Defining a straight solar EV

[offGridDownUnder]

This is for discussing how to solve a problem. This probably isn't the thread about solving the problem yet - this is about defining the problem.

A primary question is what forum the solving thread would be under - I'm not certain of that yet.

The problem to solve is: how to run an EV/ebike/etrike directly from solar panels while still providing full use of regeneration braking from the motor. WITHOUT using lithium anything - supply chains break down, and I don't expect to be able to rely on a replacement lithium battery. A solution that lasts my lifetime would be best, or a solution that is locally renewable. Perhaps there isn't one - but that's the goal, or the best approximation we can conjure. Solar panels can last over 20 years - that's a good goal. I can easily mount 300W of solar panels as a roof on my trike (ignore getting it through the door then).

I do want to define a practical solution, or a practical experiment - no miracles.

I don't need to hear about whether this is practical or why not, I can tell the sun does not shine sometimes - that can be solved by adding some power storage (battery, anti-matter conversion, etc.) and that is another discussion, and mostly already known. I want to define what is the minimum or best for running off solar panels without muddying the solution so that the solution is well-defined.

Ignore the hills - assume flat ground. I expect we can solve the hills by adding more storage - that is not a part of the problem. The problem is defining what is needed not to charge a battery to then run from - but just run directly off the solar panels, and possibly without any battery at all.

Regeration will require some energy storage - or is dissipation better? - I don't want to constrain this so that ideas may be discussed. My first thought is super-caps, but perhaps SLA is better and achievable. Or NiMh. Or something else. Happy to consider real possible contenders.

Further questions are what types of motor/controller? I have Grin Base/Phaserunners, and hope that can work.

Again, first question is - what forum? @neptronix et al, please move this thread to the best place. If it's already discussed, please point me.

 

[JackFlorey]

This is for discussing how to solve a problem. This probably isn't the thread about solving the problem yet - this is about defining the problem.

A primary question is what forum the solving thread would be under - I'm not certain of that yet.

The problem to solve is: how to run an EV/ebike/etrike directly from solar panels while still providing full use of regeneration braking from the motor. WITHOUT using lithium anything - supply chains break down, and I don't expect to be able to rely on a replacement lithium battery. A solution that lasts my lifetime would be best, or a solution that is locally renewable.

You can't store regen energy without energy storage.

Some options:

Flywheel storage
Compressed energy storage
Lead acid storage
Nickel metal hydride storage

 

[Chalo]

Seems like sodium ion is your thing. Look into that I guess.

 

[JackFlorey]

Seems like sodium ion is your thing. Look into that I guess.

But if he's worried about supply chains, they have similar problems to lithium chemistries.

 

[amberwolf]

I've quoted the specific parts I'm replying to at the bottom, if it helps clarify my reply:

Some thoughts, based on electronics knowledge, failure analysis of assorted posted failures of various equipment, and some speculation of how such a system might practically function (as I don't know of one that has been built to do all this):


Many controllers, probably all the BLDC ones, especially those with regen capability (whether you're using it or not), depend on the impedance of a battery to dampen voltage spikes. Without this, any sudden change in motor current (provided by controller due to change in command or feedback from riding conditions, or sourced from motor due to change in motor speed from riding conditions, etc) could create a voltage increase inside the controller that could cause damage or failure.

It's one of the things that makes certain very specific situations with DD hubmotors (or other clutchless drive systems), common-port BMS'd batteries, and starting from the top of a hill with a full charge potentially dangerous to the controller and anything else on that battery bus.


So it's probably a good idea to have *some* form of battery or low-enough-impedance capacitive storage, with enough unfilled capacity to deal with any situations that arise that will need it. There will have to be something that drains the storage to keep it empty enough to handle regen events. If it has enough total capacity then that can be done after a ride, otherwise it would need to be done during the ride, perhaps by automatically switching it over to a load (dissipative wasting as heat, DC-DC to power lights or accessories or to charge lower voltage portable devices, etc).

