Just a question for you guys with panels and an EV...

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pkulak

Well-known member
Joined
Sep 19, 2013
Messages
758
Location
Portland, OR
Does it bother you that you're capturing power in DC, losing some of it through an expensive inverter, then loosing more again when your car's rectifier turns it right back into DC? Anyone ever think of just hooking some panels into a battery and using CHAdeMO exclusively to charge the car?
 
pkulak said:
Does it bother you that you're capturing power in DC, losing some of it through an expensive inverter, then loosing more again when your car's rectifier turns it right back into DC? Anyone ever think of just hooking some panels into a battery and using CHAdeMO exclusively to charge the car?

Not one bit. Let's pretend that this additional loss is 33% (that seems really high though). That means I could cut my 300kwh of charging to only 200kwh a month. So to save $120 a year I would need a seriously more complex system that would be very expensive as the most practical way would be to use a CHAdeMO converter that could take AC and DC at a varying levels based on a constantly changing solar PV output then there would also have to be a way for all the excess DC from the panels to inverted to AC. Then my state incentive is paid on AC production so that would not work well. I would have to replace my microinverters which are helping deal with my shade to central inverters. Lastly I charge in the early morning so the car is ready when I leave for work but there is no solar PV output at night.

I'm much happier generating more than 100% of my homes electricity usage including heating, cooling,
water heating and the LEAF. Using net metering I give the grid all my excess production and then when I need it the grid gives it back to me. This is extremely simple, doesn't require any special equipment, passes electrical inspection and is extremely cost effective.
 
I suppose it bothers me more that for each 1,000 watts hitting the panels, you get 200 watts out. :)

Meanwhile, unless you can keep the DC output from your panels at exactly 394 volts, you are going to need something to adjust that voltage for you...something that looks an awful lot like another inverter ;)
___
Analogies greatly simplified in order to make a point without adding a lot of disclaimers or explanations
 
If just hooking some panels into a battery and then using CHADeMO to charge another battery were simple it would be done that way - the idea of DC to DC is appealing. But instead of efficiency at the local level consider efficiency at the grid system level. AC power is dynamic and generally peaks in the late afternoon and with a low demand in the early morning before sunrise. By contributing energy to the grid during high demand with solar PV and using AC energy to charge EV battery during low demand is actually helping the grid and the power company. As end use of electricity gets smarter and can turn itself on during low demand and off during high demand then more stability can be introduced into the AC power grid. Eventually, some feedback and control from the utility company or independent system operator (ISO) will also tell the PV system to produce less or more if the grid stability needs that. Currently the PV systems run at maximum output from the available solar flux so any type of grid control is likely years away. There is some degree of feedback operating now, each of the microinverters monitor the AC line and will not deliver power to the grid if the voltage is out of range or the AC frequency is out of range.
 
pkulak said:
Does it bother you that you're capturing power in DC, losing some of it through an expensive inverter, then loosing more again when your car's rectifier turns it right back into DC?
Not at all. In addition to what others have written, I will point out that the losses due to power conversion are already *very* low and will get lower in the future. The efficiency of microinverters is above 95% while the electrical efficiency of the LEAF's charger is also above 95%, so total electrical losses are less than 10%. In addition to the electrical losses, there is power wasted to run the cooling pumps. You could argue that this could be eliminated, but doesn't the LEAF run them during CHAdeMO anyway? (I wonder why?) Expect these efficiency numbers to get above 98% on both ends in the future, particularly for three-phase systems like they have in Europe. Small inverters at that efficiency level are already being deployed in three-phase PV generation systems.
pkulak said:
Anyone ever think of just hooking some panels into a battery and using CHAdeMO exclusively to charge the car?
As QueenBee said, that would be a one-trick pony. Also, 240VAC is quite a bit safer than 400VDC.
Nekota said:
But instead of efficiency at the local level consider efficiency at the grid system level. AC power is dynamic and generally peaks in the late afternoon and with a low demand in the early morning before sunrise. By contributing energy to the grid during high demand with solar PV and using AC energy to charge EV battery during low demand is actually helping the grid and the power company. As end use of electricity gets smarter and can turn itself on during low demand and off during high demand then more stability can be introduced into the AC power grid. Eventually, some feedback and control from the utility company or independent system operator (ISO) will also tell the PV system to produce less or more if the grid stability needs that. Currently the PV systems run at maximum output from the available solar flux so any type of grid control is likely years away. There is some degree of feedback operating now, each of the microinverters monitor the AC line and will not deliver power to the grid if the voltage is out of range or the AC frequency is out of range.
+1, and I would take this a bit farther: The best case is to never curtail renewable generation. If the on-board chargers in EVs can be replaced by four-quadrant power converters that can act as either a charger OR a generator, then we can have our EVs provide electricity to the grid during peak demand periods. As more and more PV and wind generation and more and more EV storage is added to the grid, we should eventually be able to curtail the more polluting generation systems rather than curtailing the PV.

