Is there any reason that solar panels can’t be placed on the towers of wind turbines? I’m thinking mostly down low rather than up high. Perhaps only on the lowest 10 to 20 meters of the tower. The only possible objection I can think of is weight. Possibly it would require a change in design to allow enough panels to make it worthwhile.
I don’t see why not, but would it be worth it? You’d have to build some kind of scaffold structure around the tower to support the panels, and you would only be able to hang a relatively small number of them off of it. It probably would not be a money-maker. And it may interfere with maintenance of the tower down the road.
Why on the towers? Why not a solar panel farm on the ground with the turbines sticking out?
Building the towers have already chewed up certain amount of land. I’m thinking of how to increase the energy output without chewing up more. Putting the panel farm on the ground does that. Solar panel farms are not totally ecologically friendly, after all.
But if panels can be added to structures already there, it’s a very minor additional disturbance to the environment. Also, wind turbines are already connected to the grid, so there’s no need to add more power lines.
ETA: OK, interference with maintenance may be an issue. Hadn’t thought of that one.
Answering my own question, I just thought of why they don’t do it. Or at least one reason why.
Adding solar panels would provide bird perches. And that would lead to more bird deaths from them being hit by the blades. It’s the reason why the towers are smooth-surfaced rather than an open trusswork.
OK, well never mind. Scratch that seemingly good idea. Unless there’s a way to add the panels without giving birds a place to perch. We probably could, but probably not worth it.
Covered by this xkcd flowchart.
The towers are not that (relatively) wide, nor are the blades that (relatively) far from the tower itself. Given solar panels are angled towards the best sun & not vertical you’re not going to get much power from putting them on the tower itself, especially if the blade side is towards the sun.
The related question is is it worth it to put them on high-tension catenary? They are bigger/wider towers & don’t have moving parts. Probably need to add a low tension wire to collect the energy from each of the towers collectively.
One problem with putting them on catenary-wire towers is that you’d be greatly increasing the cross-sectional area of the towers, and hence their wind loading. You’d also be shading whatever is behind them (often forest or cropland), which the owner of that land might not like.
Not really. There’s open space nearby, but I’ve already ruled it out. Most land near wind turbines is agricultural. Putting a solar panel farm there means you can’t farm it anymore.
There’s certainly a fair amount of already-human-impacted but not very productive land underneath power lines, and, if the area isn’t too shaded by neighboring trees, seems like not a bad place for solar panels. But wires and even the towers don’t block much light, so I don’t know why you’d bother trying to get the panels above them rather than simply on the ground.
Avoiding “bird perches” is neither the reason modern towers are enclosed nor why solar panels are not installed upon them. Conical towers are used for modern horizontal axis wind turbines because they create less vortex shedding and fluid interaction with the blades as they pass, have fewer modal frequencies, and for really long-bladed turbines requiring greater height are stronger for the mass of structural steel used.
Large solar panels attached to the tower would create more drag, interfere with the rotor, requiring the nacelle to be much longer and the overall diameter and strength of the tower to be greater to accommodate, and of course would be a massive pain in the ass to install and maintain in a highly elevated position. Wind towers are made tall and placed in locations specifically because there are regular high winds at that location, and it is obviously not desirable to handle large flat assemblies in wind even if there were some practical way to mount them that wouldn’t interfere with the rotor.
Solar power does necessarily have a large footprint, which is one of the major downsides of solar, but it isn’t as if the small reduction in ground area to be had by mounting the panels in an elevated position somehow justifies this concept. PV panels have to be angled to maximize solar incidence and spaced to prevent shadowing one another (which is one of the significant limitations of rooftop solar), and have to be regularly maintained.
There is a lot of open space in the American Southwest that also has an ideal climate and an almost ideal latitude within the continental United States, and many of these areas are contaminated with mine tailings or are otherwise undesirable for development. There is literally no reason to add great expense and inconvenience to the construction of wind turbines to save a very small amount of ground space.
Stranger
One thing that may be a option is to use the ground around the tower for farming, grazing or other like purposes. Yes it won’t get more energy out of it, however it will greatly reduce the land area of the turbine if the land needed to have the tower was used productively. The footprint of the tower itself is very small.
There are acres of empty roof space available on buildings all over the country.
They are horizontal, so better exposed to sunlight. They already have access built in. They are often unobstructed by trees, so exposed to sunlight. They are located near people, where the electricity is needed. The solar panels would absorb sunlight on the roof, reducing the need for air conditioning in the summer. The roof space is largely unused, so won’t reduce agricultural or recreational space.
One drawback would be the increased weight, which some buildings are not strong enough to hold. But buildings can be strengthened, and solar panels are getting lighter all the time.
The wind turbines I’m most familiar are seen on tops of ridges along I-84 in Eastern Oregon. There’s some wheat farms around but these turbines are in standard sagebrush country generally used as rangeland.
Lots of sunshine, of course, so PV’s would work. Some pluses of co-locating (on the ground). Use the same power lines to the main grid, maybe use the same converters, access, rights already in place, etc. But lots of wind so it is going to be cheaper overall (for now).
I would not be surprised if it’s economically important that the PV panels are close together for maintenance and other reasons. Such clustering is anathema for wind turbines.
But how many rooftops of such buildings are actually being covered with PV? I sometimes see pictures of panel farms out on open ground, but not a lot of building roofs being covered, except some houses. You’d think they’d cover the latter before the former, but that doesn’t seem to be the way things are going. But I may have the wrong idea, since it’s just what I happen to see.
There are several reasons for angling solar panels, but there are no absolutes, only costs. Solar panels used to be dynamically mounted so that they could fallow the sun. That’s not done any more because it’s cheaper to buy more panels than it is to provide dynamic mounting. Roof tiles are angled at the angle of the roof. An important reason for angling is to allow self-cleaning: a benefit of putting panels in separated rows is to allow walking access.
You can just put panels flat: if you cover the surface, you catch all the sun, just as you would with perfectly angled panels. Now that panels are so cheap, “solar incidence” is less significant than it once was.
It’s hard to see rooftops! Anyway, Walmart is putting solar panels on top of many of their buildings as well as some others.
This is one key thing to remember about solar power: If Walmart has crunched the numbers and decided they will make money on this, then it isn’t some sort of environmental feel-good thing. Solar Power: It’s Serious Business! 
Well, it’s mostly what I see happen in the news. And I follow the renewable-energy news relatively closely. But the sites I read don’t have much on retail stores installing solar for some reason. Not sure why not. From that article, it looks like Wal-mart is not the only one, Target and IKEA are doing it too.
OK, that’s retail stores, but what about all the suburban lowrises out there? They have vast amounts of horizontal rooftop real estate.
Much of the land around wind turbines is farming/grazing land. Since height isn’t a factor in solar panel placement it’s much more effective to build the farms close to the ground.
When my company added turbines in Western Kansas we had to lease the land from farmers. The lease covered just the footprint of the turbines so that the farmers could use the land under the turbines for crops or grazing.
I imagine that we could have leased more land for solar but that would have substantially increased costs.
At first the farmers were reluctant to lease and there was some concerns over the possibility of eminent domain action.
But as the project unfolded and the farmers started seeing their monthly/annual checks roll in for land that still was +90% usable we had some farmers contacting us to complain that they wanted in on the deal too and would we please install some turbines on their land.
The most obvious reason is wind resistance.
The second reason cost vs. voltage drop. Solar panels generate in DC which is subject to line loss over distance so optimally you want the panels closest to the batteries. You can counteract this by using higher gauge copper wire but this could get very expensive.