If the power converter that's on the panel has low enough impedance on the output side to the controller, and can handle potentially high voltage spikes and damp them, it might be ok without a battery.


Regardless of method chosen, storage or no storage, it may also help to use "surge suppression" techniques, such as MOVs, TVS diodes, TSPDs, inductors, chokes, additional capacitance, etc. on the battery bus of the controller / panel connection, to protect the whole battery bus device set from spike damage during regen events or anything else that happens that causes votlage spikes.







Somewhere around here is a bike that can run only off the power from the panel(s); probably from around 10-12 years ago? I don't recall if they have a battery in the system or not, or if the panel output is directly tied to the controller or goes thru converters, etc. I think they were here in Arizona, but it could've been southern California. If I remember more I'll see if I can find the thread.

AFAIK the absolute minimum to *safely* run the controller from the panel, without considering regen, is some form of MPPT or DC-DC that can regulate the voltage output of the panel to a constant voltage (range) for the controller, regardless of load conditions on the motor the controller is driving, current demanded of the panels, lighting conditions on the panels, etc.

You could run the panels directly to the controller, but then performance and safety of the electronics is determined by all those things always lining up to be within the controller's voltage range, and always lining up to not overload the panel from current demand and not overvolt the controller, etc.



To use dissipative regen with a controller not specifically designed for it (I don't know any that are, but some may exist), you'd need some sort of circuit that switches in the dissipative load *before* the regen event begins, but not so long before that the controller loses power and shuts down, preventing use of it to control the regen. It would also have to switch back to the supply circuit before voltage dropped from regen far enough to shutdown the controller...*and* that event has to shut off the regen function. (if it doesn't, then without the dissipation load it may shoot up in voltage enough to damage something).

That may require some fast switching. I'm not sure if a contactor or relay would be better, or if some form of solid-state-switching. Or, if the voltage source (panels, etc) is tolerant enough of sudden hard loads / current spikes, you could use make-before-break switching and it would be safer for the controller during the switchovers.



If it was a brushed motor, regen can be started without any control over the system, depending on the specific design of the controller, though any time the controller loses power (during switchover, etc) it would be uncontrolled (sometimes called plug braking; though this term gets used for more than that). Once regen begins (after switching to the dissipative load)



I had some other thoughts but I've dozed off several times since I started, so I don't remember what they were.

The problem to solve is: how to run an EV/ebike/etrike directly from solar panels while still providing full use of regeneration braking from the motor.

I want to define what is the minimum or best for running off solar panels without muddying the solution so that the solution is well-defined.

The problem is defining what is needed not to charge a battery to then run from - but just run directly off the solar panels, and possibly without any battery at all.

Regeration will require some energy storage - or is dissipation better?

 

[offGridDownUnder]

So it's probably a good idea to have *some* form of battery or low-enough-impedance capacitive storage, with enough unfilled capacity to deal with any situations that arise that will need it

How would I (or some future enthusiast looking in the knowledgebase) calculate this capacity?

A way to think of this is minimum battery equivalent needed to provide the regeneration capability. This is separate from any driving battery capacity.

 

[neptronix]

The problem to solve is: how to run an EV/ebike/etrike directly from solar panels while still providing full use of regeneration braking from the motor. WITHOUT using lithium anything - supply chains break down, and I don't expect to be able to rely on a replacement lithium battery. A solution that lasts my lifetime would be best, or a solution that is locally renewable. Perhaps there isn't one - but that's the goal, or the best approximation we can conjure. Solar panels can last over 20 years - that's a good goal. I can easily mount 300W of solar panels as a roof on my trike (ignore getting it through the door then).

I think we have bigger problems if we can't acquire a staple of modern life.

You're going to need some sort of battery, as other devices for storing energy have awful density/weight/size. If you use something else, you're severely compromising the vehicle's range/cost/size.

I'd consider lithium titanate, as the battery lifespan can be up to 20 years. The problem with it is that it has half the density of your average lithium battery.

Again, first question is - what forum? @neptronix et al, please move this thread to the best place. If it's already discussed, please point me.

