The only renewable energy that does not take off in Europe is thermal solar energy: solar panels to collect heat for domestic uses (hot water, heating, even air conditioning!).
It should however be strongly supported: its yield is excellent, and (contrary to photovoltaic and wind), it stores its output very simply in the form of hot water. Domestic heating and hot water count as major sources of energy consumption (>25% of the total - to be confirmed), so that replacing the current use of fossil fuels by renewable energy makes great sense (even if the solar panels generally cover only 40% of the needs, this is still a very significant gain).
The determinant factor for the take-off of photovoltaic and wind energy has been the guaranteed feed-in price for the electricity generated: the electric grid operator was mandated to purchase the energy, at a pre-determined, guaranteed and high price, whatever the quantities. This regulation created the profitability of the investment - and spawned initatives all across Europe.
I propose that the same logic be applied to solar thermal energy: the gas / urban heat operator would be mandated to purchase back the heat generated by solar panels, at a fixed, guaranteed price, above the price of fossil energy. This would create the rationale for investment in this very promising and important renewable energy.