New Solar Panels for Hybrid Cars Improve MPG

I just wanted to drag this thread back up because it was my first read through it. I found something else in the maker's response that I haven't heard contested yet...

He says they can't charge the HV battery with the panels because that would expose the driver to high voltage at the panel. NOT. The low voltage would be carried by two wires down to the DC-DC step-up converter that would most logically be stuffed in next to the battery that it charges. You'd never put the converter up on the roof, and carry the high voltage via relatively exposed wires to the battery. Not for thes short distances!

There's so much wrong with this that it boggles the mind. 10% increase? Must have turned around and went back down hill!

 

Hello folks:

Just thought I would add some info on the PV prius project I built last summer. Seems there is much disbelief regarding the potential of PV to power a real car. Keep in mind that Univeristy solar car teams now routinely drive 1000's on km on nothing but the sun, but let's do some math first. I am not trying to sell my project, or kits. My car is the one with high efficiency 3 x 90 watt panels connected to the NiMh pack through custom designed circuits. I have years of experience with electric cars, do not do this without high voltage DC experience.

Ok, the prius has mass of 1400 kg, requires about 150 Wh per km at moderate speeds (research this with SAE papers if you do not believe me), so we can create a number = 150Wh/1400kg = 0.107 Wh/km.kg. That is, it takes 0.107 Wh to move each kg of Prius 1 km. This is a common number to use to look at electric vehicle efficiency.

Now my prius has 270 watts of PV at present, with batteries and other stuff, a PV system mass of about 60 kg, and with 5 hours of full sunlight (a good summer day in Canada), gets about 1300 Wh of energy, about the max my buffer battery can hold. Now that is enough to move the Prius 1300/150 = 8.7 km not accounting for inefficiencies of wiring battery charge etc. The energy required to move the 60 kg of PV hardware the 8.7 km is about 0.107 Wh/kg.km x 60 kg X 8.7km = 55.8 Wh, or only about 4% of the total energy collected by the PV panels. That means there is lote left over to actually help propel the prius.

The % imporvement in mileage depends totally on your driving pattern. Short trips will get more PV boost, on really long daily trips, the PV will become a small part of the overal enegry used, and you will see little difference. Being able to suppress the engine coming on would be useful, a modification I have not made. How much can this improve a Prius, I would estimate in Phoenix, with a well engineered PV Prius, hood and back with some PV too, 60 km daily trips, probably 20% better fuel economy. I have modelled this.

Is the system perfect, no, can it be more efficient, yes, is it meant to demonstrate the possibility, yes. In any case the PV can certainly carry itself and provide useful enegry to the vehicle, can it be cost effective, well, that depends on how much you value clean air and gasoline.

For those people that equate sun energy to energy in gasoline, remember, the gasoline is used by an engine and system that gets maybe 5 to 15% overall efficiency to the wheel power, depending on your driving cycle, the electric drive train is probably 50 to 70% efficient, so you cannot do direct gasoline to electric efficiency comparisons without including gas to wheels, or battery to wheel efficiencies.

So, now you too can work out what 30 watts of PV can add to the fuel efficiency.

Hope that helps.

 

Evan- I think the 12V battery connection is a misunderstanding on your part, or the merchant's description was too vague.. As far as I understood Steven's original design, yes he was charging 12V batteries, but it was *not* the car's tiny aux battery. Instead, he had a bank of *additional* 12V batteries that were charged by the solar array, and this bank of batteries powered a custom inverter which paralleled into the car's HV rail. A fair bit of difference there.. In another thread I posted some rough guestimates that confirmed that this type of system could provide MPG benefits. This type of system could also be easily turned into a "mild plug-in hybrid" (did I just coin a new term) by connecting a standard charger onto the 12V battery bank in cases where insolation is insufficient..

 

Mr. Lapp's numbers could be expressed as approximately 5 solar miles per day. I recall this number from theoretical calculations done in Prius groups several years ago for "full solar roofs", and do not doubt them.

We can hope for a hybrid minivan, with twice the roof area!

 

I don't doubt them either, and am happy to have Lapp's input here!

But we also must realize that this is with optimum conditions. Winter, garage parking, shaded driving - will all take significant tolls on this number. When I was doing this math long ago to decide if it would make any sense to add PV to my EVs... I came up with a year-round average of under one mile/day boost. And all this at an expense of MANY thousands of dollars. I'll stick with the PV on my garage roof for now - which provides me with 100 miles/day or power if needed.

 

Hi Steve,

Nice to have you join us here at Priuschat! I for one have long been a fan of exactly what you've done. My sums suggest that a near future solar PHEV could manage up to 20 miles per day from onboard solar, (my thoughts on that here), not insignificant given the rising cost of gasoline.

Did you know that a countryman of mine has made a solar conversion of his Bedford van? Can't be too many solar vehicles in the world in private hands! We don't get much sun over here, but he still gets about 20% of his commuting from onboard solar, and another 40% from onboard wind power. Here's his website:

http://www.solarvan.co.uk/

Things are looking good for solar with the new nanotech and infra-red PV cells coming out soon. Exciting times!

Clett

 

I am new to this group and just read thru this thread. Nice work debunking the original claims on this product.

