Around the world on a solar ebike

[Cephalotus]

Hi there,

U assume that Covid-19 destroyed your trip so far :-(

Have you already been on the road?

Any news on the technology of your solar bike?

 

[solarEbike]

U assume that Covid-19 destroyed your trip so far :-(

Have you already been on the road?

I'm stuck in Oakland, trying to focus on the positive aspects of not having to deal with the pandemic while traveling. The trip is on hold for now but my intention is to go ahead when it becomes feasible.

In the meantime, I have some experimental results to share from work I did a couple of months ago.

IR Pictures can be made easy and cheap with a dark room, a suitable DC power source to reverse power the solar module (bypass any diodes) and an old Sony F717 or Sony F828 with s small magnet to put it into "nightshot" mode.

So... electric motors are also generators, speakers are also microphones and now photovoltaic cells are also light emitting diodes?! Weird. Steve Mould explains on YouTube. If you like deep dives, you might like this paper: Review on Infrared and Electroluminescence Imaging for PV Field Applications (PDF, 4.9MB).

I picked up a used infrared-capable Sony DSC-F717 on eBay for $25 plus $25 for a memory stick and charger. Add a $15 DC/DC converter as a power supply and I have a basic setup for electroluminescence analysis of my solar panel collection. It feels a bit like being able to take x-ray photos. I don't have "before" photos to compare to these "after" photos but I think the results give some interesting anecdotal evidence of how flexible solar panels degrade over time with real world destructive testing. Here's the test setup.





Here's one of my oldest panels. The electroluminescent infrared photo on the left shows many small cracks and two cells which are half dark/half extra bright showing that half of the cell is electrically disconnected from the series string. None of this damage can be seen in the visible light photos of the same panel on the right. This panel has seen several months of wear and tear riding around on my commuter bike but it's never been in a crash.

It's rated at 50 watts and I seem to remember it performed close to that when new. I'm now getting 24 watts at 770 W/m² and 35°C cell temp on the input side of my MPPT charge controller. Using a power coefficient of -0.35%/ºC, I get an extrapolated power rating of 32 watts at STC (1000 W/m² and 25°C cell temp). That's a 35% power loss.




Next up are my two Solbian panels from my 1" thick red foam trailer. There's a visible dent in the upper left corner where something struck the panel but otherwise these look pretty good. Both panels tested at the full 94 watts when new. The top panel is now down to 83 watts and the bottom one 88 watts.




Finally, we get to the custom panels I'm planning on taking on the road with me. The roof panel has had a full year of road testing adding up to 6000 miles (10,000 km). In spite of my best efforts to take care not to damage the panel, it now has several small dimples. The source of these is a mystery to me. You can see them as the dark areas along the bottom edge in the IR photo and they can be seen in the close-up color photos. The 0.25 mm ultra lightweight encapsulation leaves the cells more vulnerable to damage than the more common 2-3 mm thick EVA encapsulation. I knew this was a risk I was taking.





The three pristine panels destined for the trailer are free of cracks but have several cells which are emitting noticeably less infrared than the others. Given that the Solbian cells are much more evenly lit, I suspect this may be due to cell mismatch. However, it's possible that the differences between cells are exaggerated because I wasn't able to maintain the same exposure, warm-up time and post-processing settings for all photos.




According to the bare cell specifications, these 4 panels should each output 3.63 watts per cell at STC for a total of 87 watts per 24 cell panel. The roof panel is giving me 76 watts and the other three 79-80 watts so about 4% loss due to the physical damage and the rest are largely encapsulation losses.

I measured irradiance with a Daystar meter, power with a couple of WattsUp meters and estimated cell temperature using irradiance values and ambient air temp because my IR thermometer wasn't working. I was relying on factory calibration with all of these so there's plenty of room for measurement error.

I had WattsUp meters on both the input and output of my GenaSun boost solar charge controller and they measured 93% efficiency going from 13V input to 40V output. This was disappointing given that their manual claims "96% - 98% typical" efficiency for 36V nominal output. I wonder if higher input voltage would give better efficiency? I selected my solar panel size based on physical constraints (bike mounting and airline luggage regulations) and mitigation of shading losses but perhaps electrical efficiency should have played a larger role in the decision.

