Answer: lack of investment.
Making investors aware is a good start.
Reality is few of our green energy opportunities are fully developed. Investors seem to lack confidence that the investments will payout. Better returns expected in fossil fuels.
How much of a WalMart’s parking lot would have to be covered with solar panels before it would only have to buy power at night? If they covered it all would they be able to store enough to not even have to buy it at night? Multiply that times factories, shopping centers, airports. People at airports would probably even pay extra to have their cars under solar panels in long term storage. I have no background in electrical engineering or energy finance, but this seems like a way to do a lot of good things, green energy and jobs, and save or make money for investors.
Solar panel covered parking lots are pretty common in Hawaii. Covered tennis courts too. But Hawaii has lots of sun and high electricity costs.
According to this cool map, France isn’t a great location for solar:
Covering a parking lot is a lot more expensive than putting panels on a building. For a parking lot you need infrastructure: poles in the ground, supporting structure, and of course, making sure you’re orienting everything to the sun. That’s not how parking lots have historically been envisioned or built.
Put solar panels on a rooftop? Well, there’s already a rooftop to put them on.
At some point (as electricity becomes more expensive) this sort of scheme makes a lot of sense. At today’s prices vs construction costs I’d sort of doubt it - unless there’s a subsidy for carbon reduction, but I don’t see a program of the magnitude needed to move the needle in the immediate future.
Goofy plenty of mall parking lots have coverage. Plenty of buildings have parking garages. People part with money to get things done. Is there something wrong with getting things done?
I get Walmart is almost out of money. I am about as concerned about it as you are.
Solar panels in parking lots are pretty common around me. A lot of schools have them. Even a local Walmart has solar panels over about 1/2 of their parking lot.
To Goofy’s point, the structural support isn’t all that complex. Typically, they’re on two poles with a beam between them. Then the panels are on supports placed perpendicular to the beam and angled appropriately toward the sun. For longer runs, there might be an additional pole or two along the length of the beam. That seems to work pretty well. Is it more expensive than a rooftop installation? Possibly, but I suspect not all that much more. In the case of the Walmart I mentioned above, the roof is already covered in solar panels. Apparently, they wanted more, so going to the parking lot is the only option. Looking at an overhead photo, my eyballing says they doubled their solar production by using the parking lot.
–Peter
It’s vastly more expensive than doing nothing. A carport system is roughly 40% more expensive than a ground mount system. A ground mount system is roughly 40% more expensive than a rooftop system. That makes your break even point pretty far out in the future, not an enticing way for a local manager to spend hundreds of thousands, or even millions of dollars when there are other things needing funding too.
Yes, there are some forward thinking bosses, and a few who want to flaunt their green credentials in public, but mostly I suspect it’s just costs. If people aren’t running out and putting them on their homes for next-to-nothing, I’m not surprised that owners of parking lots aren’t rushing to put them up at half-again or double the price.
Doing it because it’s “good” is only going to get it so far. Doing it with subsidies will help, and doing it by government dictat (as France is doing) will get it done a lot faster yet, but I don’t see that kind of government interference on that scale in the US in the near future. I wish I was wrong about that.
Well, I am in California, where electricity is in the 30-50 cent per kW range, and we get a lot of sun that produces a lot of electricity. Not in the TVA area, where electricity is still pretty cheap and afternoon storms in the summer curtail solar production. So even a large increase in costs over rooftop can still be a good investment. And ground mount simply isn’t an option - the dirt is too valuable to dedicate to strictly solar.
Based on the number of parking lot systems around me (they are everywhere), I have to believe they are cost competitive, even if rooftop is significantly cheaper.
–Peter
Add battery storage and the question becomes,
"How much of a WalMart’s parking lot would have to be covered with solar panels before it would power 24/7/365?
How much might it make selling power to the grid at peak hours?
The Captain
it’s the batteries, stoopid! 
The HS that I attended installed them a few years ago. Here’s a 1 minute time lapse of the process. I think that the install / lease netted the school district about $5.3M over the next 15 years. Not a bad payback!
Solar Panel Installation Time-Lapse | Dighton-Rehoboth School District
'38Packard
Plenty of crop land around here has been converted to fields of solar panels. Don’t see where it would be meaningfully more expensive to do this in Walmart parking lots. And what customers wouldn’t enjoy parking in the shade during the summer? Might even lead to increased sales.
Famous last Boomer words…
Game Set Match!
Doing nothing has no current cash-outlay cost. However, it may be better to do something productive with the space. Remember: Southern California is mostly naturally desert. Yet, for some reason, they chose to NOT “do nothing”.
Except for the new panels coming out which are translucent to blue light. Power is generated from the red end of the spectrum and plants underneath thrive in the blue light.
A couple of complications with putting solar panels in a parking lot compared to a field.
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The isles of the parking lot might not be orientated at the best angle for sunlight.
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In a parking lot the lowest level of the solar panel may need to be seven or more feet high for so there would be enough clearance for cars. The highest part may be 15(?) feet high in a parking lot. Existing parking garages may not be designed to hold all that weight on the top floor.
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Running the power lines through a field is easier than through a concrete or asphalt parking lot. Fields that solar panels are located in are selected because there is a large power line nearby. In an urban area running a new power line from a Walmart to a power line that is a half a mile away could be difficult and expensive.
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Safety is more of an issue in a parking lot. A support pole would need to be able to handle a car hitting it and if solar panels fall due to weather or damage it may damage expensive cars or hurt people.
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In a parking lot you would need to have lighting under the solar panels for at night for safety. Probably security cameras too in some areas. In cold areas ice and snow may accumulate under a solar panel and be a liability for people trying to park under them even in areas that only get snow a few times a year. A regular snow plow might not be able to clear out the snow.
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Vandalism and theft are more of a risk in a parking lot. I would think it would be pretty tempting for people to load a couple of thousand dollars worth of solar panels into a pickup and drive off.
Some of these could be handled better in new construction but there are a lot of “gotchas” in tryin to add them to existing parking lots.
Trying to grow plants (on an industrial scale) underneath solar panels seems folly. You also need to harvest them, which means big machines - even for those which are picked by hand (increasingly rare) to transport them back and forth. It would seem there are easier targets for solar farms, at least to me. You also need to till the soil at the beginning of the cycle, which also means machines, usually tractor size, often dragging multiple harrows around. Hit a pole with one of those and you’ll have a seriously bad day.
Its reported that livestock like sheep or goats grazing between the solar panels helps control weeds. You need space enough between panels for easy access. Wide enough for a pickup or golf cart/gator. Hay might be possible. Land value is not gone. Choices have to be adapted.
It can also be possible that the highest economic use of the land is to produce electricity.
Unlikely as the property is “close enough” to be able to readily access a high-power line. Thus, the issue is trying to determine which competing additional use(s) is/would be best.