[larrycren]

I see that an add-on switch is available in North American Priuses to let the car run on battery only at low speeds (and that the switch is standard elsewhere). So, does anyone have a combination of battery-only around town and solar panels to keep the battery charged? Thanks.
Larry--who has now owned a Prius for 21 hours.

 

[clett]

I thought about that. You can read my ideas here:

http://mysite.wanadoo-members.co.uk/ecotech/socar7.htm

But basically, for a DIY solar powered Prius (ie solar cells on the roof that top up your battery when it's parked so it always has about 2 miles city range in EV mode) I'd suggest:

1) Put the panels on the roof and bonnet - there's maybe 4 metres squared of easily panelled area.
2) Use SunPower solar cells - might cost about $2000/m2, but are 20.4% efficient, so worth the extra.
3) Only park in the sunshine!
4) Somewhere sunny (say, California), you're looking at a yearly average of 5.5kWh from the sun per m2 per full day. You'll only get 20.4% of that converted to electrical energy, but times four (4m2 panels) means you could get about 4.5kWh electrical into the battery per day.
5) That's a lot more than the OEM battery can store, so you might want to put a second battery in to store it all!

4.5kWh might not sound very much, but at 4 miles per kWh, it's 18 free miles per day which would go a long way to preserving your ICE and could suffice for a lot of people's commutes. At $10k for an install, however, it'll only start paying for itself when gas hits $4.10 / gallon!

Still a nice idea though.... 8)

 

[Daniel]

Larry, what you are suggesting is far from a trivial project. First of all, the added battery capacity requires very sophisticated controls and protections, and must be integrated with the car in a way that works properly with the existing circuitry. Wayne Brown (on the Yahoo group) has done this, and maybe a few others, but compared to the EV switch it is tricky and dangerous. If you do not add battery capacity, your maximum distance on an 80%-full battery is only going to be around 1.5 miles, and if you bypass the car's own controls to charge the battery above the 80% that the car likes, you may drastically shorten battery life.

The 18 miles that clett feels those solar panels might net you would require about ten times the present battery capacity.

Putting solar panels on the roof would also be problematic, due to the curved shape. You might end up with a car that has poor aerodynamics at highway speeds.

Finally, the maximum speed in EV mode is 34 mph, and you must accelerate gently or the ICE will kick in.

In my opinion, turning the Prius into a solar-powered car is not practical. You'd be much better off putting those solar panels on the roof of your house and using that electricity for home uses. Or use home solar panels to charge an all-electric car.

Those solar race cars are extremely light, and extremely wide and long to maximize solar capture area, and low to minimize drag.

 

[patrickg]

Daniel, A most excellent response. Prii don't lend themselves to being electric cars. Going to extremes to try to run on electricity without modification is a lost cause as ultimately all the electricity comes from running the ICE. Running the ICE to propell the car is much more efficient than running the ICE to charge the battery so you can pretend to have an electric car.

Most commonly available solar panels are not nearly as high voltage as the Prius "propulsion" battery and so you would have to have the equivalent of an inverter, and a battery charger made for the higher voltage. All this introduces additional losses. It might get "interesting" in a crash to have all those high voltage wires running from the roof to the "guts."

If someone really wants an electric car then by all means get one and try to fing a less poluting menas of charging the battery than running the ICE in the Prius.

The Prius is a gasoline powered vehicle. The battery and electric motor relieves the automotive designer of the responsibility of including an ICE with enough power to meet peak demands thereby increasing fuel efficiency by load shifting. There is one similarity to an electric car. You get to recycle energy with regenerative braking. It isn't perpetual motion but it helps.

Pat

 

[Bob Allen]

To "convert" a Prius to charge itself on solar power, one would need to be either: 1. very rich, so that voiding the warranty and possibly trashing a 25-30k Prius wouldn't be a big deal, or, 2. extremely adept with electronics, computers, autobody shop skills, and overall engineering problems..
On both this chatline and on Priuschat.com, there are many posts from owners who feel that Toyota only got it about 80% right. No doubt, this car will be improved and improved yet again as the hybrid technology unfolds, but I think Toyota did a great job with the Prius. Why try to make it something it isn't and wasn't intended to be?

 

[ehurtley]

The 18 miles that clett feels those solar panels might net you would require about ten times the present battery capacity.

I agree with most of your comment, but I just felt this part needed a clarification. I think clett meant that over the course of a day, you could get 18 'EV' miles that you wouldn't have gotten without the panels. (18 miles that without the panels, the battery would have been too low to operate in EV-only mode.) Of course, I drive about 50-100 miles a day, in varying conditions, and I doubt I would have 18 miles a day that would have been EV capable, if only the battery was more full. So it would probably help a little, but in the long-run, I doubt adding solar panels (without increasing battery capacity,) would help much, unless you spend a LOT of time stuck in 0-10mph traffic.

