diy solar

diy solar

Need help with off grid EV charging system design

But what if the car is charged mainly on weekdays with the solar panels directly to the car without a battery? That way the battery would only be used sparingly during a few weeknights. Wouldn't that factor heavily into the ammortization cost and make it cheaper than getting energy from the grid? Or am I missing something here?
I charge my EVs any day they need kWhs. The 42 kWh battery poweres my home but not the EVs when there is no solar. My amortized cost was based on using 25 percent of my battery each day or a full cycle every four days. I do not charge the EVs from stationary storage because I do not want to shorten life of stationary battery. The cost benefit was not worth it to me.
 
I charge my EVs any day they need kWhs. The 42 kWh battery poweres my home but not the EVs when there is no solar. My amortized cost was based on using 25 percent of my battery each day or a full cycle every four days. I do not charge the EVs from stationary storage because I do not want to shorten life of stationary battery. The cost benefit was not worth it to me.

You're using batteries though to power your home every night though right? What's the difference then? Are you just looking at # of days of useful life for your batteries vs. cycles (because an EV would absorb much of your battery nightly)?
 
You're using batteries though to power your home every night though right? What's the difference then?
When I charge my EVs at night I use as much as 30 to 40 kWhs.That is a big chunk of my stationary pack and would leave me no reserve if the next day is cloudy and or we have a power outage. Therefore I do not use battery power to charge overnight, I use the grid. The difference is that overnight charging is more cost effective than using batteries. During the day I use available solar energy.
It is simply a matter of risk management..I do not expect everyone to have the same risk adversity. It all depends on where you are standing.
Do you have an EV?
 
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OK so going back to the question of charging an EV using an off grid PV system...
We have a PV system and now we have an OpenEVSE charger. The charger can take 2 inputs: Power being backfed to the grid(grid_ie) and PV output(solar). Both are specified in watts.
I am using their http api protocol to send this data to the charger. Just got it setup and will see how it work later today when the EV comes back with a dead battery.

We are grid tied.
But the idea of how do you charge if off grid? How do you tell the charger how much to charge (automatically) based on potential PV production. Because an off grid system has no excess power going to the grid and excess PV production depends on solar radiation and power used by the house.

It's like you would need to monitor solar radiation and then using that info to estimate your PV system's output->then tell the charger how many watts it can use to charge the EV.

Am I missing something here or ?
 
OK so going back to the question of charging an EV using an off grid PV system...
I'm completely off grid and adjust my charger based on staying positive for conditions. If sunny then I can set it to 40amps and still run all the loads and charge. Depending on clouds 6 amps is to much to keep charging the banks and other loads.
 
OK so going back to the question of charging an EV using an off grid PV system...
We have a PV system and now we have an OpenEVSE charger. The charger can take 2 inputs: Power being backfed to the grid(grid_ie) and PV output(solar). Both are specified in watts.
I am using their http api protocol to send this data to the charger. Just got it setup and will see how it work later today when the EV comes back with a dead battery.
Great start. While OpenEVSE gives those inputs specific names, you can just send the commands in watts and do the calculations on your own.
We are grid tied.
But the idea of how do you charge if off grid? How do you tell the charger how much to charge (automatically) based on potential PV production. Because an off grid system has no excess power going to the grid and excess PV production depends on solar radiation and power used by the house.

It's like you would need to monitor solar radiation and then using that info to estimate your PV system's output->then tell the charger how many watts it can use to charge the EV.

Am I missing something here or ?
I'd look at battery current, if the battery is charging you can pull more wattage into the EVSE. If the battery is discharging,you need to turn down the EVSE. The adjustment steps on the EVSE are 1 amp intervals, so roughly either 120 or 240 watts. Try to keep the battery between 0 and 240 watts and it should work great.

This strategy does require you start charging the EVSE before the house battery is full or getting close and tapering current for end of charge/absorb.
 
I'm completely off grid and adjust my charger based on staying positive for conditions. If sunny then I can set it to 40amps and still run all the loads and charge. Depending on clouds 6 amps is to much to keep charging the banks and other loads.
That is the same logic I use. I have found settings on my Emporia EVSE enable me to automate that process somewhat.
 
Electricity is getting more and more expensive now, photovoltaic with battery charging is very affordable.
 
So these guys make chargers that go directly from solar to EV battery without converting to AC. They have large commercial units but also office/residential sized units. The small "EVDC" units are grid-tied, I think, and it doesn't seem their off-grid products do EV charging. But they've got the pieces for a small, off-grid EV charger that goes direct from solar without needing a separate battery.
 
Can't buy one... What you really want for a 'direct' solar is to control the charge rate based on available PV. If your EV needs 450vdc to charge DC direct, you need to feed it a stable 450V. If your panels are putting out 300v in a string, you will have to upconvert somehow. The best ticket is a box that just hits the car's charger and cuts down your charge rate to match available PV being inverted. PV is generally somewhat volatile., and that is the problem, your charge rate needs to track your solar panel output.
 
If your EV needs 450vdc to charge DC direct, you need to feed it a stable 450V.
Actually an EV battery voltage will vary base on the State of Charge. Therefore the voltage at the interface between the device providing voltage and the battery will increase as the battery becomes full. The important issue is not to exceed the battery pack maximum voltage which varies by EV. That is typically done by the communicaiton interface which is presumably coming from the EVs battery management system, and is implicit in any DC fast charging system. Every vehicle has a different voltage depending on the pack configuration.
 