I just wanted to make a small comment on the idea of using a DC to DC converter to make this 30w panel charger the high voltage system.

Any time you want to step up voltage you reduce current. It is 30w no matter how it is presented. Any DC to DC conversion is also going to have less than 100% efficiency, more like 80%. So 30w at 18v = 1.67 A charging current. 30w at 270v = 111mA – 20% = 89mA of charging current. I don’t think that would be even close to the amount of current needed to overcome the internal resistance of the high voltage battery array.

I don’t know what the internal resistance of the high voltage battery array is but I don’t think this would yield any noticeable charge on the high voltage system. You would have to do something like Steve’s system where you use a 12V array to collect the solar energy and once that is full Dc to DC convert and charge the high voltage array.

 

Solar is indeed facinating.... I'm glad someone is pursuing it or we will never get there!
As batteries and solar cells get more effecient and cost drop we will arrive, but for now its a big cost for a tiny payback for the small surface area we have to put the cells.

If we get plug in going, then we could mount cells on our roof of our houses and indirectly get free power for the car that way.

Prob the wisest and simplest way will be to put it back in the grid to offset electric costs to our home and them pull off the same grid to charge the car.

Unless they want give us "less credit" for every Kwh that we give than what they charge us for later. Presently its a wash.... for every kwh you put into the grid, you get credit for to use later or get paid for it if you don't use it at all.

At any rate, the main drawback I see to most of the solar cars is that they don't also have the prius technology. Alot of power is wasted in braking. We don't really need regen on coasting because free coasting would actually be more efficeint than charging batteries and then reusing the power.

The only reason the prius is not set up that way now is it would throw off drivers habits of how to drive too much... usually when we take our foot off the accelerator.. its because we want to slow "more" than free coasting would do... it also simulates the normal transmission drag of other cars too.

At any rate, I wish they would give us a choice.. to turn regen off for coasting or leave it on if we preferred.
Gentle braking would do the same thing if needed. It would take a little practice to get use to...
but some bozo would take thier foot off the gas while talking on the cell phone and rear end someone because they expected the car to slow much faster than it did.
All it takes is someone to jump in thats not used to the prius!

But regen for braking is a biggy... how many times do you spend all your energy to get up to 50 or 60, just to have to shut it down again and lose all that energy?

Solar cars need that too if thier numbers are going to look good.

 

Now you're singing my song. This, of course, is exactly what I do. I still call my cars "solar powered" since that's where my energy comes from... though it comes from the roof of my garage - not the roof of my car.

OK, you lost me here! Most "solar" cars I see are pure battery electrics with some solar boost added to the mix. All the production battery electric cars had regenerative breaking that is so far superior to the Prious, that you might as well pretend the Prius doesn't have any! The Prius counts in Whrs, and in a car like the Rav, we have to count it in kWhrs for it to be a reasonable number! So I'm wondering... which cars are the "most cars" that use solar power and don't have regenerative braking?

And also for the record, most production EVs have a button somewhere handy so the driver can choose regen when slowing or pure coast. Almost everybody uses pure coast for most activities, and just switch into regen when it is a benefit to slow down without the brakes. Nobody's sued about the coasting yet, and a good EV like the EV1 can coast for MILES.

 

you want free coasting in a prius? feather or throw it in Neutral.
.
_H*

 

I'm curious to know how many panels and amps your making and using and feeding into the grid... maybe you can PM me..
I lived for 12 years with a hydroelectric system I built and lived off of... 60amps X 24 volts 24/7 was nice!

I may be moving back to Texas where there is 300 days a year of sunshine and lots of wind, so I may explore that option again.

As far as the regen.... I am ignorant of actual electric cars.. I was not aware.. thanks for the info!

I was just thinking of cars that had been modified.. I didn't think that too would be modified.... but you should know.

 

Sorry Evan- I did read the whole thread, but from the similar description, was always under the impression that Solatek had licensed Steven Lapp's working PV system, which does include a secondary 12V battery bank and *does* generate measurable MPG gains.. See http://www.lapprenewables.com/hybrid%20project.html

If the Solatek is indeed charging only the 12V aux battery, then yes, it is a useless system in terms of MPG gains- I've recently put a 15W monocrystalline panel (to replace a 5W thin-film) in my car to keep the 12V battery topped up- the monocrystalline panel probably nets 75% of the real output of the 30W thin-film panels and I see absolutely *no* contribution to MPG, although the 12V battery is now consistently "full" whereas with the old 5W thin-film panel, it only produced about 30 mA over the parasitic drain on good days and in general barely broke even..

Contrary to most opinions here, I believe that the PV concept is sound, subject to some limitations.. Looking at the totally ideal situation: assuming sufficient insolation and a solar panel that really produces its rated output, 30 Watts x 10 hours a day is 300 Watt-hours, which even with conversion losses up to 200V, represents a fair number of "leaf-cars" worth of regeneration. They key however is that this energy must be first accumulated offline (the bank of 12V batteries) and then converted. If the vehicle is "on-the-move", the real-time contribution of the PV is, as everyone has pointed out, absolutely neglible.. The difference is that when the car is moving, an additional milliamp to the HV battery makes no difference, but if you store it up so that a burst of tens of amps is available to assist with acceleration and other high current demands, then you start to see the benefits. How much benefit will depend on the size and efficiency of the PV solar panels, the storage system and the conversion system, and ultimately, your driving habits..