Finally, I will point out that the motors used in the mass-produced EVs in the world are AC motors. Perhaps we should be using DC motors to eliminate a conversion there! ;)
 
RegGuheert said:
Finally, I will point out that the motors used in the mass-produced EVs in the world are AC motors. Perhaps we should be using DC motors to eliminate a conversion there! ;)

Or AC batteries!
 
RegGuheert said:
QueenBee said:
Or AC batteries!
I thought about typing that. But then I thought "Nah, too corny!" (Even for me!)

But apparently not for QueenBee!! :lol: :lol:

It's a solution that kills both the motor's AC/DC inverter and the on board charger's ;)
 
Older electric cars used DC, which required sophisticated and heavy relays to utilize regenerative braking. All modern EVs use AC as 1) the diodes are all there to recapture energy on brakingand 2) the motors are lighter and easier to control. AC also provides the ability to transform voltages with coils (transformers), not possible with DC. The present systems for PV electric are excellent, don't require storage batteries, and pay for themselves quickly (about 7 years), giving a return on investment of 9-14%.
 
Our previous electric car was a VW Golf converted to electric with a 120 volt battery. I have 5 PV panels arranged in series that I could plug directly into the car and charge it directly from the PVs as the output voltage of the panels fairly well matched the charging curve of the batteries--as the battery voltage increased, the current output of the PVs dropped significantly, down to an allowable trickle charge rate for the batteries. However, the microinverters on the other PVs that I have allow them to produce a higher wattage output because of the MPPT function of the inverters, and they are also giving e usable power whenever the sun is shining, not just when the car was plugged in, as the other inverters did. I came to the conclusion that it was more efficient overall to reconnect the 5 panels that had been used to charge the Golf, using microinverters, and have them feed into our home system also, and the end result, even considering inverter losses and charger losses, would overall be more efficient. Still need to find time to do that, though.
 
How would you regulate it? From what I've heard the leafs batteries can have anything between 300 and 400 volts on them depending on the state of charge. From what I know about charging batteries, most of the "resistance" of electrical flow comes from the voltage on the battery, not the resistance of the cells, so if you increase the voltage of the charger just a little bit, the current goes up a ton. (because you've already overcome the voltage on the battery, all that's left to slow down the current is the resistance of the cells, which is quite small) So no matter what you do you are going to need electronic switching on the charger end. So the only inverter you would save would be the one that converts the solar panel to ac. All kinds of people make those and like the previous posters have said, they have become quite efficient. Plus, I wouldn't want to trust my expensive battery to a charger I built with my limited resources and knowledge. Big corporations like Nissan have a sea of engineers working in a huge cubicle farm. surely they could come up with a better plan than I could in my cluttered garage.
 
Solar panels are a current source, their output voltage will change based on the load resistance. The current depends on the light input. At least that what I was reading about when I installed my PV system last year. The Leaf battery could directly take my 5.7kW output all the way to 90% SOC, but the people in the Nissan cubicles made sure I will not try that.
 
camasleaf said:
Solar panels are a current source, their output voltage will change based on the load resistance. The current depends on the light input. At least that what I was reading about when I installed my PV system last year. The Leaf battery could directly take my 5.7kW output all the way to 90% SOC, but the people in the Nissan cubicles made sure I will not try that.
You'd need ~500Voc in order to attempt that, which shouldn't be too hard. Maybe 12 panels in series. You would also have to monitor the battery extremely closely, as you would have a significant chance of overcharging. Li batteries just don't have the overcharge tolerance of SLA.
 
Im pretty happy with my set up.
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IMAG1636_zps4c795964.jpg
 
My 2170 watts of panels generated 103% of all the electricity I used to fuel my LEAF and power my house last year. Net metering is a lot simpler and safer than trying to fuss with regulating a DC charge to the car. Not that I could, since my LEAF doesn't have a DCFC port.
 
dgpcolorado said:
My 2170 watts of panels generated 103% of all the electricity I used to fuel my LEAF and power my house last year. Net metering is a lot simpler and safer than trying to fuss with regulating a DC charge to the car. Not that I could, since my LEAF doesn't have a DCFC port.
How many miles do you drive? That is some serious conservation! You obviously have gas for space and water heating?

It takes a 17.9kW system (east/weast/south facing with lots of shade) to produce about 13.5 kWh annually for space/water heating, driving ~10k miles, and the rest of my electricity needs.
 
jimbo69ny said:
Im pretty happy with my set up.
How much more output do you expect to achieve based on that extra tilt? I presume the extra spacing help keep the wind loads limited significantly?
 
Thanks to the idiotic company I used to install the pv system I am only going to be producing maybe 80 of what I use. Probably less actually. I used a local company called Solar Liberty in Ithaca NY and they were a bunch of idiots! I told him I was going to be soon heating a 690 sqft place using electric that was not heated previously and that I drove a PIP but I was going to be getting a fully electric car soon. He completely undersized my system and because it was through NYSERTA I am not able to modify or add to the system. I am Fing pissed! It only confirms to me that if you want it done right, you do it yourself.

The system is on a duplex that I also live in. There are two PV systems and the panels on the right are solar hot water. The PV systems are 3 kw and 5 kw I believe. The solar hot water is huge because it also contributes to heating the radiant floor.
 
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