Solar Charging Design Feedback

[ohmslaw]

So I hate the fact that I have an electric car I could theoretically power by the sun and I am not doing that. I also a realist and know that the battery bank I would need to charge my daily use (Roughly 20kWh) would be really expensive and I would probably never recoup the cost of the batteries over the life of the vehicle.

I think I may have come up with a middle ground and a system that will be paid off after about 35k miles of Solar driving at my current electric rates.

• Off-Grid configuration
• 5 kWh salvaged batteries. ($650 with BMS)
• Hybrid Inverter/Charger Split Phase 220 ($900)
• ~2kW of used solar panels ($1200)
• Misc hardware/wiring ($500)

The plan would be to disconnect our current Ford connected charge station and feed it through the inverter. The inverter I am looking at auto switches from battery power to grid power when batteries become depleted. Plug in every night and deplete the 5kWh batteries with the inverter switching to finish the charge. The charge station would be set to a max rate of 6A when plugged in during the day on weekends (to use as much Solar directly as possible to charge vehicle. while still trickle charging home batteries) and a higher value during the week to get to desired charge level daily.


The questions I have:
1.) Am I crazy? Is this worth the effort?
2.) How well does the onboard charger handle voltage transients?
3.) Any suggestions/tips for my proposed solution?
4.) Any other ways to approach this problem?

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[Maquis]

What advantage would this provide over conventional grid-tied solar? Need to know the solar tariff policy of your utility / state to answer.

 

[ohmslaw]

What advantage would this provide over conventional grid-tied solar? Need to know the solar tariff policy of your utility / state to answer.

Less permitting (only hardwiring the inverter backup power rather than a full grid tie setup). Cheaper equipment. Will work better for my personal needs as a backup (already have a generator transfer switch that this setup will go into).

 

[CHeil402]

I think this isn't worth the effort. There's a measurable round trip loss between charging and discharging the solar batteries, probably at least 10%. Your best bet would be to charge when the solar is active if you did that, but you'd obviously need batteries if you're not grid-tied to smooth out the power. Also, you'd be wasting a lot of solar if you only have 5 kWh but 2 kW of panels as it would recharge in a few hours then have to cutoff. The inverter also has losses. Also your charge rate of 6 A is VERY low. What EVSE are you planning on using to accomplish that? And what brand BMS/Inverter are you using? The power factor / total harmonic distortion of that equipment may impact the ability to charge at all if it's poor.

What is your electric rate currently and does your utility offer time of use billing so you can charge at a lower rate at night? For example, your equipment is totaled to $3,250. Assuming it's $0.14/kWh from your utility, that's 23.2 MWh of power to offset the cost.

 

[ohmslaw]

I think this isn't worth the effort. There's a measurable round trip loss between charging and discharging the solar batteries, probably at least 10%. Your best bet would be to charge when the solar is active if you did that, but you'd obviously need batteries if you're not grid-tied to smooth out the power. Also, you'd be wasting a lot of solar if you only have 5 kWh but 2 kW of panels as it would recharge in a few hours then have to cutoff. The inverter also has losses. Also your charge rate of 6 A is VERY low. What EVSE are you planning on using to accomplish that? And what brand BMS/Inverter are you using? The power factor / total harmonic distortion of that equipment may impact the ability to charge at all if it's poor.

What is your electric rate currently and does your utility offer time of use billing so you can charge at a lower rate at night? For example, your equipment is totaled to $3,250. Assuming it's $0.14/kWh from your utility, that's 23.2 MWh of power to offset the cost.

Batteries I would prefer to go a LiFePo route; but second hand availability isn’t too good from what I’ve found. Reclaimed UPS 18650 packs with Chinese BMS is my current plan. Only way I can get down to around $100/kWh built. Battery expansion would be a future goal to get more out of the system.

The plan would be to charge whenever there is sun as much as possible. The car is used during the week to commute to work. So during the week that isn’t possible. It would probably be on the charger 6-8 hours a day on weekends.

The Ford Connected charge station has settings down to 6A.