 

[Cephalotus]

Hi,

good that you have not been caught "somewhere" on the road. Closing of borders did happen very fast and you probably would have lost your bike.

very interesting. The F717 is a good and cheap chose. I fail to understand why other solar ebikers do not test their modules.

The general knowledge seems to be that Sunpower cells do not degrade under mechanical stress. They may be more resilient, but that idea is false.

In my opinion your panels that you will use on your trip are perfectly fine at the moment.

I measured the eta of my Genesun chargers on a 13s battery. Not perfect, but you get an idea...

Eta is optimal at high power and when voltage difference is small.

Imho partial shading is a bigger problem, so I would suggest to use more lower voltage instead of many serial cells when partial shading could happen.

Eta gets significantly lower at low power input. 20W is still okay, At 10W eta seems to degrade significantly.

The measurement has not been ideal, so take everything with a grain of salt. maybe others have done better measurements.

 

[Cephalotus]

Hotspots in modules with cracked cells...

IR:



Thermo when shorted, not maximum sun (rotate picture):



It is not so bad under MPP, maybe +20K for the worst cell, but I can't find the picture...

So under bad conditions bad cells will be able to melt through cheap PET modules. Such things did happen. Also heat is useless energy that does not go into your battery

 

[Cowardlyduck]

This is really useful info thank you for posting. It explains exactly what I've seen happen to a number of panels mounted to the front of my recumbent over the years. I've just usually upgraded to a bigger panel before it got too bad each time, although I did have one panel drop to <3W which was rendered useless.

So what is the solution? Can we buy any better panels that won't have this problem? Or can we encase our 'flexible' panels in something to strengthen them before they develop these issues?

Cheers

 

[solarEbike]

It explains exactly what I've seen happen to a number of panels mounted to the front of my recumbent over the years. I've just usually upgraded to a bigger panel before it got too bad each time, although I did have one panel drop to <3W which was rendered useless.

So what is the solution? Can we buy any better panels that won't have this problem? Or can we encase our 'flexible' panels in something to strengthen them before they develop these issues?

I think the key here is to understand that "flexible" panels are designed to conform to slightly curved surfaces but should not be mounted in a way where they continuously flex while in use. Keep mechanical stress and thermal expansion to a minimum. I suspect your 3D printed mount is creating point loads where the mount is in contact with the back of the solar panel.

Here's how I mounted my 50 watt panel (with the 35% loss described above). I tried to spread the load with some aluminum flat bars and angle brackets on the sides but apparently it wasn't enough.



My preferred solution is to bond the solar panel to a solid surface. I made my own composite sandwich panels because I'm a masochist but there are alternatives. Canadian start-up LightLeaf Solar offers lightweight structural solar panels. I have no pricing info but don't expect them to be cheap. You can buy carbon fiber or fiberglass panels or make your own on a budget: Steven Roberts explains fiberglass over cardboard. Raf Van Hulle bonded his panels to 1 mm thick aluminum which strikes me as very heavy but it's hard to argue with his success.

I'm tempted to do some experiments to compare the power gain/loss with mounting on a thermal insulator vs. free air vs. a heat sink. I already have all the materials I would need and the data would put an end to the speculation.

 

[solarEbike]

In my opinion your panels that you will use on your trip are perfectly fine at the moment.

Agreed. I'm a little disappointed because I had expected slightly higher output. I'll need to add module degradation as a factor in my solar production modeling and route planning but I don't expect it to play a huge role there. The much bigger uncertainty is what kind of pace I'm going to be willing and able to maintain once I've been on the road for weeks and months. I'm making conservative assumptions with the hope that it will give me plenty of flexibility later.

I measured the eta of my Genesun chargers on a 13s battery. Not perfect, but you get an idea...

