Environmental engineers consider geophysics and ecology for the purpose of providing recommendations and making plans for expanded infrastructure that extends outside of already human inhabited space or for repairing or renewing current infrastructure that extends into such an environment. The main thing is that they attempt to understand and predict what the effects on the environment would be for such projects.
Environmental scientists collect and analyze the information that environmental engineers will use in the future if projects ever extend into that place. They also study the actual effects of human activity and infrastructure on the environment.
Researching renewable energy falls entirely outside the scope of those two fields, except in considering the effects of deploying those technologies in the places planned. It actually falls under the general fields of electrical, mechanical and chemical engineering, along with physics and chemistry.
Research in solar panels is primarily done by electrical engineers and physicists, with help from chemists and chemical engineers for new chemical processes in manufacturing the devices. Understanding exactly how a solar panel works requires advanced optics, solid-state physics and quantum mechanics as well as semiconductor manufacturing processes.
Research in wind turbines is done primarily by mechanical or aerospace engineers, with electrical power engineers helping design the system to connect the energy generated to the grid (not a simple task, mind you, the voltage, frequency and phase of the electrical signal must be locked to the voltage, frequency and phase of the power grid at that point, and doing so is complex). Design of the blades and the mechanical system requires understanding fluid dynamics and distributed object mechanics and strengths, as well as understanding how the power generation will affect the movement of the blades.
A problem that I've noted in all the "green energy" subsidies that the federal government is handing out is that comparatively little of the money goes to improving the technology so that it can be feasible and actually be worth deploying on a large scale, most of it goes to offsetting the cost of deploying the technology and keeping the prices for the energy artificially low so that people are willing to have it hooked to their grids. If we cut off the subsidy for deployment and poured it all into R&D, then I predict that we would have an initial stopping of new solar or wind projects for a few years, but after those few years new projects will be deployed anyway because the technology works well enough to be worth deploying.