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Actually an EV battery voltage will vary base on the State of Charge. Therefore the voltage at the interface between the device providing voltage and the battery will increase as the battery becomes full. The important issue is not to exceed the battery pack maximum voltage which varies by EV. That is typically done by the communicaiton interface which is presumably coming from the EVs battery management system, and is implicit in any DC fast charging system. Every vehicle has a different voltage depending on the pack configuration.
Not much. The physics of charging a battery do not change just because you have a higher/lower voltage pack. If you want to charge a 52V lithum you need to push something more than 52v at it. Usually ~54v nominal, maybe up to 58v for a boost charge. If you want to charge a 400V ev battery you need to push something more than 400v at it. This charge voltage is going to be in a pretty narrow window, and never lower than the nominal voltage of the pack, I'd doubt it would get over 430v, I could look it up.

The BMS on the car is going to request a restriction of current not voltage as the charge state approaches 100%. The available current flow is going to be based on the internal resistance of the battery which increases as it gets charged. The voltage reading at the connector will go down as the current flow is restricted into the batteries, since the resistance goes up. A meter reads the voltage drop across a load, so the closer you get to 100% the lower the voltage reading should be, as the current is restricted, the voltage should approach whatever the nominal is for the battery.

Almost all current vehicles are either 400v or 800v systems. Some of the older stuff, mostly CHAEDMO I think varied, like 240, and 320 and stuff. I know the J1772 AC spec reasonably well, but with DC the rate logic moves into the charging pedestal from the car. You will obviously be coughing up the required charge voltage along with the desired current/rate on the control pin. One of the problems with NACS is the Tesla stations only support up to 500v charging, and some of the newer cars want 800v for maximum charge rate. They obviously charge by bank if they have to negotiate a lower voltage.

Which takes us back to:

If your EV needs 450vdc to charge DC direct, you need to feed it a stable 450V. Doesn't matter what the number is, if you are rolling juice from a solar panel you will have to get the voltage up above (but not too far above) the nominal voltage of the battery you are trying to charge. It will need to be relatively stable or it's likely to get shut down. It ought to be easily doable as long as the car doesn't get pissy if you repeatedly drop output. We are really just talking an MPPT for a 400v battery, the problem is most MPPT's require PV voltages above the charging voltage. So now you need to upconvert or come up with a string that outputs well over 400v. Then it needs to hit the batteries direct and not have any of the electronics in between get mad. God help you if it backfeeds, you will need a good diode.
 
The BMS on the car is going to request a restriction of current not voltage as the charge state approaches 100%
Yes that is how the CV stage works. Lowering current is the way a charger can maintain constant voltage. It happens that way when there is no communication from the BMS, as well on command from the BMS. Conversely raising voltage on the charger will allow more current to flow. This is the Constant Current stage.

This is starting to drift from the topic of charging off grid, which in its simplest form would be easier just using AC from the inverter and let the onboard charger deal with the complexities of managing the DC voltage and current.
 
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One of the problems with NACS is the Tesla stations only support up to 500v charging, and some of the newer cars want 800v for maximum charge rate. They obviously charge by bank if they have to negotiate a lower voltage.
Good points. Note the NACS proposed standard allows up to 1000V and many say Tesla's v4 Superchargers support 1000V. We'll see.

I think 800V cars use internal DC-DC converters when hooked up to 400V chargers. The base Porsche Taycan comes with a 50 kW converter, but there's an optional 150 kW converter available at extra cost. Taycan can do 280 kW on a proper 800V charger. I'm not 100% sure about Hyundai/Kia's e-GMP, but I think they use a 100 kW DC-DC converter.
 
I downloaded he NACS specs a whlle back, and they do allow for up to 1000v. I'll have to re-visit the charge tricks. The problem with up-converting or switching in the vehicle is you have to have gear that supports the obscene currents desired. 400000W/800V = 500A. Ouch I say. MCM1000 wire or something. Even at 1000v we are sill talking 400A for a 400KW charge rate. That's still around 15 minutes to charge a 100KWH battery pack. This is the achilles heel of EV. It will help for solar as well, but we really need a break thru with Aluminum-Ion or Solid State that can increase the energy density of the batteries. If we could just double it then you take the range problem out of the equation for the majority of people. My ev gets between 225 and 300 miles on a 64K pack. If tthat changed to 450-600, then I only have to stop every 5-8 hours, instead of every 2-3 (at best because of station availability). This means you can more easily just plan around a normal bio or meal break and puts EV on par with current ICE based offerings.

From what I've seen Aluminum, if they can get it close to the hype, holds the most promise as the materials are recyclable and inexpensive. We shall see.
 
The problem with up-converting or switching in the vehicle is you have to have gear that supports the obscene currents desired.
Yeah, that's why they only provide 50-100 kW when upconverting. Or 150 kW with the Taycan optional upgrade (I read it's $460 extra, a bargain if you mostly have 400V chargers on your routes).

My ev gets between 225 and 300 miles on a 64K pack. If that changed to 450-600,.....
Lucid Air is really the only 500 mile EV. A couple models are higher on the unrealistic Chinese cycle, I think, but you have to discount those almost 50%. Chevy Silverado is 450 miles, but with a crazy 212 kWh pack. Then of course there's the mythical Aptera 1000 mile three wheeler.
 
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