[Project] Extending EV range by offsetting auxiliary 12v loads using solar

meetyg

Solar Enthusiast
Well, I have this crazy idea that came up a while ago, and now I'm going forward to implement it.

The motivation is like this:
We all love solar, many of us like/have EVs. We would love to put some solar power to use in order to extend our EV range.
But as some of us know, connecting solar to an EVs high-voltage battery system is complicated, not so practical for the amount of solar panels we can mount in/on an average car, not to mention dangerous.
So my idea was to offload some the 12v loads of the EV (which can get as high as 20-30 amps at times) using solar. Having that most if not all EVs have a 12v system, that is supplied by an on-board DC-DC converter (taking high-voltage of the main battery pack and supplying 12v output), offsetting some if this load will in effect save some of the HV battery's capacity, and extending overall range.

I started a thread a while ago on an EV forum, so for brevity, you could just start reading about the idea there (I suggest you start from this post of mine, as my ideas have changed a bit from the original post, but feel free to read it from the beginning):


Anyways, I would like to hear your opinions and thoughts about this.
I'm adding a basic schematic of my idea here. I will keep you posted as I advance in this experimental project of mine :cool:

SolarRE.png
 

eXodus

Solar Addict
Many people in the BMW i3 forums are replacing their 12V 20AH Lead batteries directly with 12V 20AH LFP batteries.

Plugn Play swap. Even people with the small range extender engine, have no issues with a LFP.
Why do you want to keep the lead battery? Do you got a hybrid?

Adding a solar panel sounds interesting for street side parking - but I'm always parked under cover in a garage - so no use for that.
 

meetyg

Solar Enthusiast
Many people in the BMW i3 forums are replacing their 12V 20AH Lead batteries directly with 12V 20AH LFP batteries.

Plugn Play swap. Even people with the small range extender engine, have no issues with a LFP.
Why do you want to keep the lead battery? Do you got a hybrid?

Adding a solar panel sounds interesting for street side parking - but I'm always parked under cover in a garage - so no use for that.
I have a BEV (totally electric).

I suppose that thos i3 owners do that in order to get better battery life than lead-acid. But I'm not worried about that, the car is fairly new.
I'm just looking to extend the range a bit using solar. I'm keeping the 12v lead-acid (SLA) because I'm trying not to make any permanent modifications, and it won't help extend the range anyways.
 

eXodus

Solar Addict
I have a BEV (totally electric).

I suppose that thos i3 owners do that in order to get better battery life than lead-acid. But I'm not worried about that, the car is fairly new.
I'm just looking to extend the range a bit using solar. I'm keeping the 12v lead-acid (SLA) because I'm trying not to make any permanent modifications, and it won't help extend the range anyways.
changing a battery I wouldn't count under permanent modifications :p

Adding a second battery is much more involved. Just switching the primary SLA to LFP already helps with range - since they discharge slower between stops.

Then adding a solar panel to charge that battery should be easy.
 

meetyg

Solar Enthusiast
Still, what will happen is that the on-board DC-DC converter (step down) will supply the load using the HV battery capacity.

I am trying to overcome it, basically making it supply minimal current to the 12v system by supplying a parallel power source (with voltage a bit higher) which will supply most of the load untill the "buffer" battery is empty (and no solar energy is being produced at that moment).
 

eXodus

Solar Addict
Still, what will happen is that the on-board DC-DC converter (step down) will supply the load using the HV battery capacity.

I am trying to overcome it, basically making it supply minimal current to the 12v system by supplying a parallel power source (with voltage a bit higher) which will supply most of the load untill the "buffer" battery is empty (and no solar energy is being produced at that moment).
the 12V Lithium swap does that almost automatically. A fully charged LFP sits somewhere around 13.2-4V
While a fully charged SLA sits a 12.8V

So they EVs DC-DC charge controller "sees" an already full battery even when the LFP is only at 75%
SOCVoltage
75%12.85V
50%12.75V
20%12.55V
10%12.24V
5%11.90V

