Introduction and advice on solar charged go kart

[florida cracker]

Simple introduction, I am a teacher that has taken over sponsorship of an engineering club project. Nobody else wanted to do it and it looked interesting so here I am.

Project is a solar powered go kart.... I am updating the solar panels and electronics as rules have changed to allow for more solar panel and our old electronics are just that, old

We are allowed to run up to 1050 watt of panels and are limited to 720 watt hours of battery

I am an old gearhead and while I understand how to make things go fast, solar power and electrical engineering is the black arts for me.

I have kids researching changes to be made to charging system but I need to know what they are looking at so I can help when needed. I see that Renogy is the only company that makes flexible 175 watt panels so it seems like a no-brainer to go with 6 of those. Charge controller is next, would 60 amp box do the job? How much solar power can the 60 amp controller handle??

How would be the best way to wire panels? 3x3 or 2x2x2 to get either 24 or 36 volts to charge controller to sort out??

Lots of questions to come I am sure

 

[MichaelK]

We are allowed to run up to 1050 watt of panels and are limited to 720 watt hours of battery

I have kids researching changes to be made to charging system but I need to know what they are looking at so I can help when needed. I see that Renogy is the only company that makes flexible 175 watt panels so it seems like a no-brainer to go with 6 of those. Charge controller is next, would 60 amp box do the job? How much solar power can the 60 amp controller handle??

How would be the best way to wire panels? 3x3 or 2x2x2 to get either 24 or 36 volts to charge controller to sort out??

Lots of questions to come I am sure

First off, will the cart be powered via a docking station while parked, or is this live power, with the cart carrying the panels?

Having previous experience buying Renogy, my advice would be to stay away from them. Just about every other panel I've tested performs better than Renogy.

Are you limited to 12VDC, or can you have 24V? Panels almost never put out their rated output, so you need fudgefactor (FF) for compensation. For panels facing directly at the sun, I use 85%. For panels laying flat (horizontal) 60%.

For your above question what can a 60A controller handle, the simple answer is 12V X 60A = 720W of panels. In the real-world, utilizing the charging voltage and a FF the answer is more like (60A X 13Vcharging)/60% = 1300W. Hey, that is almost double.

Are the motors on these things 12V, or some other voltage? In general, you'd wire strings of panels in series to reduce resistance loss. If you can utilize a 24V motor, I'd rather see it running at 24V instead of 12V

 

[florida cracker]

First off, will the cart be powered via a docking station while parked, or is this live power, with the cart carrying the panels?

Having previous experience buying Renogy, my advice would be to stay away from them. Just about every other panel I've tested performs better than Renogy.

Are you limited to 12VDC, or can you have 24V? Panels almost never put out their rated output, so you need fudgefactor (FF) for compensation. For panels facing directly at the sun, I use 85%. For panels laying flat (horizontal) 60%.

For your above question what can a 60A controller handle, the simple answer is 12V X 60A = 720W of panels. In the real-world, utilizing the charging voltage and a FF the answer is more like (60A X 13Vcharging)/60% = 1300W. Hey, that is almost double.

Are the motors on these things 12V, or some other voltage? In general, you'd wire strings of panels in series to reduce resistance loss. If you can utilize a 24V motor, I'd rather see it running at 24V instead of 12V

Kart is self contained and carries panels and all charging equipment with it, hence the desire to go with flexible panels as it will save us 100 pounds that is mounted at the highest point on the kart. If you would not recommend Renogy, who would you recommend that makes something we would get comparable power from that is flexible? Keep in mind that we will not be able to point these right at the sun and while they are not completely horizontal, they are not far from it. We may be able to design something to allow us to adjust the angle between heats to allow us to point directly at the sun though.

Wiring panels is something of an unknown to me, I don't know if I could wire them all in series and feed that to the controller hence running two sets of three panels (wired in series) parallel to get me to 36volts and double amps to start and let controller sort it out

The parameters of the race are as follows: 4 heats that start every 30 minutes, two laps per heat at approx 1.88 miles per lap. each heat took us roughly 10 minutes to complete leaving us the remaining 20 minutes to just sit and re-charge.

We competed this past year by simply wiring the kart as it sat and trying to decrease rolling resistance as much as possible as we had a little over a month to work and neither myself or the students knew much about any of this. We came in second overall to teams that have been spending money hand over fist.

We do run a 24 volt motor and will be keeping that but putting newer speed control on it so we can program it a little bit. Will be experimenting with sprockets as well to fine tune the gearing (that might be the only part of this whole thing I understand, lol) I would like to run at 48 volts just to get the sped but battery limitations kind of make that unreasonable

 

[MichaelK]

A good rule of thumb is to pair your panels to a MPPT controller such that the raw solar voltage is at least 50% higher than the voltage the battery wants to charge at. So, for a 24V battery, panels that are putting out at least 36V are appropriate. You might do this by either selecting a panel with a Vmp >36V, or wire two 18V panels in series to get 36V. Keep in mind that all series strings need to be the same voltage, so you can pair two, four, or six panels, but not three or five. On the other hand, three panels in a single series string might be fine if the Voc is less than your controller's limit. This is where design and careful selection of components will make a big difference. I'm assuming that the physical space on the cart is going to be the most critical factor, so you just have to work that out on your own.

