Solar in the Cities: Meet Nahid Mohajeri, Visiting Academic

Nahid Mohajeri of the Swiss Federal Institute of Technology in Lausanne (EPFL) joins the Department for the next two years as a Swiss National Science Foundation Mobility Fellow.

During her time at Oxford, she will be looking at ‘integrating urban form and sociotechnical potentials of decentralised energy supply for sustainable urban development’ – which for the uninitiated means that she will be looking at the challenges and potentials for solar energy production in high-density urban environments.

Nahid will be be part of our Sustainable Urban Development programme.

Research in support of renewable energy

Both Switzerland and the United Kingdom have ambitious goals for increasing their use of renewable energy and reducing CO2 emissions.

The Swiss Energy Strategy 2050 aims at phasing out nuclear energy by 2035, with a possible 50-80% reduction in CO2 emission by 2050. The UK aims at obtaining 15% of its energy consumption from renewable resources by 2020, as well cutting its CO2 emissions by 80% by 2050.

For both countries, these targets can be reached only through a great increase in the production of renewable energy.

‘Built environments have the largest share in energy demand in Switzerland,’ says Nahid. ‘Space heating, ventilation, and air conditioning account for more than 40% of Switzerland’s overall energy demand. In particular, 32% of the electricity demand in the country is attributable to buildings (heating, ventilation, air conditioning, and lighting). In order to reduce the energy demand and greenhouse gas emissions, buildings need to become much more energy efficient and the demand should be primarily (increasingly) satisfied through renewable energy resources. Solar energy is regarded as particularly important in urban areas, with the energy supply being largely in-situ, that is, on the roofs or facades of the buildings, as solar photovoltaics (PVs).’

In solar energy, the good news is that over the past ten years, the price of photovoltaic technology has dropped. This is due both to technology advancements and to increased competition in this field. Solar energy production is on the rise, and as it becomes more affordable, it comes within reach of more and more consumers.

Solar energy – to centralise or decentralise?

Much of current solar energy production takes place in large solar farms in rural areas. This is ‘centralised’ energy production, in which energy is gathered at one large location and then transmitted to the place it will be used.

Solar farms currently exist at Melton Mowbray and Ledbury. But rural solar farms have disadvantages. They require large amounts of space, for one thing; and because the energy produced has to travel large distances to reach the consumer, some energy is inevitably lost in the transmission.

The alternative is to shift the solar energy production closer to the end-user – by moving the entire process into the cities. This is ‘decentralized’ energy production - in which energy is produced close to, or at, the site where the energy is used.

A decentralised system offers advantages: it has reduced transmission losses and lower carbon emissions. It also has security advantages, since communities are less reliant on a few large providers which, if they fail, can cause major outages. While short term initial installation costs may be higher, over time, decentralised energy may offer more competitive prices than traditional energy.

But urban environments present unique challenges to solar energy production.

Bringing energy production home to the city

Creating a decentralised urban energy supply, particularly through the use of photovoltaics, requires a comprehensive assessment of several elements.

First, the urban environment must be considered: the buildings, the street networks, the population densities. Is the built environment compact or sprawling? Second, the very shapes of rooftops and what directions they face can have a large impact on the efficiency of solar energy production.

Along with the urban environment, one needs to consider:

  • Weather condition – expected number of cloudy vs sunny days
  • the available photovoltaic technology, and its various performance potentials
  • social acceptance and public awareness – how do people use electricity produced by solar PV and save energy using solar PV technology, and what is their comfort level with photovoltaics? Income, age and education of residents play a role in the level of awareness of solar energy technologies and the decision to implement solar PV technology at home.
  • cost – what do consumers and the community stand to gain as a return on their investment, and what is the potential of selling surplus energy back to the grid?

Says Nahid, ‘While much research has focused on each of the above topics individually, there are very few studies exploring the connection between these topics (i.e. engineering, social, and planning-and-policy studies). This study tries to fill this gap and connects the urban analysis to the socio-technical, and then to policy aspects of solar PV energy supply.  

Nahid will be examining all of these individual factors on a national scale, and her results will be analysed within the framework of the Swiss and UK projected climate scenarios for 2035 and 2050.

Additionally, Nahid’s work is expected to bring benefits to other regions of the world.

‘There have been very few systematic studies of solar PV electricity supply in different cultural and geographic contexts,’ says Nahid. ‘One aim of my work is to transfer the results from the detailed study of the solar PV potential in Switzerland and the UK to developing areas such as in Africa, which are highly favourable in terms of solar-energy potential. Africa has a very high irradiation and has the potential of producing highly solar PV electricity at a comparatively low cost, in virtually every part of the continent. This is particularly important because currently the number of people without access to electricity in Sub-Saharan Africa is on the increase (from 587 million in 2008 to estimated 968 million in 2030).’

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Published 14 September 2017