Solar Electric Vehicles

Their claims are borderline ludicrous, and wishful thinking...

1. In their logic, a 215 W/h solar panel is going to give you 20 miles driving distance? Let's look at that and take LA as an example: on June 19th, the longest day, you get 18h 07m of sunshine (if it's not cloudy). So if your car were to sit in the sun all day (and let's give them the benefit of the doubt by assuming the 215W/h is valid for every sun angle on the panels), you'd get 18.1 * 215 W/h = 3.891 kW, which, according to prienrg.com will propel your Prius for 24 miles @ 40mph, or 15 miles @ 70 mph. That is assuming that

- all that energy was able to be stored in your battery without loss
- all that energy was able to be retrieved from your battery without loss

Surely, your car won't be sitting in the sun all day either. So those numbers seem vastly exaggerated. Let's use some sensible numbers and repeat:

2. Average sun exposure over the year to be taken as 15h daily, but you park your car at work in a garage, not in the sun! So your exposure might shrink to as little as 4 hours or so, if you park outside at home. 860 W/h is what's left. that'll get you 5 miles at 40mph and 3.3 miles at 70 mph. Not impressive...

Oh, and decrease those figures by about 20% for battery efficiency losses.

Cheers

- Balt

 

<div class='quotetop'>QUOTE(nerfer @ Feb 11 2007, 11:52 PM) [snapback]388789[/snapback]</div>

In principle I could, but I need a guaranteed very long level stretch. Where I live there are way to many variables to trust any data, without repeating it very many times (under same engine temperature at start, etc.)

Anyone live near the Bonneville Salt Flats?

Dave M.

 

<div class='quotetop'>QUOTE(nerfer @ Feb 12 2007, 10:34 AM) [snapback]388975[/snapback]</div>

I've had a picture of it (with link) on my Prius -> Misc page for over a year now. No worries. We're on top of it.

 

<div class='quotetop'>QUOTE(TonyPSchaefer @ Feb 13 2007, 05:05 AM) [snapback]388952[/snapback]</div>

As I understand a solar mod like that is going to cost you around $6k! Not exactly cheap...

<div class='quotetop'>QUOTE(nerfer @ Feb 13 2007, 05:34 AM) [snapback]388975[/snapback]</div>

haha, maybe not by the laws of geometry, but certainly by the laws of spherical trigonometry. That's why the sun never sets north of the polar circle in summer.

Check out my little freeware for that: http://astro.phys.unsw.edu.au/~balt/ (scroll all the way to the bottom, the software is called "PEMACS" and gives you the number of dark hours. Subtract that from 24 and you have the amount of sunshine time.

 

<div class='quotetop'>QUOTE(nerfer @ Feb 12 2007, 01:52 AM) [snapback]388789[/snapback]</div>

I talked with them via email a month or so ago and their "kit" includes adding extrea lead acid batteries to get the 19-20 mile electric. They also told me that they include a plug in for all the batteries, all for around $4500.00 ( reasonable ). I asked them the reason for using lead acid vs NiMH/Lithium, and, they said cost and the unknown life exp. of Lithium in particular. They said that by the time you need to change the lead acids, better technology batteries may be available at a reasonable price. I am going to visit them in the next month or so and will gladly update if any one is interested.

 

I'd be interested in your results, please let us know how you fare. Personally, I wouldn't do it for the abovementioned reasons (also would worry about lubrication issues, unless they address that?). But then again, I don't get to drive a G-IV either... so please, do let us know (and send some pictures from the flight deck! )

Cheers

- Balt

 

I've been thinking of solar panels lately. Powering a Prius off of one, no. What I've been thinking is powering an engine block heater, a catalytic converter heater, maybe even a fuel tank heater, all off of solar power. Plus a 12V recharge to counter the SKS drain. (And of course a plug for when parked in the garage at night.) It wouldn't help EV mode any, but I'd imagine it'd do wonders for winter fuel econonmy and improve emissions. I'd probably use thermistors to shut down the heaters when temps are warm enough, especially in the gas tank. Keep the bladder pliable, not flamable. Heh heh.

That and a project for insulation with an automated temperature-controlled shutter around the engine block.

I just wish I had the money to start doing projects like these.

But definately no one is making a solar-powered Prius. Solar recharged EV-add-on pack, sure. Direct solar? No way. Not until a Prius weighs a heck of a lot less. (Which a Prius never will.)