Just try it - switch your SLA to a LFP and add the solar. You can still add later the curcuit you proposed - but in my opinion it is not necessary.
Less parts - more reliable.
 

meetyg

Solar Enthusiast
the 12V Lithium swap does that almost automatically. A fully charged LFP sits somewhere around 13.2-4V
While a fully charged SLA sits a 12.8V

So they EVs DC-DC charge controller "sees" an already full battery even when the LFP is only at 75%
SOCVoltage
75%12.85V
50%12.75V
20%12.55V
10%12.24V
5%11.90V

Just try it - switch your SLA to a LFP and add the solar. You can still add later the curcuit you proposed - but in my opinion it is not necessary.
Less parts - more reliable.
I understand what you are saying...
You are correct that if I just swap the SLA to LFP and add solar, less energy will be needed from the onboard DC-DC to charge up the LFP, as it will seem to be at a higher SOC to the DC-DC.
But still, the onboard DC-DC will supply all the other loads, therefore taking power from the HV battery.
That was my original idea, but as mentioned I decided to add a buffer battery (using LFP for safety and less weight) so that during most of my driving time, 12v loads will be supplied from it, basically bypassing the onboard DC-DC converter.

From my testing, it seems that the DC-DC supplies a constant 14.2-14.4 volts to the 12v system. I presume that if I add a buffer battery with my own DC-DC step up converter (setting its voltage to ~14.4 - 14.6v), it will supply the 12v loads and the onboard DC-DC will just "rest".

Just like charging batteries, you need a slightly higher voltage in order to cause current to flow.
In short, if I just connected an LFP in parallel (or swapped out the the SLA for LFP), it wouldn't overcome the onboard DC-DC.
 

eXodus

Solar Addict
From my testing, it seems that the DC-DC supplies a constant 14.2-14.4 volts to the 12v system. I presume that if I add a buffer battery with my own DC-DC step up converter (setting its voltage to ~14.4 - 14.6v), it will supply the 12v loads and the onboard DC-DC will just "rest".
Ok, now I got a better understand of you want to do.

Not only you want to not charge the 12V from the High voltage, you also want to supply all loads while driving from the auxiliary 12V?

Have ever measured about how many watt hours per hour of drive we are looking at? A shunt between the DC/DC and the vehicle 12V should give you some insight.

Are we talking a few watt hours or a kwh?
 

meetyg

Solar Enthusiast
Great, finally I was able to explain correctly :cool:

I have done some testing using a clamp meter on the positive lead of the 12v battery (which the DC-DC is connected to in parallel) the car was fully on.
The minimal load (all possible accessories off) was around 5 amps.
Then I turned on the infotainment, headlights, A/C fan on high. This showed about 20 amps going out.

I suppose that if I were to connect my phone to the charger and maybe press the brakes, it could have gone even higher.

So at 12 volts we're are talking about around 60 to 300 watts consumption just by the 12v system.
So let's say the average is around 180 watts.

In comparison, my EV consumes an average of 155Wh per KM from the HV battery.

If I will be able to offset this load from the HV battery, let's say even only once a day, I will get 1 KM per day.

Most of my trips are from home to work and back, about 45 minute drive. But at work the car sits in an open parking lot with almost no shade for several hours. That's when the buffer battery will get fill up the most, and ready to supply power for the evening drive home.

A bit complicated to explain but pretty cool, isn't it ?
 

eXodus

Solar Addict
If I will be able to offset this load from the HV battery, let's say even only once a day, I will get 1 KM per day.
since you are speaking of Km you are probably in Europe with higher electricity prices?

Are you at the edge of your range are you doing this as science experiment?

So at 12 volts we're are talking about around 60 to 300 watts consumption just by the 12v system.
So let's say the average is around 180 watts.
180w per hour - at your 45 minutes (total / day or per trip?) that's 135wh. The good thing about that low of a consumption per trip - is that you neither need a large solar panel (weight and drag) nor a large battery (weight)

But you need 7+ trips to save one kwh.
I know in Germany they got like 30 cents per kwh - you still need a lot of of patients that your systems makes any financial sense.
Removing the floor mats to save some weight is probably more effective for total power consumption.

