Charging directly from solar panels

[ajdelange]

I think ajdelange calculated about 2.5 miles per hour in optimum conditions. so 8 hours In direct sun for about 20 miles minus "phantom drain" so maybe 15?
seems wierdly low as elon said 15 for JUST the vault panel.

Lot's of people think AJ is nuts because his numbers don't come out to 15 miles for just toneau panels. Elon didn't say you would get 15 mi per day. He said you could get as much as 15 miles per day. Let's think about that for a minute. Suppose you live in the desert at 20N latitude. At the spring equinox here's what the sun does:

The blue curve shows the elevation of the sun and the red one the relative intensity of the collected radiation assuming that you keep moving the truck so that the panels are pointed directly at the sun. Whenever the sun is above about 65 ° you get close to it's full intensity (1.00) but when it is below that you start to lose some because of atmospheric absorption. The integral under the red curve gives the equivalent hours of full sun which, for this picture is 10.325 hours. Let's assume the CT is going to consume 350 Wh/mi. For 15 miles of driving that would mean 5250 watt hours consumed. If we have 10.325 equivalent hours of full sun we would need panels that produce 5250/10.325 = 508 watts when in full sun, That's the production of 2 of the panels going onto roof tops today. Thus if you live in a sunny desert 15 miles a day doesn't seem unreasonable.

Now let's go to where I live at 39N. Here's what the sun does on a January day:

The sun does not rise as high in the sky and isn't up as long so the received insolation is less both from less time shining and greater extinction losses. Plus, as it isn't practical to go out and reposition the truck to "track" the sun this picture assumes the truck is parked for the whole time the sun is up with the panels oriented south and inclined at 60 °. The result is that the effective time of full sunshine are only 4.11 hours. Assuming the same 508 W panels that would give me 508*4.11 = 2087.88 Wh good for 6 miles per day. Not so impressive as 15 miles, especially when you take out the 10 or so miles worth of phantom drain. But, unfortunately, we aren't finished yet. The sun doesn't always shine here in the winter. Last Jan 17th I actually got 3.05 hours of equivalent full sun and the average per day for the month of January was 1.86 with this last number corresponding to about 2.7 miles per day.

So 500 W of solar cells are pretty useless in January if you live in a temperate zone. But we don't go camping in the winter (though we do go hunting). We go camping in the summer months. At my location on a sunny day near the solstice I should get 7.12 hours equivalent full sun. In June of last year I got an average if 4.96 (the sun doesn't always shine here even in June and it gets hazy too). Five hours per day would give me 7.2 miles for an average day of charging in June around here or as much as 10.3 mi on an optimum Jun day.

Someone will probably chime in and argue that the panels that will go on the truck will be twice as efficient as what is available today. If you want to believe that just scale all the mileages by 2. Some will argue that the CT's will have consumptions less than the current Tesla models. If you want to believe that then scale all the numbers by whatever consumption you want. If someone argues that he can move the sun, put that guy on "ignore".

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[ajdelange]

"One of the greatest challenges in this world is knowing enough about a subject to think you are right, but NOT enough about the subject to know you're wrong" -Neil deGrasse Tyson

He's talking about Dunning-Kruger effect. There is no better place to see it in action than in these internet forums,


Socrates put it as "The more I know the more I know I don't know." That's not a direct quote, of course, because he said it in Greek.

 

[Newton]

He's talking about Dunning-Kruger effect. There is no better place to see it in action than in these internet forums,


Socrates put it as "The more I know the more I know I don't know." That's not a direct quote, of course, because he said it in Greek.

yup, its a shame we die. so much knowledge and wisdom wasted, just for the next generation to attempt to learn it all again.

so what do you expect average from the vault panel? nevermind, reread your post

 

[TyPope]

doc, i think 120v at home charges at like 5 miles per hour

edited becuase a mistake...
It really dosnt seem worth it unless your letting it sit for days at a time.
I think ajdelange calculated about 2.5 miles per hour in optimum conditions. so 8 hours In direct sun for about 20 miles minus "phantom drain" so maybe 15?
seems wierdly low as elon said 15 for JUST the vault panel. but 10 to 15 + 15 is still 20-30 miles charge just sitting there all day

For what I would use it for that's actually fine as it would probably sit for 3 or more days doing nothing while I camp or hunt or whatever. Although it would most lo likely be in the shade

Once I get the truck, maybe I'll do it and make a video to show people the real numbers.

