# How Far Can Solar Go? **URL:** \ **Category:** Factual Questions\ **Created:** [March 8, 2013, 8:24pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424 "2013-03-08T20:24:35Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![beagrie](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@beagrie](https://boards.straightdope.com/u/beagrie)\ **Post date:** [March 8, 2013, 8:24pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/1 "2013-03-08T20:24:35Z")
Hello All, I’ve tried to find some figures, but they either aren’t there, or (more likely) my feeble brain is struggling to assemble the facts, but I wonder the following; Is there an upper limit on what we can get out of a solar panel? I don’t mean theoretically - like, how efficient the panel could theoretically be without breaking some laws of thermodynamics, or something - although I would be interested in that too. I’m curious if there’s a practical limit that we might reach in the relatively near future, and what that might translate to in the real world. For example, does the future potential of solar panels, mixed increasingly efficient motors, allow for a future electric vehicle that is powered solely by a sunroof-sized solar panel? Or is there simply not enough energy in sunlight? Them’s my thoughts. ---
**Author:** ![RedSwinglineOne](https://avatars.discourse-cdn.com/v4/letter/r/a9adbd/32.png) [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)\ **Post date:** [March 8, 2013, 9:00pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/2 "2013-03-08T21:00:14Z")
> [@beagrie](#): > > Or is there simply not enough energy in sunlight? From Wiki, > [@](#): > > The total amount of energy received at ground level from the sun at the zenith is 1004 watts per square meter, which is composed of 527 watts of infrared radiation, 445 watts of visible light, and 32 watts of ultraviolet radiation. I don’t think thats very much. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [March 8, 2013, 9:07pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/3 "2013-03-08T21:07:02Z")
And that is only at noon on the summer solstice. All other times and days are going to be significantly less. Solar is “free” in terms of having to produce the energy, but the footprint required to collect a useful amount is large. Stranger ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [March 8, 2013, 9:15pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/4 "2013-03-08T21:15:18Z")
Once the sun goes down, the traffic jam is stuck there until the next morning? Solar energy is about (as mentioned above) conveniently 1kW/m^2. IIRC one horsepower is 0.7kW, so your approx 12-foot by 6-foot (ugly) vehicle in best sunlight develops 8kW or about 11hP - assuming the solar minivan is sleek and made of lightweight foam and fibreglas, you might get 30mph out of it. Throw in Aunt Maddy and her two suitcases, and you better plan a route that does not include climbing hills. Add a factor of let’s say, 30% of top value for lack of direct sunlight. Add another factor, let’s say “times 10” which says for every daylight hour you drive, you spend 10 charging the batteries. Also, figure in the cost of converting your garage to a greenhouse. ---
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [March 8, 2013, 9:21pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/5 "2013-03-08T21:21:01Z")
> [@Stranger\_On\_A\_Train](#): > > And that is only at noon on the summer solstice. All other times and days are going to be significantly less. … Not really. If the solar panel is aimed at the sun, it doesn’t make any difference what time of year or time of day. Except early morning or late afternoon (when the sunlight has to penetrate more atmosphere), the primary factor is the earth’s distance from the sun. The best time of year is January when the sun is closest to the earth. ---
**Author:** ![beagrie](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@beagrie](https://boards.straightdope.com/u/beagrie)\ **Post date:** [March 8, 2013, 9:22pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/6 "2013-03-08T21:22:26Z")
Okay, but let’s consider the other side; Picking a random example from the Wikipedia page on Electric Cars, a Fiat 500e takes (on average) 29kWh per 100 miles. If a solar panel were to absorb, say, 400 watts of that 1004, which I’ll (arbitrarily) round down to an average of 200 watts an hour, when you consider that light isn’t as strong at all times of the day, that’d be somewhere in the region of 1-2kWh a day, I think. Not enough to get 100 miles, but perhaps enough for 10. But, then, presumably, electric cars will get more efficient, maybe bringing that 29kWh down to 15, or 10. The figure of 1004 watts of solar energy was over a square meter, but there’s more than a square meter of surface that could reasonably be put to use as solar paneling on an average car, and, the bit I really wondered about, solar panels should be getting more and more efficient, right? Basically, I’m curious as to whether a truly solar-powered car is possible in my lifetime. ---