Since this is about racing, I'd think that you'd want to pour in as many amps into the motor as you can, so I'd select a controller with a higher amp limit than lower? Plus, have a battery that can also discharge at the highest rate. This sounds like the perfect application for a Li battery pack. Not knowing any better, I'd suggest selecting the brand/model that has the highest discharge capacity?

If you are stuck with flexible panels, I have no advice for you other than use at least a 50% fudgefactor in your calculations. Meaning, if your math says you need 250W of power, then you'd better install at least 500W of panels.

The parameters of the race are as follows: 4 heats that start every 30 minutes, two laps per heat at approx 1.88 miles per lap. each heat took us roughly 10 minutes to complete leaving us the remaining 20 minutes to just sit and re-charge.

I'd guess that there will need to be an inrush of current to get the cart started, but once moving, most of the power will be coming from the panels. Since you have a 720Wh limit for your battery, that works out to be 720Wh/24V = 30Ah battery, which is small. If you are creative enough, you might find space for the 1050W of panels.

Since you will be sitting for 20 minutes to recharge, is there the possibility that you could create a second set of panels to serve as a "docking station".

 

[florida cracker]

A good rule of thumb is to pair your panels to a MPPT controller such that the raw solar voltage is at least 50% higher than the voltage the battery wants to charge at. So, for a 24V battery, panels that are putting out at least 36V are appropriate. You might do this by either selecting a panel with a Vmp >36V, or wire two 18V panels in series to get 36V. Keep in mind that all series strings need to be the same voltage, so you can pair two, four, or six panels, but not three or five. On the other hand, three panels in a single series string might be fine if the Voc is less than your controller's limit. This is where design and careful selection of components will make a big difference. I'm assuming that the physical space on the cart is going to be the most critical factor, so you just have to work that out on your own.

Since this is about racing, I'd think that you'd want to pour in as many amps into the motor as you can, so I'd select a controller with a higher amp limit than lower? Plus, have a battery that can also discharge at the highest rate. This sounds like the perfect application for a Li battery pack. Not knowing any better, I'd suggest selecting the brand/model that has the highest discharge capacity?

If you are stuck with flexible panels, I have no advice for you other than use at least a 50% fudgefactor in your calculations. Meaning, if your math says you need 250W of power, then you'd better install at least 500W of panels.

The parameters of the race are as follows: 4 heats that start every 30 minutes, two laps per heat at approx 1.88 miles per lap. each heat took us roughly 10 minutes to complete leaving us the remaining 20 minutes to just sit and re-charge.

I'd guess that there will need to be an inrush of current to get the cart started, but once moving, most of the power will be coming from the panels. Since you have a 720Wh limit for your battery, that works out to be 720Wh/24V = 30Ah battery, which is small. If you are creative enough, you might find space for the 1050W of panels.

Since you will be sitting for 20 minutes to recharge, is there the possibility that you could create a second set of panels to serve as a "docking station".

It's not that I am stuck with flexible panels as much as I would love to be able to shed that extra 100 pounds from the top of the kart. It has 3 solid 270 watt panels up there now and they are the heaviest thing on the kart and the highest point....

The kart is basically battery powered throughout the run. From what we could understand from our Bluesky 3024 charge controller, batteries got down to between 50-60% at the end of a heat and it is more of a marathon (short marathon but you get the picture) than a sprint

What I know the least about with this thing is how fast could I reasonably expect this to charge that battery bank assuming South Florida sun in April/May. I am thinking we should be able to design a mounting system that would allow panels to be tilted between heats to get maximum sun

edit: reading this thread now

Flexible Panels hit Prime Time?

I think that would meet Gnubie's elevation requirement. But for me at least... it would need to come with training wheels or other balance system; preferably something high tech like this gyroscope motorcycle. Whoa... that would be a weird feeling for cycle riders when entering a sweeping...

diysolarforum.com

 

[NVS]

You could use these panels and use them as body side panels on an angle to catch more sun. You get 2 144watt panels for $200 and they are glue or velcro mounted.

2-Pack Uni-solar PVL-144 144w Amorphous Flexible Solar Panel

We are down to our last pallet. These solar panels are PERFECT for many applications because they are flexible, can be glued down, and work for many different surfaces curved and flat. The best part is these can be shipped Fedex ground and we fit 2 in a box. No expensive freight. You get 2 solar...

batteryhookup.com

What are you using for your batteries?

 

[florida cracker]

You could use these panels and use them as body side panels on an angle to catch more sun. You get 2 144watt panels for $200 and they are glue or velcro mounted.

2-Pack Uni-solar PVL-144 144w Amorphous Flexible Solar Panel

We are down to our last pallet. These solar panels are PERFECT for many applications because they are flexible, can be glued down, and work for many different surfaces curved and flat. The best part is these can be shipped Fedex ground and we fit 2 in a box. No expensive freight. You get 2 solar...

batteryhookup.com

What are you using for your batteries?