And if that's what you're looking for, you'd probably be better off adding a standard solar kit to your garage and using the much greater surface area of your roof (or a wind turbine) where panel efficiency isn't as much of a concern (or so expensive), and just charging the EV-array overnight off of the home's battery you charged during the day. Not the most efficient method mind you, but free energy is free, so who cares if you waste some in the process? And what the Prius doesn't use, the rest of your house can. Win-win. Much better than a car-only solution IMHO.

Though I suppose for round trips to and from work and such using both garage and car recharging of the extended-EV system would make that a win-win-win since you'd have extended-EV both ways plus free electricity at home. Of course for the price of all that you might be better off investing in your own helicopter...

At what point does a Prius become an obsession?

 

Just firstly to point out that if you dig down into their figures (http://www.solarelectricalvehicles.com/articles/prius-white-paper.shtml) it does show the range from the solar panels on the car roof as up to 5-8 miles per day, based on 850-1300 Wh added to the HV battery indirectly from the nominal 215W panel.

The 20 miles figure seems to be when the batteries are topped up overnight through the plug-in option (and for green-ness sake they describe that as being from static solar panels via net metering).


I've not seen much discussion of this system anywhere though - are they actually making and delivering these already (in which case where are the customers, as I've not seen any opinions?) or do they so far only have the one prototype which is shown in their picture?

Seems to me that if this works as advertised, this could a little more economic sense in the UK, as although we get less intense sunlight, the saving compared to petrol prices approaching £1 per litre ($7.5 per US gallon) would be rather more than comparing with the cheap gas that USA residents get.


Any update from "G-IVSP Pilot" per the Feb 12th post?

No blazing rush, as it'll probably be next year before I'm in the market for one, but I do very much like the idea of being able to run short errands with essentially zero incremental environmental impact, even though I realise it won't completely pay for itself.

To be honest, I'd quite happily buy the charging circuit and plug-in transformer from their solution without the expensive custom solar panel... (and also source the heavy and expensive to ship lead acid batteries locally). This system including the solar panel seems to be cheaper than some other plug-in conversions, and also leaves more of the original systems intact and running as Toyota intended...

 

So what they're really making is a plug-in Prius with added solar panel on the roof. But in real life conditions, the roof of your car is the worst possible place to have solar panels. It is horizontal, not inclined toward the sun, and in a city situation, will very often be in shade.

A much better idea is to do like Darell: Put those solar panels (and more of them) on your roof, where you can get maximum sunlight, and then charge your EV (or plug-in Prius) from there.

BTW, I've seen a CalCars Prius, and those lead-acid batteries leave them no place for the spare tire, which ends up in your rear cargo area, or else sitting back in the garage where it does no good.

I give them an A+ for promoting a plug-in Prius, but a D for putting the solar panels on the car.

 

Yes, solar panels on cars is NOT an efficient use of power. Remember that manufacturing a solar panel takes a LOT of energy. Solar panels have two pay-back times, one is the time it takes to pay back the cost of the panel in energy savings, and the other is the time it takes to generate more energy than it took to make it.

A solar module that isn't harvesting as much as it can is going to have a greatly increased energy pay-back period.

Your car is a really BAD place for a solar module. Ideally, your modules should be facing south, tilted at an angle that is the same as your latitude (30-45 degrees, for most of the US), and in full sun all the time.

Because of how modern solar modules work, if one part is shaded, the entire module quits generating power, because of the series configuration of the cells. Its like a long hose, if you pinch it shut anywhere on the hose, the flow stops. How often is the roof of your car in COMPLETE sun? Not often!

Then there is the harvest rate issue. On your car, sitting on the street, it will generate energy until the battery is full. Then it just sits there... The same problem exists with off-grid solar systems, which have a much longer energy pay-back period than grid-connected systems. Grid connected solar system generate a maximum power ALL the time. Any excess power is sent into the grid, and lowers the load on the main power plants. REAL energy harvest and CO2 avoidance is highest with grid tied solar systems.

It makes a lot more sense to have grid connected solar on your home, and use that to charge an EV or a plug in hybrid (I've got some customers who do just this). Your actual energy generation rates are much higher, and you pay the modules back, in money and energy and CO2, much faster. I actually doubt that a solar module on a car will EVER save more CO2 then it took to make it. The car will probably be in a wreck long before that happens. If the module is damaged before its energy payback period (as little as 5 years in ideal circumstances, and over 30 in poor conditions, like on a car), then your attempt to save greenhouse gases and money, actually results in the waste of greenhouse gases and money.

