Sorry, did I spill some knowledge?
Well, it turns out that investments in clean tech can actually be quite good for the economy. Not every bet can be a winner, but on average, clean technologies are good for economic growth thanks to an effect called "knowledge spillover", says a recent study coming out of the Business School of the Imperial College in London, UK. The general idea is that clean technology as a whole is a lot less mature than the old dirty industries that it aims to replace, and so there's more innovation low hanging fruits to be harvested, and advances by one lab or company can more easily spillover to others. One way to see this in action is with patents; the authors of the study found that clean tech patents were being cited 43% more than 'dirty' patents, and that knowledge spillovers from clean technologies are "comparable in scale to those observed in the IT sector."
This means that a new technical breakthrough or a new business model makes much bigger waves in this young industry. Coal power plants might be getting incrementally better over time, but they are pretty mature. On the other hand, if you look at electric cars or solar power, the past decade has brought dozens of breakthroughs and game-changing change (in price, performance, quality, availability). For example, batteries developed for electric cars can have a big impact on grid storage, one company's solar breakthrough can be rapidly adopted by the rest of the industry, etc. All of this snowballs and ends up being good for the economy, according to the study.