Solar Panels Recharge Rate?

[RoxChkPlusOny]

I read that the solar panels on top of the Aptera serve to cool the car and to recharge the battery. Any ideas how much residual potential will be available to charge the battery on a cold day? On a hot day?

[IanO]

I think that was misreported and the small solar panel only cools the cabin (probably driving a small fan). Aptera themselves only mention the solar cells on their preorder page. Vehicles which use solar power for any significant fraction of their drive power require much larger panels. Aptera's panel is only a small strip on top.

[LQUAN]

That tiny solar pannel can produce 100 to 150Watts/hr at most under full sun. It's hard for me to calculate the amount of current use since I don't know what voltage it takes to charge the car battery. Assuming the battery is 36V, and the solar pannel can pump 150W, 150W/36=4.2A. Cooling fan and other accessory probably drain about 0.5A/hr to 0.8A/hr. Charging the battery at 3.5A/hr would only be good for 3 miles or so under 8 hours charge. Every little bit helps I guess.

Without a real AC system while driving in Southern California summer can be very sweaty without windows. They'd better get those power windows in if they want to sell. We get about 1 month/yr of high 90F to 105F here in Southern California.

[IanO]

Oh, they also have a full environmental system based on a heat exchanger, which is only active while driving. One of the videos (http://www.apteraforum.com/showthread.php?t=9) shows LEDs on the air vents which light up red when heating or blue (green?) when cooling. (A surprising feature; I worry that will be distracting while driving. Do any other cars have that kind of indicator?)

The solar powered ventilation system is just to keep the cabin temperature near ambient while the car is parked in the sun, without draining the main batteries.

Sounds like this should be in their FAQ.

[KarenRei]

Interesting that this topic should come up; I just did a post on my latest wiki on the subject. The math dictates that solar cars simply aren't realistic vehicles for transportation, as they provide way too little power even when plastered in solar cells:

http://www.daughtersoftiresias.org/greenwiki/Solar_car

Any feedback that anyone can provide would be great.

[cogito]

The best triple junction solar cells I’ve seen (from spectrolab) are 28.3% efficient, but they are pricey. I imagine pulling an extremely lightweight, low rolling-resistance flat trailer, covered with solar cells. Its front would be the same height and thickness as the trailing edge of the aptera and perhaps become even thinner at its trailing edge, lowering the aptera Cd? (yes, I know we aren’t supposed to pull anything, I read the aptera faq. This is theoretical) Experimentation either in a wind tunnel or in software would be needed to make a shape that was efficient but also allow for turns. Maybe it fits flush with aptera but has an internal pivot to allow turns. I’ll make a drawing if this is difficult to follow. I said it was theoretical.

One would leave the trailer at home giving power to the grid and lowering your electric bill while commuting, but you could take it with you on a trip and extend the range whether you’ve opted for the full electric or the plug-in hybrid. The trailer would also hold whatever the best batteries exist at the time, (I currently use nano phosphate A123 batteries and charge them at 10C no problem) the trailer can’t be too light or it’ll be a sail-like safety hazard.

If someone wants to do the math on how long the trailer would need to be to materially help, please have at it.

-Craig

[KarenRei]

So, the trailer, what, doubles the area? 1 meter by 2, so two square meters plus the two on the car, so 4 square meters total? In optimal conditions, perhaps 20% capacity factor over the course of a 24-hour day, 1000W/m^2? That's an average of 224W. In peak, noontime conditions, so 100% capacity factor, that's 1.1kW. I don't know how big the motor on the Aptera is, but Zenn's glorified golf carts have a 15kW motor. Aptera is reported to get as good as 120Wh/mi at highway speeds (let's ignore how much a trailer would ruin that), so that'd mean a draw of 7.2kW.

Remember, we're looking at best case here.

Solar cars really just don't work as practical vehicles. There's just simply not enough surface area. You need solar panels on fixed installations, not vehicles. If you want a vehicle to run nonstop on green power, get everyone to go electric and then electrify the roads (say, resonant inductive charging)

Speaking of solar panels, however, is everyone here as thrilled as I am about Nanosolar? ;) Current solar cell prices: ~$4/W. Nanosolar production cost: $0.30/W. Price Nanosolar is selling cells to Germany at: $0.90/W.