Thanks for sharing your results. I suspected that higher input voltage and power would give better efficiency. It's great to see the correlation mapped out so clearly. My roof panel and front-most trailer panel will each be on their own Genasun controller due to shading and mismatched orientations so they'll typically see the lower 93% efficiency number but my two rear-most panels will be wired in series to a single controller giving twice the voltage and power. Hopefully, the overall efficiency of all three controllers will be closer to 95%.

 

[kiltedcelt]

I'll be building a cargo trike - tadpole configuration. Ideally I'd like to have a removable awning framework to support solar panels for recharging either while riding or when parked for when I'm using the trike for extended trips. Most of the around town trips can be covered by my current battery which is a 52v 28.3AH triangle pack battery. I'm using a BBSHD instead of a direct drive motor though, so no regen. It's also super-flat where I live so I don't know how much use regen would be anyway. I'm not planning on suspension for this trike, but it will be using a nominal 26x3.0 wheelset, setup tubeless which will convey some mild suspension. I'm building in the ability to have 26x4.0 tubeless wheels as an option for rougher terrain or winter/snow riding. Also some substantial passive suspension with that sort of wheelset. My total length for a solar panel awning will probably be about 8 feet. Since I won't need solar all the time on the trike I'd like to make the panel able to be disassembled into two halves for storage. Also, since reading the thread and seeing that many panels can be flexed and damaged, even when mounted to a firm substrate, what do you think about a design whereby the awning itself might be isolated or somehow given a suspension independent of the trike itself? What sort of wattage of panel would I need to be putting charge back into a 52v battery and be able to extend range, or be able to sufficiently recharge the battery when not riding?

 

[john61ct]

Did not read all that but suggest it's worth starting your own thread.

Shorter bite sized posts with specific questions and only the relevant background details usually collect higher quality responses.

 

[solarEbike]

Coronavirus Diary. Week 8 of lockdown. Cabin fever.

Riding about 150 miles (240 km) per week but getting bored with the same loop over and over again. Outdoor exercise, including bike riding, is permitted in the SF Bay Area but non-essential travel is not.

Scouring Google Maps for fresh ideas, I spot this delicious solid green line on the Richmond bridge. It wasn't there before. When did they add a bike path to this bridge? In November? Why am I just learning this now?



I've been wanting to bike all the way around the bay ever since I moved here 20 years ago. I always assumed it would take a 2-3 day camping trip unless I want to take ferries or shuttle vans across inaccessible stretches. I do not. This bridge is a game changer. Time to tick off an item on my bucket list.

First stop, map out the route. Total distance is 139 miles (224 km) with only 1400' (420 m) climbing. Better get an early start and pack a lunch.



Second stop, check the SOLAR ebike Trip Planner 2.1 to see what kind of solar Wh/mile I can expect. The weather forecast calls for sun all day which means I can reasonably expect to get the max daily Wh based on typical meteorological data for this period: 1766 Wh plus 518 Wh from my battery pack which works out to about 16 Wh/mi (10 Wh/km). Perfect.



I'll be towing my old 2-wheel Burley Flatbed cargo trailer because I've been using it to test thermal performance with different mounting options (free air vs. foam seen here). With no suspension, the trailer bounces around like crazy and I really have to slow down on rough roads and paths reminding me that I made the right decision to go with a single-wheel suspended design for touring.



The new bike path on the bridge is a delight as is this new signage.



The first rest stop is the Golden Gate Bridge vista point, eerily free of tourists except for the four who ask me to take their photo. The guy asking is wearing a mask and gloves so I assume he's not completely unaware of the situation but the prospect of touching his phone is not appealing. I offer to take the photo with my own phone and use Air Drop to send it to him wirelessly. A good option if you're both on iOS.



The route is a mix of bike paths along roads in industrial areas with relatively little traffic and trails through parks and wildlife sanctuaries.



...including this one short stretch which was paved with carpet remnants (seriously?) and dead-ended in a construction site. Thanks, Google bike maps.



More new bike infrastructure. I thanked these guys for their service but they were not amused by my shenanigans.



