Advice for a project: Charging a plug-in car with solar panels

[Karen in Tucson]

I have been working on a more "green" focus for life here in Tucson, and the latest change was buying a Plug-In Prius. Love it!! It's a hybrid but it can get "999 mpg" (use about 4kWh of electricity instead) for any trip under 10 miles, which is lovely.

I have toyed with solar panels for a recharging system for an RV in the past, but that was easy because the "coach" batteries on an RV are basically the exact same animal as those in a small solar system anywhere. What I want to do now it throw a couple of solar panels on the roof of the carport and charge the Prius with them, which doesn't seem quite as simple.

The fully charged battery on the Prius is approximately 4kWh, it's designed to plug into a household 110 outlet and takes 3-4 hours to charge. I don't know what kind of amperage it draws. I have a 2000 watt inverter. I guess the big question is, does anyone know if I need a separate battery (i.e. panel-battery controller-battery-inverter-car) or could I get away with panel-inverter-car. (the car has a "shut off" when the battery is charged, so maybe don't need a separate controller in this scenario?). Does anyone know if the car needs a constant stream of energy vs a trickle charge? I don't.

I'm ok with waiting for the sun (trust me, Tucson is not lacking in sun), I don't need to charge the car at night. If I need a separate battery, do you think it would be possible to go with a smaller capacity than 4kWh, as the panel should be recharging the battery at the same time the car is drawing from it, or will this put too much strain on the battery?

Any creative thoughts or advice appreciated, TIA!

Karen

[Mike90250]

All said and done, a Grid Inter-Tie inverter and PV panels would be the way to go. Recharging batteries, the conversion losses approach 50% loss, of your harvest, and you have a mess of batteries to deal with.

The straight forward way would be to get 1-3 KW of PV installed on your roof, permitted, and then Grid-Tie with your electric company. No batteries to maintain, and when not charging your car, you are unwinding your electric meter.

[Sunking]

Just get a grid tied system and use the utility as your battery. To do what you are thinking is a huge waste of resources and money. Not to mention would require a very expensive custom built charge controller.

FWIW your Pirus does not get 999 mpg, not even remotely close. Using a conversion of heat energy of BTU's your MPG conversion 4 Kwh battery contains roughly 13,650 BTU's. A gallon of gasoline contains 114,000 BTU's. Your Pirus has a battery to wheel efficiency of roughly 400 wh/mile so you get about 10 miles per charge. That works out to roughly 110 mpg.

If you factor in the all the losses from the generation station to the battery down to 75 mpg. Try to go solar the way you want and now down to less than 20 Mpg.

[Karen in Tucson]

I forgot to mention ...

I'm trying to get away from a centralized infrastructure, my work is toward a more sustainable green focus. Definitely not interested in the deal my electric company has to offer, which keeps me TEP-indentured for another 20 years. But I am also definitely not ready for full-on off grid power yet, I'm looking toward three digit expenditure, not five, as an intro to getting off grid. We have some of the necessary items for a small system, including an adequate inverter, it's the question of how small we can go as a starting point and still charge the car without damaging it.

Re the "999 mpg", I find the whole concept of mpg in an electric car rather cumbersome and pointless, there is no "g", mpk would provide a much more useful bit of information. The nutshell is that we're paying about 25% for the electricity that takes us as far as the equivalent amount of gas in our other car. (But it is fun to see 999 come up on the dashboard!) The next step for me is making sure that electricity is produced as cleanly and independently as possible.

-- I realize that a solar panel array is never going to be cost effective, most especially if it's only used to charge the car. We will hopefully expand at some point, but this is more about exploring the envelope and laying groundwork for a more expanded system later on.

thanks for the responses so far!

[Sunking]

I'm looking toward three digit expenditure, not five, as an intro to getting off grid.

Cal it quits then. Anything you take off-grid is going to cost you a minimum of 10 times more than buying from the power company for the rest of your life. Used the way you want much much more than that because you cannot utilize the all the potential power. Most of it would never be used and wasted. Three digits would not even buy the solar panels. The custom charge controller would be 5 digits alone.

Do it your way and you are looking at 5 digits easily and you get no help from your neighbors paying for most of it. Go Grid Tied will cost 4 digits after your neighbors pay for most of it. Not to mention doing it your way is not earth friendly and would be a very heavy pollution contributor.

That is how the cookie crumbles like it or not.

[green]

Charging a car from panels is a nice thought, but once it's planned out and numbers put to it, it really doesn't look so good any more.