If you do this as proof of concept or as learning hobby - don't be discouraged :) This is my opinion from my pure Return on Invest point of view.

I'm doing a lot of solar projects which make no financial sense whatsoever, to learn the technology.

My initial point still stands - I would swap an LFP first and measure again - that might already gain you that 1km you are looking for - less weight and far more efficient charging.
 

MattiFin

Solar Addict
since you are speaking of Km you are probably in Europe with higher electricity prices?

Are you at the edge of your range are you doing this as science experiment?


180w per hour - at your 45 minutes (total / day or per trip?) that's 135wh. The good thing about that low of a consumption per trip - is that you neither need a large solar panel (weight and drag) nor a large battery (weight)

But you need 7+ trips to save one kwh.
I know in Germany they got like 30 cents per kwh - you still need a lot of of patients that your systems makes any financial sense.
Removing the floor mats to save some weight is probably more effective for total power consumption.

If you do this as proof of concept or as learning hobby - don't be discouraged :) This is my opinion from my pure Return on Invest point of view.

I'm doing a lot of solar projects which make no financial sense whatsoever, to learn the technology.

My initial point still stands - I would swap an LFP first and measure again - that might already gain you that 1km you are looking for - less weight and far more efficient charging.
changing the tires to narrowest low rolling resistace tires probably would make bigger difference but you dont get to play with solar..
 

meetyg

Solar Enthusiast
since you are speaking of Km you are probably in Europe with higher electricity prices?

Are you at the edge of your range are you doing this as science experiment?


180w per hour - at your 45 minutes (total / day or per trip?) that's 135wh. The good thing about that low of a consumption per trip - is that you neither need a large solar panel (weight and drag) nor a large battery (weight)

But you need 7+ trips to save one kwh.
I know in Germany they got like 30 cents per kwh - you still need a lot of of patients that your systems makes any financial sense.
Removing the floor mats to save some weight is probably more effective for total power consumption.

If you do this as proof of concept or as learning hobby - don't be discouraged :) This is my opinion from my pure Return on Invest point of view.

I'm doing a lot of solar projects which make no financial sense whatsoever, to learn the technology.

My initial point still stands - I would swap an LFP first and measure again - that might already gain you that 1km you are looking for - less weight and far more efficient charging.

OK, here goes:
1. My drive to/from work is about 45 minutes (35 KMs) each direction. That would be an hour and a half total driving per day.

2. My electricy prices are fairly low, at around $0.16 USD per KWh.

3. I'm not at the end of my range. It would be nice though to have a few KMs to spare each week. There are some owners of older EVs (like Nissan Leaf) that have very little range because of battery degradation. You can find some of these guys that put some solar panels on their cars, added a battery bank and a DC to AC inverter. The solar charges up the battery bank during the day, and they charge up the EV using a mobile charger connected to the inverter.
It's pretty crazy, adds alot of weight and drag, and is inefficient in my opinion. But I can understand these guys. It's either go through all this trouble with solar, or have the battery replaced for thousands if not tens of thousands of dollars, just to get the range needed for daily driving.

4. I know that this is not going to be cost effective. I am trying to cut costs down, mainly ordering parts (that have good reviews and should be OK quality) from Aliexpress. But the return of investment on this could be some good years. But again, it's not for saving money.
It's not that I have money to waste, but everyone has their hobbies, so you could look at it as a hobby of mine.

It's mainly an experiment, and for fun.
If it's successful, I wouldn't see a reason for EV manufacturers not to do this. It would probably be more efficient and cost effective at scale during the manufacturing process than my solution. The advantage here is that while there are a few EV makers trying to integrate solar power into their EVs HV battery pack, it's very complicated to do this for charging the HV battery. An average EV has a 400v battery pack. You would need either some serious solar to get up to that voltage, or a very efficient (and probably costly) DC-DC boost converter (which will need higher amp input) to boost from standard solar voltages.

