Half a croissant, on a plate, with a sign in front of it saying '50c'
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Parking Lot Solar Farms

Locate solar panels or reflectors above the parking lots of suburban sprawl.
  [vote for,

In many areas, there are large single level parking lots around malls, stadiums, etc.

During hot weather, cars parked in those lots get really hot inside. One of the easiest solutions is to have covered parking so the sun doesn't shine directly on the cars, but generally that's not cost effective for a mall owner.

Solar energy is also a technology that is currently not cost effective in most cases. But what if the cost of solar installation was reduced by making the real estate free, and getting additional value from the installation by using it as a sun shade above parking lots?

The parking lot owner benefits by giving shaded parking to their customers and getting "green" publicity. The utility gets a convenient location to install the panels or reflectors with no real estate costs, and has a nice paved surface to work from when doing maintenance.

The cost of the installation might be increased slightly since the pannels will need to be high enough to drive under, but it seems like that might be offset by the fact that the area is already level and paved. The parking lot owner might also be willing to pitch in a bit on the cost since they are getting some benefit as well. There shouldn't be problems with people complaining about how it looks since parking lots are ugly to begin with.

scad mientist, Jul 14 2004

(??) done http://www.lgc.org/...jun2002/page02.html
[Laughs Last, Oct 05 2004]

solar parking lot https://www.google....mgrc=mlLRnGKiDh0mcM
[xandram, Feb 13 2022]

2021 Yale Study of this idea https://e360.yale.e...een-energy-solution
The article is in favor of this idea, but quantifies cost: "building solar on developed land can cost anywhere from two to five times as much as on open space." [scad mientist, Feb 14 2022]

Market forces in storage; some clues about why they are complicated https://www.woodmac...ia-with-renewables/
[pertinax, Feb 19 2022]

The biggest of the dinosaurs is going down ... https://www.bbc.com...s/business-60411622
... shot full of little photovoltaic arrows. They're proposing to replace it with a 700MW battery. [pertinax, Feb 19 2022]

Way to go Macaroni! https://www.indepen...ctors-b2012331.html
France has always been smart about nuclear power. Then they got dumb and started shutting them down, now they're getting smart again. [doctorremulac3, Feb 19 2022]

We’ve been having the wrong debate about nuclear energy https://yaleclimate...out-nuclear-energy/
[Voice, Feb 19 2022]

Where they are on nuclear fusion. https://www.researc...with_fig2_302632920
Just a couple of details to iron out. [doctorremulac3, Feb 19 2022]


       The merchants could advertise on the panels -   

       "This parking space shade and resulting electricity provided by See's Candy"
normzone, Jul 14 2004

       I had this idea, but you got there before me, so (+). There are two options here, either a roof covering the entire car-park, or individual solar arrays positioned over every space, probably cantilevered against each the array covering the adjacent space.   

       Although the latter design would make a visually striking parking lot, I think that the former would be more suitable; it allows for bulkier equipment, and while the individual solar arrays would have to be photo-voltaic, that is, electricity-producing, the roof idea would allow for the ones that directly heat water as well.   

       I actually wonder why people like Wal-Mart or Carrefour haven't done this already, it really makes sense, and as you say, major environmental brownie points. Someone should probably write to them.
duh_don, Jun 08 2009

       A great idea - but maybe it would be a lot cheaper to just put the panels into the parking lot ground itself. I'm sure someone could come up with a surface that is both strong and could generate heat. That way you don't need all the raised structureal elements. sort of like laying tiles with wires attaching them together and sending electricity back to the store or whatever. Spray 'em down once a month to get rid of dust/oil spills etc.
marquisdenet, Jun 08 2009

       I'd imagine the stores don't do it because the empty space of the parking lot actually has value based on how far away their signs are visible. Putting a shade over the area hides their sign from people parked there.
ye_river_xiv, Jun 08 2009

       There are many unused rooftops and open places where one might put solar panels. The fact that they are not there suggests a cost/benefit analysis finds them to be too expensive for the return.
bungston, Jun 08 2009

       [bungston] Either that, or just a lack of imagination on behalf of the populace, which is endemic in society today. Even if it doesn't generate any income directly, a green company is much more attractive to investors, and indeed to customers, than one stuck in the oil-ridden past.   

       [ye river] I don't think I understand you; what you seem to be saying is that, if someone is in a car- park, but can't see the signs to the store which owns the car-park, then they'll be less likely to go into the store. If that is what you're saying, I think we can safely assume that, if someone's inside the car-park, they got because they wanted to shop at the shop, and if they're outside, then a roof on the car-park won't affect the visibility of the signs. Please explain.   

