An introduction to tidal stream power was given on Monday in this post: “The MeyGen Tidal Stream Power Station: Pentland Firth, Scotland”. The simplest way to imagine tidal stream power of the MeyGen variety is an underwater wind turbine deployed in an area of high tidal flow. Two ebb and two flood tides daily produce four daily spikes in generation with nothing in between.
One aspect not covered in the above post was longevity and maintenance. This press release says this:
Sitting in 30-50 m of exposed fast flowing turbulent waters where the Atlantic meets the North Sea, the steel tripod gravity foundations have been designed from first principles to enable year-round turbine operation over a 25-year life with no maintenance, the awards website states.
It’s a bit ambiguous, but I believe refers only to the steel tripod base and not the turbine itself. But it does imply that the system is designed to last 25 years. It raises the question about repair and maintenance of the nacelle. Recovering the nacelle for repair and maintenance requires the services of a jackup rig and ship. Purpose built light-weight jack-ups are estimated to cost ~ €70,000 / day that could lead to hefty repair bills. If turbines break down and are left idle for lengthy periods this also negatively impacts electricity production and EroEI.
Previous entries in this series:
The Externalities of Energy Production Systems (Day 1 Coal)
Energy Externalities Day 2: Gas-fired-CCGT
Energy Externalities Day 3: Biomass-Fired-Electricity
Energy Externalities Day 4: Nuclear Power
Energy Externalities Day 5: Wind Power
Energy Externalities Day 6: Hydroelectric Power
Energy Externalities Day 7: Solar Photo Voltaics
Energy Externalities Day 8: Diesel
Energy Externalities Day 9: Solar Thermal or Concentrated Solar Power (CSP)
Energy Externalities Day 10: Tidal Lagoon Power
Energy Externalities Day 11: Geothermal Electricity
Energy Externalities Day 12: Wave Power
Geothermal energy extraction involves drilling wells into hot rocks that lie close to the Earth’s surface. Given the right geology, i.e. permeable rocks that contain very hot water, the hot water or steam flows to the surface under its own steam (to coin a phrase). Temperatures are typically in the range 200-350˚C, and at surface pressure, this super-heated water will flash to steam that may drive a turbine. The cooled “waste water” is then returned to the geothermal reservoir where it heats up again given time.
With solar thermal, I am beginning to wander further away from systems where I have a reasonable grasp of their operation. There are two main classes of concentrated solar power (CSP) namely parabolic mirrors that focus solar energy onto a pipe filled with water that raises steam and a central tower configuration where an array of mirrors focusses the Sun’s energy onto a central tower, raising steam to drive a turbine (inset image).
Diesel powered electricity generation is a niche common on isolated island grids like El Hierro and in certain countries, like the UK, recently adopted as peaking plants. They have the advantage that they can quickly and easily be switched on and off and the disadvantage that they are expensive to run. Answering some of the questions below for diesel is a bit tricky. For example, when it comes to fatalities we need to consider fatal accidents in the Global oil production and refining industries. But diesel for power generation uses only a tiny fraction of global oil production (<1%?). Power diesel accidents therefore need to be pro-rated accordingly but then adjusted to the amount of electricity produced. Not an easy task to scale in your head.
Solar PV is a multidimensional energy system difficult to evaluate on a global basis. Maximum concentration required from The Game players! First, there is solar thermal hot water, solar thermal power generation (also known as CSP) and solar PV. Today’s game is exclusively on the latter. And in solar PV there are two main families of panels: 1) thin film and 2) polycrystalline. Today’s game is exclusively on the latter. Add to that the fact that solar PV works much better at low latitude than high, not only from the resource perspective but also from the seasonal storage one. In short, solar PV makes much better sense in Arizona and Mexico than it does in Aberdeen. Politicians tend to see devices that generate free, clean electricity, while I tend to see expensive devices made from coal in China that produce electricity some of the time.
Hydroelectric power produces no pollution once the dam is built and the valley flooded. It is dispatchable and widely regarded to be the “Rolls Royce” of renewable energy. Based on trapping rainfall produced by solar energy trapped in high valleys that were created by plate tectonics that is driven by spontaneous nuclear fission within the lithosphere. 
It’s now day 5 of the Energy Externality Game and time to move onto the first of the new renewables, namely wind power. Loved by Green groups who see only reduced CO2 emissions, wind farms are hated by many others who see a blot on the landscape. Here at Energy Matters we normally just see high cost noise being added to a grid that needs to be balanced from second to second with some precision. This high cost noise needs to be mitigated and the cost of that mitigation is normally borne by others, not the wind farm operators.
Its day 3 of the Energy Externality Game already and we move onto biomass-fired-electricity. Most biomass electricity currently resides in Europe, where much of the fuel is imported from North America. In evaluating biomass we need to consider the whole supply chain from timber operations in N America, transport to and from the wood pellet factory, transport across the Atlantic Ocean, off-loading and transport to power station. We then need to consider the externalities associated with power generation.
