Tag Archives: solar energy

Ample sufficiency of solar energy?

Global energy budget from Trenberth et al 2009

I have written several times about whether or not the Earth is a closed system [see for example: ‘Is Earth a closed system? Does it matter‘ on December 10th, 2014] & ‘Revisiting closed systems in Nature‘ on October 5th, 2016).  The Earth is not a closed thermodynamic system because there is energy transfer between the Earth and its surroundings as illustrated by the schematic diagram. Although, the total incoming solar radiation (341 Watts/sq. metre (W/m²)) is balanced by the sum of the reflected solar radiation (102 W/m²) and the outgoing longwave radiation (239 W/m²); so, there appears to be no net inflow or outflow of energy.  To put these values into perspective, the world energy use per capita in 2014 was 1919 kilograms oil equivalent, or 2550 Watts (according to World Bank data); hence, in crude terms we each require 16 m² of the Earth’s surface to generate our energy needs from the solar energy reaching the ground (161 W/m²), assuming that we have 100% efficient solar cells available. That’s a big assumption because the best efficiencies achieved in research labs are around 48% and for production solar cells it’s about 26%.

There are 7.6 billion of us, so at 16 m² each, we need  120,000 square kilometres of 100% efficient solar cells – that’s about the land area of Greece, or about 500,000 square kilometres with current solar cells, which is equivalent to the land area of Spain.  I picked these countries because, compared to Liverpool, the sun always shines there; but of course it doesn’t, and we would need more than this half million square kilometres of solar cells distributed around the world to allow the hours of darkness and cloudy days.

At the moment, China has the most generating capacity from photovoltaic (PV) cells at 78.07 GigaWatts or about 25% of global PV capacity and Germany is leading in terms of per capita generating capacity at 511 Watts per capita, or 7% of their electricity demand.  Photovoltaic cells have their own ecological footprint in terms of the energy and material required for their production but this is considerably lower than most of our current sources of energy [see, for example Emissions from photovoltaic life cycles by Fthenakis et al, 2008].


Trenberth KE, Fasullo JT & Kiehl J, Earth’s global energy budget, Bulletin of  the American Meteorological Society, March 2009, 311-324, https://doi.org/10.1175/2008BAMS2634.1.

World Bank Databank: https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE

Nield D, Scientists have broken the efficiency record for mass-produced solar panels, Science Alert, 24th March 2017.

2016 Snapshot of Global Photovoltaic Markets, International Energy Agency Report IEA PVPS T1-31:2017.

Fthenakis VM, Kim HC & Alsema E, Emissions from photovoltaic life cycles, Environmental Science Technology, 42:2168-2174, 2008.

Re-engineering engineering

More than a decade ago, when I was a Department Head for Mechanical Engineering, people used to ask me ‘What is Mechanical Engineering?’.  My answer was that mechanical engineering is about utilising the material and energy resources available in nature to deliver goods and services demanded by society – that’s a broad definition.  And, mechanical engineering is perhaps the broadest engineering discipline, which has enable mechanical engineers to find employment in a wide spectrum areas from aerospace, through agricultural, automotive and biomedical to nuclear and solar energy engineering.  Many of these areas of engineering have become very specialised with their proponents believing that they have a unique set of constraints which demand the development of special techniques and accompanying language or terminology.  In some ways, these specialisms are like the historic guilds in Europe that jealously guarded their knowledge and skills; indeed there are more than 30 licensed engineering institutions in the UK.

In an age where information is readily available [see my post entitled ‘Wanted: user experience designers‘ on July 5th, 2017], the role of engineers is changing and they ‘are integrators who pull ideas together from multiple streams of knowledge’ [to quote Jim Plummer, former Dean of Engineering at Stanford University in ‘Think like an engineer‘ by Guru Madhaven].  This implies that engineers need to be able work with a wide spectrum of knowledge rather than being embedded in a single specialism; and, since many of the challenges facing our global society involve complex systems combining engineering, environmental and societal components, engineering education needs to include gaining an understanding of ecosystems and the subtleties of human behaviour as well as the fundamentals of engineering.  If we can shift our engineering degrees away from specialisms towards this type of systems thinking then engineering is likely to enormously boost its contribution to our society and at the same time the increased relevance of the degree programmes might attract a more diverse student population which will promote a better fit of engineering solutions to the needs of our whole of global society [see also ‘Where science meets society‘ on September 2nd 2015).

For information on the licensed engineering institutions in the UK see: https://www.engc.org.uk/about-us/our-partners/professional-engineering-institutions/

Limitless energy

neil hunterThe Sun supplies approximately 100,000 TeraWatts (TW) of energy to the Earth continuously. To put this into perspective the entire generating capacity of China is 1TW and the global population as a whole uses 15TW. Plants use about 100TW via photosynthesis. Most our energy consumption is derived from biomass created millions of years ago by photosynthesis and stored as coal, gas or oil when the plant died and was crushed by geological processes.

I am stealing and paraphrasing from Professor Neil Hunter’s presentation at the Royal Society’s Scientific Discussion Meeting on Bio-inspiration for New Technologies. Of course, as Neil pointed out, the energy from the Sun arrives across a range of wavelengths some of which are damaging to our health. So fortunately for us the Earth’s atmosphere filters out a number of wavelengths but nevertheless a broad band of wavelengths still arrives at the Earth’s surface. Photosynthesis only makes use of two relatively narrowbands of light….

Mankind’s efforts to use solar energy look pathetic alongside Nature’s performance and should be humbling to any engineer or scientist. But it is also an inspiration to do better. We need cheap clean energy for everyone. It is being delivered everyday but we don’t know how to use it.

Tidal energy

Photo credit: Tom

Photo credit: Tom

The world is slowing down! According to Max Tegmark, in his book ‘Our Mathematical Universe’, the rotational velocity of the Earth is being reduced as some of its kinetic energy is dissipated as tidal energy. It is possible to estimate the age of planet from the rate of slow down by assuming that at its birth it was spinning as fast as possible without the centrifugal forces pulling it apart. The answer turns out to be about 4 to 5 billion years which roughly agrees with radioactive dating of the oldest rocks in Western Australia and bits of meteorites that imply the solar system came into being about 4.5 billion years ago.

So does this imply that tidal energy is not really a renewable energy source? I think it is just an issue of timescale. Fossil fuels are seen as non-renewable because the formation of coal and oil substrates happens on geological timescales. Biomass is a bit quicker because we skip the fossilisation process and renewal is measured in months. Fossil fuels and biomass are both ways of storing solar energy in chemical bonds. Nature is much better at converting and storing solar energy than mankind. But, solar energy would appear to be the ultimate renewable energy source. Every morning its there, though often hidden by cloud where I live. The sun will eventually die but again this won’t happen anytime soon but on a long geological timescale.