But my point is that I think EV manufacturers are overlooking the simple fact that a few hundred watts hours are being wasted for auxiliary loads. Many manufacturers use common 12v automotive components (lights, infotainment system, locking mechanisms, brake pumps, A/C fans, etc...) for EVs, which help them keep costs down.
But these components are pretty power hungry, I suppose because ICE cars have a powerful alternator anyways, so they don't really have to be that efficient.

5. I like your idea of starting small, just swapping out the 12v for an LFP.
But, I would need an automotive grade LFP, which are very costly. I would be very worried putting a cheaper LFP as the single battery in my car.
The 20Ah LFP I ordered from Aliexpress cost me less than $100 (shipping included) !
It will probably take a month or two to get here, but no hurry. I will need to thoroughly test it and it's capacity before connecting it to my "system". But in the worst case, I threw away $100.
Also, using a non SLA battery in my car as the main battery might revoke the car's warranty.

So I'm willing to shell out a bit more money for some panels and parts rather than risk my car's warranty or worse risk myself.
In case my experiment fails, I could still put those parts for good use here and there.

I will be posting a BOM (bill of materials, or in plain English a parts list) when my system will be all setup and working.

Thanks for your interest and suggestions!
It makes this project/experiment more fun and productive. I'm always happy to hear suggestions and comments, even if I don't always agree with them (y)
 

eXodus

Solar Addict
Thanks for your interest and suggestions!
It makes this project/experiment more fun and productive. I'm always happy to hear suggestions and comments, even if I don't always agree with them
Happy to help! Science is not necessary about agreeing. You support your thesis and I support mine.
And we found some common ground in the middle. All good :)

I think you have a interesting idea there - I support 70% of it.

But these components are pretty power hungry, I suppose because ICE cars have a powerful alternator anyways, so they don't really have to be that efficient.
1 Gallon of Gas = 33kwh of energy. My BMW i3 has exactly that as battery capacity.
1 Liter of Gasoline = 8.4kwh

Fossil fuels are just an amazing dense energy storage.
 

curiouscarbon

Science Penguin
Great, finally I was able to explain correctly :cool:

I have done some testing using a clamp meter on the positive lead of the 12v battery (which the DC-DC is connected to in parallel) the car was fully on.
The minimal load (all possible accessories off) was around 5 amps.
Then I turned on the infotainment, headlights, A/C fan on high. This showed about 20 amps going out.

I suppose that if I were to connect my phone to the charger and maybe press the brakes, it could have gone even higher.

So at 12 volts we're are talking about around 60 to 300 watts consumption just by the 12v system.
So let's say the average is around 180 watts.

In comparison, my EV consumes an average of 155Wh per KM from the HV battery.

If I will be able to offset this load from the HV battery, let's say even only once a day, I will get 1 KM per day.

Most of my trips are from home to work and back, about 45 minute drive. But at work the car sits in an open parking lot with almost no shade for several hours. That's when the buffer battery will get fill up the most, and ready to supply power for the evening drive home.

A bit complicated to explain but pretty cool, isn't it ?
it’s cool!
 

meetyg

Solar Enthusiast
Happy to help! Science is not necessary about agreeing. You support your thesis and I support mine.
And we found some common ground in the middle. All good :)

I think you have a interesting idea there - I support 70% of it.


1 Gallon of Gas = 33kwh of energy. My BMW i3 has exactly that as battery capacity.
1 Liter of Gasoline = 8.4kwh

Fossil fuels are just an amazing dense energy storage.
Yeah, fossil fuels have a high energy density, but most of that energy is wasted in combustion engines and goes to heat (because of internal friction and ignition).

Combustion engines have an efficiency of only around 30%. Electric motors are far more efficient. That's why your i3 can drive farther on those 33KWh than an average car can go on one gallon of gas.
 

Hedges

I See Electromagnetic Fields!
... until the ICE driver decides to turn on the interior heater and take advantage of his CHP system.
What does THAT do to your i3's mileage?