At around mile 100, my legs were starting to get rubbery and I found myself fighting a stiff headwind which is always present on this part of the route but I had forgotten to account for it. The sun was starting to go down and I was down to 100 solar watts from a peak of 255 watts at solar noon. My battery was nearly full but I was draining it too fast to make it all the way home. The solution was to pull over at mile 120 for 40 minutes and top up the battery with some optimally tilted panels. This trailer isn't designed to tilt while riding so stopping meant the difference between getting 50 solar watts vs 230 solar watts. Note that such gains are only possible early/late in the day. Around noon, the sun is overhead and the 0° tilt is nearly optimal.



After the break and a snack, my legs got a second wind and I made it home with 20% battery to spare. My Analogger is on the fritz so here are some screen captures. Distance units are in miles. Solar total was 7.5% higher than the model predicted, possibly because my 20% shading loss estimate was too high.



Given my relative lack of training, I'm surprisingly free of aches and pains the next day so that's something to be thankful for. Stay safe out there and go tackle something on your bucket list.

 

[john61ct]

fantastic stuff

 

[solarEbike]

I'll be building a cargo trike - tadpole configuration. Ideally I'd like to have a removable awning framework to support solar panels for recharging either while riding or when parked for when I'm using the trike for extended trips. Most of the around town trips can be covered by my current battery which is a 52v 28.3AH triangle pack battery.

Sounds good to me. Stick with the battery for around-town use. A large solar array can get pretty cumbersome for casual everyday use.

I'm using a BBSHD instead of a direct drive motor though, so no regen. It's also super-flat where I live so I don't know how much use regen would be anyway.

I ran a BBS02 for 3 years (16,000 miles / 26,000 km) on a two-wheeled recumbent. Loved it. After I got the direct front hub, I loved that more. I wouldn't go back unless it was for a mountain bike or maybe a cargo situation with lots of slow hill climbing. I find I get 10% regen on flats and 20% or hills for most around-town riding which involves more stops than touring. Even yesterday's 139 mile trip had 8.8% regen.

I'm not planning on suspension for this trike, but it will be using a nominal 26x3.0 wheelset, setup tubeless which will convey some mild suspension. I'm building in the ability to have 26x4.0 tubeless wheels as an option for rougher terrain or winter/snow riding. Also some substantial passive suspension with that sort of wheelset.

I rode an unsuspended tadpole trike for a year and found the ride to be fine on smooth roads but very harsh on bumpy terrain but that was with 1.5" tires. The fatter tires will make a big difference but how much will depend on what kind of terrain you're riding.

My total length for a solar panel awning will probably be about 8 feet. Since I won't need solar all the time on the trike I'd like to make the panel able to be disassembled into two halves for storage. Also, since reading the thread and seeing that many panels can be flexed and damaged, even when mounted to a firm substrate, what do you think about a design whereby the awning itself might be isolated or somehow given a suspension independent of the trike itself?

Keep in mind that the cell damage from flexing and debris hits accumulates slowly over time. Barring any extreme damage like a crash which folds the panel in half or delamination which causes water intrusion, your solar power losses may not be an issue until you've ridden many thousands of miles with your solar panels. I'm building for a 40,000 mile trip so my idea of long-term reliability isn't applicable to more casual use cases.

Until I find an inexpensive and easy to source "substrate," my advice for first-time solar builders is to stick with aluminum support "ribs." Use the lightest weight aluminum that will support your panel. Space them no further than 2 Sunpower cell-widths apart (10" / 25 cm). Only use panels made with Sunpower cells because the metallized back surface minimizes the effect of cracks on power output. Use 3M VHB foam tape product number 4952 to attach the panel to the aluminum after meticulously cleaning both surfaces with isopropyl alcohol.

I think a suspension element just on the solar mount will help reduce hard shocks but will not eliminate the constant flexing of the panel. Personally, I wouldn't do it. It's hard enough to make a strong, sturdy but lightweight mount that doesn't also move independently of the trike body.

What sort of wattage of panel would I need to be putting charge back into a 52v battery and be able to extend range, or be able to sufficiently recharge the battery when not riding?