Of course, you could get one of those solar 12v trickle chargers, to keep your accessory battery permanently topped off. (So you wouldn't have to jump start your car ever.)

 

[larrycren]

Thanks greatly to everyone for the thoughtful comments. As I drive and learn, it seems to me that the Prius is most of all a masterpiece of integration--mechanical, internal combustion, electrical, and computer technologies put together nearly seamlessly. It might make sense to take a little advantage of the battery power on the edge before the gasoline engine kicks in, but in most cases you pay a little later with a lower charge on the battery. It seems usually best just to drive mindfully and a little gently and let the system do the rest--that and wait for the next generation.

Thanks again.

 

[patrickg]

There is nothing wrong with a flight of fancy or wishing you could substitute magic for engineering. Any sufficiently advanced technology is indistinguishable from magic. To significantly modify the Prius toward being a more than just barely part time electric car just isn't economically feasible. Everything you need to do to make it more of an electric car, beyond the EV switch (defered ICE operation not avoided ICE operation) interferes with some of the clever preexisting engineering.

Think about this. Install a trailer hitch to "pull" a solar trailer with extra batteries and a folding canopy of PV units to be deployed as a shade over the car when parked (solar charge mode). It would need to be aerodynamic when folded up and tucked in close behind the Prius.

Alternatively you can hope for commercially available cold fusion energy generators.

Yet another alternative is to drive a stock Prius responsibly, encourage others to do so, and be alert for opportunities to do even better.

Pat

 

[Jeffand]

:idea: Just to let you know that it seems to me the max speed i can get in electric mode is 40 mph. As soon as i hit 40 the engine starts every time. My 2004 Prius does not have the EV mode button.
I'm getting about 50 MPG doing combination driving.

 

[ehurtley]

I've coaxed my Prius to engage 'electric-only mode' (not EV switch) as high as 62 mph, but I'm assuming that the ICE is spinning gasless at the time. (VERY slight downhill, so even if I feather it so I'm truly coasting, I slightly decelerate, so slightly more pressure on the pedal, and it shows only electric power on the 'Energy' screen, holding 60 steady, sometimes even going up to 62.)

In true electric 'stealth' mode, with even the ICE not spinning, I've coaxed it to 42 a couple of times. The SOC meter has to be in the green, though. If it's even one bar short of green, it'll kick in the ICE 'no matter what' above about 35, no matter how hard I try to feather.

 

[patrickg]

All of this "electric mode" activity is somewhat interesting but not directly connected to solar powering a Prius. I too "play" at having the Prius stay electric sometimes but ultimately since the power ALL comes from the gas tank via the ICE it is mostly a mind game with little impact on overall economy, polution, or reality.

You could relatively easily retrofit a charger/maintainer for THE BIG battery so you would start each trip at full charge. This charger could, with a proper inverter or enougn panels, be a solar charger. The range on a "full" battery in EV mode is so restricted that allthough it might be making a statement, in reality it would be essentially futile.

Like the flight attendants sometimes say... "For those of you who do NOT have Dallas in your travel plans today, you might want to deplane and consult the agent before the jetway is rolled back." For those of you who have some notion that a Prius is not a gasoline/ICE powered car or that it is electric, you need to consider selling it and buying an electric car.

Likewise, solar power for a Prius is not economically feasible. If you really intended to get a solar powered car and thought the Prius was a likely candidate for conversion then I'm sorry to be the one to burst your bubble but, "wrong answer Hans!" The Prius is also a bad candidate for conversion to be powered by a wind-up escapement, flywheel energy storage, hydrogen peroxide, ruber bands or a plethora of alternative schemes including cold fusion (for the forseeable future.)

Meanwhile, you have a really nice near state of the art convenient gas powered hybrid. Under all that technology the MAIN source of economy in the Prius is undersizing the engine and supplementing for short bursts with electricity. The short bursts could come from stored compressed air or wound up ruber bands if they were easy to harness and regulate and had the efficiency and ease of use of electricity. Just think... then we'd be reading posts asking about how to wind up a rubber band with solar power.

Pat

 

[Daniel]

You could relatively easily retrofit a charger/maintainer for THE BIG battery so you would start each trip at full charge.

Apparently, from reports, this is not so easy to do at all. You have to connect to the computer, so it "knows" that you are charging the battery, or it becomes very unhappy. -- Just one more reason why "improving" the Prius is best left to Toyota, who will no doubt come up with some wonderful improvements for the next major model revision in 5 or 6 years.

