Wind and solar power have gotten so cheap that other forms of renewable energy have been relegated to science labs and the dustbins of history. As wind turbines and solar farms sprout around the world, investments in other technologies that produce power — from waves, geothermal steam pockets, rivers, biomass and more — have dropped off a cliff. Even those gleaming mirrors in the desert that focus sunshine onto thermal generators can’t compete on price with photovoltaic panels, and they probably never will. As the modern green energy industry was starting to take off, investors poured money into all kinds of ideas. Bets on wind and solar have paid off, but the rest have mostly fizzled. Turbines and panels received about half the spending on renewables in 2004, according to Bloomberg NEF. This year, the two technologies will suck up 93 percent of global spending. “The reality is that wind and solar got to scale first,” said Gabriel Alonso, an executive with Quantum Energy Partners, a Houston-based private equity company. “Other renewables have been cornered by the now-permanent success of wind and solar.” Bloomberg