When we think of renewable energy sources, we can all come up with a few alternatives for the unsustainable fossil fuels we still use nowadays. Think about for example, solar panels, wind turbines and hydropower. The alternatives for non-renewable energy sources are already here, however the world does not succeed in implementing these new forms of energy rapidly nor at low costs. Especially in urban areas, the realization of switching to green energy is quite difficult. This is because large projects with great impact are difficult or impossible to apply to urban areas. Giant wind turbines are obviously not suited for the city centre. Another example is that putting solar panels on every free inch of roof in the city is not considered as an improvement on the picturesque townscape.
The characteristics of urban areas are therefor, in terms of the development of sustainable energy, rather problematic. On the one hand, 50% of the world population lives in cities and this percentage is ever growing. On the other hand, cities leave little to no room for efficient renewable energy sources. This can be understood quite literally, as there is no space left for large renewable sources in densely populated cities. But also, municipalities have regulations of what is allowed in a city and what is not. For example, you cannot just place a solar panel on your roof; you have to take into account some basic rules. As for, the wind turbines, no one would be surprised that the municipality has made rules on that topic, since no one would be thrilled to have an energy generator the size of the Statue of Liberty in their backyard.
Now, what would work for a municipality like Leiden? First of all, it would not be a bad idea to liberalize some regulations concerning implementing renewable energy sources in the city. To take the cliché solar panels as an example again, to make an impact in producing energy with those, we might even think about covering the sidewalks with solar panels, let alone the roofs!
This would not be convenient, which is why I suggest for us to think out of the box. Cities need smaller projects that are adapted to the characteristics of urban areas. My favourite example of something like that are algae fuels. Algae organisms convert sunlight to energy and the plants can grow in various environments. What is beneficial to us is that algae can be converted into different types of fuels and that the burning of algae is CO2-neutral, since the plants absorb CO2 from the atmosphere in order to perform photosynthesis and grow. One day, perhaps when we are able to maintain algae under different weather conditions, we can grow algae in the canals of Leiden!
U.S. Department of Energy