Half cut solar cells - Page 1
Forum section: electronics / general

author: tszaboo
author_rank: Super Contributor
timestamp: February 28, 2021, 01:04:44 pm
content: I was browsing for solar panles, and I've encountered this term: "Half cut cells."Whenever I'm searching for the technology, I always find technobabble like this:QuoteThis makes no sense to me. So they use smaller cells, therefore the current on the cell is less. But they use more, so I guess the voltage should be higher? It isn't. So they must have she strings in parallel. Does anyone know how are these better?The other thing caught my eye is the nameplate capacity of new panels. Last year (when I decided not to make an installation after all) The panel sizes on the local market was 310-330W. Now I'm seeing panels that are 450W rated. Sure the panels are larger, even 2mx1m, but still, it makes a lot of sense. The installation material, frame, cabling, and so on scales with the number of panels.Let's say, you want to max out a 230V 16A connection (3600W). Not so long ago, this was 12x 320W. Now its 8x450.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 28, 2021, 08:29:46 pm
content: They might be specifically talking about the losses in the top electrode of the individual cells. That might get better if you use half size cells since the current doesn't have to travel as far on average to get out to a copper bus bar.

author: sandalcandal
author_rank: Unknown
timestamp: March 01, 2021, 12:02:35 am
content: Pretty common to do. You'll very often see it in anything trying to shift the optimisation a bit more towards performance/density over cost and has been done for a very long time afaik. I remember it being a standard but notable design point for solar cars when I was in my uni's solar car team. I had a quick look but most of the stuff seems like marketing technobabble as you say, no immediate good quality technical papers unfortunately. I think the gist is generally correct though, the standard wafer and cell size is good for manufacturing lots of cells a bit suboptimal electrically so by cutting them in half, better performance can be had for the same area of cells.

author: penfold
author_rank: Frequent Contributor
timestamp: March 01, 2021, 12:51:03 am
content: It could perhaps give some benefits for partial shading, particularly as it divides the module in two across the middle (at least as google suggests a common configuration to be).Since the module is divided into two smaller parallel modules, the total round trip of each "conductor" strip in each sub module is reduced.. I wouldn't consider it to be a dominant resistance unless they're really skimping on the conductor thickness.About 15 years ago during my PhD I was under the impression that half cell modules were made using the good halves of broken cells... I can't remember if there was any genuine basis to that assumption, but it was certainly most common in the earlier "cheap" imported modules. The benefits of series resistance being slightly lower would be a solution to a very "cost-down manufacturing" problem when using very thin copper tracking.I would be somewhat wary of them cracking at the "sharp" corner... the traditional shape is also somewhat optimised for thermal stress reasons (emphasis on "somewhat").

author: tszaboo
author_rank: Super Contributor
timestamp: March 01, 2021, 11:09:42 pm
content: Quote from: penfold on March 01, 2021, 12:51:03 amThat's what I see as well. I've found an article that makes sense:https://www.solarquotes.com.au/blog/half-cut-solar-cells-panels/So the cells are cut so the electrons have shorter paths to the strips. This increases efficiency by 3% according to this source, so a panel with 300W is 309W. And partial shading is smaller problem, since there are 6 strips, not 3. The vertical arrangement helps with shading due to a tree for example.If I go to JA solar's website (for example), they only list half cut cells. Same with Longi solar.Its interesting to see, that Chinese companies are actually more innovative than LG or Sharp or Q-cell. Q-cell on their website claim world record 19.5% efficiency, JA is 21%. The huge innovation on LG's site is black frame...

