Solar trailer build

[guerney]

Well you haven't been slack mathewslack! Very nice build! Solar panels are not cheap and appear to be fragile - can you add downforce using skirts on the sides and some sort of aerofoil underneath like an F1 car, to stop it taking off in the wind? Maybe curve the panels, or keep a hinged middle panel slightly lower while the trailer is in motion, so that they're slightly concave when pointed skywards, thereby reducing lift? When stationary, you could put them all back in the same plane?

 

[matthewslack]

Trial of two battery setup.

For my Shimano solar bike, I am using a generic battery in parallel with the Shimano one, with Schottky diodes linking the positive cables to the feed to the motor and controller. The normal Shinano communication wires remain in normal place from the Shimano battery to the rest of the system. The solar charging will feed into the generic battery.

The operating principle is very simple: whichever battery is at the higher voltage drives the bike. Most of the time this will be the solar charged generic battery.

I have just completed a 16km, 200 metres of climb test ride of the parallel battery setup without the solar connected. The generic battery was nearly full, 40.8V, and the Shimano one about 60%, 37.8V at the start. My two channel datalogger was watching the output from the batteries. Finishing voltages at rest after recovery time were 38.1 and 37.5V respectively.

The result was as expected, but of course I needed to see it to believe it. 85Wh taken from the generic battery and 8Wh from the Shimano. Those few are when under load up hills, the voltage of the generic battery is pulled down to that of the Shimano, and they then share the load.

The Shimano display only notices the Wh taken from the Shimano battery, which is a nice easy reference to what's going on. So 16km in level two assist, took indicated range down from 64 to 61! In normal times that would have gone from 64 to about 30.

The charging side of things is already tested. Now I have to complete the trailer build and make everything robust and weatherproof.

 

[matthewslack]

Tales of two batteries, two charge controllers and one EU.

Generic batteries

I recently bought a new cheap 48V 20Ah Psppower 21700 Samsung cells claimed, but haven't looked inside, for my conversion bike, which tested at 17.5Ah and 840Wh on my charge/discharge rig. It is no doubt 13S4P with cells named 5000mAh, giving the 20Ah nominal capacity. I don't know whether only 17.5Ah down to 3.0V per cell is normal for any Samsung 21700 cell or not. I was a bit disappointed, but it was a £293 delivered battery.

I even more recently bought a secondhand hardly used Greencell brand 36V, 13Ah, 468Wh claimed battery as the generic second battery for my Shimano running on the sun project. It tested at 473Wh and 12.9Ah, so near enough exactly as labelled. Very pleased with that for £153!

Boost charge controllers

Solar bikes usually have higher battery than panel voltage, so need a boost charge controller. There are also no known (to me) 36V normal charge controllers.

I bought three cheap Elejoy mu400sp controllers which in my early experiments worked as expected. These can be programmed with a set output voltage, and they then do 'maximum solar power' followed by constant voltage (CV) charging to that voltage.

I had a glitch last week, which seemed to be charge controller related, and with my inaugural long solar trip getting rather close, and no quick source of new Elejoy, I ordered with fingers crossed one of the 'gold standard' Genasun controllers from the makers in the Netherlands. It arrived today, in an opened inner box within an opened outer box, but as it is solar equipment and zero tariff, and was exactly what the labels outside said, came with no delay and no added taxes or fees. Phew! How far it has travelled with the boxes open, I have no idea.

I wanted one anyway, but at €235 plus €39.50 for p&p I needed a very good reason!

The Elejoys turned out to be fine, that issue is not fully understood but the workaround is to charge via the battery output rather than the charge connector. The BMS wasn't allowing the solar input to switch charging on for some reason. Having now observed on the Elejoy LED displays the CV behaviour at top of charge, I am content for now that overcharging should not happen as the BMS balancing is in play, and I set the finish voltage a bit below 42V as well.

 

[Nealh]

One will only get near full capacity at the minimal discharge of 0.2a, typically bikes discharge rate though is anything from 13% of the controller rating to 100% so depends on the controller type & rating used and the PAS level used.
A current controller will be more frugal then a speed controller.

The generic Sam 5000mah cell used will be the 50e, typical capacity though can vary from 4750 - 4900 mah though mooch did get just over 5000mah on the pair he tested but that was down to 2.5v at 1a.
4600 - 4750mah is more typical with a 1a load to 3v.

What average current load is being applied to the Sam 21700 battery ?

For capacity/range I look at the typical load I will apply to a particular cell then search for discharge graphs of the cell at the current share I expect it to operate at to see the expected mah I can expect. Multiply that by the cell count in parallel to have an idea of total battery mah and range I may need.
Typically I use base line of 3.3v so not to deep discharge the cell and nearly all my BMS cut power at approx.3.2v.

 

[matthewslack]

One will only get near full capacity at the minimal discharge of 0.2a, typically bikes discharge rate though is anything from 13% of the controller rating to 100% so depends on the controller type & rating used and the PAS level used.
A current controller will be more frugal then a speed controller.