       [Marquisdenet] I agree, but I think that that would only work for the water-heating kind of solar panels, the photo-voltaic ones, which produce electricity directly, are much more fragile. As far as I know, you could just do a sort of reverse- underfloor heating, where pipes carry the heat away from the tarmac rather than bringing it to it. Excellent idea, though.
duh_don, Jun 09 2009

       Definitely baked in some locations. At this point photovoltaic panels are just coming down to the price point where installing them on pre-existing structures makes sense in moderately sunny or better locations. Having to build an elaborate structure to place them generally does not make financial sense. As the cost of panels continues to drop, however, I expect we will start to see this much more frequently.
MechE, Jun 09 2009

       Wallie world (Wal-Mart) and similar are starting to be putting in permeable concrete recently in some parts of the USA anyway. It allows water to drain through the concrete and soak in or run off underneath the surface. Good strong permeable concrete has 17% or less 'free space' between the rock and it must be about 1.5X as thick as 'normal' concrete for the same strength. If made with half as much cement and replace it with flyash, it will take longer to harden, but will be just as strong and much 'greener'. To make it last longer, it needs some elastomers added, but that costs abot $15/yard but adds about half again to the life of the concrete (Instead of deteriorating after 20+ years, it will start to deteriorate after 30+ years, kind of a thing).   

       All this to say we can get greener by doing other things to make our parking lots 'green' other than just genrating power.   

       Collecting heat using pipes and liquid is probably the easiest, but it does take some infrastructure installation in the parking lot that many are not willing to 'gamble' on. And collecting heat using large flat plate collectors like this will not collect a lot of 'high quality' heat, but it will collect a lot of 'low quality' heat. My guess is it can collect 10 to 30 deg F above ambient temperatures much of the time, but using that effectively may be an issue. Because using low quality heating / cooling require large storage facilities (think, HUGE tanks).   

       When I was a kid, my dad did do something similar in our back patio. He put garden hose in the patio slab when it was being poured, and by running sprinklers in the yard it kept the concrete bearable for me to play on (think 3 to 5 years old here), and he just watered the grass with the heated water. (Think 1950's for energy conservation... not much thought was put into it back then.)   

       I have seen parking canopies used to mount solar cells on ... a good way to keep the cars cool and get extra use out of the parking areas, without having to drive or park on the solar cells!
servant74, Nov 21 2009

       Even if you can not cover the entire lot due to night lighting , a single row or perimeter row of collectors will provide some shade and power some store lighting or hot water.   

       The nice thing about using parking lots vs other existing structures is you don't have to calculate wind loadings of the preexisting building.
popbottle, Jul 07 2013

       Believe it or not, I actually registered "Solarparkinglots.com" a few years after this post. I thought it was an original idea. (it clearly wasn't)   

       This should be a standard in every parking lot. And just because it's being done doesn't mean it shouldn't be done more.   

       Somebody else got solarparkinglots.com. Oh well. There's a growth industry there still IMHO.
doctorremulac3, Feb 08 2022

       With the increasing prevalence of electric cars, this will NEED to be a growth industry. Doesn't need to cover the whole area, just a square metre or 2 above each space (or something).
neutrinos_shadow, Feb 08 2022

       [doctorremulac3] I just tried going to http://solarparkinglots.com and ended up at Renology (https://www.renogy.com/), who sells solar panels etc.
RSMilward, Feb 08 2022

       The only financial incentive to do a much more expensive parking lot instead of a patch of desert is the parking lot is closer to the demand. I doubt that's sufficient.
Voice, Feb 08 2022

       Yea RS, I didn't follow through with that, had other smaller projects that ate my time.   

       Well, it cuts the power bill of the business and does afford covered parking which is a thing. Plus there is a lot of loss in having those transmission lines coming from the desert.   

       I always thought the best way to use these things was for peak summer A/C loads. Flatten that spike a little bit.
doctorremulac3, Feb 08 2022

       That's not quite true, [dr3], because peak heat often lags peak sunshine by hours.   

       The more important role of small solar installations is that, by gradually eliminating "base load", they are dragging grid operators kicking and screaming into the energy storage business.   

       In essence, grid operators are compelled to install storage, just to put a floor under minimum demand; without that floor, minimum demand is going to hit zero on our main state grid on some fine day no more than two years from now, and maybe sooner, and, if they haven't done something about it by then, they won't be able to maintain a stable voltage.   

       They're installing a 100MW battery this year for precisely this reason. That buys them some time, but not much. We have bred the world's most aggressive duck curve, and it's coming at them, quacking.
pertinax, Feb 11 2022

       They might not be exactly lined up but when that solar load starts heating up building envelopes through the glazing and taxing the A/C systems with rising ambient temps that's when you're getting your most solar power.   

       And if you have passive heat (or cold) storage like slab on grade construction, keeping that cool through the peak sunlight hours with solar powered, or at least solar augmented A/C is going to extend that cooling effect later into the day.   