Our current electric rate is $0.26/kWh; and they are applying for a rate increase.

 

[ohmslaw]

The inverter I plan on is a pure sine wave 3kW inverter with less than 3%THD

 

[AKgrampy]

I am not going to say you are crazy or if it is worth it or not. I will ask once again why people spend $60,000 on a car and then go cheapo on electric service equipment. Our current rate is also $0.26 here in Alaska and if I did not live surrounded by a forest I would install solar. I would just connect it to my utility electrical system and take the benefit that a utility interconnection does provide. I would certainly be concerned about any power quality issues that may affect charging for a non-grid connected system but I have no experience so that may not be an issue.

 

[CHeil402]

So adjusting for those electric rates, that's an offset of 12.5 MWh. Assuming you're only able to fully deplete the batteries each day every day and assuming an efficiency of 95% (which is probably generous) that would take:

12.5 MWh / (5 kWh * 95%) = 7.2 years to break even with this setup. And that's assuming none of your equipment breaks. Also, the batteries will lose capacity if you're deep discharging them every day for 7 years.

To me, this setup just doesn't make sense but your opinion obviously can vary and I'm not saying not to do it, but if your utility offers some form of net metering and a time of use policy there are MUCH bigger benefits there, including charging overnight when electricity is cheap and selling solar back during peak hours at a higher rate (and bonus, if they raise their rates, you get paid more!).

 

[Scooby24]

2kw is going to be peak. For reference my 13.86kw system rarely gets over 11kw... I produce 80kwh on the best day and that's with panels on east, south and west roofs so I make power all throughout the day.

Most systems I imagine you'd see at best 10kwh produced a day...on the best of days. ROI would be a long, long, long time for that for an off grid system with battery backup.

 

[kltye]

So I hate the fact that I have an electric car I could theoretically power by the sun and I am not doing that. I also a realist and know that the battery bank I would need to charge my daily use (Roughly 20kWh) would be really expensive and I would probably never recoup the cost of the batteries over the life of the vehicle.

I think I may have come up with a middle ground and a system that will be paid off after about 35k miles of Solar driving at my current electric rates.

• Off-Grid configuration
• 5 kWh salvaged batteries. ($650 with BMS)
• Hybrid Inverter/Charger Split Phase 220 ($900)
• ~2kW of used solar panels ($1200)
• Misc hardware/wiring ($500)

The plan would be to disconnect our current Ford connected charge station and feed it through the inverter. The inverter I am looking at auto switches from battery power to grid power when batteries become depleted. Plug in every night and deplete the 5kWh batteries with the inverter switching to finish the charge. The charge station would be set to a max rate of 6A when plugged in during the day on weekends (to use as much Solar directly as possible to charge vehicle. while still trickle charging home batteries) and a higher value during the week to get to desired charge level daily.


The questions I have:
1.) Am I crazy? Is this worth the effort?
2.) How well does the onboard charger handle voltage transients?
3.) Any suggestions/tips for my proposed solution?
4.) Any other ways to approach this problem?

You're probably better served asking this question over at diysolarforum.com (if you haven't already). Those guys have lots of experience with every part of the solar chain (panels, inverters, batteries, BMS, etc).

 

[woody]

Solar Charging Design Feedback

Joseph,
(copied from previous post w/ some additional comment)
Everything electric:
2017 Volt (trade in for MME)
2019 Bolt
2021 MME
Heat pump heat/air conditioner (Mitsubishi). Works great (most HVAC guys here told me it is impossible)
Heat pump water heater
10.695 solar array, ~20-60kWh/day average, 80kWh max.; 9kW normal max. power (charge cars directly with solar as often as possible, daytime, rotate car usage, one of the EVs is charging from solar array most of the time, level 1.*)
battery back up (30kWh AGM, which is only enough for minimal back up)
critical load panel (back up)
stove/oven, clothes dryer, etc.
NO GAS line
zero fossil fuels for energy ( I produce more electricity than I use)
fighting COGU (Coal Oil Gas and Utilities) has been quite a challenge, hopefully the war will be won by us sooner than later

*should you be able to find a competent, certified SOLAR man, have him set your system up to charge directly from your solar array. This is what we do - most of the time one of our EVs is plugged into 120 during the sunshine. In other words, no out of pocket expense. We only rarely use our EVSE now, which is currently not directly tied to solar panels.
(next EV will be bidirectional. Additionally, will add more battery capacity in house)

"NUTS", he said.
Still crazy after all these years.