I think plug in hybrids are a great idea, but solar on cars is really not a practical solution for society. Solar should be restricted to grid-connected systems, or systems that are so remote that grid connection is not possible, and it is worth paying a financial and greenhouse penalty just to maintain operation.

Block heater and other 12V battery topping up ideas are nice ideas too, but probably impractical. For one thing, generating HEAT from electricity is highly inefficient. The block heaters are probably at least 250 watts, which would require about 1.5 square meters of modules, or close to 1000$ in modules alone (wholesale, not including the charge controllers or other electronics).

Peace,
Sam

 

I agree with most of what you write here... but not this.

<div class='quotetop'>QUOTE(phidauex @ Apr 18 2007, 02:14 PM) [snapback]425613[/snapback]</div>

Not the case with modern PV panels. You can shade a percentage of the array, and you lose a similar percentage of production while the rest of the system happily generates away. I watch this happen as my system slowly has shade crawl across it every evening.

Oh and Daniel - the top of the car is not THE worst place for PV panels. I'd think that under the car would be worse.

 

<div class='quotetop'>QUOTE(phidauex @ Apr 18 2007, 05:14 PM) [snapback]425613[/snapback]</div>

So ideally this should wait until the technology exists to manufacture some form of solar panel using much less energy...

It is a really bad place for generating power from fossil fuel too (much better done at a large efficient power station.... ).

I have to admit I didn't realise quite how long solar panels took to become carbon-neutral even under ideal conditions. But time to finally do a few more back-of-envelope calcuations: assuming the car is driven enough that the stated 850-1200 Whr of electricity gets used every day or two, the 5-8 miles this allows should be equivalent to a tank of fuel every 3 months or so.... or 4 tanks a year...

How many tanks of fuel would need to be saved to pay back the environmental impact of manufacturing this? Money-wise if this does offset 4 tanks of fuel per year, then even at UK fuel prices it'd take about a dozen years to pay back just the $4500 cost of the system, and that's before shipping, taxes, and installation costs are taken into account. Also the system will generate rather less electricity in the UK climate and latitude...

I'd partially disagree - I'm sure they will be a part of a practical solution for society when the technology has progressed further. The big plus they have is that the energy is captured from the sun where it is needed. Most people will never have the option to plug in a car at home due to parking arrangements.

Current "solar prius" seems to have cells at nominal 16% efficiency. Perhaps in a few years something similar with double the efficiency and half the manufacturing cost will be available - then the numbers will be looking somewhat different.

In the meantime though, I guess covering any south-facing roof with some form of solar panel is much easier pickings.....

 

Hi all! I am new to the prius chat group...

I have been looking into the Solar Panel idea for a while. I have received two seperate quotes from solarelectricalsystems.com and solartecllc.com. Both are around $3000 - $4000 not installed. The interesting thing is that they are making the panels so they are molded to the roof contours.

Like someone else stated earlier, if there is any way to reduce the time my prius uses the gas engine to recharge the batteries, I'm there. To bad that any modifications like this void the factory warranty...
:blink:

 

<div class='quotetop'>QUOTE(MicaAngelo @ Apr 18 2007, 06:37 PM) [snapback]425755[/snapback]</div>

Not true. Search around a bit.

 

<div class='quotetop'>QUOTE(darelldd @ Apr 18 2007, 03:46 PM) [snapback]425628[/snapback]</div>

This could be the topic of an interesting thread: name the WORST place for a solar panel.

<div class='quotetop'>QUOTE(MicaAngelo @ Apr 18 2007, 07:37 PM) [snapback]425755[/snapback]</div>

Read this whole thread, then put those solar panels on the roof of your house rather than on your Prius. Are you really willing to spend $3,000 or $4,000 in order to save two or three gallons of gas per year?

 

<div class='quotetop'>QUOTE(darelldd @ Apr 18 2007, 05:46 PM) [snapback]425628[/snapback]</div>

Thats not entirely true. You do lose much more percentage generation than the percentage shade. This is particularly true with mono-crystalline and poly-crystalline silicon junction cell modules, which are what nearly all modules use. Amorphous silicon modules are slightly more complex, but still follow these basic principles.