Last year we were limited to sealed lead acid batteries with a maximum of 720wh (we used two 12v 30ah batteries). This year they are going to allow lithium type batteries but wh limit would remain

Those panels look cool but we are not planning on having any side panels....

 

[curiouscarbon]

cool project!! ?

 

[florida cracker]

cool project!! ?

I thought so to, that's how I ended up sponsoring the damn thing

 

[42OhmsPA]

Nice project, I learned so much from all the engineering / technical classes I took back in HS.

For something like this I'd be looking for high discharge batteries and high current chargers, as others have stated. If you're allowed to source online check batteryhookup, they normally have high C rate cells and packs that may work perfectly for your project.
Iirc they had tubular panels a while back, probably wouldn't be economical for a school project with shipping unless your local.
Also as others have stated, hinging a few regular panels so you can deploy them during pit stops would be a great concept, you could even introduce an aerodynamics lesson into it.
Good luck. Keep us updated.

 

[florida cracker]

Nice project, I learned so much from all the engineering / technical classes I took back in HS.

For something like this I'd be looking for high discharge batteries and high current chargers, as others have stated. If you're allowed to source online check batteryhookup, they normally have high C rate cells and packs that may work perfectly for your project.
Iirc they had tubular panels a while back, probably wouldn't be economical for a school project with shipping unless your local.
Also as others have stated, hinging a few regular panels so you can deploy them during pit stops would be a great concept, you could even introduce an aerodynamics lesson into it.
Good luck. Keep us updated.

If we were to put panels on hinges to open during pit stop time, we would lose whatever charging time we spend running that heat. The faster you run the heats, the more charge time you get between the heats. problem is much like any form of racing, going fast costs.... Power in this instance is the cost.

This is why maximizing charge capacity/speed is a big deal (flexible panels helps lower weight and center of gravity so it isn't top heavy

If we can get charging system optimized, the going fast is easy

 

[houseofancients]

check out vextex karts, their 18650 powered racing kart is about to hit the market

 

[florida cracker]

check out vextex karts, their 18650 powered racing kart is about to hit the market

It's a school project, the kids are going to be designing and building this (we already have a working kart so designing and modifying might be a better way to put it).... I am simply the sponsor that wants to know what this thing is all about and how to steer them in the right directions

 

[houseofancients]

they have documented their entire journey, and a such i may help you in yours

 

[florida cracker]

they have documented their entire journey, and a such i may help you in yours

Vextex or Vertex?? can't find anything on a search

if you have a link, I would appreciate it

 

[florida cracker]

Time to revisit this thread, it seems that the rules changes I was expecting are what is going to happen. 1050 Watt in panels and same 720ah in battery.

I still have not seen anything that seems to be better in a flexible panel than the Renogy 175. I do understand that flexible panels don't put out as much power as solid but they also won't need as much power to mover them around either and the Kart will be safer with less weight up high. The district has already sent us Renogy Rover 60 amp SCC.

Would like to know how would be the most productive way to wire them together 6s or 3s2p (hope I got the terminology right).

Posting Specs for Panels:




Specs for SCC:

 

[curiouscarbon]

Vextex or Vertex?? can't find anything on a search

if you have a link, I would appreciate it

Vextrek

We sell bolt-on electric drivetrain and lithium ion battery kits to convert gas powered go karts to electric power.

vextrek.com

 

[florida cracker]

Vextrek

We sell bolt-on electric drivetrain and lithium ion battery kits to convert gas powered go karts to electric power.

vextrek.com

While that does look interesting, there isn't a lot of overlap in what they are doing to what we are doing.... I will show this to students just to see what they think of it though

I like speed as much as the next guy but 100 mph on a go kart??

I need advice on the solar part of this thing more than anything

 

[12VoltInstalls]

Have you considered something like these?

I don’t think those are exactly what you want but the idea is individual solar modules that you can configure however you’d like on the ‘body’ of the cart and series/parallel to whatever electrical output you need. Plus the students get to learn about diodes and string performance.

Also, potentially saving the weight of commercial panels because there’s be no frame will increase performance. You could even laminate your own glass or polycarbonate wafers to protect them (or leave them as is?)
I can see weight and insolence advantages that could make yours a winner over others who may use the manufactured panels.

 

[florida cracker]

Have you considered something like these?

I don’t think those are exactly what you want but the idea is individual solar modules that you can configure however you’d like on the ‘body’ of the cart and series/parallel to whatever electrical output you need. Plus the students get to learn about diodes and string performance.

Also, potentially saving the weight of commercial panels because there’s be no frame will increase performance. You could even laminate your own glass or polycarbonate wafers to protect them (or leave them as is?)
I can see weight and insolence advantages that could make yours a winner over others who may use the manufactured panels.

They do have rules prohibiting building your own batteries so they can be verified to fall inside the rules, Don't see rule prohibiting building panels but they do have a specific rating they have to fall under...

Interesting