Elon was probably talking about a full 8 hours of good sun with optimized panels. Right now, it looks like panels produce about 320 watts and would just about take up the roof and vault cover area for 4 of them (no wings necessary so no parking lot issues). That would be about 1280W per hour, or 10,240Whr per day. If the CT uses 500 per mile, that would be about 20 miles a day.

I, personally would be happy if it eliminated vampire drain and maybe added a few miles a day on average. I mean, I commute just under 16 miles round-trip a day.

 

[ajdelange]

Elon was probably talking about a full 8 hours of good sun with optimized panels.

Why would we assume that he was talking optimum panels with sub optimum sun? When he says "up to" I would assume he means optimum panels and optimum sun. If he were doing something like that I would guess he would say "typically". In any case as I said you can make any assumptions you like with respect to any particular parameter you want to except the motion of the sun. You are not free to make assumptions about that. So whatever the the "up to" number you choose to use based on assumptions about panel efficiency, converter efficiency, number of panels you can get on the roof, panel orientation etc. the January number is going to be 40% of that (without clouds) simply based on ephermeris considerations. I'm still not at all confident that people understand this.

 

[TyPope]

If someone argues that he can move the sun, put that guy on "ignore".

But wait. Isn't the earth flat?

 

[TyPope]

Why would we assume that he was talking optimum panels with sub optimum sun? When he says "up to" I would assume he means optimum panels and optimum sun. If he were doing something like that I would guess he would say "typically". In any case as I said you can make any assumptions you like with respect to any particular parameter you want to except the motion of the sun. You are not free to make assumptions about that. So whatever the the "up to" number you choose to use the January number is going to be 40% of that (without clouds) simply based on ephermeris coniderations. I'm still not at all confident that people understand this.

Fair enough. I was thinking of my situation. It'll be parked in the sun for 8 hours while I'm at work. 9, actually.

 

[CybertronUK]

Well you always tow a trailer
https://cleantechnica.com/2020/06/04/solar-trailer-added-to-tesla-model-3-video/

 

[ajdelange]

What you are not grasping is that even though you be parked in "full sunshine" for 9 hours you are not getting 9 hours full sunshine equivalent but rather more like 4 (January number). The sun never goes higher than 30 degrees in January at your latitude which mean
1)Loss of sun energy from having to pass through more atmosphere
2)Loss from the fact that the suns rays strike the panels obliquely.

Solar panels are rated by power at "full sunshine". Thus a typical 300 W panel (250W after inversion) will deliver 250*4 = 1 kWh if given 4 hrs equivalent full sunshine.

This is with perfect weather. As I said in an earlier post I actually got an average of less than 2 hours equivalent in January.

 

[ajdelange]

Do look at the trailer video. It is not only entertaining but instructive. It will also give you an idea about how much power you can collect with an array that approximates the size of the one he cobbled together.

But note that he is completely naive with regard to the concept of equivalent full hours. He assumes that because he is getting 600 W (from his 800W array) at one point in time he will get 6 kWh if he sits there for 10.

 

[Newton]

What you are not grasping is that even though you be parked in "full sunshine" for 9 hours you are not getting 9 hours full sunshine equivalent but rather more like 4 (January number). The sun never goes higher than 30 degrees in January at your latitude which mean
1)Loss of sun energy from having to pass through more atmosphere
2)Loss from the fact that the suns rays strike the panels obliquely.

Solar panels are rated by power at "full sunshine". Thus a typical 300 W panel (250W after inversion) will deliver 250*4 = 1 kWh if given 4 hrs equivalent full sunshine.

