Here are some of the key reasons to oppose geoengineering, which are discussed in more depth below:
It doesn’t work: None of the technologies have a track record, all of them come with major risks and unknowns, and in some cases the effects would be obviously catastrophic.
Detracts from real solutions: By promising a quick fix, geoengineering threatens to delay the implementation of a transition away from fossil fuels, and could redirect funding and investments away from real climate solutions. Some geoengineering proposals require vast amounts of energy, which means less climate-friendly energy for everyone else.
Human rights and biodiversity: Many geoengineering proposals require the intensive exploitation of vast amounts of land (in the case of BECCS, twice the size of India!) and increasingly the oceans too . Those projects would inevitably displace millions of people and potentially wipe out entire ecosystems.
Weaponization: Computer models show that geoengineering interventions can have regional winners and losers; should governments and corporations decide that geoengineering can successfully change climate patterns, it will inevitably be weaponized.
The bottom line: geoengineering techniques do nothing to address the root causes of climate change, and evidence points to a high likelihood that rather than improving the climate, they would make things worse—potentially in catastrophic fashion.
You might be interested in taking a look at the following site. It is called Geoengineering Monitor.
Key reasons to oppose geoengineering
Or their section that is about solar, specifically