 

[patrickg]

Daniel, Thanks for helping me make my point and for the additional info. So you need a powered "treadmill" for the Prius so you can simulate coasting downhill while parked with the car turned on. That way the regen braking you get while coasting will charge the battery. A light sensitive diode placed on the display can monitor the SOC indicator and energize the rubber tipped solenoid that presses the power button to turn the car off when fully charged.

Alternatively we can realize that the Prius is neither an electric car, nor reasonably convertable to a solar powered car and use it like it was intended. If someone feels like they just have to do a little extra to "save the planet" they can get involved in "Zero Population Growth" or population reduction strategies since over population is the single greatest threat to the planet and human life on it. Overpopulation exacerbates ALL of the ecological and environmental problems. //SOAPBOXMODE OFF//


Pat

 

[AgentElrond]

A solar trickle charger for the traction battery could still be useful to help maintain a charge, even if you couldn't directly power the car with it. A good example might be a trip to a theme park; if the car is left in the sun all day, any improvement on the charge between when you arrive and when you leave is better than none.

 

[Daniel]

So you need a powered "treadmill" for the Prius so you can simulate coasting downhill while parked with the car turned on.

We could have Prius-charging solar treadmills at selected parking meters.

TechnoMage:
You miss the point: You cannot simply connect a trickle charger, or any other charger to the traction battery. It requires a very complicated mechanism that "talks" to the computer at the same time.

As Patrick says, if you want a car you can charge from an outside source, you'll have to get an electric car. The Prius isn't it. -- There is a group trying to figure out how to do this, as well as add additional battery capacity. I think they call themselves the Prius Plus Project, or something like that. For my money, Toyota is likely to do it first, in 5 or 6 years, with the next major model revision, or in 10 or 12 years, with the one after, while the amateurs are still trying to figure out how the computer works.

 

[AgentElrond]

TechnoMage:
You miss the point: You cannot simply connect a trickle charger, or any other charger to the traction battery. It requires a very complicated mechanism that "talks" to the computer at the same time.

Daniel: Which point... pen, pencil... compass?
I wasn't contemplating building one myself; rather that Toyota might pursue it as a feature/option on future models - let them figure it out. 8)

 

[patrickg]

I think it is EXTREMELY unlikely that Toyota would either include a battery charger for the tracton battery or build in provisions for attaching one as it would invite a lot of negative speculation as to a need for such (which there isn't.) "Oh, you have to plug it in?"

They probably won't be including a built in defibrilator either.

A very small percentage of owners might be interested in having a charging capability and a smaller one yet might actually receive benefit from it. Even a poll taken here would not be valid as we constitute only a very small minority of owners and the demographics are skewed toward (searching for politically correct or at least acceptable term...) uhh, err ahh... geeks. Make that BUFFS!

Pat

 

[hyperion]

It is also my understanding that you don't really know when "ICE" is running unless you have installed the aftermarket engine on light. When the engine is running to heat the coolant and catylitic converter it is not always indicated on the energy display.

 

[patrickg]

OH! Hyperion... Say it isn't so!!!! The ICE running a bit without any indication. Heresy! Well anyway, I meant to find out about a forthcoming user installed kit that is sort of like the EV button but is an ICE button which when depressed prevents the electric motor from operating except for reverse (safety consideration.)

The upscale version will be a three position toggle allowing the driver/user to select ICE only, EV only, or automatic. Then "knowledgeable" users can make their own "informed" decisions about when to be electric and when to be gas. Of course many are avidly awaiting the introduction of the add-on that lets the user "dial-in" their preferred "coasting" regenerative braking bias and aren't stuck with the Toyota engineer's "guess" as to how best to simulate the compressive braking of a traditioinal gas engine (maybe your Lamborghini Miura "felt" different.)

Later (introduction date to be announced) the kits for user setting of valve timing, mixture control, and so on will be introduced. There are just lots of things the uninformed driver takes for granted that Toyota engineers may or may not have got right for a specific user's special needs. Over time this can be corrected by the application of aftermarket "enhancement" products. Don't let a little thing like prolduct warranty deter you from doing what in your heart you know is right. Take for example the auto diming rear view mirror... Shouldn't it have a user setable glare vs dimming ratio control? Surely the production version is a compromise suitable at best for only certain persons in certain situations. ...and on and on and on...

Pat

 

[Daniel]

TechnoMage: Sorry. I thought you were suggesting a charger for the traction battery as an aftermarket mod.

maybe your Lamborghini Miura "felt" different

Hmmm. No, maybe I better not say it...