This is with perfect weather. As I said in an earlier post I actually got an average of less than 2 hours equivalent in January.

indeed this is true. my little panel on my porch is facing south in CA, angled roughly toward the sun i.e. not horizontal . I only get really good power during miday and the couple hours before and after. so realistically the 8-10 hours the sun is up, im getting fullish power like 5 hours

 

[Dids]

What is this requirement that the DC from the panels be inverted to AC? Why wouldn't they just charge the DC batteries with the DC current from the panels?

 

[Newton]

What is this requirement that the DC from the panels be inverted to AC? Why wouldn't they just charge the DC batteries with the DC current from the panels?

im sure ajdelange knows. and im sure tesla will do that.

but for me as a non-electric wizard, I have no idea how to charge the battery anyway other than how tesla allows.
which is from the charging port.
which would require an inverter to change the panel voltage to 120v to use the included plug.

 

[Ryan95738]

Why would we assume that he was talking optimum panels with sub optimum sun? When he says "up to" I would assume he means optimum panels and optimum sun. If he were doing something like that I would guess he would say "typically". In any case as I said you can make any assumptions you like with respect to any particular parameter you want to except the motion of the sun. You are not free to make assumptions about that. So whatever the the "up to" number you choose to use based on assumptions about panel efficiency, converter efficiency, number of panels you can get on the roof, panel orientation etc. the January number is going to be 40% of that (without clouds) simply based on ephermeris considerations. I'm still not at all confident that people understand this.

Thank you for making it so clear and educating us I'm glad to know now

 

[ajdelange]

indeed this is true. my little panel on my porch is facing south in CA, angled roughly toward the sun i.e. not horizontal . I only get really good power during miday and the couple hours before and after. so realistically the 8-10 hours the sun is up, im getting fullish power like 5 hours

I thought some might be interested in seeing what happens on a typical sunny day this time of year at mid lattitude:

The heavy red curve (values read from the right hand axis) is the theoretical insolation (with 1 representing full, theoretical sun) and the thinner red line what I actually got yesterday. It was a typical June day in that it was a little hazy (hence even at apparent noon, 17:07 Z - the plot is in GMT) the received insolation is less than one and in the afternoon some clouds rolled in. Note that the theoretical curve is for a panel tilted 60 ° and aimed south. I have 58 panels on my roof and none of them is aimed exactly thus hence some of the deviations between the theoretical and actual curves. I hope this will further illustrate the sources of difference between Elon's best case prediction and what one is likely to experience in the true world.

which would require an inverter to change the panel voltage to 120v to use the included plug.

An inverter, followed by a rectifier is clearly required as the solar cells are low voltage devices and the vehicle battery is nearly 400 VDC. Plus a sophisticated inverter incorporates MPPT (Maxium Power Point Tracking) which extracts the most power it can from the solar cells even if they are in shade and producing a DC voltage that is a fraction of what they produce in full sun.

The Level 2 charging system in the current Teslas looks like this

Mains ==> Rectifier --> Inverter ==> Transformer ==> Rectifier --> Battery

==> represents AC power transfer and --> DC. This is a very flexible design in that the rectifiers can be used as inverters and conversely so that the architecture is inherently bi directional. For purposes of the present discussion the diagram is clearly modifiable to

PV Array --> Inverter ==> Rectifier --> Inverter ==> Transformer ==> Rectifier --> Battery

which is essentially what I get when pluggin the UMC into the red box in No. 2 but it is also clear that the PV Array --> Inverter block could be plugged in elsewhere or even that a separate

PV Array --> Inverter ==> Rectifier --> Inverter ==> Transformer ==> Rectifier -->

system could be built just for the solar array and its output connected directly to the battery, This could be considered a separate "battery charger". I've also suggested in an earlier post that a single

==> Rectifier --> Inverter ==> Transformer ==> Rectifier -->

could have multiple (toneau plus external)

PV Array --> Inverter

units plugged into it.

Bottom line is that there are many possibilities. What they actually choose to do will be what they actually choose to do.