I dunno, i guess it belongs here!

 

[offGridDownUnder]

circuit that switches in the dissipative load *before* the regen event begins, but not so long before that the controller loses power and shuts down, preventing use of it to control the regen

My regen is initiated by the switches attached to my brake levers. Currently, they signal my motor controller - perhaps they could rather initiate some other actions changing the circuit connections to configure for other requirements - such as switching dissipation in and ?

My controllers can also initiate regen under other circumstances, but I'm not insisting on using what I have. I want to understand the problem domain.

Part of the issue here is to fill in the information about what controllers can and can't be used for this - and in my case fill in my understanding of how controllers work, types of motors, etc.

There are other people who also don't know this, so I want to develop a full description of whatever turns out to be a viable part of a solution, and reasons why other approaches can't contribute. I'm not looking for a list of parts to buy - at least until a possible approach has been defined.

 

[offGridDownUnder]

I think we have bigger problems if we can't acquire a staple of modern life.

Yeah. We do.

I'd consider lithium titanate, as the battery lifespan can be up to 20 years. The problem with it is that it has half the density of your average lithium battery.

So, how large would such a battery need to be to provide the regen capability, and leave the question of what provides the driving power as a separate question? How would this be calculated?

As I mentioned, I will use solar panels as the main drive power source. I don't need to hear that this only works when the sun shines. I am investigating what is needed for this design.

 

[amberwolf]

How would I (or some future enthusiast looking in the knowledgebase) calculate this capacity?

A way to think of this is minimum battery equivalent needed to provide the regeneration capability. This is separate from any driving battery capacity.

You'd have to guesstimate the amount of regen you'd use, as a function of capacity (so either in Ah or Wh; Ah makes things simpler later).

So you'd choose what regen current you'd need for the braking force you're after with your drive system and riding conditions, and estimate how much actual time the regen would be used for. If it's just for braking during riding in traffic, then it's probably just very short (a second or two) engagements intermittently throughout a ride. If it's for maintaining speed on downhills, it's probably going to go on for several seconds or even much longer depending on the length of the descent.

Total up all those seconds for how many fractions of an hour or how many hours, then multiply that by the Amps you use for the regen current, to get Ah. That's a rough guesstimate of minimum capacity required. Since storage degrades over time, I'd get at least twice that capacity. If you think your riding places / style / conditions / etc will change over time, guesstimate using the worst case you might expect to ever need.

 

[amberwolf]

My regen is initiated by the switches attached to my brake levers. Currently, they signal my motor controller - perhaps they could rather initiate some other actions changing the circuit connections to configure for other requirements - such as switching dissipation in and ?

If you use a solution that requires swithching a dissipation device or other regen destination in and out, then yeah, you'd need your braking swtich to engage that switcing system just before your braking control begins telling the controller to brake, and disengages it just before the brkaing controll stops telling the controller to brake.

That's assuming a system requireing break-before-make switching to avoid damaging / overloading the panel source. If that's not an isseu you can use make-before0break swithcing which means you don't need a delaying control, just a raw swithing mechanism between panel source and dissipative load. .

My controllers can also initiate regen under other circumstances, but I'm not insisting on using what I have. I want to understand the problem domain.

Every controller is a little different, hardware, software, etc., and anything that's programmable is more configurable for a specific setup but more complex to set up and to make sure all it's settings are what you need for a specific situation...rather than adapting the rest of the system and situation to a "hard coded" hardware-only controller's needs and abilities.

Part of the issue here is to fill in the information about what controllers can and can't be used for this - and in my case fill in my understanding of how controllers work, types of motors, etc.

The latter kinda exceeds the possible scope of any replies I could make; that would be a (not small) book. Your best bet is to read up on the various controller design and build threads, and the threads and posts about various motor types, as well as articles such as you can find on wikipedia about the different motor types.

