Each week Jason chats to people who are seeking clarification or understanding about their 12 volt set ups and what they can do to improve them. From those who are complete novices, know little/nothing about 12 volt and are starting from scratch, to those that have a few bits and pieces and just want to be able to camp off-grid for longer.
I pour over these emails myself, asking questions when they hit technical points that I don’t fully understand, and learn so much. I feel like the conversations he is having would be beneficial to others, so over the next few weeks (at least) I’ll be putting together a series of small articles. They’ll be written by me (with Jason ensuring my basic understanding is correct), and so will be easy to understand. Be aware that because they are written by me, the explanations are often a simple overview of how things work - there are exceptions to rules and if you do need more technical answers feel free to drop us a line!
To kick off, lets start with this one…
“I’ve seen really cheap flexible panels with SunPower cells, what’s the difference between theirs and yours??”
The first thing to clarify is what is, and isn't, a SunPower cell. SunPower are global leaders in solar technology, and their name often gets bandied around and used (particularly on eBay) for listings which actually aren't SunPower cells. Some retailers will use the words “sun power cells” – which is technically true, cells are powered by the sun, but they are not “SunPower” cells. Others will outright lie, saying they are when they aren’t, while others will say they are, genuinely believing that what they have been told by their supplier is true, but have never bothered to checked.
So how do you tell?
Well, short of buying two panels and chopping one up (the backing on SunPower cells is distinctive, see image below), there’s a few ways.
The back of a SunPower cell is distinctive
Firstly, SunPower make a back contact cell, and as such, do not have lines running across individual sections of the cell, nor do they have tape connectors running across the front of the cell. Below is images from two listings which have "Sunpower" in the heading on eBay. You can see the lines running across the front of the cell, meaning this is absolutely not a SunPower cell.
Lines across a cell indicate this is not a SunPower cell
What if the product photos aren't detailed enough to see up close? Simply ask. If they dodge your question and cannot provide any proof/information to back up their claims, back away quickly. While they aren’t likely to provide documentation from their suppliers (to protect their own products from being copied), chatting to them and gauging their responses will give you a feel for whether they are being truthful. If its really Sunpower, they cost more to make and as such cost more to buy. The would have back up to prove their claims if legitimate.
The problem now arises that while some retailers can honestly say they have SunPower cells, they then may do one of two things. Firstly, they may continue to use the efficiency rating attributed to the premium range, when in fact, the reality is the efficiency is likely much lower. Which (in "Kathleen" language) means that a panel marketed as a 100W panel may not actually be 100W after all. Alternatively, they might not give you the efficiency rating at all, and just overstate the power of the panel outright.
How do you know a SunPower panel is actually the watts stated??
To work out what's really going on, to determine what you are actually buying, is simple math. Start by counting up the number of cells on the panel shown (they are squares with corners cut, which may or may not be cut into 2 or 3 pieces), divide the panel wattage stated by the number of cells.
For example (NB. this is a random image and not a panel in question):
Let's say this panel is stated as being 200W. It is 6 cells wide and 8 cells long.
6 x 8 = 48
200W/48 = 4.1666W/cell
Then have a look at the table below, which shows the premium SunPower cells available, and their price per cell (there are different generations and differing grades - this information is freely available on their website). If the number you get is over 3.64W, then you know for sure they’re telling porkie pies, because the Ultra Premium Performance Cells are the highest performing cells that SunPower makes available for purchase by distributors (there are higher performing cells, but SunPower keeps these for their own panels).
Let's do another example (again, just an image grabbed from Google):
This panel is listed at 100W.
4 x 8 = 32 cells
100W/32 = 3.125W/cell
Now, as you can see, the watts per cell on this panel are below the lowest wattage on the price list above. When SunPower manufacture their cells they have exact standards that each cell must meet in order to make it into their own panels. Everything else is on sold to distributors (these are those in the table above), who can then manufacture their own panels, still with "SunPower" cells, just not meeting the specifications set by SunPower for their own panels. 3.125W, however, is well below the lowest cell that SunPower list, which means that these cells are very low quality. This is what is called "Out of specification" cells and are actually rejects for third party sale.
