How can any system be made more efficient? By making its internal parts working better together—which is also the literal meaning of synergy: working together. Synergy can thus be regarded a means for optimizing systemicefficiency, as opposed to the more conventional mindset of maximizing individual efficiency, achieved by increasing output per device or per process.
Renewable energy systems are generally made more efficient by pushing the limits of engineering, often in regard to scale; continuously constructing bigger dams, taller wind turbines and larger solar plants that require increasingly bigger landscape changes and ever more comprehensive technological support systems for realizing the efficiency of the technology system.
This strategy is not necessarily unreasonable. Especially for wind turbines, where power output increases quadratically with rotor size. Even so, this maximization strategy triggers a cascade of negative consequences for systemic efficiency (negative synergies). For example: (1) Very large turbines require very large roads and machines for construction and maintenance, (2) massive accumulation of energy in remote areas requires transformer stations for stepping up voltages for long-range transport. (3) Very high voltages require gas-insulation (SR-6 [1] ) of switching gear and (4) a dedicated transportation grid must be built between generation site and distribution grid. Together, these factors make out the main crux that (5) one giant wind turbine cannot alone defend such a comprehensive support structure.
The caveat, however, is that in order to utilize the external construction efficiently many very large turbines must be built in the same area, thereby motivating systematic over-exploitation of the implementation site, rather than adapting turbine sizes and numbers to minimize ecological impact. This loss of systemic efficiency must be weighed against the increase in individual efficiency, before the most efficient solution can be identified. A synergic approach would decide the size and type of turbines by how the overarching technological-ecological system could be optimized rather than how the individual energy output per generator could be maximized.
[1] The most climate-warming gas known since it is has the best insulation properties for electrical equipment