The former: I don't know offhand of any DC-powered controllers that literally can't be used, as long as you provide all the extra stuff any particular system may require for your specific conditions and usage, which you'd have to figure out once you know which contorller and solar system you're using, and the specifics of the conditions that will happen during your usage, and how those will react.



If you are trying to limit the field of possibilities to simplifiy the task, you'd need decide some parts of the system so yuou know how they work, then figure out the rest of the ssytem based on the limitations that imposes.

 

[bananu7]

I second flywheel storage for this application; it's an interesting thought experiment.

Flywheels can store absolutely massive amounts of energy and have a long and successful history of being used in vehicles from bikes, buses, through satellites. With enough spent on bearings etc., you can store almost arbitrarily high amounts of energy in one, and it will operate virtually forever. Converting the energy back can be done mechanically or electrically, both interesting to calculate and solve.

Speaking of satellites, though, there's effectively only one source of energy on earth and that's nuclear fusion. Everything else we call "renewable" energy is a result of fusing hydrogen. If you then take the leap to "all energy is nuclear", then a truly lifetime vehicle could be powered by an RTG - no sun needed.

 

[neptronix]

I second flywheel storage for this application; it's an interesting thought experiment.

Size and gyroscopic effects are going to be a huge problem, in addition to safety ( you are riding next to an extremely powerful grenade, therefore you need a way to shield it, which would be very heavy ).

A 10lbs fly wheel can rip through a car's engine. 10lbs might not be enough for a considerable amount of energy on an ebike.

There are a lot of engineering problems to solve with that route..

 

[JackFlorey]

How would I (or some future enthusiast looking in the knowledgebase) calculate this capacity?

A way to think of this is minimum battery equivalent needed to provide the regeneration capability. This is separate from any driving battery capacity.

Sufficient energy storage to store the energy from the longest anticipated descent.

Low enough impedance that the voltage does not rise more than a volt or so during strongest anticipated braking.

Both are easy to calculate.

 

[neptronix]

Lithium Titanate can have a charge rate up to 10C, has good weather resistance, a huge C rate for output ( meaning it makes very little heat at high power )

20A of regen current is extremely strong, a 4ah battery with 10C in/out would be totally sufficient.

A grin all axle or 9C clone would make for an excellent motor because they are DDs that have very low drag ( you may lose 1-2mph of pedaling speed ). If you live in Perth, you don't live in a hilly region, so a DD would perform great there.

 

[JackFlorey]

Lithium Titanate can have a charge rate up to 10C, has good weather resistance, a huge C rate for output ( meaning it makes very little heat at high power )

Yeah, I thought of that, as well as LFP (cheaper.) Not sure why he wants to avoid all lithium chemistries.

 

[neptronix]

Peak lithium theory incoming?

Personally i'd love to have a battery that lasts 20 years... i would not attempt to buy such a thing.. because the rate of change in technology is so high it will be obsoleted like a computer in the mid 90's during the era where processors were getting ~2x faster per year..

..but there is a few lithium chemistries that fit the bill of.. 'will last a damned long time'

 

[Chalo]

Personally i'd love to have a battery that lasts 20 years... i would not attempt to buy such a thing.. because the rate of change in technology is so high it will be obsoleted like a computer in the mid 90's during the era where processors were getting ~2x faster per year..

I would buy that if the price were reasonable. "Obsolete" ≠ useless! Almost all of my bikes, cars, motorcycles, houses etc. have been obsolete by the time I got them. What we do with computers is really different from 30 years ago, but bikes? In the way they've changed (not that much, honestly) it's about all in the direction of foolishness.

 

[neptronix]

Bikes have not changed much, but for me, wanting to go long distances, at high speeds, is pretty important for an evehicle.
Generally my bikes have an extreme emphasis on efficiency and i ride in a tuck and pedal like a monster to just barely meet my speed/range needs out here in the land of no bike lanes suburb. If i had a motorcycle, i'd have the same range problems. And battery technology has progressed at a slug's rate for the last decade, up until now. So i've been waiting for at least a +50% for well over a decade.

