The answer depends on your frame of reference. If, for example, you assume that the necessary facilities to produce the energy are already in existence, the answer is possibly. If a solar collection station is already in existence, it can generate power without using any fossil fuels to do so. However, that's not the whole story. The facility itself could use fossil fuel as vehicles or other equipment operating as part of the facility might use fossil fuel. Similar situations exist for wind, biomass, and hydropower. If the facility is not in existence, you have to consider all of the energy required to get the facility operational before you can make the call about whether or not it saves fossil fuels. I would expect hydropower installations like dams, etc. to take a tremendous amount of energy to get built before they could ever generate one KW of power without fossil fuels.