At $1/W, even solar power in Alaska becomes cheaper than coal ;) That's like handing Nanosolar a license to print money. And they're hardly the only thin film company out there, either -- they're just leading the pack.

[3-4-me]

shwooosh
The sound of air rushing over my head was deafening on that one.:eek:
It's nice too see some big brains airin' it out here.:D
Interesting concept on the solar trailer to hook to the grid during down time.

[cogito]

I don’t imagine one would bother with a trailer if it didn’t have a surface area of at least 4 sq. meters. But I get your point.

[3-4-me]

The nanosolar technology sounds incredible. I'll have to google that.
I'm almost in need of a roof, and was considering solar shingles.
Do you have any expertice on the subject?

[KarenRei]

Well, I am the author of this solar power economics calculator:

http://www.daughtersoftiresias.org/progs/insolation/

But if you're asking if I can, say, recommend specific companies for you to do your installation or whatnot, no. But I can point you to where you can do price shopping on components:

http://www.solarbuzz.com/Moduleprices.htm

(Update: Hmm, looks like they don't list as much info as they used to :P)

Note that Nanosolar's products aren't on the open market yet; the entire capacity of their plant, which is only at partial capacity right now, is going to municipal installations in Germany, and will be for a couple years. But again, they're not the only new kids on the block ;) In about a year, with all the new thin film capacity coming online, market prices should start falling at a pretty quick clip, and over the next 5-10 years, should end up around $1/W.

[LQUAN]

I still see some room on the roof of the Aptera that they can squeeze in at 60% more solar pannel area.

We have got to be realistic with the actual milage that the car can get from the solar pannels in ~8hrs while parking at work. Don't forget that it used energy to run all the LCD monitors, screens, possibly day-headlights, fans, lights, radio, etc.

[cogito]

Looks like someone built a solar trailer of about 6 sq. meters and is using it to (partially) power an electric car trip around the world.

http://www.solartaxi.com/film-archive/india-3/

[KarenRei]

Of course, it's a little tiny vehicle, requires a six square meter trailer, and even still sunlight only adds 60-120 miles (depending on sunlight levels) onto its daily range. :) The driver himself advocates solar cells on rooftops providing the power for EVs.

That said, sure, there's no reason why it would *hurt* for cars like Aptera to be plastered in thin film once CIGS starts coming online. Who wouldn't buy solar at under $1/W? :) Even in Alaska, that'd be a sound investment.

[Aptera 1103]

I already have them on the roof of our house. Last year we had a surplus of energy that SCE got for free due to the way they made the agreement for Energy producers like us. This will not be the case when we have a car t plug into our system. I have already started to think where I can put more panels on the roof. The way our roof is they are almost from the ground.

[LQUAN]

I already have them on the roof of our house. Last year we had a surplus of energy that SCE got for free due to the way they made the agreement for Energy producers like us. This will not be the case when we have a car t plug into our system. I have already started to think where I can put more panels on the roof. The way our roof is they are almost from the ground.

My wife and I are thinking of getting solar pannels for our home for a while now, but the initial cost just don't make sense to us. How many KW is your system? Will the pannels last over 25 years?

[KarenRei]

Check out the calculator at the top of this page for how economic such an investment would be for you.

In general, larger KW systems are more economical as the supporting electronics, such as the inverter, become a smaller portion of the costs. But present-day, the panels will almost certainly still be your biggest cost.

As for the lifespan of the panels, they will degrade, but unless they're outright shattered, they're going to keep producing a good chunk of their original rated power 25 years into the future -- 70, 75%, maybe even more. The rate of degradation slows down a lot as they age. Often, if you find old panels producing little to no power, merely cleaning the terminals and checking the connections can restore them to health.

[c0mp13x]

So... for the Aptera's application, does the Nanosolar technology offer any gains in efficiency (per sq ft), beyond the cost advantage?

I understand that their technology can be "printed" on substrates that can be curved, so could the top surface of the Aptera be covered in Nanosolar cells? Or, will Nanosolar's current production on large rolls of sheet metal restrict their use to non-complex curved surfaces?