I would need to know your Wh/mile and miles per day (really, just solar Wh per day) and where/when you'll be riding. Your battery voltage is irrelevant as long as your can find a boost-type solar charge controller controller than can output your battery's peak voltage. If you're doing 100% solar then your battery capacity is only a buffer which determines how long you can go without sun and how long you can stop in the sun until your solar panel's output has nowhere to go. If you're doing some plug-in charging in addition to solar, you'll need to add that to your own calcs.

Assuming your 8' (2.4 m) panel length limit and 125 mm x 125 mm Sunpower cells (4.9"), you could fit up to 6 * 18 or 108 cells. At 3.125 watts/cell based on the most commonly available semi-flex panels gives us a maximum solar array size of 340 watts. Plugging that into my SOLAR ebike Trip Planner 2.1 and using Chicago as the location with some reasonable assumptions about shading and charge controller efficiency losses, these would be your average daily Wh:



If you're riding all day with a 0° tilt to your panel, use the red numbers. If you're parked all day and adjusting the panel tilt and azimuth every 15 minutes to get perfect positioning, use the blue numbers. In fact, you can add 40% to the blue numbers if you can park in the sun and avoid all shade. Keep in mind that these are monthly averages. A cloudless day will be higher and the cloudiest/rainiest/snowiest day of any month will naturally be lower. If the numbers are too low for you, you'll need a bigger solar panel and/or supplement with plug-in charging. If the numbers are too high, get a smaller solar panel.

 

[amberwolf]

...including this one short stretch which was paved with carpet remnants (seriously?)

Carpet remnants, if large enough, are MUCH better than mud (especially clay) in rainy / wet weather, especially if you are on a narrow-tired bike or trike, etc.

I use that kind of thing (and sheets of cardboard from pallets of stuff we get in each week at work) in parts of my yard that the dogs prevent grass from growing on, so that they don't break their necks running thru it, and so I can get the trike past those areas.

 

[thundercamel]

Nice trip! I laughed at e-bikes being better than ok I have a dream loop of rails to trails southwest of Madison that I'll do one day, but just with a large battery. In a funny coincidence, it's also 140 miles.

 

[kiltedcelt]

solarEbike - thanks for your input. Also, I enjoyed your trip report. Your comments about the panels and damage and such are good to hear. Solar in my use case is not going to be nearly as rigorous as yours so certainly it sounds like I don't need to build nearly as robust of a system as what you're designing. Building in some form of tilt would be nice though, and having watched Justin's Sun Trip video with the tandem recumbent with the rowing gizmo, what sticks out on that build is the curved support rails up on the awning that allowed for nominal tilt. Solar will be the last thing I do on this trike build, but thinking about the watt hours question has me wondering - how much does weight of the 'cycle affect the amount of watt hours used? On a bike such as yours, the frame is reasonably light and your trailer and such similarly so. I was doing some rough calculations on materials for making my frame and the least expensive will be 1 1/2" 16 gauge square tubing. That will yield a frame weight roughly around 60 lbs, or maybe around 47 lbs if I use a non-DOM welded steel tubing. I did price out building it with 4130 chromoly steel and the weight differance was dramatic - only about 25 lbs for a 4130 frame, but the cost for tubing was $525 versus around $160 for non-DOM mild steel tubing! On my current cargo bike which weighs around 120 lbs (with battery and motor), and a decent amount of pedaling (and keeping the assist level lower), I can average below 12 watt hours - often below 10 watt hours, at least according to the display. I guess keeping frame weight lower will mean I need to work less hard to keep the 'cycle moving and the motor will be more efficient. Unfortunately chromoly or other exotic materials are off the table based on budget for the project. Thoughts on vehicle weight as a factor?

 

[solarEbike]

...including this one short stretch which was paved with carpet remnants (seriously?)

Carpet remnants, if large enough, are MUCH better than mud...