The generic Sam 5000mah cell used will be the 50e, typical capacity though can vary from 4750 - 4900 mah though mooch did get just over 5000mah on the pair he tested but that was down to 2.5v at 1a.
4600 - 4750mah is more typical with a 1a load to 3v.

What average current load is being applied to the Sam 21700 battery ?

For capacity/range I look at the typical load I will apply to a particular cell then search for discharge graphs of the cell at the current share I expect it to operate at to see the expected mah I can expect. Multiply that by the cell count in parallel to have an idea of total battery mah and range I may need.
Typically I use base line of 3.3v so not to deep discharge the cell and nearly all my BMS cut power at approx.3.2v.

Discharge resistor is 26 ohms or so, a 2kW panel heater repurposed. Current varies from 2A at full charge down to 1.5 at 39V cutoff. I expected a bit of a drop from 5000mAh, but the curves did not suggest as much as I got! However, per Wh it is cheap ish, and for my low power riding, it should do. I'd just rather have an extra 2.5Ah in the tank! I may open it up and see what cells I really have, but I won't be sending it back unless it fails.

 

[matthewslack]

Getting close to takeoff.

 

[matthewslack]

Just completed a three day shakedown trip with the Shimano bike and the solar trailer. A few lessons learned, and some insights into how to stay 100% solar powered.

Days of 71, 105 and 54 miles, fairly flat the first day at 280m ascent, but then 1200m and 450m, total of 1930m climb. All up weight close to 150kg, depending on how much food and water onboard.

The main result is that the parallel battery setup, necessary because the Shimano battery cannot be charged by any means other than its proper mains charger, works reliably.

The side effect of this is that the Shimano battery is a real weakness: if it ever goes flat, which it did on this trip, the system cannot be turned on, and cannot be revived except by a mains charge. I carried a spare Shimano downtube battery as an emergency reserve, and a charger so that I could revive my flattened system. I came home with energy to spare, but having had to make one short charging stop.

I was undone by extra distance and unanticipated hills along the small road along the south/east edge of Loch Tay. The sign in Kenmore said 17 miles to Killin. I measured 33km, which is nearer 21, and the OS map shows about 300m of ascent! One of the short, sharp shocks dragged my batteries down to the BMS cutoff! At rest later on, they showed 33.3V, so without the hill I would have made my camp spot. The following day became sunny quite early, and by the end of it my solar battery was back up to 39V, having powered me the last 37 miles with negligible support from the Shimano.

Rough figures show about 13.5 Wh per mile even in that hilly terrain,with that weight.

 

[guerney]

That's fantastic! Those ascents sound quite the test. Your new solar supported ebike charging system seems to have achieved it's design goals? Or is next up, Land's End to John O Goats? At 37 miles a day, you could do it in 23.6 days! It'll probably provide you with solar powered escapes into the wild, for many years to come. I've squirrelled away details, just in case I ever need to cook up something similar. I'd possibly consider adding four bumpers on the corners, to prevent the solar panels touching the ground, for if it ever does get blown upside down by the wind, or by the wake of very large lorries passing by at high speed.

 

[matthewslack]

That's fantastic! Those ascents sound quite the test. Your new solar supported ebike charging system seems to have achieved it's design goals? Or is next up, Land's End to John O Goats? At 37 miles a day, you could do it in 23.6 days! It'll probably provide you with solar powered escapes into the wild, for many years to come. I've squirrelled away details, just in case I ever need to cook up something similar. I'd possibly consider adding four bumpers on the corners, to prevent the solar panels touching the ground, for if it ever does get blown upside down by the wind, or by the wake of very large lorries passing by at high speed.

The next trip looks more challenging as the weather is not looking too bright. 450 miles or so down to North Wales for a holiday. Unlike this trip, which had a deadline of me back at work today, that one can be more relaxed. I just have to arrive, and if I can do that on 100% solar I should have learnt most of the lessons!

That blue water pipe on the front corners of the trailer has earnt its keep already: without it every little bump would be disaster, with it I am gently guided back to the rightful path! Pictures coming soon.

 

[guerney]

The next trip looks more challenging as the weather is not looking too bright. 450 miles or so down to North Wales for a holiday. Unlike this trip, which had a deadline of me back at work today, that one can be more relaxed. I just have to arrive, and if I can do that on 100% solar I should have learnt most of the lessons!

That blue water pipe on the front corners of the trailer has earnt its keep already: without it every little bump would be disaster, with it I am gently guided back to the rightful path! Pictures coming soon.

Oh no... North Wales?!?!?! Lovely landscape, but in my experience the wind tunnel effect in the valleys, is strong enough to pin people to walls! Horizontal raindrops which travel clean through the ear canal to hit one eardrum, is another of it's delightful features. Perhaps a rapid parachute deployment system would be a sensible addition, for softer solar panel landings? If you're travelling from Scotland, you should be able to avoid most of the speed demon Sterling Moss wannabes on the narrow and snakey A5.