Here is a thought. I don't know if I missed it in your posts, but what time of day do you drive this thing? Is it sitting in your driveway everyday between 10AM to 2PM? Because those are the hours it would need to be parked and charging every day. Most people drive their cars during the day and park them at night. If you are gone during the day, a Grid Tied System would be producing electricity and building up credits for you to use to charge your car at night.

If you are a prepper (sorry but I kinda hear that in what you are saying) you can look at it this way. If you install a Grid Tied System, when TSHTF you will have all the panels you need to build a different system with already.

[russ]

Re the "999 mpg", I find the whole concept of mpg in an electric car rather cumbersome and pointless, there is no "g", mpk would provide a much more useful bit of information. The nutshell is that we're paying about 25% for the electricity that takes us as far as the equivalent amount of gas in our other car. (But it is fun to see 999 come up on the dashboard!) The next step for me is making sure that electricity is produced as cleanly and independently as possible.

The cost is per energy unit whether you call it kW or pigs knuckles. An electric car charged off the grid is really no different than any other car - except that you get to prepay the energy costs for years ahead.

[Mike90250]

-- I realize that a solar panel array is never going to be cost effective, most especially if it's only used to charge the car.

I wish I could afford to think like that.

[Sunking]

I wish I could afford to think like that.

You can Mike. You live in Calaphonie and your Governor Jerry says you can.

[Karen in Tucson]

Charging a car from panels is a nice thought, but once it's planned out and numbers put to it, it really doesn't look so good any more.

Here is a thought. I don't know if I missed it in your posts, but what time of day do you drive this thing? Is it sitting in your driveway everyday between 10AM to 2PM? Because those are the hours it would need to be parked and charging every day. Most people drive their cars during the day and park them at night. If you are gone during the day, a Grid Tied System would be producing electricity and building up credits for you to use to charge your car at night.

If you are a prepper (sorry but I kinda hear that in what you are saying) you can look at it this way. If you install a Grid Tied System, when TSHTF you will have all the panels you need to build a different system with already.

Prepper? Lol. DOOMER, Dude. I am thoroughly convinced that we are the icing on the cake of environmental collapse that's been baking for the last 10,000 years or so.

I'm not rich but I have enough, and I'm investing what I have in a sustainable ... glide path. No machine guns, no Nostradamus, no underground bunker in the back woods, just a personal infrastructure in a city that can be disconnected from the whole if necessary. Not asking for agreement with my POV, just some technical advice!

I get what you're all saying, GTS is less hassle, less learning curve, provides for a multitasking power source, and takes some of the sting out of the price tag. All good things, just not where I'm coming from at the moment.

My driving schedule is extremely flexible and yes, it can sit in the driveway from 10-2. But the insolation here is astonishing, I feel like a bug under a magnifying glass and I can't understand why the whole damn city isn't powered by the sun. I'll let y'all know if I find a solution to my dilemma, and meanwhile thanks, this website is intense!

[green]

Well, sorry about the prepper comment. We get a few passing through here, and they usually don't admit it right away. So we have to read between the lines.

As stated before what you want to do is possible, but it will require thousands of dollars and is definetly not the most economical solution. You will get a lot of that around here. The experts are just trying to find you the most bang for your buck so you don't make a very expensive mistake. I hear it quite a bit because everything I do is paid for out of my hobby budget. I build DIY panels and gadgets for fun, not to save money on my energy bill. I do it to learn and see what is possible, so I understand where you are coming from.

You can learn how to do what you need to here, but remember everyone will put their two cents in on what the best solution is. Just keep an open mind and learn as much as possible.

[thastinger]

OP, have you read the stickys in the off-grid section? I think all of your answers will be found in there.

FWIW, an off-grid system capable of producing 8Kw a day will cost you about 11-14Kish up front, and then battery replacement every few years after that.

[Mike90250]

If you figure out your charger power requirement is (how many amps from the 120V or 240v outlet) you may be able to use a PV array of about 150% of the wattage (If you need 120V @ 18amps = 2160watts for charger, and therefor 3240watts of solar) a 200ah, 48V battery (8, 6v golf cart batteries) any name brand MPPT controller, and any 48V inverter that meets 130% of the chargers power draw (you don't want to run it at 95% capacity) Grid independent, you manually plug in at 10 am, unplug at 3pm only on sunny days, and you could run a fridge and a light off it days there is no shopping to do with the car.

And get blackout curtains on your windows, you don't want your house to be the "candle" attracting the "Moths" to the flame. Maybe do a stealth install of panels in your backyard, not the front. People see stuff, they want stuff.