First, critically, while there probably is still true slavery especially in the UAE illegally, slavery, the ownership of human persons as property, the thing described as wrong livelihood in the EBTs, does not legally exist in either the PRC or UAE. Labor under horrible conditions, whether those conditions were caused by the employer (Emeratis taking their employees passports) or simply the accidents of history (nearly half a billion Chinese people still being rural poor in abject poverty who, until recently, would frequently break the law and illegally migrate inside of China from rural to urban Hukou to work these jobs) is not literally the same thing as slavery, despite also being bad. There is an important moral distinction, especially in the Buddhist context, between systems where human beings are traded / treated as property and those where they are not.
Secondly, while China is the single largest producer of solar power (plurality), it is far from the majority. The USA, India, and Japan combine on their own to produce as much as China, and while all tragically still likely have some illegal slavery (especially in black market sectors) none have legalized slavery in their solar industry, and have much better labor standards than China and the UAE. So clearly slavery is not necessary for for solar.
Third, there are an abundance of publications out there showing paths forward, produced by highly educated experts, which I’m reasonably confident never include slavery, but do often include things you neglected to mention like carbon capture through (re)forestation and carbon taxes.
Fourth, even if it weren’t so unreasonable to believe that slavery was the only way out of catastrophic climate change, despair is not a productive message. For example, there are goals we genuinely cannot achieve (eg 0 degrees warning by 2025), but there’s no use saying, “No level of investment, market driven or policy driven, will achieve that!” Instead it is always better to focus on what is achieveable and encouraging the hard work necessary to achieve it.