 

[matthewslack]

Oh no... North Wales?!?!?! Lovely landscape, but in my experience the wind tunnel effect in the valleys, is strong enough to pin people to walls! Horizontal raindrops which travel clean through the ear canal to hit one eardrum, is another of it's delightful features. Perhaps a rapid parachute deployment system would be a sensible addition, for softer solar panel landings? If you're travelling from Scotland, you should be able to avoid most of the speed demon Sterling Moss wannabes on the narrow and snakey A5.

Sustrans route 5 most of the way, leaving out the bit up in the hills. But Runcorn bridge instead of 'ferry 'cross the Mersey' this time, as the big trailer won't fit.

 

[matthewslack]

Highest point:



Manual 'tracking' for improved yield during stops, in a second by removing a wheel:



or a few seconds by unhitching for a steeper angle:





Laybys are a fruitful source of campsites this quiet time of year. There were 14 camper vans here when I passed by last June! This time, only three.



Having to stop and charge has it's compensations. Real Food Cafe vegan breakfast. Just testing, still take milk in my tea.



Tomorrow, the technical stuff!

 

[matthewslack]

Infrastructure challenges:



Lovely sculptural entrances on route 78, mostly easy to roll through. But layout is not consistent:



That one needed some manual shoving of wheels sideways. The next one was a tight fit, after several miles without obstacles. Another few inches of width and there would have been a mammoth uphill retracing of route and much cursing. Just fitted!

 

[guerney]

If this is a recurring problem: add a lifting and tilting mechanism under the panels? Could also be useful for manual sun tracking. Or pack a saw to widen problematic narrow apertures?

 

[guerney]

Real Food Cafe vegan breakfast. Just testing, still take milk in my tea.

View attachment 46298

Is that a deep fried white flour pizza base quarter? It'll provide a complete amino acid chain when combined with the spinach, vegan sausage and burger. I like the very slight grilling of the tomato, and those don't look like canned mushrooms. Full on vegans do seem to neurotic and nervy people, I was when I exclusively ate food from the planet Vega for a time - I think it's the dearth of vitamin B12, which isn't easily replaceable in a form that can be absorbed.

 

[matthewslack]

Is that a deep fried white flour pizza base quarter? It'll provide a complete amino acid chain when combined with the spinach, vegan sausage and burger. I like the very slight grilling of the tomato, and those don't look like canned mushrooms. Full on vegans do seem to neurotic and nervy people, I was when I exclusively ate food from the planet Vega for a time - I think it's the dearth of vitamin B12, which isn't easily replaceable in a form that can be absorbed.

That is a tattie scone, alongside Macsween vegetarian haggis and vegetarian sausage. Real mushrooms, which are the difference between the vegan and vegetarian versions - the vegetarians get eggs instead. Everything they use is trying to be locally sourced, and always freshly prepared.

All very tasty, although perhaps a little less filling than the meat version.

 

[matthewslack]

If this is a recurring problem: add a lifting and tilting mechanism under the panels? Could also be useful for manual sun tracking. Or pack a saw to widen problematic narrow apertures?

Version 2 will have tracking panels. For now I will learn where I can go and where I can't. The panels are only 600mm above the road, and most obstructions are a metre or so, too much risk to my £600 panels to lift them over!

 

[guerney]

That is a tattie scone, alongside Macsween vegetarian haggis and vegetarian sausage. Real mushrooms, which are the difference between the vegan and vegetarian versions - the vegetarians get eggs instead. Everything they use is trying to be locally sourced, and always freshly prepared.

All very tasty, although perhaps a little less filling than the meat version.

I'm not veggie or vegan anymore, but I was veggie for about 27 years. Processed vegan food isn't terribly healthy - if they've made vegetarian sausages using soy, that isn't good for male hormones. The Macsween haggis is pretty low in protein:

Macsween | delicious every day - Vegetarian

www.macsween.co.uk

... and the amino acids are not complete without a grain based bun or something, neither are the beans, spinach and mushrooms. As a general rule of thumb:combine a bean with a grain and you have yourself a complete amino acid chain. Athletes do seem to be going vegan these days, for the carb-sourced glycogen in muscle advantage for endurance sports.

 

[guerney]

Version 2 will have tracking panels. For now I will learn where I can go and where I can't. The panels are only 600mm above the road, and most obstructions are a metre or so, too much risk to my £600 panels to lift them over!

You could probably just get an old ironing board with lightweight aluminium legs, put the panels on that atop an alternative board, so that when you meet one of those narrow channels, you could hoist the panels up high and lock - the legs of the ironing board would have to slide on rails within in the trailer.

 

[matthewslack]

You could probably just get an old ironing board with lightweight aluminium legs, put the panels on that atop an alternative board, so that when you meet one of those narrow channels, you could hoist the panels up high and lock - the legs of the ironing board would have to slide on rails within in the trailer.

I'm thinking of a lightweight deck stiff enough to do away with the aluminium panels with a longitudinal tube down the centre line as a pivot, which is linked to the axle ends tetrahedrally. But not until I have run out of learning with version 1.

Tracking is really important at the ends of the year in high latitudes. For now I can simply take a break when the sun comes out and track manually. I get over 200W in full sun, so a sunny hour at the ends of the day is very valuable.