What this means in practical terms, is that this panel, at 100W, will be significantly bigger than a 100W panel using a higher grade SunPower cell, ie. you get less watts per area - and space is always at a premium on top of a van or fourbie.
The next thing to look at when comparing flexible panels is the laminate used. This is the top layer on the panel and is what stands between the cell and the elements.
Flexible panels should be laminated with ETFE, which is manufactured in Japan or US by companies like Dupont. It is a fluorine-based plastic, designed to have high corrosion resistance and strength over a wide temperature range. If a manufacturer/retailer uses ETFE they will advertise it, 100%. It is about 6 times more expensive to purchase compared to PET or TPT, so if they use it they will list it. Flexible panels are not supposed to be made with PET. It's a cheap manufacturing shortcut and will significantly reduce the longevity of your flexible panels. Ever seen what a plastic water bottle looks like when left in the sun for 12 months? Totally discoloured, turns milky and is no longer clear. They break down in the UV and your panel loses its ability to receive sunlight on the cells. These are the type of panels that melt, blister, delaminate, catch on fire etc and are where the horror stories about flexible panels comes from.
Finally, are you wanting to use the flexible panels in parallel (ie. join them together)? The vast majority of product pages for cheaper flexible panels state that they cannot be connected in parallel. If you are planning on purchasing more than one, or hooking it up to an existing panel, this should be a big red flag to bypass this retailer.
Jason and I set out to create products that we could stand behind 100% and would be happy with for our own family. We chose SunPower cells for our AllSpark flexible solar panels and blankets because of their high rates of efficiency (which, simply put, is their ability to convert sunlight to electrical power in a comparable surface area to other cells), ability to deal with the high temperatures found in Australia, their performance in shade and their longevity. We chose to go with the more expensive, higher performing cells, because we felt that getting as much solar into a small amount of space is important. We also use the ETFE laminate, which protects the cells long term. This was an absolute non-negotiable for us. There is no point going to the time and effort to fit these panels only to have them quickly reduce in efficiency, and then have to replace them a year later when they begin to peel or discolour.
If you’re looking to purchase flexible panels, we believe your best option is to wait until you can afford good quality, especially if they are going to be exposed to the elements for long periods of time.
In the end, though, the key here is to be informed and educate yourself when making a purchase. Everyone has a budget that they need to stick to, and yours may not stretch to high performing SunPower cells with an ETFE coating. If you are purchasing a cheaper panel, here’s a few tips/suggestions:
- be prepared to change it over in a year or so, understand the longevity of it and keep an eye on when your warranty term is coming to an end – anything wrong? Contact the retailer and hold them to the terms of their warranty.
- if you are not travelling full time/for extended periods, ensure the panels do not sit out exposed to the sun unnecessarily when not in use.
- don’t direct stick a panel that may not last, fix it securely knowing that it may have to be removed in the future – using Sikaflex or similar will more than likely damage the surface when removing the panel.
- speak with the retailer before purchase, make sure the numbers add up and that they will actually answer your questions and return your calls. If they insist their numbers are correct, ask for evidence – testing results from their own panels, not manufactured graphs/tables (unfortunately official looking specification tables can be completely fabricated).
- make sure the cable size is correct for the panel you are using – small cables can result in substantial voltage drop, meaning your much larger, but cheaper panel could produce less power than a good quality, slightly more expensive, smaller one (more on cable sizing in an upcoming article).
- make sure the controller is the correct volt and amp rating for your panel, and of the best quality you can afford – a good quality controller can help draw the most power out of a lower quality panel (only to a point though).
As always, we are here to help, and not just with products we sell. If you can’t stretch to high quality products, please don’t hesitate to throw up a question on the Offroad Living Facebook Tribe group about what you are looking at, Jas will give an honest opinion which will help you determine the best option for you within your budget.
PS. I want to clarify that I believe that most mis-information on product pages is not deliberate. Often retailers don't understand solar well enough to question what they are told by their suppliers. During the writing of this article I sent out three questions to query specifications (I asked for the actual watts on the panels, as the stated watts are generally not exact round numbers, eg. our 115W panels actually tested between 118W and 122W), all three have said they don't know the answer to my question and will get back to me...I am still waiting...