[MattsAwesomeStuff]

And the huge weight of a true semi-trailer would not be suitable

He said "semi-flat trailer", using "semi" to mean "partially", instead of to mean a trailer without a front axle (big rigs).

The car and trailer together only came in at 1650lbs, boasted a top speed of 55mph and claimed to get 133wh/mile.

That's nothing.

I could drive a Tesla with a top speed of 120mph and get 25wh/mile.... just not at the same time.

But let's say he averages 133wh/mile across the whole trip. That's only 2-3x as good as a modern electric vehicle.

Good for 45 miles of range you say? (seems reasonable).

His claim: 32,000 miles in 17 months = 63 miles a day.
Your claim: 32,000/45 miles a day = 711 days = 24 months.

Pretty close to what he claims, in the right ballpark anyway. Maybe he'd sneak more when considering prevailing winds, or... maybe he drove at a more optimal speed.

If he's only going 63 miles per day average... almost all of his time is going to be spent doing nothing anyways. It would be silly to travel at 55mph for an hour and ten minutes, and then just sit all day. Might as well drop down the speed to half or 1/3 of that and get more range.

"All day long", bullshit. All day long without overheating, sure. All day long for power? No.

Granted, a relatively fit person could easily outdistance it on a bicycle, and since it is a fair weather proposition anyway, it would be a lovely bike trip.

Record-wise: Unsupported, 4 months. Supported, 2.5 months. But they take a tighter route by nearly half (18,000 miles). Still 6 months a world-class athlete could do it. I agree, anyone reasonably fit could hit 1/3 of that speed.

That's only 3 hours of moderate-paced biking a day. Heck, if you started out as a chubby desk-jockey who'd never ridden a bicycle... by the end of the first month by virtue of attempting the ride you'd be in as good of shape as an ambitious amateur and pulling 3 hours a day easy.

...

I know a guy who took a Motorino Xpd (Honda Ruckus scooter with EV drivetrain) with a solar trailer (3 panels, the sides which could hinge to angle better) on an 800 mile trip, that he wanted to take all the way to South America. Had a decently-big Leaf battery stack on it. Max speed was 50km/h (30mph), pulling about 1kw (33 watt-hours per mile), and he said even at biking speeds the solar was pretty much useless. Had almost no impact on his daily range. He stopped everywhere and every night to plug in to charge, and eventually gave up before even leaving Canada it was such a disappointment. Even when he'd park for a whole day just to recharge, his only goal became "limp it to the next gas station and hope they'll let me use their power".

 

[OR-Carl]

Looking at their website again, I do find they claim a 60 mile range on solar alone, and also a little bit of creative accounting.

"The solar cells on the trailer produce enough electricity to run the car up to 100 km a day.

If we need to drive more than 100 km a day, we need to charge our battery with additional solar power. For this purpose, we have a solar power plant on a rooftop in Berne, Switzerland. This electricity is fed into the grid, offsetting electricity generated by using fossil fuels. It's like paying money into a bank account and withdrawing the money somewhere else: We feed solar electricity into the grid and charge it into our battery anywhere in the world, from the grid. "

With really high efficiency solar panels, and really low speeds, I would believe 60 miles in a day. Also, as Matt's story illustrates, I think it is really important to not discount the amount of engineering talent and university endowment money that went into making this project possible.

If you really want to drive around on solar power, leave the panels where they belong; on the roof of your garage.

 

[brian_]

Thanks for the link and excellent analysis, Carl.

The car and trailer together only came in at 1650lbs, boasted a top speed of 55mph and claimed to get 133wh/mile. The solar panels on the trailer came in at about 6 square meters. It used a liquid salt Zebra battery, and claimed 250 mile range, but it also mentions 14kwh when discussing battery costs, so I might be missing something. The whole thing feels a little light on facts, which I am guessing is because it does not quite deliver all it promises. Or because the whole thing was built by a bunch of engineering students, and the guy who drove it did not really fully understand how it all worked.

So, yeah, that array, if it was really efficient would be nearing 1.5kw. My array happens to be that size, and on a sunny summer day at 45degrees north lat. I can pull in 6kwh in a day. If that was feeding a car that used 133wh/m, it would equate to a 45 mile range. Some form of battery would be a must, as you would burn through that 45 miles in a couple hours, while needing a good 7 or 8 hours of sun to accumulate that much energy.

1500 watts of solar input divided by 133 Wh/mile means 11.3 miles per hour (18 km/h) - way short of 60 mph. As already mentioned, that's only at peak and can't be sustained "all day" even in ideal conditions. And even using the battery, it can't make 60 mph.

The daily range would be determined by the 14 kWh stored in the battery (charged from the grid) plus up to 6 kWh added by solar. That 20 kWh divided by 133 Wh/mile would be 150 miles; the 185 mile value is just fiction but the "250" value might charitably be 250 km, converted from 150 miles and "rounded up".

So not 60 mph ever, and not anything all day... anyone paying up on that million dollar bet?

If you really want to drive around on solar power, leave the panels where they belong; on the roof of your garage.

Absolutely. Although a panel on the roof that you have anyway is nice to run a ventilation fan when parked in the hot sun without running down the battery, and can provide a trickle for maintenance. A layer of cells can make a decent tint in a glass roof panel.

 

[mike kirschbaum]

I really appreciate seeing these posts. Like I said before, my experience was on a solar racer, just like one shown in this thread. It inspired me to try adding solar panels to a daily driver. I'm going to take it one step at a time, build a lightweight mini truck with the best batteries I can afford. I'll see how a solar array on the shop does charging the truck, will try to find a meter to measure the KWH added.

 

[john61ct]

Best to just use the nominal voltage of the target battery

and stick to Ah as measured by a coulometer reading a shunt right at or near the post.

One-way is enough for just charging energy flow

but a two-way unit is useful if you also want a "gas gauge" guesstimation of SoC% while discharging too.

kWh appear attractive as a unit in theory independent of voltage

but in fact are derived from Ah anyway, and do not reflect the real-life usage patterns we seek to measure.

 

[mike kirschbaum]

Thanks, John. I have a nice watt meter for AC use, it shows current draw and total watt hours used. It would be nice to have one for DC, I'll check the internet.