In the Milky Way Galaxy there exists a small star, sometimes referred to as The Sun. Orbiting it is a (third) rock which appears to be inhabited by some carbon-based organisms. The main heat engine/energy source for the planet is the Sun. It provides more energy than any and all of the organisms on the planet could ever reasonably or unreasonably use (at least for the next 1 billion years or so).

Fight the SOBs.
Make it work.
Win the war!
Save the planet.
We will be dead, but Life goes on.
And we will have had fun.
And all that rot.

ps. Solar power will not make money for you (not at 5 mils/kWh, which is what our utility company "pays"). However, the money saved will pay for the investment. Solar powered electrical devices do not earn you money nor do the same devices using fossil fuels.
The idea is to not use fossil fuels. Maybe make life on Planet Earth better?
-our array is about 5 times your proposed array and we are grid tied, due to more than needed overall production.
BEST ADVICE: hire a competent, certified SOLAR man (Hope there is one in your neck of the woods.) as a consultant, not an engineer. No offense, but solar work is a certified, knowledgeable solar man's expertise. I made the mistake of not hiring one initially and it cost me. Fortunately the true solar expert was able to put everything in order. When he first came out to look at my original install he immediately knew all that was wrong. His conclusion(which agreed with my evaluation) was that they might have intended to set up the system correctly, but realized they could not do it half way through and tried to make it appear as though it was functional. I tried for months to get the system to work to no avail. The original installer (both mechanical and electrical engineers) even had the Schneider inverter replaced with the exact same model/unit. They simply had no clue. My first indication was when the owner came out to set up the Schneider and it took him 2+ hours to do the set up. (The installer went back and forth with the Schneider call desk guy, who of course was just reading from a script. One blamed the other and the other blamed the one. No resolution for me from them.)
Cannot verify the crazy.
But yes, it is worth it. Just for the fun of it. As an engineer. I am a biologist and it is worth it an fun.
Chew it up, swallow it or spit it out. I am confident you will get it right (I did), hopefully from the get go.

 

[ohmslaw]

2kw is going to be peak. For reference my 13.86kw system rarely gets over 11kw... I produce 80kwh on the best day and that's with panels on east, south and west roofs so I make power all throughout the day.

Most systems I imagine you'd see at best 10kwh produced a day...on the best of days. ROI would be a long, long, long time for that for an off grid system with battery backup.

Thankfully our home faces pretty much due south; all of these panels would be in an optimal location.

is why I plan on putting 2kW of panels to be able to hopefully charge at a rate of 1.2kW on weekends while still maybe getting 1-200 watts of charging into the batteries as well

The ROI point I found at my current electric rate would be approximately 100 miles for every dollar spent.

I agree there are probably better (more expensive ways). This allows me to utilized used/surplus equipment; so the install myself and have a backup system that will allow me to ditch my generator.

To me, this setup just doesn't make sense but your opinion obviously can vary and I'm not saying not to do it, but if your utility offers some form of net metering and a time of use policy there are MUCH bigger benefits there, including charging overnight when electricity is cheap and selling solar back during peak hours at a higher rate (and bonus, if they raise their rates, you get paid more!).

No net metering; no time of day discounts. Just a straight $0.26/kWh all the time. Our utilities really got us here.

 

[ohmslaw]

ps. Solar power will not make money for you (not at 5 mils/kWh, which is what our utility company "pays"). However, the money saved will pay for the investment. Solar powered electrical devices do not earn you money nor do the same devices using fossil fuels.
The idea is to not use fossil fuels. Maybe make life on Planet Earth better?