author: penfold
author_rank: Frequent Contributor
timestamp: March 02, 2021, 12:10:18 am
content: Quote from: NANDBlog on March 01, 2021, 11:09:42 pmI don't see how the electrons travel any shorter a distance on each cell (if I understand you correctly) unless they're adding any additional metallisation, (maybe I'm visualising it wrong, but,) it could even be worse at the cut edge since it no longer shares the parallel path of the metallisation on the cut-away half it once had... shorter total round path length on sub-par copper strips though would still be my suggestionThe partial shading can also show up due to surface contamination collecting mostly on the lower half of the module which could explain why they're split in the horizontal plane rather than verticalI'm only basing this on a few optical measurements I did with various modules 15 years ago, but some imported modules did often perform better in direct tests... but they lacked some of the coatings and surface treatments the "big brand" ones use to reduce reflectivity and have self-cleaning-ness, the encapsulants too can be more or less prone to discolouration... so be wary of claims unless they're substantiated to the same test standards and there's some lifetime issues to think of so look for guarantees of performance

author: tszaboo
author_rank: Super Contributor
timestamp: March 02, 2021, 09:15:33 am
content: Quote from: penfold on March 02, 2021, 12:10:18 amThey cut it "the other way". So the busbar is on the longer edge.Honestly, I've seen so much change in the last 3 years alone, that I have to do my own research for it.3 years ago, the general consensus was that microinverters are stupid, and they increase the payback time, with no added benefits. Now an Enpahse inverter is only about 15% more expensive than an SMA, if you have a 2.5KW system.Or looking at Solaredge, their 15KW inverter is about twice the price of a 3KW. Too bad, i dont have the roof for such a big system.And besides, you cannot buy the panels. by the looks of it each webshop that I'm looking at has 1-2 LG or panasonic panels, all of them twice the price of the import one, with smaller capacity.I think the bang per buck right now (at least here):Big import panels, place Solaredge or Enpahse on the panel, so if it breaks, the rest keeps on working. Buy a system that is as big as it fits on the roof. Installation cost is 1/3 the system cost, so make sure they dont have to come twice.

author: nctnico
author_rank: Super Contributor
timestamp: March 02, 2021, 10:09:20 am
content: If you buy 2nd hand panels you can get a better ROI on solar panels if you install them yourself. Payback in less than 3 years is doable if you manage to get a good deal.

author: tszaboo
author_rank: Super Contributor
timestamp: March 02, 2021, 11:50:56 am
content: Quote from: nctnico on March 02, 2021, 10:09:20 amFor sure. But it's not all about ROI.I dont wan't to work on my roof, it's big and scary, and I dont know how to do it safely. Its 45 degree, and spans 2 floors. And if I break a window, getting it installed is suddenly cheaper. I would also need help with it.Electrical work is also needed, as I probably end up needing cabling that is more than 16A or maybe 3 phase (I am still debating myself if 3 phase would make sense)I mean I could do it, if I would have a flat roof, to just throw a few used panels there and wire it to the junction box.But like 14 panels on 4 different heights... I much rather spend a week in the office or take some extra consulting job and let the professionals do it.

author: nctnico
author_rank: Super Contributor
timestamp: March 02, 2021, 06:05:26 pm
content: A flat roof has it's own problems like needing a significant amount of ballast which the roof may not be suitable for. Anyway, if you can't do work on the roof then you have to be satisfied with a much longer time until payback (currently crawling towards a decade in the NL) and lower ROI. The installers basically eat your profit. From a financial perspective it might even be more interesting to invest the money in a large scale solar panel project. In such projects the installation costs are much lower compared to a single roof so you can get much more solar panel surface for the same money.

author: tszaboo
author_rank: Super Contributor
timestamp: March 02, 2021, 10:55:55 pm
content: I've been calculating with 7 years ROI. It is kinda hard to calculate, since they dont tell us what the feedback price is, but I've counted with 7 cents. But I only have 1 roof, doing any work is expensive, so I probably going to install more than what I actually need right now, anticipating EV. So my ROI will be not so great.If it would be only about ROI, then it would make sense to buy the panels for mortgage or the green loan. That way the cost is practically zero, so ROI is infinite.But honestly, I found it very difficult to find any investment, that would come even close to the same as solar panels. I know there supposed to be those legendary 7% interest rate investments, that will make you rich.At least the panels are on the roof, right? And saving the polar bears.