I have commented a number of times on the fact that every source of electricity has pros and cons. For example, both fossil fuels and nuclear power provide reliable baseload electricity, but fossil fuels create air pollution and emit greenhouse gases, and nuclear power generates long-lived radioactive waste; the "fuel" for solar and wind power is free, but solar and wind power have intermittent availability and require vast quantities of materials.
Recently, I've become aware of a new issue related to solar panels. At least, it's new to me. Solar panels create large volumes of waste when they reach the end of their working lives. Since solar panels have no moving parts, I had never thought of them as having a limited life span.
It turns out that, unlike many other electricity-producing technologies, which can operate for decades, solar cells slowly lose efficiency, and therefore, are expected to need to be replaced after only 20 or 30 years of operation. This is much less than the lifespan of fossil plants or nuclear reactors. And because solar energy is diffuse and large numbers of solar cells are needed, the increasing use of solar energy will result in huge volumes of waste in the coming decades.
The cited study comes from Japan, where they are trying to increase the use of renewable energy dramatically following the closure of a large fraction of their electricity supply after the Fukushima accident. Their estimate is that, a couple of decades from now, solar energy will result in around 700,000 to 800,000 tons of waste annually. Dealing with that would require getting rid of 110,000 panels per day.
Efforts are being made to figure out how to handle this waste, but all options have complications. Panels may be recycled for less intensive uses, but panels degrade at different rates and would need to be tested before determining if they have enough remaining capacity to justify transporting them for reuse, perhaps to other countries. And ultimately, of course, they would decay further and still need to be recycled or disposed of. Recycling the materials from the panels is also complicated. Panels are composed of several layers which would need to be separated, and existing processes for doing so are fairly costly.
Work is underway to improve all these processes, and no doubt the coming years will see improvements in the technology for handling "spent solar panels." But even with improvements, it is clear that the issue of dealing with old solar panels will be a significant part of the life cycle for solar panels, and the cost, energy use, and necessary infrastructure to move and process hundreds of thousands of solar panels will need to be considered.