductors on top of a solar cell are a
problem because sunlight has a hard time passing through metal. If
you ever come across light that easily passes through metal then
what you are probably dealing with is not sunshine, but some kind
SunPower solves this problem by putting a transparent
conductive layer on top of the cell instead of wires. They do this
with their X and E series panels and LG Solar appears to do the
same with their NeON2 R
panels. Unfortunately, while
it works well, this option is not cheap. Another solution is to use
small solar cells that overlap, so the electrical contacts of one
cell are covered by the cell on top. This method is used by several
manufacturers including SunPower in their Performance Series panels:
An example of overlapping solar cells in a SunPower
doesn’t prevent all shading from electrical contacts, but it does
cut it by around half or more. This is done by eliminating the need
for the thickest wires that run across the top of a cell called
busbars. Instead of having them on the surface, Metal Wrap Through
wraps metal through the solar cell by cutting holes in it with a “laser” and
placing metal electrical contacts in them. From the contacts spread
extremely fine metal wire “fingers”.
Phono Solar MWT cells have 25 holes each. As you can see below,
this makes them look rather dotty:
In case you are wondering, these are
not quantum dot solar cells. Quantum dots are less
than half that size.
Potentially Half A Percentage Point Efficiency
Improvement MWT can increase the amount of light entering a solar
cell by 2.5% or more. For a 16% efficient panel a 2.5% increase in
sunlight entering cells increases its efficiency to 16.4% and would
increase an 18% efficient panel to 18.45%.
MWT Improves Heat Tolerance
Lasering 25 holes through a solar cell and stuffing
them with highly conductive metal is apparently very useful for
transferring heat from the surface of a solar cell to the back.
Phono Solar says:
operating temperature is 3-5 degrees Celsius less than that of the
traditional modules, which allows an additional 3% power
means if a typical solar panel has its efficiency reduced by 0.4%
for each 1 degree increase in temperature about then MWT panels
should only have their efficiency decline by about 0.3%③.
MWT May Save On Materials
MWT panels are not a new idea. People have been working
on them and producing them for years now, but so far not a great
deal has come of them. A major reason why it can take so long for
advances that work in the lab to take off in the market is because it
is often difficult to work out how to mass produce them cost
effectively. An important part of this process is often lowering
the cost of materials used.
Solar claims its MWT panel reduces the need for silver paste④. If this is correct, it’s an important development as
one of the disadvantages of MWT cells used to be they required more
cells also apparently suffer less breakage during panel
manufacture, which is another useful way of lowering manufacturing
both material and manufacturing costs aren’t much higher than those
of standard panels, then MWT will be able to compete with other
methods of improving efficiency. While overlapping cell panels are
capable of slightly higher efficiency because it is possible to
make them so they don’t block any light, they do have the added
expense of requiring extra silicon because of overlapping, so it
will be interesting to see which method will win on price per
Panels Look Pretty — If Installed 3 Feet From Your Face Phono Solar’s MWT panel looks very pretty close up.
Here’s a picture provided by Phono Solar which for some
reason only has 25 “laser” holes per cell and 36 “laser” holes
cells are coming soon.
The fine wire “fingers” surrounding
the contacts in the holes look kind of like little snowflakes or
maybe coral polyps. Phono Solar says the patterns can be customized
to suit people’s preferences. Here are some examples :
Don’t they look wonderful? Wouldn’t
you love to be able to customize solar panels like this if you were
some kind of nutter in the habit of installing solar panels three
feet from your face?
Should You Buy MWT Panels?
While MWT panels haven’t taken off so far, maybe their
time has arrived and we’ll soon see multiple panels with the
technology appearing on the Australian market. So you may be
wondering whether or not you should buy MWT panels.
I say you shouldn’t really care whether or not a panel is MWT.
many people in the market for rooftop solar are experts on the
technology. To expect the average person to decide whether it is
better to put grids on solar cells, laser holes in them, overlap
them, or slap a transparent conductive layer on top is basically
nuts. Most people simply don’t have the background required to
judge the benefits of different types of solar panel technology.
what anyone can do is:
Look at whether or not a panel is tier
or if it’s not tier one, if it is made by a company with an
Look at a panel’s warranty.
If generating the most electricity possible
from a limited amount of space is important, you can look at
If you are diligent, you can even check how
they are affected by heat.
And of course, there is the price per watt.
Taking Phono Solar’s claims at face
value, their MWT panels certainly tick the top 4 bullet points. If
Phono Solar announce competitive pricing, these holey panels may
end up ‘Robin’ market share from the premium end of the market
currently dominated by Sunpower and LG.