**Author:** ![RedSwinglineOne](https://avatars.discourse-cdn.com/v4/letter/r/a9adbd/32.png) [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)\ **Post date:** [March 8, 2013, 9:53pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/7 "2013-03-08T21:53:01Z")
> [@bizerta](#): > > Not really. If the solar panel is aimed at the sun, it doesn’t make any difference what time of year or time of day. Of course it does. The time of day and season affect the angle of the sun. The less overhead the sun is, the more atmosphere the light must travel through and the more that is scattered. > [@](#): > > … the primary factor is the earth’s distance from the sun. The best time of year is January when the sun is closest to the earth. The eccentricity of the earth’s orbit is less than 2 percent. That amount weould be negligible in this situation I think. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [March 8, 2013, 10:14pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/8 "2013-03-08T22:14:50Z")
> [@bizerta](#): > > If the solar panel is aimed at the sun, it doesn’t make any difference what time of year or time of day. **Except early morning or late afternoon (when the sunlight has to penetrate more atmosphere)** > [@RedSwinglineOne](#): > > Of course it does. The time of day and season affect the angle of the sun. The less overhead the sun is, the more atmosphere the light must travel through and the more that is scattered. Nice job of deleting part of what **bizerta** wrote, then basically writing the same thing as if you thought of it on your own. ---
**Author:** ![RedSwinglineOne](https://avatars.discourse-cdn.com/v4/letter/r/a9adbd/32.png) [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)\ **Post date:** [March 8, 2013, 10:58pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/9 "2013-03-08T22:58:55Z")
> [@ZenBeam](#): > > Nice job of deleting part of what **bizerta** wrote, then basically writing the same thing as if you thought of it on your own. If somehow you are trying to imply that I wish to take credit for something in **Bizerta’s** statement, you would be wrong. I chose to comment on what appeared to me to be the basic idea of his post: That time of day and season don’t matter (I think it does), and that our distance from the sun matters. (I think it doesn’t). I suppose I could have asked **Bizerta** why the angle of the sun only matters with regard to early morning and late evening but not to a lesser degree at other times of the day, but I chose not to at that time. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [March 9, 2013, 1:55am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/10 "2013-03-09T01:55:10Z")
> [@bizerta](#): > > Not really. If the solar panel is aimed at the sun, it doesn’t make any difference what time of year or time of day. Except early morning or late afternoon (when the sunlight has to penetrate more atmosphere), the primary factor is the earth’s distance from the sun. The best time of year is January when the sun is closest to the earth. This is absolutely not true. The difference in solar incidence betwen perihelion and aphelion is about 6% at Earth orbit. The attenuation by the atmosphere versus the Sun at the equator on solstice (when the Sun is at top dead center when it crosses the meridian, and follows the celestial equator for an exact 12 hour day) is about 6% at at +/- 3 hours of solar noon, and drops radically after that (~20% at 4 hours from noon, 50% at 5 hours. Average solar incidence over an 8 hour day is about 80% of solar maximum. Aveage solar incidence compared to peak incidence will depend on latitude, but anything significantly above or below 23 degrees will have less annual average duration than at the equator. Solar is great in terms of bieng freely, renewable and significantly less polluting than combustion energy generation, but it requires a considerable footprint and the utility and consistency vary considerably with location and climate regardless of eficiency improvements in solar collection and conversion capability. Stranger ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [March 9, 2013, 2:44am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/11 "2013-03-09T02:44:27Z")
Of course there is a lot of footprint (e.g. on factory rooftops) that can be exploited … if it was cheap and efficient enough. [The world’s fastest solar powered car.](http://www.gizmag.com/sunswift-ivy-claims-record-for-worlds-fastest-solar-powered-car/17525/) (Just over 55 mph.) Not exactly your suburban commuter. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [March 9, 2013, 2:47am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/12 "2013-03-09T02:47:38Z")
How far can solar go? The hope for [this vehicle](http://www.economist.com/news/science-and-technology/21572731-attempt-fly-around-world-solar-powered-plane-its-moment-sun) is around the world. 🙂 ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 9, 2013, 3:24am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/13 "2013-03-09T03:24:00Z")
> [@bizerta](#): > > Not really. If the solar panel is aimed at the sun, it doesn’t make any difference what time of year or time of day. Not true. **Stranger** ’s comment was that the “footprint required to collect a useful amount is large.” The amount of sunlight that can be collected for a given footprint (i.e. for a given amount of land) is a strong function of the sun’s elevation. Even if you put the solar panels on tracking platforms aim them at the sun, efficiency goes down when the sun is lower in the sky because each panel casts a shadow on the adjacent panel (or you need to space them out far enough to avoid it). Besides, if you use a tracking platform, you’d never recover the cost of building and maintaining the platform. It’s much more cost-effective to use stationary panels. ---