I figured it was something like that. It was just so unexpected to find in the middle of nowhere. One moment I'm on a paved bike path and suddenly it's the Villa Strailight from Neuromancer. I snapped a pic and thought, wait till the guys on ES get a load of this!

Building in some form of tilt would be nice though, and having watched Justin's Sun Trip video with the tandem recumbent with the rowing gizmo, what sticks out on that build is the curved support rails up on the awning that allowed for nominal tilt.

Being able to quickly and easily tilt the panels whenever you stop is essential. I went through several iterations of building tilt mechanisms that were easy to build but hard to deploy and ended up making ones that were harder to build but easy to deploy based on road testing. I want it to be effortless and it really pays off many times per day.

Tilting a roof panel while riding is tricky. It needs to be much higher to avoid obstructing your view to the side. I opted for a roof design that only has 25% of my solar panels and doesn't tilt while riding which allows for more effective shading of my head and has a lower center of gravity with the trade-off that I lose some solar generation. Maybe you already saw it but Justin also has a detailed design and build video about the curved rails.

Thoughts on vehicle weight as a factor?

If you use online calculators like the Grin Motor Simulator you'll find that vehicle weight doesn't seem to make much difference in the power required to maintain speed on flat ground, apart from a small increase in rolling resistance. I find this doesn't match up with my real world experience riding a fully loaded ebike vs an unloaded ebike, even on seemingly "flat" rides. I suspect this is some cumulative effect of relatively gentle slopes and the additional energy needed to accelerate a heavier bike, not just getting up to speed from each stop but all the times I slow down just a little and then get back up to speed (as evidenced by my cumulative 8.8% regenerative braking energy on my recent trip).

Quick example using the Grin simulator: doubling the weight on 0% grade results in 7% increase in energy consumption. Doubling the weight on 2% grade results in 22% energy increase.

To be honest, I haven't been able to adequately quantify the net impact of weight on a solar touring bike. Unlike a traditional touring bike, some kinds of added weight like a bigger battery or more solar panels will increase your range so it can be hard to know where to draw the line. Subjectively, a lighter bike handles better and is more fun to ride. It's easier to push through mud or sand, easier to carry up the occasional flight of stairs or lift over the unexpected gate on a trail and less complicated to pack up as luggage on a commercial airline flight.

My advice is to get plenty of riding experience with your fully loaded rig. A watt-hour meter is a must (you can get a cheap one for under US$20). Figure out how many watt-hours per day you need for your touring style, pedaling effort, daily range, etc. Add the solar panels last.

 

[amberwolf]

Add the solar panels last.

Yes. You may find that it would be a waste of time, effort, and money, to have them on the bike/trike, depending on your use case and the panels in question. Or just plain cost too much for the result.

In my case, I managed to get four low-power panels for a little more than $30 at a thrift store; at the price I decided to get them anyway despite knowing they probably wouldn't really work the way I wanted.

https://endless-sphere.com/forums/viewtopic.php?f=41&t=106119

The three identical panels hooked in series directly connected to the battery, at a little more than half-charged, only nets about half an amp of current at noon on a very sunny day in Phoenix, AZ, panels pointed as close to perpendicular to the sun as possible while laying on top of the trike's canopy. They're not very good panels, mind you....

In my case, the 31 pounds of panels themselves would, at best, net me another couple of Ah, maybe three, in dawn-to-dusk riding (which I don't do). The 38lb (IIRC) pack they're charging provides about 40Ah, so it would be better in my case to add another identical pack (if there was room), based on weight vs capacity, especially since a fair bit of my riding is at night, or at times when the sun would be so far from overhead as to not give significant power output. And the ride segments are usually so short that the only benefit would be while it's parked out in the sun while at the destination.


On a much lighter trike than SB Cruiser, with lower power usage, that doesnt' have a big battery or room for one, it might be worth it, for long rides in the sun.



Now, if I had one good panel the size of the top of the trike (roughly eight feet long by just under three feet wide ), that could produce 200-300w, at something like 60v (or just under) open-circuit (ideally 58v so it could literally never overcharge), I could direct-connect the panel to the battery and just leave it that way, and it would just get any energy available, whenever there was any, and it might be worth carrying around, at around 4A or so charge current.