       Point is, solar powered A/C is beneficial, but as far as storage, I'm not sure why the free market hasn't taken this up. Seems like even if there are cheaper ways to get electricity, and certainly there are, government credits should fill any business model gaps. Pretty sure, at least here in California, you come up with a solar plan you can factor in tax credits and other gov benefits to make it work.   

       Haven't looked into it though, just seems like that would be a thing.   

       And by the way, when I registered, "Solarparkinglots.com" electric cars weren't a thing. That's something where certainly the peak load of cars parked at businesses recharging is going to line up nicely with peak sunlight hours.   

       Wonder what the square footage of solar panel needed to charge a car is assuming worst case winter sunlight input.
doctorremulac3, Feb 11 2022

       Dhunno, just to get a minimum I'd say, Northern California enough juice to power a 2 hour roundtrip commute all year round with the most popular Tesla, whatever that is.   

       And Pertinax, as creepy as it is for me to consider political implications to getting an engineering problem solved, it's the reality. So even if the numbers aren't quite there from a strictly practical engineering standpoint the fact that it's got the title "solar" is going to help grease the wheels to get it done. Not pretty, just practical reality. I say that knowing full well that that's lead to a lot of solar power pipe dreams that crumbled in the face of reality. Solyndra being one example. The defunct plant in my neck of the woods got bought by Tesla, somewhat ironically, but I guarantee old Musk got every single government credit for having that sweet "carbon neutral" goodness patina that the old tenant was taking advantage of. "But what if the electric cars are being powered by coal burning power plants?" "Hey citizen, sounds like you've had a bit too much to think."
doctorremulac3, Feb 11 2022

       Yea, you're right, it's very wordy. I'd like to see that old style reporting where instead of going for the maximum amount of reading time per click they just give you the headline or basic idea then the story goes "Still want more details? Okay."   

       So if the question is "How many solar panels to recharge a Tesla?", rather than just qualifying the question forever with "Well, depends on what you mean by recharge." "Depends on what you mean by solar panels." "Depends on what you mean by Tesla." they would understand that a general overview is perfectly fine.   

       So I'd answer the question "How many solar panels to power a Tesla?" with "Here's an example of somebody who has solar panels in their home and never need to recharge anywhere else but their garage. They live in San Diego, have 1,000 square feet of panels on their roof and drive on average 1 hour a day." And I'd specifically leave out what model Tesla it is because, who cares?   

       Nobody's going to read that and say: "Huh? I'm totally confused! Now I have no idea how many solar panels to power a Tesla! What if it's a 3 story tall Tesla at South Pole and there's a solar eclipse?"   

       I mean, thanks for the link a1, obviously not your fault, but this whole not getting to the point thing with internet posts really is way too common.
doctorremulac3, Feb 11 2022

       1000 sq ft will give you about a 14kW max output array, as installed. Somewhere like SoCal will get a fairly reliable 6hr/day, so about 80kWhr. Tesla battery capacities range from a small/older pack of 50kWhr to new ones at 100kWhr. So you're in the right range. Although, you'd have to charge in the day and drive at night.   

       There's a few other inefficiencies in the system to consider, solar panel efficiency drops with high temperatures and progressively with age. You'll lose a few percent in AC/DC conversion, then a few more converting back for the car. Lithium is good at charging efficiency, but you still lose a percent or two. A reasonable fudge factor would be 10% of the panel output doesn't make it to the car, but you're still fine.   

       Move away from the sunnier parts of the world and the numbers quickly look dreadful. You'd have to cover Scotland in PV panels to run a 1/10 model of a Tesla.
bs0u0155, Feb 11 2022

       I think I realized the fatal flaw with this idea. If you build racks for solar panels in a solar farm, they have to be just strong enough to hold the panels up during worst case weather conditions. The structure cost can be optimized to trade off with the cost of replacing some panels if they break. Over a parking lot, they have to be able to withstand impact from a vehicle, and they need to have a large safety margin so they can't fall down and hurt a person underneath. The first picture in the "Charging your Tesla" link looks very expensive. The picture near the end of the article is more what I had in mind, but still requires large steel beams, and has poles that will make parking more difficult and/or reduce the parking density.
scad mientist, Feb 13 2022

       The main supermarket in the small town where I'm now sitting has already covered its roof with solar panels, but just the roof, not the car park, and I think that reflects your point, [scad]; slapping panels on existing structures is a lot easier than putting up additional structures, just so as to put panels on them. They do the latter at mine sites in the Pilbara (I hear), because those have large energy demands and small buildings, but not in residential/ commercial areas.
pertinax, Feb 13 2022

       Wow Scad, very astute observation. That structural cost is probably way more than the panels themselves. Roof mounting makes financial sense but by the time you basically build a new building without walls, which is basically what this is, you’ve moved into an entirely different financial category.   

