Compact-lens Fresnel reflector, parabolic-trough mirror and other solar-thermal power arrays — referred to as concentrating solar power (CSP) in the United States context — are ideal for being fitted on any medium- to large-scale urban surface — atop high-rise buildings, schools, bus terminals, parking lots, office parks. These sophisticated and highly efficient systems rely on direct sun presence and therefore work best in areas of the world with high sun incidence. They generate steam, are capable of driving Sterling or Rankine cycle engines, power turbines and generators, yielding a combination of heat and electricity that can be used also for solar air conditioning and freezing, industrial process pre-heating.
The most commonly used and cost-effective of all urban solar-thermal energy application is the trusty solar collector, in all of its guises, used for household, pool and industrial water as well as general heating. The most basic and inefficient system deploys black plastic mat absorbers, while the very common flat plate collector, endearingly awkward in its insulated metal case, is more sophisticated and commonly used, channelling and heating water as energy medium against a sealed black surface. Highest efficiencies are achieved with vacuum tube collectors, where very little heat loss occurs at all. Examples of these systems can be deployed in individual units or linked arrays. They are perched atop houses in all parts of the world, and active even on overcast days. But in their more efficient incarnations, they are also happily integrated in larger building rooftops, in industrial installations and public recreation facilities, including as pools and baths; heating water and space in residential developments, airports and rehabilitation centres alike.
Small cities make the largest progress in solar water heaters. The efforts of the quasi-autonomous Austrian solar villages have been legendary for a considerable time; and in 2005 the German city with the largest locally integrated solar-thermal area was Rottenburg am Neckar, a small community of 40,000 — with almost one square metre of collector area per ten inhabitants installed in the last four years alone, with its district of Oberndorf sporting one square metre for every two inhabitants. The town has become a veritable solar theme park, an open-air display of solar thermal installations. (Alt, 2005.3)
Urban wind power
Wind generators are among the most traditional, direct and productive forms of converting renewable energy flows into mechanical — and today mostly electrical — power. Micro- and mini wind power applications are powerful additions to the built environment, and, deployed en masse, can help transform the electricity supply profiles of urban areas and city regions. There has been a traditional bias against wind power in urban areas due to the wind flow disturbances created by built-up areas - but in these city eddies and gusts can lie a vast and to-date untapped resource. Buildings and other structures — such as skyscrapers, bridges, stadia, theme and entertainment parks, shopping centres and telecommunication towers are often in the reach of air layers with effective wind speeds, generate sufficient turbulence in ambient wind flows to allow the sustained generation of electricity, or can be streamlined and designed to drive building-integrated wind energy collection devices.
Cities should pursue wind power as integral to the energy performance of their buildings and facilities — and their overall energy web. Buildings should be crafted to harvest the powerful wind forces that can exist at their top, the edges of structures and internally. This may involve building-integrated rotor assemblies, vertical axis generators for eaves, edges and corners...