Solar Energy

Solar panels and shade: using “negative space” to increase climate resilience

Nov 18, 2021 3:09PM

I’m generally a fan of solar power, both photovoltaic and thermal. As I’ve said for a while now, I think our best bet for a resilient society is to have a diverse set of tools available, so that the strengths of one kind of power generation can help reinforce the weaknesses of another. I like distributed power generation for its potential to make it harder to control people’s access to electricity, which in turn gives more political power to everyday folks, similar to how a solid mutual aid network or strike fund can allow communities to survive unexpected hardship or to win the “siege” of a strike. I also very much like the portability of solar panels. As circumstances like rising sea levels or persistent heat force us to abandon some of the places in which we currently live, the whole process will be much easier if we can bring our power sources with us.

One problem with solar power is that whether you’re using mirrors to concentrate heat, or photovoltaic cells to generate electricity, both depend on a large surface area covered in the relevant material to “catch” enough sunlight to use. While I don’t buy the idea that we can run our entire society with just wind or just solar, scaling up renewable power in general can potentially conflict with the equally important goals of re-wilding parts of the landscape, and growing “carbon crops” for sequestration.

The solution that’s most commonly offered – at least for photovoltaic power – is to mount the panels on places like rooftops or parking lots, where there’s already guaranteed direct sunlight. I like this for a lot of reasons. Part of it is that it provides a failsafe for individuals and communities – if your building generates at least some of the power you use, that’s a huge benefit for surviving the various dangers of the growing climate crisis. At the same time, there are things that require a lot of power in one place, and power is always lost in transmission. That’s one reason why the whole “we could power the whole planet if we just cover a section of the Sahara with solar panels” idea has never actually been seriously considered – even with magically indestructible transmission lines, too much power would be lost getting to to where people live.

Rooftops are nice because they generally have at least some correlation to the amount of power being used; more people consume more power, and more people means more rooftops. On the other hand, I think as the temperature continues to rise, cities are going to need to introduce a lot more plant life if they want to keep outdoor temperatures at survivable levels. It’d be nice if I didn’t feel the need to keep saying it, but we’re at the point where we need to be deliberately engineering our surroundings to account for lethal heat. If we can, it would be wise for us to also take some action to help our ecosystems cope with the chaos we’ve caused. Fortunately, with solar panels, there’s a way to do that while also getting the benefits of centralized solar farms.

While we should be reducing our use of highways for rapid transit lining those that we do have with solar panels, either on the roadside or even covering parts of the highway is one option. Another is covering canals.

California’s water system is one of the largest in the world and brings critical water resources to over 27 million people. Brandi McKuin, a postdoctoral researcher at UC Santa Cruz and lead author of the study, found that that shading the canals would lead to a reduction in evaporation of water, kind of like keeping your glass of water under the shade instead of out in the open on a hot summer day prevents evaporation from stealing sips. Putting up a solar panel using trusses or suspension cables to act as a canal’s umbrella is what makes the double-whammy of a solar canal.

“We could save upwards of 63 billion gallons of water annually,” she says. “That would be comparable to the amount needed to irrigate 50,000 acres of farmland, or meet the residential water needs of over 2 million people.” Water is of especially critical importance to California, a state regularly stricken with drought.

The actual water savings aren’t huge, but there are also benefits to shading the water that go beyond losing less to evaporation:

Aquatic weeds also plague canals and can bring water flow to a standstill, but the researchers found that by adding shade, and decreasing the plant’s sunshine slashes the amount of weed growth. McKuin says preventing weed growth would also lighten the load for sometimes costly mechanical and chemical waterway maintenance.

As usual, the United States is lagging a bit behind on this one. India has been covering canals with solar panels for some time now, and have found that not only does it keep the canals cooler and more functional for human use, but the lower temperatures and limited sunlight reduce algal blooms that can make people sick, and that suck oxygen out of water, making it difficult for organisms like fish to survive.

Not only do we get those benefits, but the evaporation that does occur also helps keep the solar panels cool, improving their efficiency:

And while the water can benefit from the solar panels above, so do the panels from the water below. The running water helps the panels to remain cool, which increases their efficiency by at least 2.5-5%.

As most articles I’ve read on this point out, the up-front cost of solar farms over water tend to be higher than building on dry land, but I hope I don’t need to point out that cost should not be the primary concern when responding to global climate chaos. I’d like to see more research into the effects of things like shading ponds, lakes and rivers, but with those feeling the burn of climate change too, I think it’s worth trying out.

Going forward, I think there’s going to be a lot of austerity propaganda surrounding climate change. Whenever society has a ruling class, those rulers will always talk about the need to show “the resilience and ingenuity of our people”, by making everyone else suffer more, so that those at the top don’t have give up their power.

There are a lot of ways to combat that, but one is to relentlessly insist on framing the conversation about what collective investments will yield the biggest improvements to life for people in general. Reducing algal blooms and creating shaded swimming and boating areas, for example, could make a hotter climate far more bearable, and we’re going to need as much “more bearable” as we can get.

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Paul McGarry

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