I poked around a teeny bit, and found nothing at that voltage for that wattage of panel, but I did find several in that wattage range that would physically fit in the space available, and weigh around 40lbs (so no more than the four I have now, but much better efficiency). The closest stuff I found was about 40v-45v....


To really be worth it it'd need to be about 1000w panel (which is impossible) in that size, to practically power the trike during daylight rides.

 

[solarEbike]

Fast forward to today and we have "active diode" or "smart diode" devices like this Texas Instruments SM74611. It's not small enough to encapsulate within the cell but the cost ($3-4), forward voltage (26 mV) and reverse leakage current (3 µA) make it feasible to put one for every 4 or 8 cells.

Note that that one works by turning on and off rapidly, so when they are active you will see a ~30KHz voltage signal coming out of the array. It will be about .6 volts riding on top of the voltage at the output. This _probably_ won't affect the Genasun controller, but it's possible if that signal frequency lines up with the sampling period of the MPPT algorithm.

Hi Bill, remember these smart bypass diodes? I finally got around to testing them out today and got some puzzling results. I'm hoping you might be able help me make sense of this? Everyone else, please feel free to chime in. Thanks.

Here's the PV module wiring diagram. The PV is connected to the Genasun controller which is charging a 36V battery.



With one PV module, 24 cells in series, bypass diode every 8 cells as shown above I get:

• 78 watts with no shade
• 8 watts with simulated shadow on one of the sub-strings, blocking direct irradiance but not indirect irradiance. The diode is not shorting across the shaded cells as expected. This is exactly the kind of disproportionate power loss I'm trying to avoid.
• 44 watts with complete coverage (blocking both direct and indirect irradiance, diode is now activated). The expected output would be 78 watts * 2/3 minus a few milliwatts power dissipation by the diode but the PV input has dropped from 14.0V to 7.9V so the Genasun efficiency is lower.

This protects the module from localized cell over-heating due to fallen leaves on the module but is useless for mitigating shading losses.



Repeating the same drill with two PV modules in series, 48 cells total, bypass diodes as before, I get this perfect result. Each 8 shaded cells results in about 33 watts power loss without needing to resort to completely blocking the cells.



The second result is the desired outcome: the output loss is limited to just the cells on the same substring. Isn't each diode seeing the same voltage (~4.4V) and current in both cases? Why would the results be different?

On a hunch, I tried putting a diode on every 4 cells with a single PV module (24 cells total) and that works about half of the time. Sometimes the diode actives, sometimes it doesn't. It looks like this configuration is right on the threshold of whatever conditions are needed to start bypassing the shaded cells. It seems to work more consistently when the sun is stronger (900-1000 W/m²) and less so when it's partly cloudy (500-800 W/m²). The middle photo is with the diode on 4 cells, the right image is with no diode on those shaded cells.



I have 3 of these PV modules going on my trailer and I can't connect all three to the same Genasun controller (voltage is too high in series and current is too high in parallel) so I have one module on it's own Genasun and two on a second Genasun. Is there anything I can do to get better shading mitigation on the single module? I've tried re-reading the datasheet but I'm just not wrapping my head around the fundamental principle of how diode forward/reverse bias works (or its equivalent in this device). I think I'll try it with traditional diodes tomorrow to see if I get a better result.

 

[john61ct]

Solution for partial shade impact mitigation:

one SC per panel, full stop.

Side benefit: no need to match panels

 

[solarEbike]

Solution for partial shade impact mitigation:

one SC per panel, full stop.

I already have 3 solar charge controllers for 4 panels. As soon as one or two cells are shaded, I lose the whole panel. This is a way to get back 30-140 watts.

 

[john61ct]

Yes that is normal.

There were tiny MPPT ICs intended to go in per cell, or at least many per panel, never really took off.

Park in the sun!

