Chevy Bolt EV Forum banner

1 - 20 of 21 Posts

·
Registered
Joined
·
2,811 Posts
You want to grid-tie your solar. Plenty of info out there on design. What use case would require dedicated solar charging? It would waste the charging capabilities any time the car is fully charged or not present, unless you install a storage battery, in which case it would waste the charge any time the battery is full... which leads us back to grid-tie.
 

·
Registered
Joined
·
857 Posts
The only way a dedicated solar charging station would make sense if you lived miles away from any electric grid infrastructure. It would be crazy expensive to buy one since you would need an inverter or have a way to run DC directly to your car.
 

·
Registered
Joined
·
2,385 Posts
Has anyone built / installed a dedicated solar charging station? If so, would you please share your design specs?

There are off-the-shelf solutions built-in to solar inverters. Me thinks this isn't what you're looking for. Rest assured, what you ask is technologically possible, but likely would be impractical and prohibitively expensive.
 

·
Registered
Joined
·
643 Posts
+1 for what @GregBrew said - you want a grid tied solar system - and then charge the car at night when rates are low - power used at night to charge your EV will be offset by the solar power you generated during the day...

what you are asking for is technically feasible but for reasons already mentioned, plus

1. solar does not generate a continuous current - all day it changes - you'd need a charger to ramp up/down to match current solar production - technically feasible but impractical
2. power will be lost when the car isn't there to receive it
3. you can't charge at night
4. solar generates DC, EVSE charging on the Bolt uses AC, unless you build a Fast DC charger that is run off of solar
5. you'll want to charge the car on cloudy days and in the winter when solar produces less, you'll need the grid to make up any short fall.
6. people typically drive their cars during the day and particular during prime solar production hours 10 am - 2 pm

what you are asking is technically feasible, but from a practical point of view there are existing better solutions and solar still ends up providing a lot of the power you use to charge your car - but it's usage is shifted to off peak hours using credits you generated during the day.
 

·
Registered
Joined
·
735 Posts
Ditto. My car is solar powered. The grid is my energy storage ["battery"]. I make about 6 mWh/year, use about 5 for the house and 1 for the car.
How many miles do you do in the car? My Bolt EV uses a lot more annual. Its about 4 miles per kWh, so 10000 miles uses 2500 kWh or 2.5 MWh. So, for the average 12000 miles annual, most Bolt EVs should be burning 3 MWh per year. So, unless you drive a very few miles, 4000 miles a year, your numbers are a bit off. Not as though its very important to anyone but me, my roof solar gives my 10 MWh per year, and I use 2-3 MWh per year driving.
The real magic is the net cost of driving an EV. So, for example, if your solar covers all your electrical needs then fuel for your EV is $0 per mile. If your solar covers 50% of your needs, then half of your KWh come from the grid, which is very likely dependent to some degree or other on fossil fuels and costs you actual money, but only half of what it would cost you without roof solar.
 

·
Registered
Joined
·
885 Posts
This place has solar

I know nothing about the solar side. In the state of Wisconsin, it's very solar unfriendly. In fact, it's in the news this week that the utility is raising the rates for solar customers, using the argument they have to have the same infrastructure in place, etc. But this is at a Tesla Body Shop, they have lots of Tesla's there and they will be the first to tell you the repair times are much shorter than reported here. In any case, send me a PM and I can give you the owners contact info if you have any interest. He has a bank of chargers, all types, Tesla and non. All free and he has a large solar array as well. He's a techie.
 

Attachments

·
Registered
Joined
·
36 Posts
Discussion Starter #9
Thanks for all of the replies. I should have said that I ultimately plan to get to a grid-tied system. Permitting is a PITA here in Maryland even though we claim to encourage green endevours. To make things worse, I live in a critical area near the Chesapeake Bay which adds yet another level of pain. For the capstone, I want to install the system myself (I'm a EE with many years of practical experience) and have gotten all kinds of reasons why I can't. My life and career have proven that part wrong so it's more of an irritant than anything else.

So in the meantime, I would like to start experimenting with the components as a learning exercise in a "temporary", grid-DISconnected configuration. I envisioned a minimal number of panels and an inverter. used along with the EVSE I already own (which I installed). I want provision for storage, however, I'm not sure when I would actually buy that part because it is still too expensive for me to justify. I am not pursuing this as a purely monetary exercise BTW so I don't care overly much about break-even times, fully charging the Bolt or any other reason why this would be ill-advised from a practical, long-term perspective.
 

·
Registered
Joined
·
857 Posts
I have no idea how to do this using a minimal number of panels. The Bolt would need a continuous draw from an EV charging unit and fluctuations from a small unit wouldn't be possible. You would need a larger system and preferably have a battery back-up to capture the remaining electrons. I would imagine you would need a 4 kW to 5 kW array to charge at 16 amps. What would happen as well if it was cloudy? your system would be constantly shut on and off for charging. I don't know how the Bolt would handle this. So to charge at under 2 kW you would need to spend about $10,000. If you add battery back-up it would be even more.
 