**Author:** ![beagrie](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@beagrie](https://boards.straightdope.com/u/beagrie)\ **Post date:** [March 9, 2013, 8:50am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/14 "2013-03-09T08:50:20Z")
Okay, so, unless solar panels get up to, like, 80% efficiency, and they make cars that can run on 5kWh per 100 mile or less, entirely self-powered solar cars are unlikely. Looking at the “footprint” aspect; is it possible there could be a noticeable effect on the atmosphere of _lots_ of efficient solar panels? As in, if we could make panels that absorbed a huge portion of the sun’s light, and then covered every feasible surface (rooftops, unused ground space, [floating solar islands](http://www.wired.co.uk/news/archive/2013-02/27/solar-islands), is it possible that, for example, we could lose a degree or two in atmospheric temperature because of the energy that’s not bouncing back up? Or is the amount of solar panels we’d need to make that kind of difference too great? ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [March 9, 2013, 8:59am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/15 "2013-03-09T08:59:15Z")
There’s been talk of a monorail in the Southwest that’s supposed to run throughout Arizona. IIRC it would go from Tucson to Flagstaff via Phoenix, with a few offshoots to smaller cities. (It may also go to LA or something, can’t recall). The idea was to put solar panels over the whole thing and I was told that it was predicted that such a long solar panel array – if properly maintained – could easily provide enough power for the entire American Southwest even at current levels of technology. Is that a reasonable prediction or incredibly optimistic? ---
**Author:** ![beagrie](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@beagrie](https://boards.straightdope.com/u/beagrie)\ **Post date:** [March 9, 2013, 9:02am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/16 "2013-03-09T09:02:01Z")
> [@Jragon](#): > > Is that a reasonable prediction or incredibly optimistic? Ultimately, that’s what I’m curious about; what are reasonable predictions, and what are incredibly optimistic. Could solar power one day become our sole source of electricity, or is that, practically speaking, unlikely… or theoretically impossible. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [March 9, 2013, 10:14am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/17 "2013-03-09T10:14:28Z")
> [@scr4](#): > > Besides, if you use a tracking platform, you’d never recover the cost of building and maintaining the platform. It’s much more cost-effective to use stationary panels. :dubious: Most solar panels used for remote area power generation are placed on [tracking platforms](https://www.google.com/search?hl=en&safe=off&q=solar%20panel%20tracking&psj=1&bav=on.2,or.r_qf.&bvm=bv.43287494,d.dGY&biw=1173&bih=789&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&authuser=0&ei=WAo7UZeCIbHRmAWk7oGYDQ). Nobody seems to think that the amount of extra energy required is even measurable, much less insurmountable. The platforms use light sensors, and the angle is adjusted by tiny electric motors, I’m guessing something like 1/10 horsepower, or by tiny air compressors, the type that you run off your car cigarette lighter. Since the motors/compresors only run for about 10 seconds every hour to keep the panel positioned, I seriously doubt the energy used would even be detectable, much less “unrecoverable”. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [March 9, 2013, 11:36am UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/18 "2013-03-09T11:36:41Z")
Cover the roads with a solar panel canopy and equip the cars with a contact pole to pull down the required juice. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [March 9, 2013, 12:22pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/19 "2013-03-09T12:22:27Z")
[Solar roadways.](http://en.wikipedia.org/wiki/Solar_roadway) > [@](#): > > If the entire United States Interstate Highway system were surfaced with Solar Roadways panels, it would produce more than three times the amount of electricity currently used nationwide.[5] Couple with inductive charging and solar powered EVs are not constrained by the footprint aspect. Just the cost, practicality, and driving at night ones. The theoretic potential [is there](http://www.americanenergyindependence.com/solarenergy.aspx). The issues of using it _alone_ are not that there is not enough exploitable square footage, but that it is uneven. Once priced competitively (hard to compete with natural gas right now) it would need to be coupled with other sources that offset its weaknesses, including wind which tends to be greatest as a resource at night, and/or better more cost-effective load shifting technologies, before it could be anything other than a limited part of the mix. ---
**Author:** ![sevenwood](https://avatars.discourse-cdn.com/v4/letter/s/6de8d8/32.png) [@sevenwood](https://boards.straightdope.com/u/sevenwood)\ **Post date:** [March 9, 2013, 1:22pm UTC](https://boards.straightdope.com/t/how-far-can-solar-go/652424/20 "2013-03-09T13:22:32Z")
> [@naita](#): > > Cover the roads with a solar panel canopy and equip the cars with a contact pole to pull down the required juice. Ooohhh!! High-speed bumper cars! [Next page](https://boards.straightdope.com/t/how-far-can-solar-go/652424.md?page=2)