Arrays are built out of several series strings of modules (which are series strings of cells), all in parallel. Modules are made out of series strings of individual cells.

Take a Suntech 170 for instance, it is made up of 72 monocrystalline silicon cells. You might put 9 of these modules in series, for nominal voltage around 300V. Then maybe you would make 3 of these series strings (total of 27 modules), and put them all in parallel with a combiner to bring them into the inverter.

Now, in perfect conditions, with perfect sun, each string is outputting 300V at around 5A. The whole array is 300VDC, 15A, which the inverter converts to 240VAC for your home.

A silicon cell is a current source, a resistor, and a diode, from an electrical standpoint. When one is shaded, that junction goes from a current SOURCE, to a current consumer. This heats the cell, and increases internal resistance. If one cell is partially shaded, it will decrease the output of the entire module, since the module cannot source more current than its lowest performing series component. If the shading gets worse, current drain will get higher, and the module will protect itself by shunting current through its bypass diodes, and will stop contributing to the string. Now the entire string of modules will begin performing worse, because they cannot source more current than their lowest performing member. Now one string of your array is performing at reduced, or 0 capacity, depending on how many cells are fully shaded. Your other two strings are fine. In this sense, your array continues to perform, but one hard shadow can still shut out 1/3 of the array.

Incidentally, this also decreases inverter efficiency a bit, since the maximum power point tracker can only follow an average I/V curve of all the strings, and if one of them is producing wildly differently than the other, it will invariably be tracking a point which isn't really the maximum power point. This is a small effect you don't need to worry about in residential, since its only a 2-3% loss, and its nothing compared to what you lost by shading the array. But its a big deal in very large (70kW and up) arrays that use central inverters with single power point trackers. 2-3% is a lot of energy, in that case.

Here is a diagram from Kyocera which neatly illustrates this principle. It shows one of their 36 cell modules in partial shading. Full link (a good read, btw): http://www.kyocerasolar.com/solar/modules.html



This protection mode can actually damage modules. Sanyo warns us that their module warranty is invalid if we install with a persistent hard shadow, like a vent pipe on the roof that shades the same place every day, since the module will consistently overheat that cell, and eventually wear out the bypass diodes, and damage the module.

There are a few ways to combat this problem. Of course, avoiding any and all sources of shade is the first way! Another way is to choose modules with a higher voltage, so you can put fewer of them in a string. Sanyos are a good example of a higher voltage module. Instead of strings of 9, we may use strings of 5. More parallel strings means that if you lose the output from one string, you are losing less total power. If you know one area of a roof will be shaded at one point in the day/year, you can arrange the strings such that all the shaded modules are part of one string. Instead of the shade from a chimney hitting one module from each of the 5 strings, you have all 5 of those hit modules in one string, to limit the total effect on the array. One can also use lower voltage inverters, requiring fewer modules per string. However, these usually carry their own efficiency hit, so that needs to be weighed against the shading issue.

Actual power loss from partial shading, as you can tell, is really hard to compute, and predict. Markets that base tax incentives and rebates on actual system performance usually require a monitoring system to report actual power generation. They can't rely on estimates of power generation, since one little thing wrong can make a major dent in power generation.

BTW, Darrell, am I right that you have a PV system on your home? What size is it? You seem to know a lot about grid tied solar, which is great, since it is probably the most effective type of home PV system, and it is really catching on.

Do you have a monitoring system on it yet? If not, I'd highly recommend a Fat Spaniel (http://www.fatspaniel.com), its an internet based inverter monitoring system that can measure things like power generation, building demand, and even fun stuff like cell temperature, air temperature, wind speed, and actual irradiance. Then it compiles nice, easy to read graphs, that update in real time, viewable over the internet from your browser (Its like a CAN-view, but for your PV array ). It works with almost all the major inverters. If you have SMA "Sunny Boy" inverters, then you can use their Sunny Webbox, which is nice too. Nothing compares to actually being able to see what your system is doing in real time. Prius owners totally understand that.

Peace,
Sam

 

Darrell - What is the status of the solar panels on the top of the Prius I saw on your web page. I tried to send an email at the link but they never responded. BTW, I made the jump and will be getting a 6 KW system (with a 80gal water solar system) for my house. When I get back from Iraq I was thinking about getting the Prius plug-in mod and possibly solar panels for the top of the car. The car parks in the sun all day while at work. Only the weekends is it in a garage but then my solar panels would be able to charge it.