·
Registered
Joined
·
643 Posts
@glassTransition - ok I understand your goal - the problem is there are no EVSE's that will "change" their output (input into the car) to match the current solar production...

you'd have to build an EVSE that is constantly matching it's output to current solar input/production...I'm not even sure the J-1772 protocol is rapid enough to have the car change it's demand to match supply…I _KNOW_ the J-1772 protocol allows the charge rate to be changed during the charging session - I know this because my Tesla Wall Chargers do this with my Bolt all the time, but they change the charge rate up/down over like a 15 minute period

I've seen my solar doing 12,000 watts and 10 seconds later when a cloud come it drops to 800 watts, and then 5 seconds later it's back to 5000 watts...

the challenge is a J-1772 compatible AC EVSE that will adapt it's output rapidly enough to match current solar production...if you can do that the car will only draw the amount of power it's told from the EVSE...

there is your problem statement - build an adaptable EVSE that matches output to current solar production.

nearly all the EVSE's I'm aware of assume a constant rate of power and will not change their output to adapt to current power available...so you need to build a custom EVSE that will adapt it's published charge rate within the constraints of the J-1772 protocol (which is what the Bolt uses to charge in North America).

at a minimum you'd need to build a "switch" that turns off the EVSE circuit when solar production drops below X,xxx watts - since you know solar is no longer providing enough power to match the EVSE draw - you'll have to turn it off…and then back on when power is above the threshold- I would also suspect you'd want to rate limit the switching it to avoid "trashing" the EVSE and Car charger with the power coming/going multiple times per minute...

the _ONLY_ product I'm aware of vaguely like what you're asking is various home battery setups - where the battery charges from solar - the Powerwalls do this exact thing only pulling power from solar, and only pulling exactly the amount of power solar is currently producing - they have monitors and change the charge rate at the millisecond level so that the Powerwalls is only drawing exactly the amount of power Solar is currently producing....

Powewalls solve the problem by changing the "draw/demand" from the battery point of view - so that the battery never "asks" for more power than the solar can provide - to my knowledge you do not have the ability to do that - you'd have to hack the Bolt's charging software to change it's demand based on your solar's current production - and while I know the Bolt can ramp it's charging demand up/down (it does so to match EVSE charging rate, and to taper the charge when the battery gets close to full) - I don't believe it's possible or practical to hack the Bolt charging software to do this this rapidly enough to match it's demand to current production…

so that leaves trying to change the Bolt's charging rate indirectly via the EVSE/J-1772 protocol - i.e. the Bolt will not draw more power than the EVSE reports it can provide, so if you build an EVSE that changes it's reported power/provided you would trick the Bolt into changing it's draw to match the current solar production - but I'm not aware of if the J-1772 protocol's ability to do this rapidly enough to match current solar production…and we are of course now talking about a custom EVSE....OpenEVSE provides electrical specs and open source software source code for the EVSE - so probably start there and see I you can modified an OpenEVSE charger to change it's reported power supply in response to a Solar production monitor, or at a minimum turn itself on/off above/below a certain solar production threshold.

I see the whole project as technically feasible in theory, but all the off the shelf components (and in particular the black box of the car) simply are not designed/tested to charge in a manner where the charge rate needs to be modulated at a rate rapidly enough to match demand…

I wish you luck - but will be whole unsurprised if it takes you a very long time, a lot of modifications, and a very large amount of money…
 

·
Registered
Joined
·
36 Posts
Discussion Starter #12
The Bolt would need a continuous draw from an EV charging unit
I'm wondering why you think this? Have you read the SAE J1772 charging protocol? There is a 1 kHz control pilot signal whose PWM duty cycle indicates the charger's current capacity. It ranges from 6 to 48A. If you have knowledge of the Bolt's interpretation of this then please share. It could be that it is only sampled at the start of a session, but even so, would the Bolt abort the session if the charging current drops?

Some of the Inverter vendors provide transformer-based devices to stabilize the voltage of their built-in charging ports so I do think that the voltage is monitored and must be kept within some range, but I have no idea what that range would be and would be grateful if anyone that does know would share that information.

Also, to say it again, I don't care if I don't fully charge. I don't care if it's cloudy. I am fine with only charging 0.5 kWh if that's all that's possible with a minimal system. I can switch back to the grid and charge the rest of the way. This is just a learning experience.
 

