Last week, we discussed how renewable energy can help reduce the carbon footprint of urban areas. In sunny Singapore, solar energy appears to have the greatest potential to offset our consumption of non-renewable energy sources. But how much energy can it provide? I looked up a few sources and did some simple math to figure out a rough estimate (hopefully my calculations are correct!).

First, let’s find out how much incoming solar energy Singapore receives:

• This source by the Energy Market Authority (EMA) of Singapore estimates this at 1150 kWh/m²/year

Next, let’s see how much of that energy can be converted to a useful form:

• This link reports that the most efficient rooftop solar panels are currently around 22% – this means we can get about 22% * 1150 = 253 kWh/m²/year

According to the Energy Market Authority (2015), Singapore’s total energy consumption in 2013 was about 156 TWh. Using this value, we would have needed:

• 156TWh/(161kWh/m²) = 616.6 km² of solar cells to sustain our energy consumption entirely in 2013

(Just out of interest, I did another calculation using the most efficient solar cells as reported by Shazan (2014). Even at 46% efficiency, we’d still need about 203km² of land – just under a third of Singapore covered in solar cells.)

These values mean that we’d need to blanket most of Singapore in solar cells to sustain our current energy use. Of course, solar is not the only form of renewable energy but it does show the limit at which such alternative energy sources can support the population.

The main issue here appears not to be just the lack of land space but more so the density of our population and our high per capita energy consumption (Low Carbon Singapore, 2009). Together, these factors result in a high energy consumption density – meaning we need to provide more energy per area of Singapore. This has significant implications – and not just for Singapore.

As most of the world’s population moves into urban areas, population density in these areas will likely rise. By extension, it is also likely that the amount of energy we need to provide in an urban area will rise (as the energy consumption becomes more concentrated within the area). Denser cities could resort to importing renewable energy (just as we currently do with non-renewables) but transporting electricity generated in one place to another is not without its issues.

If we are to switch over to renewables then, it appears that we cannot simply increase renewable energy generation. Rather, we would need accompanying measures which help to reduce the overall consumption of energy and also improve the efficiency at which energy is used.

Sources

Energy Market Authority (2015). Singapore energy statistics 2015. Singapore: Energy Market Authority. Retrieved from https://www.ema.gov.sg/cmsmedia/Publications_and_Statistics/Publications/SES2015_Final_website_2mb.pdf

Energy Market Authority (2016). Solar photovoltaic systems. Retrieved 14 April 2016, from https://www.ema.gov.sg/Solar_Photovoltaic_Systems.aspx

Low Carbon Singapore (2009). Energy consumption per capita. Retrieved 14 April 2016, from http://www.lowcarbonsg.com/tag/energy-consumption-per-capita/

Shahan, Z. (2014). Which solar panels are most efficient? Retrieved 14 April 2016, from http://cleantechnica.com/2014/02/02/which-solar-panels-most-efficient/

Wesoff, E. (2015). ‘World’s most efficient rooftop solar panel’ revisited. Retrieved 14 April 2016, from http://www.greentechmedia.com/articles/read/Worlds-Most-Efficient-Rooftop-Solar-Panel-Revisited

(aka how far can a rollercoaster on steroids get you in 30 minutes)

“An hour wide”

Back in the first lecture, we briefly visited Marchetti’s constant and how this limited travel time limits urban growth.

Marchetti’s constant: the average commute time per person is about approximately 1 hour a day (so about 30 minutes either way if you’re only moving to and from work)

Essentially, this implies that most cities remain an hour wide simply because many people (especially those who live in and around regions named Woodlands and Pasir Ris) instinctively refuse to exceed a daily “travel time budget” (Marchetti, 1994). This, in addition to the factors discussed in the same slide, limits the size a city can grow to.

That being said, it is possible for commute times to stay the same even as a city grows bigger. A possible reason, as proposed by Anas (2014), may be the behavioural switch to modes of public transport which reduces traffic congestion and thereby travel times. If you’re interested, this article gives a good summary of the phenomenon.

Other than behavioural change, another (more obvious) way that commute times can drop is an improvement in the speed and efficiency of available transport modes. But given that our cars, trains, buses and planes probably aren’t going to get much faster than they are right now, surely cities can’t expand that much… can they?

Another mode of transportation?

From the brilliant mind that brought us Paypal, Tesla motors, SpaceX and much more, comes a new concept for a high-speed transportation system.

For those who haven’t already heard or read about it, the Hyperloop is, as Elon Musk puts it, “a cross between a Concorde and a railgun and an air hockey table” (Speed, 2015). Like something out of the popular children’s cartoon “the Jetsons”, the Hyperloop will transport passengers through capsules within a tube system at amazing speeds.

Capable of moving close to the speed of sound (1220 km/h), the Hyperloop will transport passengers between Los Angeles and San Francisco (600 km) in a little over 30 minutes (Musk, 2016). To contrast that to Singapore, it would be the equivalent of moving from the east to west coast (~50 km) in about 3 minutes. (Here’s an idea: toss the Cross-Island Line and build a Hyperloop along the proposed rerouted route. An additional 4 minutes would become… 6 seconds?).

A car ride from Los Angeles to San Francisco would take about 5 hours and 41 minutes, about 11 times slower than the Hyperloop. Source: GoogleMaps

Implications on city limits

As much as I would like to continue writing more about this amazing concept (and its potential issues), perhaps I should go back to how this relates to urban limits.

The Hyperloop, once developed, could be a game-changer in urban development. If 30 minutes in a car at 100 km/h would bring you 50 km from the city centre. Imagine where 30 minutes in the Hyperloop would get you (Answer: very far).

For cities which are mainly limited in size by commute time, the technology could allow for a much greater expansion of their city limits: urbanites can now live much (much) further from the city centre and still reach their work place on time. Might we see urban sprawl happening in these Hyperloop-connected cities? And might this change our ideas of what a “sustainable city” is (especially since the Hyperloop will likely be run on solar power)?

Of course, there are many other factors to consider such as geographical and bioregional constraints when determining a city’s limits. Still though, I believe that the Hyperloop has the potential to significantly change urban transport and development as we know it.

Or maybe all we need is just a new Marchetti’s constant…

References

Anas, A. (2014). Why are urban travel times so stable? Journal of Regional Science, 55(2), 230-261.

Marchetti, C. (1994). Anthropological invariants in travel behavior. Technological Forecasting and Social Change, 47, 75-88.

Musk, E. (August 12, 2013). Hyperloop alpha. SpaceX. Retrieved February 12, 2016, from http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf

Speed, B. (January 21, 2015). Elon Musk’s Hyperloop might actually get built. Retrieved February 12, 2016, from http://www.citymetric.com/transport/elon-musks-hyperloop-might-actually-get-built-663