Cannot verify the crazy.
But yes, it is worth it. Just for the fun of it. As an engineer. I am a biologist and it is worth it an fun

You seem to get it. It’s not so much about making money off of this. Knowing that my vehicle is being powered by nuclear fusion millions of kilometers away is a feeling I just can’t help but chase. But that being said; being able to pitch the fact that we can have this equipment paid for itself in 30-40k miles of us to my wife will make it much easier to put panels on the roof.

This is the first new car I bought. I don’t like buying anything new. We discard waaaay too much beyond its useful life. Hell, I’ve had the same bicycle since I was 15; I’m now 39. Just converted it to an ebike using a surplus hub motor and salvaged scooter batteries. My wife thinks I’m crazy. That’s the same approach I would take with this; quality equipment second hand.

 

[woody]

You seem to get it. It’s not so much about making money off of this. Knowing that my vehicle is being powered by nuclear fusion millions of kilometers away is a feeling I just can’t help but chase. But that being said; being able to pitch the fact that we can have this equipment paid for itself in 30-40k miles of us to my wife will make it much easier to put panels on the roof.

This is the first new car I bought. I don’t like buying anything new. We discard waaaay too much beyond its useful life. Hell, I’ve had the same bicycle since I was 15; I’m now 39. Just converted it to an ebike using a surplus hub motor and salvaged scooter batteries. My wife thinks I’m crazy. That’s the same approach I would take with this; quality equipment second hand.

some more thoughts:
I charge with a Level 1 (NOT Ford's) supply directly from my solar panels - 1kw+ of power when charging. Yields about 1% of total charge added/hour or 3mi added distance/hour. 10 hours charge time = 11% total charge added or 32 miles distance. Or ~9.5 kWh
2kW of solar panels will probably not yield much. If you could triple that amount, it would serve you much better. Of course more if you are considering all electric.
5kWh of battery storage is not much, even less when talking about salvaged batteries. And longevity is further reduced where daily or often depletion is employed.
We have 30kWh of battery back up, but would require at least 3X that much to run everything using the batteries and solar. And that would be minimal. Three or four snow covered days in a row shoot that down. So 4X would probably cover it along with a bi directional EV(remembering we are 100% electric). Currently we do not utilize the batteries for anything other than back up.
We resist going off grid since most of our excess production is when the grid needs it the most and we do not want the energy to be unused.
Second hand is less expensive initially. But solar and batteries have much reduced longevity
CARS:
I could not afford used cars, although that was all could purchase long ago. So I saved and purchased my first new car about 40 years ago. I then owned 3 new Toyotas (could not afford US made vehicles - way too expensive to maintain), two of which were Prius' which were not discarded but sold to lucky buyers. Better someone driving a hybrid rather than another ICE. The money I saved on the Toyotas paid for new vehicles.
My vehicles are new (some would say that I am meticulous or even anal about car care - descended from poor hillbillies)even when five or eight years old. So they got a good deal and hopefully they purchase an EV next.
(have not made a car payment in 35 years)
Smart of you to pick the brains of others. Hopefully it pays off. Good thing, this forum.

 

[ridgebackpilot]

My solar system includes 20 panels (6.5 kW max) and two Tesla Powerwall II batteries (24.4 kWH usable storage). I charge two MMEs through a wall charger on my garage.

My solar array and battery storage aren't big enough to allow me to go completely off-grid, especially when charging the two EVs. My system supplies about 50-60 percent of my electrical energy needs. However, the system does allow me to do one vitally important thing: Shift all my grid usage to off-peak hours.

Here in northern California, our electrical utility allows solar customers with EVs to sign up for net-metering and time-of-use rates. That means peak power costs $0.48/kWh and off-peak is half that. So it's a lot cheaper to let the sun charge the Powerwalls during the day so they can power the house during peak hours (3 pm to midnight).

Charging the EVs requires so much power you'd have a to install a massive solar system and batteries to generate and store enough energy. That would be cost-prohibitive; the best solution is to use your solar array and batteries to shift your electrical load to the cheapest off-peak grid power and set your EV to charge overnight.

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