       I know from experience the process you need to go through to get a structure designed, approved by the city and built while passing inspections during the process, structural engineer calcs, electrical engineering, even plumbing since these probably have water spigots for washing the panels. A roof mount just has to stay there without letting the panels blow off or poking holes in the roof.   

       I don’t know if that kills the bottom line but it certainly impacts it by, I'd say, an order of magnitude.
doctorremulac3, Feb 13 2022

       The hospital over in the next town has the entire parking lot roofed with solar panels and runs a portion of the electricity. I’ll look for a link.
xandram, Feb 13 2022

       Wonder what portion of a give city is parking lots. I assume lots more square footage than roofs in industrial areas.
doctorremulac3, Feb 13 2022

       That probably depends on whether the city has functioning public transport.
pertinax, Feb 14 2022

       Well I know cities that were laid out before the invention of cars are lacking, Manhattan for one. San Francisco, same thing.   

       LA was invented after the car so it's 90% parking lot.
doctorremulac3, Feb 14 2022

       Added link to a Yale study of this idea. They say it is 2x to 5x more expensive, but that it is still a good idea. I'm not 100% convinced. They talk about a long term infrastructure investment, but care would need to be taken in where these are located. For example, if the local mall where I live had installed these in 2004, that would have conflicted with the recent work of putting multi-story parking garages in the lots. So best if someone does this, they should be careful to put it in lots that they don't think will will need to be built up anytime soon. Basically, stick to the less dense suburbs. Unfortunately, it seems like it is the more dense areas where people take more interest in solar.
scad mientist, Feb 14 2022

       Only twice as expensive? Probably not in California, getting permits alone would probably cost more than the solar panels, at least in Silicon Valley where I live.   

       Still, it's worth pursuing in my opinion.
doctorremulac3, Feb 14 2022

       //political implications to getting an engineering problem solved//   

       It's probably worth noting that the political dynamics of solar play out differently in different places.   

       My impression of how solar politics goes in California is something like this:   


       {grand gesture} {grand gesture} {grand gesture}   

       ... aaaaand blackouts   

       In Western Australia, on the other hand, it's more like this:   

       "CHANGE? NO! TAKE IT AWAY! MAKE IT STOP! [...] Oh fuck, it's happening anyway. Right, what's the very least we can do to respond? Let's just do that."   

       {last-minute hack} {last-minute hack} {last-minute hack}   

       ... aaaaand blackouts.   

       In the West Australian case the blackouts haven't eventuated yet, but they're being predicted for some time in the next year or two.   

       The big difference is that, where I live, it's the state government (which owns the grid operator) that is being forced to change by consumers, not the other way around.
pertinax, Feb 15 2022

       //as far as storage, I'm not sure why the free market hasn't taken this up//   

       See link to some people talking about this.
pertinax, Feb 19 2022

       //what if the electric cars are being powered by coal burning power plants?//   

       That depends very much on the where and when.   

       For example, if I buy a nice new Tesla, and charge it up overnight tonight in Perth, then, yes, the extra energy at the margin will come from coal. However, if I charge it overnight five years from now, it'll probably be from gas, with only half the carbon footprint. And if I charge it overnight ten years from now, there's a good chance that the extra energy at the margin will come from a battery, which was charged the day before entirely by fresh air and sunshine.   

       By contrast, if I buy a petrol car today, then it will spend its entire operating life, several decades, burning petrol, because that's the only thing it knows how to do.   

       Also, even today, if I'm charging that new Tesla overnight in Adelaide, there's a good chance that all the energy will come from wind and, if I'm charging in Hobart, it'll all be hydro.
pertinax, Feb 19 2022

       Or we can just start putting up nuclear power plants now. Be up and running in a few years.   

       The other stuff's fine too, but it's going to need nuclear in there as well to get through windless and overcast days.   

       Hydro also needs to be put back in the "good for the environment" category. I've heard it said that hydro is mostly maxed out, but I have no idea if that has any truth to it. Haven't looked into the subject, but hydro is absolutely the king of clean power generation, it's basically two step solar power. But even that needs backup, we've got a bad drought going on in the west and our water reserves are at an all time low, so we need diversity in our power grid.   

       France is getting back on the nuclear thing after some wrong turns. (link)
doctorremulac3, Feb 19 2022

       Yeah, there's a good case for nuclear in some parts of the world. I don't think we're going to need it in Australia, but Russia and Canada probably will (long, cold nights in winter, not guaranteed to be windy). We can sell you the uranium; I think there's still some in the ground in South Australia, and they don't need it there.
pertinax, Feb 19 2022

       Yea, I remember the guys that got on the cover of all the science magazines with some kind of desktop rig using a beaker of something, a thermometer and a lollypop laced with LSD.   

       Might have some of the details wrong but it didnt' work.   

       Now they're working on controlled nuclear fusion and as far as I know they've got the controlled part down, they're just missing the nuclear fusion part. (link)
doctorremulac3, Feb 19 2022


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