Additionally, in reality, there are a number of technical issues to be overcome.. #1 is that insolation is generally not very high in most areas and you don't get 10 hours of full strength daylight. Second is the issue of real vs. rated output power of solar panels- even if you have sufficient insolation, a 30W panel is likely to only give you 10-15W, especially those thin-film panels, which are usually only about 8% efficient and whose output deteriorates as much as 30% in the first 6 months.. This is why Steven Lapp's system has such a large amount of PV (270W of the more efficient (as well as heavier and more expensive) crystalline solar panels vs. the cheaper and less efficient thin-film used in the Solatek)

 

It's been my experience that the A/C costs about 2mpg. Why not use solar power-assist to charge-run the only the A/C? I think I read somewhere the A/C is on the 12V system.

 

Yeah, yeah. I want to be able to simply lift my foot off the throttle for coast. If I want to slow, I'll use the proper pedal. Going through all the fancy mechanations of feathering or shifting isn't such a big kick for me. The car should help *me* save energy... not the other way around.

 

The answers are all on my solar page (can be accessed from the front page of my EV site).
http://www.darelldd.com/ev/solar.htm

quick answer: 20 panels (would be 16 today) and I make over 350kWh/month average which pays (in Time of Use credits) for ALL of my home use and ALL of my EV use.

There are many non-production cars that employ regen. It does make things more expensive, and most "back yard" conversions stick with a DC motor and ignore regen. Cheaper and easier to build. This is one of the reasons why the production cars typically get way better range than the home-builts.

Regen has two main advantages, as we see in the Prius. The obvious one is that you can reclaim some of your kinetic energy when slowing... and the other is that your brakes last longer. When properly implemented, the brakes are ONLY needed for bringing the car to a complete stop from ~2mph. I did a 0-60-0 run in the X1 in five seconds... and the brakes were only used at the very end to stop the final roll. With proper regen, a car will stop faster than it'll go... all with no friction braking. Diriving a curvy road with 100mph+ speeds between turns - and using no brakes is an amazing, connected feeling.

 

<div class='quotetop'>QUOTE(ken1784 @ Dec 10 2005, 02:42 AM) [snapback]171272[/snapback]</div>

Over here in the US, there are 60 minutes in an hour, so you would need to be going 60 MPH to get 1 mile/minute. :huh: (sorry for the jab)

I, too, question the 10 percent claim. As the saying goes " Your actual milage may vary"... The energy you are getting from the sun is a FIXED AMOUNT (on any given day). The distance you travel can VARY greatly. ASSUMING for the moment that I make enough energy to drive 1 mile (I'm grabbing this number out of the air, BTW), and my commute is 2 miles, I have a savings of 50%. Now, if I have a 50 mile commute, my savings is only 2%.

"So, what's your point?" you might ask. Even IF the numbers are accurate, it is impossible to generalize the amount of savings that any given person will receive with supplemental power such as a rooftop solar panels or a pluggable hybrid.

Of course the better answer is to charge the car from the power grid (requiring, of course, a pluggable hybrid option). "But I want to use solar power!" you say. The solution is to install a solar array at your home. The solar energy can be used immediately, or the excess will be sent to the power grid during the day (spinning your meter backwards), for consumption at a later time (no need for offline storage).

I have a 3KW solar array on my roof (at 95% efficiency), and produce about 350KWH per month, which can make a huge dent in meeting the needs of a pluggable hybrid. All I need now is a pluggable option for my Prius.

 

<div class='quotetop'>QUOTE(Hawk @ Mar 4 2006, 05:12 AM) [snapback]219800[/snapback]</div>

eh? 89 milli-amps is 89 milliamps no matter how you cut it. if your DC converter can pump it up to 270V, it will definitely flow through the HV battery and charge it up.

If you park your solar Prius in the sun, and got a nice good 5 hours of sun, that would be 445 mA-H, or about 0.445 Ampere Hours.

This is quite significant considering that the Prius HV battery is only 6 AH. That's a 7% charge-up everytime you parked your car all day in the sun. You could almost go 1/2 mile with that charge.

Jimmy

 

<div class='quotetop'>QUOTE(jimmyhua @ Aug 2 2006, 08:06 AM) [snapback]296275[/snapback]</div>

Best case senario and your right, how much does half a mile of gas cost?

Its true our present battery won't get you much furthur on a full charge, but thats not what gives us our good gas mileage anyway.

The battery acting as a buffer to give back what we wasted several times in a 5 minute period is what is helping us. Its not so much how much it will hold at one time as much as it is how much it "saves" and gets to use in say an hour as its constantly fluxing between expending its energy verses saving it.

Until we can first of all get battery storage that can go much further.. at least 20 miles, its not even worth considering the hassle and expense and maintenance of all those solor panels.. "unless you want to do it just for fun!"

Even if we could save 20 miles from the sun... we are still only saving about a 1.50.