[Aptera 1103]

LQUAN we have a 3Kw system on our house. The fact that we expect our energy usage to increase and the cost to continue to rise were important factors in our choice. So far we are very happy with our "investment."

[KarenRei]

Nanosolar is ~13% efficient. Very high for mass-produced CIGS, but lower than silicon. It's just really cheap.

Different CIGS manufacturers use different substrates.

[twelve33]

That tiny solar pannel can produce 100 to 150Watts/hr at most under full sun. It's hard for me to calculate the amount of current use since I don't know what voltage it takes to charge the car battery. Assuming the battery is 36V, and the solar pannel can pump 150W, 150W/36=4.2A. Cooling fan and other accessory probably drain about 0.5A/hr to 0.8A/hr. Charging the battery at 3.5A/hr would only be good for 3 miles or so under 8 hours charge. Every little bit helps I guess.

Assuming 150W, that's 1.2 kWh for an 8 hour day in the sun. Let's be conservative and make it 1 kWh. Aptera says the Typ-1e is designed to use a 10kWh pack. If they can get 120 miles out of a 10 kWh pack, then 1 kWh should give about 12 miles, no? Still not much, but for my relatively short commute it would be just enough added charge that I'd only have to recharge the car once a week.

[KarenRei]

It has no heliostat; you won't get that kind of power for 8 hours. Also, you forget that it's running the fan to keep the car (and thus batteries) cool.

[palmer_md]

Ev's typically take 200-300 watt-hours per mile, so 1kwH would give you about 4 miles. The Aptera being light and aero might add a little bit to that. My guess is 175 watt-hour/mile = 5.7 miles at best.

Solar panels on your home to recharge the car are your best bet. Maybe someday the cells might be efficient enough to install on the roof of a car, but not right now.

Efficiencies drop off quickly when you are not "pointing" the array at the sun, and flat on the roof of a car will kill your efficiency. This is why they are installed at an angle on the roof of a home/business. It needs to be optimized so that the array is at a good angle for capturing the most sun throughout the day. Tracking the sun with motors is even better.

[KarenRei]

The Aptera can't be even near 200-300Wh/mi. Even the Tesla is little over 200 Wh/mi. But look at the stats: 120 mile range, 10kWh battery pack. That means ~83 Wh/mi.

[twelve33]

It has no heliostat; you won't get that kind of power for 8 hours. Also, you forget that it's running the fan to keep the car (and thus batteries) cool.
I was merely trying to say that *if* you really get 100-150 Watts from the panel, then 8 hours of charging should equate to much more than 3 miles of driving (even with a fan, which if it really is only a fan shouldn't use much energy).

[alister]

Hi,

here is an important information on batteries used in solar panels.

The battery should have sufficient amp hour capacity to supply needed power during the longest expected period "no sun" or extremely cloudy conditions. A lead-acid battery should be sized at least 20% larger than this amount. If there is a source of back-up power, such as a standby generator along with a battery charger, the battery bank does not have to be sized for worst case weather conditions.

[garygid]

I thought the latest Aptera specs mentioned 17 to 22 kWh for the battery, substantially up from the "original" 10 kWh.

Probably the extra drag, gear losses, new shapes, higher weight, air-conditioning, and wanting a real-condition 100 mile range have all upped the energy requirements, to almost double the "original"?

So 20 kWh pack and 100 miles would indeed be 200 Wh per mile, or only 5 miles per eddi, down from the "original" 12 mpe!

[evmavin]

I thought the latest Aptera specs mentioned 17 to 22 kWh for the battery, substantially up from the "original" 10 kWh.

Probably the extra drag, gear losses, new shapes, higher weight, air-conditioning, and wanting a real-condition 100 mile range have all upped the energy requirements, to almost double the "original"?


It was unrealistic to get a real world 100 miles from a 10KW pack without driving it to 100% DOD and driving on flat surfaces. Aptera's original claim of 120 was unrealistic as many mentioned early on, and I'm still curious if the 100 mile real world range will require the full 22kw or 17 for some and what driving mode that is set on. Perhaps 22kwh will be an option. For those that live in very hilly areas the "real world" range will change even more as people see what hills do to range, and I'm not speaking of steep driveways. http://apteraforum.com/images/smilies/scared0011.gif It seems the large pack increase was needed to keep the numbers real.