My 2000 Civic CX gets about 35 mpg, just in line with your efficiency vs. i3
 

meetyg

Solar Enthusiast
Well, here is my first experiment, testing a solar panel laying flat on my dashboard:

Posted in thread 'Is putting PV panels inside a dumb idea?' https://diysolarforum.com/threads/is-putting-pv-panels-inside-a-dumb-idea.30194/post-365033

Just for curiosity, I also made a temporary connection to the car via the 12v socket using an 20A MPPT SCC.
The car was in "accessory" mode, meaning that the HV battery was disconnected, and the onboard DC-DC converter was off.
The output of the MPPT was pretty similar to my open circuit measurements:
20211022_103508.jpg

20211022_103522.jpg
20211022_103545.jpg

The result is that output is only around 40% inside the car, rather than outside.
But I'm planning to put a total of 3 flexible panels throughout the car, totaling at 160w STC.
Even if I only get around 60w total from all 3 panels, that should be enough to fully charge my 20Ah LFP buffer battery in about 4 hours of solar charging (while the car is parked), which is acceptable for me.

I still need to figure out how to mount the solar panel on the dashboard without it moving while driving.

More testing and experiments to come... stay tuned :cool:
 
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eXodus

Solar Addict
Combustion engines have an efficiency of only around 30%. Electric motors are far more efficient. That's why your i3 can drive farther on those 33KWh than an average car can go on one gallon of gas.
yeah, the efficiency is fascinating. When I don't floor it - 150 miles - 240km with less then 1Gallon = 4L of fuel.
My 2000 Civic CX gets about 35 mpg, just in line with your efficiency vs. i3
The i3 gets north of 115 MPGe, the Civic is a good car - but not anywhere close as efficient to the lightweight Carbon-Fiber - super-car the i3 is.

.. until the ICE driver decides to turn on the interior heater and take advantage of his CHP system.
What does THAT do to your i3's mileage?

When I turn on high 12V power draws like the Seat heater - the range is reduced noticeable.

The Interior heater comes from a High voltage Heatpump - which taking heat from the battery pack (it gets warm while driving anyhow) to warm the cabin, so the range loss there is pretty minimal. BMW was far ahead with that technology (2013), but Tesla is getting all the Media attention - with their Octa-Valve and Heatpump from 2018/2019. But BMW dropped the Ball in EVs around 2016 and decided to play ICE again..

I never drive without climate control on - so I can't really tell what the difference is A/C on vs Off :p
 

Hedges

I See Electromagnetic Fields!
The Interior heater comes from a High voltage Heatpump - which taking heat from the battery pack (it gets warm while driving anyhow) to warm the cabin, so the range loss there is pretty minimal.

I never drive without climate control on - so I can't really tell what the difference is A/C on vs Off :p

That's pretty good (at least for energy efficiency, not sure about $$)

We could have a mode which optimizes battery life by using occupants as a heat sink/source to regulate battery temperature. :)

After prior experiences, my sister decided to only drive on the newer portion of a car's life. At 135k miles she bought a new Honda (with a Clunker Credit from my Bronco II) and gave me the Civic. At 180k I pulled transmission and replaced a noisy bearing. Clutch still had 1/3 of life left, could have gone 270k miles. It is at about 270k now, I've gotten 135k and 13 years out of it for a few hundred dollars maintenance (well, about $2500 including multiple sets of tires.)
I can't afford to save money by switching to electric, even though I produce a surplus.

It sounds like electric cars will be pretty good when I need a replacement. It was Volt I was shopping for the day my car was missing - I want all-electric miles plus ICE range extender.
 

eXodus

Solar Addict
It sounds like electric cars will be pretty good when I need a replacement. It was Volt I was shopping for the day my car was missing - I want all-electric miles plus ICE range extender.
when you don't make cross country road trips the BMW i3 120ah with an REX (range extender) sounds the perfect fit for your. (gets about 220miles of EV Range)

With the tiny batteries in the i3 - that car would be the ideal candidate for a Solar Roof, when you park outside
Even if I only get around 60w total from all 3 panels, that should be enough to fully charge my 20Ah LFP buffer battery in about 4 hours of solar charging (while the car is parked), which is acceptable for me.
what EV are you driving? Why not get a flexible panel with magnets to the roof?
 
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