Shade is the mortal enemy of solar panels; even a little shade can cause a disproportionate drop in power output. [Alex Beale] reviewed a “revolutionary” shade-tolerant panel by Renology in a video embedded below. The results are fascinating.
While shading large portions of the panels using cardboard to cut off rows of cells, or columns of cells, the shade tolerant panel does very well compared to the standard panel– but when natural, uneven shading is applied to the panel, very little difference is seen between the standard and active panels in [Alex]’s test. We suspect there must be some active components to keep power flowing around shaded cells in the Renology panel, allowing it to perform well in the cardboard tests. When the whole panel is partially shaded, there’s no routing around it, and it performs normally.
It’s hard to see a real-world case that would justify the extra cost, since most shading doesn’t come with perfect straight-line cutoffs. Especially considering the added cost for this “shade tolerant” technology (roughly double normal panels).
You might see a better boost by cooling your solar panels. Of course you can’t forget to optimize the output with MPPT. It’s possible that a better MPPT setup might have let the Renology panel shine in this video, but we’re not certain. Whatever panels you’re using, though, don’t forget to keep them clean.
Could put a lens that take light from basically all different angles, and concentrates it on the solar cells, get more than the about 1kw (erp) per sq ft of sun energy iirc, more effective since you’d think a refractive lens would allow you to shove in more light energy basically collect more photons and pipe them to the panel, since the light source doesn’t need to be exactly of signt, even ambient light, shade, or moonlight could produce Some power that way…
Something like a Fresnel or a dome type lens, but thin enough to actually be usable, but refracts and reflects light down to the bottom of the lens, basically like a magnifying glass but not to see, but to focus light
The problem isn’t total output, but that in a series string of cells, a single shaded one will lower the current.
There are lumiescent solar concentrators but I think those only exist in the lab at the moment.
A normal lens will just make a hot spot somewhere on the panel, unless you actively track it to aim the spot
I think you mean 1kw per sq meter. (A common approximation I see used.)
It may be easier and more economical to use mirrors. Reflective mylar film may be about $0.11 per square foot. A 6-pack of 1 sq ft glass mirrors is $25 at Home Depot.
I’d be worried about heat buildup with any sort of concentration. To reject IR, wavelength-selective glasses and mirrors are available, but they’re not cheap.
You might see a better boost by cooling your solar panels.
https://youtu.be/Sdcbdxop8KA
Using a heat pump. Preferably a really efficient one.
https://youtu.be/KQNc4VnTOis
Surely if these ‘shade tolerant’ panels perform better in partial or even complete shade than a regular ‘normal’ panel does, surely then in full unobscured sunlight they will vastly outperform a ‘normal’ panel.
It’s basic physics, energy in = energy out – some percentage losses
I smell snake oil.
No.
Partial shading causes a conventional cost-optimized panel to to lose far more power output than the fraction of light lost.
In such a panel, the cells are wired in a single series string. When a single cell in that string is shaded, its photocurrent drops to little or nothing, and that limits the current that can flow through the illuminated cells. The illuminated portion of the panel then operates far below its maximum power current and its power output drops far below what you’d expect for the amount of light reaching the panel.
The simple solution is to add bypass diodes. Stick a (usually Schottky) diode in parallel with each cell such that it’s reverse biased in normal operation but will conduct when its parallel cell is shaded. Now a single shaded cell no longer blocks current from flowing through the rest of the string; it just imposes a small voltage drop. But those diodes take up space, add cost, and do nothing for the panel’s performance under standard test conditions, so it’s not normally done.
It’s common to see panels with a few bypass diodes — rather than one per cell, one diode is installed in parallel with some series group of cells. This is more to prevent the panel from damaging itself than to preserve power output, since a long enough string will develop enough voltage to drive the reverse-biased shaded cell into breakdown. Solar cells are big enough that they don’t break down evenly under reverse bias; nonuniformities in reverse current produce positive thermal feedback and gradually destroy the shaded cell. In large panels that operate at high voltages, bypassing sub-strings keeps the reverse voltage safely below breakdown with only a few diodes per panel.
The results in the video are tough to reconcile with either design, but maybe the manufacturer is doing something halfway to reduce the number of diodes they need to build into the panel or cheap “MPPT” controllers aren’t finding the true maximum power point when the I-V curve isn’t the usual ideal shape.
Yeah, I think you’d have to have some smarts to notice subtle changes in the output, and then spend a second or two running the panel through the full curve. And maybe some memory, and a clock, to reduce the future amount of time seeking, by remembering past situations.
If you’re not doing that, you’re depending on a simple curve with a single maximum, where the slope at the current I/V tells you exactly which way to move.
Thank you for the rundown
It’s not snake oil, it’s nothing new, and as @Bunsen says they use bypass diodes to “remove” the shaded cells in the series.
The use case is where something like a pole casts a shadow over the panel. The shaded cells drop out, giving you reduced output but better than nothing.
Wouldnt it make sense to reorient panels 90 degrees so shadow falls along the strings instead of across? Much cheaper than special snowflake panels.
The sun moves across the sky and the shadows rotate, so they tend to fall diagonally across the panel from different directions.
These have been around for a while, the use case is where the panel gets partially shaded by a building or pole or whatever. It’s not for making it work under a tree.
Because the cells are in series even a cable shadow across a panel causes 100% loss. I’ve seen this happen. They use bypass diodes to, well, bypass the shaded cells so you at least get some power out of the panel.
This is a good, succinct breakdown. I think most folks know when they have a use case like a pole, single thin tree to the South in a northern latitude, or a neighbor’s roof that only gradually cuts off cells but doesn’t immediately cover the whole panel.
If you want a longer explanation, Dave Jones from the EEVBlog made a video a couple of years back showing how just the shadow from the mast holding up his TV antenna dropped the output from a series of solar panels by 20%
https://www.youtube.com/watch?v=AbxHoQF4ADk
Modern half-cell panels are already split into two independent halves (which are connected in parallel) and then also usually split into 3 sections with bypass diodes, so shading isn’t as bad as it was with older panels.
Psst: It’s Renogy, no “Renology”
Shade tolerant panels have better bypassing of cells, so they don’t drop as much voltage, but they’re not magic. The MPPT controller is going to go crazy anyways.
The only way you can make a genuinely shade tolerant panel is to wire every single cell in parallel, but each cell is only putting out 0.7 Volts, so you always have to have some number of cells in series to make it useful.
You assemble the individual cells into series-connected modules or tiles, which is what people usually mean when they’re saying “solar cells”. Those already consist of multiple cells. You then connect the tiles in series and parallel to construct the entire panel, with bypasses and blocking diodes etc.
Any shading on an individual tile will drop the voltage of that entire tile because a blocked cell will stop generating voltage and turns into a resistor, blocking the entire series. The panel steering diodes then have to bypass that tile to keep generating power, if they can. With many tiles in series-parallel configurations, you can get into bad situations where losing one tile will lose the output of half the panel, because that half isn’t producing as much voltage to push any current out and goes into reverse blocking mode.
Integrate some smart switching of cells, integrate mppt and voilà, the smart/clever panels are born.