All Electric/solar RV

[Mark_K5LXP]

I threw the BS flag just like DonTom did because the numbers didn't add up. I guessed at 6 square meters of roof panel, 6 hours of sun a day, a Tesla 75kWh battery pack and Prius Wh/mile efficiency and it didn't come up to anywhere close to 450 miles even with full solar supplement. Missing of course were some very key time variables and operating constraints, guessing that 450 miles would be on a given day with a full charge and a full day of sun for solar supplement, plus some other operating variables that aren't in the main article. Even so, there's not a lot of solar on a moving vehicle so you pretty much run through your whole battery the first day and it takes *days* to get that back even with the solar awning deployed. It would seem you would get more practical daily range by charging with the awning during the day and driving at night, would be interesting to run those numbers. Practically speaking though even in my gasser I don't normally drive 450 miles a day so the idea of having a vehicle that may not not have that kind of daily range isn't necessarily a show stopper. Seems there would be a happy medium struck between range, speed and some payload. Between solar, range requirement and periodic charging from the grid one might make a go with this type of vehicle. But DonTom is right, even with full panels and full sun there's only so many watts there and the daily range would be fairly limited.

Mark B.
Albuquerque, NM

 

[Viajeros]

The Tesla was based on no wind, at 65MPH, level ground, 70F.

At 38 MPH, my Tesla will get 420 miles. That is where it gets the best range.

Range is tricky on EVs. Take my electric motorcycles, for an example. The best range is at ~5 MPH, every time the speed is doubled the range drops by ~50%. Even more so at higher speeds. So how does one give a range of an EV without mentioning the speed, temperature, wind, road conditions, hills, etc. Too many variables with EVs compared to ICE engines.

Of course the much lighter vehicle will do even better range than my rather heavy Tesla M3. I was using it for an example as we needed some facts. I know the facts with the Tesla, unlike the article in the OP.

-Don- (now back to riding)

I concur on range being very speed dependant. I’m pretty sure Don and I would get very different ranges with our Tesla’s. In BC speed limits are rarely over 90 kph and tons of little towns and twisty mountain roads keep you average below that. For giggles and grins I look at the plotted expected range on trips we go on. We could easily get north of 600 km of range in our car blowing the epa numbers out of the water. 130 kmh on a freeway would cut that by a third. I’m not sure what criteria epa uses.

 

[Viajeros]

I threw the BS flag just like DonTom did because the numbers didn't add up. I guessed at 6 square meters of roof panel, 6 hours of sun a day, a Tesla 75kWh battery pack and Prius Wh/mile efficiency and it didn't come up to anywhere close to 450 miles even with full solar supplement. Missing of course were some very key time variables and operating constraints, guessing that 450 miles would be on a given day with a full charge and a full day of sun for solar supplement, plus some other operating variables that aren't in the main article. Even so, there's not a lot of solar on a moving vehicle so you pretty much run through your whole battery the first day and it takes *days* to get that back even with the solar awning deployed. It would seem you would get more practical daily range by charging with the awning during the day and driving at night, would be interesting to run those numbers. Practically speaking though even in my gasser I don't normally drive 450 miles a day so the idea of having a vehicle that may not not have that kind of daily range isn't necessarily a show stopper. Seems there would be a happy medium struck between range, speed and some payload. Between solar, range requirement and periodic charging from the grid one might make a go with this type of vehicle. But DonTom is right, even with full panels and full sun there's only so many watts there and the daily range would be fairly limited.

Mark B.
Albuquerque, NM

When we tour camp a long day for us is 200 kilometres. Then we are there fit a couple or three days, then we may move 50 kilometres and do it again.

Of course, we are in bc. And lots of the places are in shady forests. Hmmmmm

 

[Lu1964]

you did see how little it was right ? I don't think in most cases it would work here more so with a family maybe little people LOL

Ya my thoughts exactly! Just a liiittle bit bigger … and a shower? How small are these students?! They’ve got their thoughts in the right direction tho so …

 

[Ernie n Tara]

Some other facts:
a. Solar insolation is anout one kw per square yard (9 ft square)

B. Drag equals 1/2 p v^2 csubd a
where: p=0.0023 (for air at sea level)
velocity is in fps
drag coefficient equals 0.0 to around 1.0 (for a flat plate)
a = area in sq ft
Note that the square function means speed is the dominent factor. Drag is about twice as high at 70 mph as at 55 mph for example.

C. Weight is the same going downhill as uphill (or starting and stopping); neglecting effeciency losses these balance out (with very careful driving).

D. Rolling resistance is low and I infer very hard narrow tires. (Tires probably have more influence on drag than rolling resistance).

The above represent the total energy required to move any free rolling vehicle. I'll leave the math to the reader (I've done it for both aircraft design and submarines). Note that cars usually are in the range of 0.3 or higher drag coefficient (motorcycles much higher) and gliders usually less than 0.1.
I don't see any real difficulty in an average vehicle driven in the usual manner requiring 1,000 times or more energy than a streamlined, narrow tired vehicle, driven for maximun efficiency in moving.

Ernie

 

[DonTom]

Solar insolation is anout one kw per square yard (9 ft square)

That would take around 70 hours to charge my Tesla's 70 KWH battery.

That also means with 630 SF of solar under bright sunlight, I will be able to charge my Tesla in about an hour.

Kinda explains why putting solar on the roof of an EV to increase range is little more than a waste of time.

-Don- Reno, NV