Part 2 of the blog series: What does COP21 mean for Engineering and Technology? Read Part 1 here.
The solar energy that lands on the Sahara desert in one year is 100x the total annual energy consumption of humankind, and the global wind power resource is estimated at somewhere between 5x and 20x global consumption.
So what’s stopping us from fully harnessing these massive sources of energy?
Well, one issue is that renewable energy resources are not evenly distributed, and so powering the world without fossil fuels or nuclear power will require countries to share them out. Achieving this is a tough ask because governments worry about sacrificing energy security and relying on other countries for their energy supply.
Although prioritisation of energy security over de-carbonisation is understandable, somehow this will need to change in order to meet the targets agreed on by almost every country in the world at COP21 in Paris – see yesterday’s blog for more details.
I should mention here briefly the issue of cost. Solar power and offshore wind are currently just over $0.20 per kWh, over 3x more expensive than conventional gas or oil or coal. However, the costs will continue to fall with increased scale (solar PV module prices have fallen threefold in the last 10 years and more than tenfold since the 80s).
We will have to find a way to afford these if we are serious about moving away from fossil fuels as a way of staying within our carbon budget.
So, let’s take a quick look at how varied and spread out our renewable energy resources are, and compare it to where we want to use the energy.
Solar irradiance varies between around 750 kWh/m2 per annum in northern countries, to almost 2,400 kWh/m2 per annum in desert regions with clear skies.
Similarly, the mean wind speed at 80m elevation varies globally between 7mph and 20mph (and wind power varies with the cube of speed so this is roughly a factor of 20x).
Population density varies from as little as 5 inhabitants per square kilometre in countries like Western Sahara or Canada, to more than 5,000 inh/km2 in populated islands like Hong Kong or Singapore.
These maps show what we are all probably aware of; that not only is the renewable energy resource spread around the international community, it is also generally not available for capture in the same geographic regions as where we want to use it.
They key question is how to move it? First though let’s just distinguish the difference between electricity usage, and total energy usage. Just one fifth of total global energy usage is in the form of electricity so the difference is very relevant!
Movement of electricity is conventionally achieved with AC power lines. Whilst very cheap, versatile, and safe, AC distribution lines have losses of up to 10% per 1,000km. Moving solar power all the way from Africa to Europe for instance (an idea that has been previously proposed by the Desertec Foundation) would be better done using High Voltage DC (HVDC) links with losses of as little as 2.6% per 1,000 km.
There are already over 100 HVDC links in the world spanning as much as 2,000 km in some places (Siemens is a key player this space and has constructed over 40 of these, but many of them are intra-national (a lot are in China where international relations are not a concern). Following COP21, we are bound to see increased interest in building more international links to enable an increased exploitation of renewable energy.
For some applications, electrical power will never be the preferred energy source, especially given that the majority of our energy usage is not of electrical energy. In tomorrow’s blog I will discuss the idea of synthesising fuels from renewable energy and transporting it this way.
So here is the first thing that the Paris agreement means for engineering and technology: If the pledges made at COP21 are to be kept to, nations will have to get better at sharing and trading their renewable energy resources. We are bound to see more large scale renewable energy plant built where it can be used most effectively, with clever ways of moving this power to where it is used, such as HVDC links, or synthesising liquid fuels from electricity (more on that tomorrow)