If you were to sell me a 33% denser battery than i currently have, i'd pay a 33% premium for the privilege.

But that's just like, my opinion, man. OP probably has very different priorities.

 

[offGridDownUnder]

Not sure why he wants to avoid all lithium chemistries.

In this discussion. Every decision cuts off possible approaches, and this problem aspect (solar power plus regeneration) does not appear to be well understood by itself.

I am not seeking a solution for a EV I have now. I want to define the characteristics of the problem so I and others may solve it for varying situations - choice of vehicle, available technologies, longevity, appropriateness and effectiveness (not efficiency - that's a different word than effectiveness) etc.

It is true I am beginning with what I know and what I have chosen, but I am consciously backing off from that where I can to permit consideration of what the core problem is, and what is involved - rather than what is constrained because of choices that I, personally, have made to date.

So, the constraints I am choosing are:

• Solar power for main propulsion - 20+ year solar panels are available now.
• Electric motor - to consume the solar electricity.
• Regenerative braking - which is available from some electric motors (and is a constraint on motor choice) as this is known to avoid consumption of brake pads and rotors without consuming other aspects - this need not consume the motor, for example.
• No constraint on the mechanism of regeneration storage or dissipation - what is possible, rather than what is convenient today without understanding the problem further.
• As I'm choosing the problem, I want to maximise utility and minimise consumption of resources. Why not? Too much is thrown away now, and we have just gone through several years of experience when supply chains were disrupted. Our go-to Li-ion batteries do not last for 20+ years - they are a consumable, and if there is a better approach, then let's flush it out. Can this be done without a technologically complex battery that requires a fairly large supply chain and economies of scale that preclude local manufacture? That would be great! Apart from the few very top-level foundaries, Li-ion batteries are prone to spontaneous combustion - better to use something else if we can. They are poisonous, too, when dumped into the environment.

My Grin All-Axle can be damaged by catastrophic events (fire, hammers, cars, lightning) and by poor electronic design (of the surrounding components and system), but apart from that, it only has bearings that can wear out - and I can easily hold on to 20 years of bearings and replace them myself. Some other motors have drawbacks (gears, no regen) and some are as well- conceived as the All-Axle. Perhaps the problem only permits the use of brushed motors? I want to know that and have it stated so others can make choices when designing their own transportation solutions.

This problem is real enough to lead to real experiments, to provoke statements of real experience, and to provide concrete information and solutions. It's not everything about EVs, but it's applicable to many facets, so it provides a useful focus to gather knowledge. That can be harvested and put in the knowledgebase so it's available for others.

 

[offGridDownUnder]

I've seen some suggestion that using brushed electric motors rather than brushless phased motors has some fundamental differences that make this problem different and possibly simpler.

If this is so, can someone explain what the difference is and how it changes the approach?

 

[JackFlorey]

• As I'm choosing the problem, I want to maximise utility and minimise consumption of resources. Why not? Too much is thrown away now, and we have just gone through several years of experience when supply chains were disrupted. Our go-to Li-ion batteries do not last for 20+ years - they are a consumable, and if there is a better approach, then let's flush it out.

Sure. Lithium titanate, as Nep mentioned above. They last for 20 years or 30,000 cycles.

 

[JackFlorey]

I've seen some suggestion that using brushed electric motors rather than brushless phased motors has some fundamental differences that make this problem different and possibly simpler.

Pluses for brushed motors:
-Simpler controller, just a chopper basically.

Minuses for brushed motors:
-Less efficient
-They don't last long before brushes need replacing.
-Higher EMI.
-Cannot seal the hub (brush dust has to be cleaned out.)
-Regen far more difficult.

 

[Hwy89]

@amberwolf; I think you were referring to parajared and the thread entitled”parajared’s solar trike”
He made a trip of a couple hundred miles and did manage to be direct solar powered for some distances, but he did have lithium batteries.

 

[PaPaSteve]

Energy storage . . .
Lead acid batteries are :
Well understood chemistries
Low cost
Abundantly available
Nearly 100% recyclable