·
Registered
Joined
·
643 Posts
yes the Bolt will adapt to the current J-1772 published rate - it doesn't this on my Tesla Wall charger when it ramps the AMP's up/down in my multi-charger configuration - however I'm not sure how rapidly the Bolt responds and the Tesla chargers are very conservative with their reported change in charge rate

Example:

two cars sharing a 60 amp circuit (48 amp charge rate - so each car gets 24 amps)
one car finishes charging leaving the bolt the only car still charging
I can observe the Bolt ramping it's charge rate up to the full 32 amps over the next 20 minutes
in monitoring the Tesla charger I see them do a "little dance" in 2 amp increments about once ever 2 minutes

it looks like this

2nd car drops charging
Bolt AMP rate 24 amps (from before)
with in 2 min it will drop to 22 amps
then go to 26 amps
then go to 28 amps
then go to 30 amps
then go to 28 amps
then go to 30 amps
then go to 32 amps

with each step taking 1 to 2 minutes…

I hope this helps.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #14
@daveo4Bolt

Thank you! That's the sort of information I was looking for.

I have a question in to a tech support person at one of the hybrid inverter manufacturers that makes a model with built-in EVSE. I'm wondering if a small battery bank would provide enough stability and if their inverters tweak the PWM according to available power.

As you mentioned, it isn't clear how fast the Bolt responds to changes, but it should be possible to change as quickly as 1 ms since the pilot is at 1 kHz.
 

·
Registered
Joined
·
643 Posts
yeah - all things consider I believe you'll need a small battery as a "buffer" to allow the EVSE and the Car some wiggle room to "absorb" rapid changes in Solar and smooth out the transitions to higher/lower power draws…

1 hz would point to a fast change rage possible, but again it will depend on how reactive the Bolt's charging software is to a change in this pilot signal…I know every time my Tesla chargers change the charge rate OnStar sends me a spurious Text message saying "charging interrupted" even though it has not been interrupted just changed...
 

·
Registered
Joined
·
885 Posts
This is the roof of the place that has the solar powered EVSE's .... I'm sending you info in response to your PM. It's a 72kW system, they have a website to look at the efficiency, so forth. Even when it's raining like today, it is putting out some serious power. I don't know much about the infrastructure, I'll let you talk to them directly.
 

Attachments

·
Registered
Joined
·
735 Posts
This is the roof of the place that has the solar powered EVSE's .... I'm sending you info in response to your PM. It's a 72kW system, they have a website to look at the efficiency, so forth. Even when it's raining like today, it is putting out some serious power. I don't know much about the infrastructure, I'll let you talk to them directly.
That should do just about anything.
 

·
Registered
Joined
·
173 Posts
How many miles do you do in the car? My Bolt EV uses a lot more annual. Its about 4 miles per kWh, so 10000 miles uses 2500 kWh or 2.5 MWh. So, for the average 12000 miles annual, most Bolt EVs should be burning 3 MWh per year. So, unless you drive a very few miles, 4000 miles a year, your numbers are a bit off.
And indeed they are off -- my apologies. If I did all my charging at home, it'd be about 2 mWh/year - we don't put a lot of miles on the Bolt. So to make my claim of a solar powered car be correct, I will have to turn some lights of in the house...
 

·
Registered
Joined
·
49 Posts
Thanks for all of the replies. I should have said that I ultimately plan to get to a grid-tied system. Permitting is a PITA here in Maryland even though we claim to encourage green endevours. To make things worse, I live in a critical area near the Chesapeake Bay which adds yet another level of pain. For the capstone, I want to install the system myself (I'm a EE with many years of practical experience) and have gotten all kinds of reasons why I can't. My life and career have proven that part wrong so it's more of an irritant than anything else.

So in the meantime, I would like to start experimenting with the components as a learning exercise in a "temporary", grid-DISconnected configuration. I envisioned a minimal number of panels and an inverter. used along with the EVSE I already own (which I installed). I want provision for storage, however, I'm not sure when I would actually buy that part because it is still too expensive for me to justify. I am not pursuing this as a purely monetary exercise BTW so I don't care overly much about break-even times, fully charging the Bolt or any other reason why this would be ill-advised from a practical, long-term perspective.
One option you may want to look at is that some SMA inverters have what they call a "secure power supply," one outlet that can be run from the inverter when the grid is down. No batteries required. I have this and I've used it a few times to charge the car. Mine will only charge the car at 110v/8A using the supplied cord, even when the system is producing over 2kW - 12A throws an error and stops charging. I've got a 3kW system so a bigger inverter may allow a higher draw but I haven't researched the specs. I assume if you set this up and didn't tie it to the grid it would just think the grid was down and allow you to use the plug while the sun was shining, and then you could use the same inverter when you do tie into the grid. I used mine like this after it was installed and before the utility gave me the OK to turn it on, as well as during a few outages since.
 

·
Registered
Joined
·
345 Posts
And indeed they are off -- my apologies. If I did all my charging at home, it'd be about 2 mWh/year - we don't put a lot of miles on the Bolt. So to make my claim of a solar powered car be correct, I will have to turn some lights of in the house...
FWIW, my solar array covers about what my two cars use. So I generally consider that as going to the cars, and none to the house. How you count it really doesn't matter in the end. You'd have to buy the electricity from the grid for the house and car without solar panels. With solar, you have to buy less or none at all.
 
1 - 20 of 21 Posts
Top