 

[solarEbike]

I think I solved the mystery of why the bypass diodes appear to work intermittently. It has more to do with the very low breakdown voltage of SunPower cells and the way they interact with the Genasun MPP tracking algorithm. I got similar results with a conventional bypass diode and the Texas Instruments SM74611 "smart diode" device. Here's the video.

[youtube]NGD3x9M3esQ[/youtube]

I spent half the day playing peekaboo with the solar panel and decided that putting a smart bypass diode on every 4 cells in a 24 cell module recovers enough additional energy often enough to warrant the hassle of installing them and potentially later having to troubleshoot them if they fail.

The key to understanding this was re-reading pages 20-23 of this SunPower white paper until I finally got it through my thick skull. Here are the highlights.

• SunPower’s backcontact design performs differently than a conventional cell, due to fundamental design differences
  a typical conventional cell has a breakdown voltage of approximately -15V to -20V, whereas the SunPower cell’s breakdown voltage is only about -2.5V
  
• With a lower reverse bias voltage there is less power, and therefore less heat, to dissipate. (15W per cell Sunpower, 138W per cell conventional)
  
• A higher reverse bias voltage is generally a desired trait for Conventional Module manufacturers [because it] ensures a bypass diode will activate at lower threshold
  
• SunPower cells operate in reverse bias with uniform breakdown across the cell, resulting in much lower temperatures, so bypass diodes are not required to ensure long term reliability.
  
• SunPower does include diodes in its J-boxes, but the diodes do not turn on when only one cell is shaded. The voltage drop across a single reverse-biased cell is not sufficient to drive significant current through the diode. SunPower includes diodes only to increase the production of the system in the case that several cells in the same substring go into reverse bias.

 

[solarEbike]

Right after completing my 139 mile trip, I started planning what will hopefully be my first double century ride (200 miles, "triple metric century+"??). The target date is June 20, given or take a couple of days so I can cherry-pick optimal weather conditions. Not only is it another bucket list item but it has served as motivation to complete my new trailer. With two weeks to go, I think I'm on track to pull this off.

The plan is to start 1.5 hours before sunrise and finish 1.5 hours after sunset for a total of 18 hours. I'll start with a fully charged 518 Wh battery pack and end with the pack completely discharged. The 315 watt solar array with sun-tracking trailer should provide about 2500 Wh so my total budget is 3000 Wh.

While crunching the numbers, some interesting questions came up.

• Will I run out of battery power before the sun comes up?
• Will I need to use more power (faster speed, less efficient) in the middle of the day to prevent the charge controller from derating output because the battery is full?
• Will I have enough in the battery at the end of the day to make it all the way home with motor assist when I'm most tired?
• Can I budget my power so I use a little less at the start of the day when I'm fresh and a little more at the end when I'm tired?

Here's what the model says. Average power consumption is 3000 Wh / 18 hrs = 167 watts which includes all stops and breaks. Average power while moving will be 225 watts. Actual solar Wh during noon will be higher than what is shown here due to the simplified averaging over the course of the day (i.e., shading losses will mostly occur at the start and end of the day but are applied to every hour here). Surprisingly, it works out just right if I maintain steady power usage all day long. If I use less power in the morning, my battery will fill up faster but I won't have extra energy at the end of the day unless I get a bigger battery.



Here's a sneak peak at the trailer under construction. Perimeter tubes to prevent the solar module from delaminating and for crash protection. 3D printed ultra-slim junction box for wiring and photo sensor mounting.



How light is too light? I'm working on several solutions to prevent this from happening:

[youtube]0xNrSQcuqPM[/youtube]

 

[fechter]

Shaping up real nice.

If you had some kind of wind force sensor, you could have it automatically flatten out during a gust. Not sure if it could react fast enough though.

 

[Cowardlyduck]

Shaping up real nice.

If you had some kind of wind force sensor, you could have it automatically flatten out during a gust. Not sure if it could react fast enough though.

I think a simple solution would be to have the panel able to shift sideways so that the pivot point is further forward into the wind direction. That way the wind will help stabilise the panel rather than catch it like above. Kind of like the trailing edge of a arrow.

Cheers