“If something cannot go on forever, it will stop.” These were the wise words by the late Economist, Herbert Stein (1916 – 1999). Decades later, similar thoughts seem to be gaining momentum in the Middle East in recent times on the topic of renewable energy, where a number of announcements indicate moves to diversify away from fossil fuels. For example, Prince Mohammed bin Salman of Saudi Arabia recently announced a sale of the stake in the state owned Saudi Arabian Oil Company and just last month the Gulf Cooperation Council states (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the UAE) pledged $100 billion for renewable energy projects over the next 20 years.
One of the main projects in the region is the $13.6 billion Mohammed bin Rashid Al Maktoum Solar Park in Dubai which is expected to generate 5 gigawatts of electricity – enough to power 1.5 million homes – by 2030. According to the Dubai Electricity and Water Authority, Dubai wants to reduce its carbon emissions by 6.5 million tons every year, with the aim of becoming the city with the world's lowest carbon footprint. The UAE has also taken steps to boost its use of renewable energy from 1 per cent to 24 per cent in the next five years.
With this in mind, I decided to read up on valves and solar energy - so what did I learn? Firstly, I consulted one of our articles (‘Renewable energy booms!’ October 2014, by James Chater) on renewable energy, and seeking out solar energy in particular, I learn that solar power has three main types: water heating/cooling, photovoltaic (solar panels) and Concentrated Solar Power (CSP). The last two, solar photovoltaics and concentrated solar power, have been projected to contribute about 16 and 11 percent respectively of global electricity consumption by 2050 (with most being located in China and India). CSP plants use heat transfer fluids, which can be synthetic oils (highly flammable and operate at temperatures around 390°C) or molten salt which has the advantage of operating at temperatures over 500°C. Valves used for molten salt are therefore often made of special materials to withstand high temperatures.
One of the challenges molten salt service presents is sealing - traditional graphite composite needs replacing by ceramic equivalents (for more information on this, please refer to our article ‘Control valves for renewable energy’ by Arnold Muschet and Aryoso Nirmolo, Flowserve). Specific valves for molten salt include 3-way valves, control valves, heat transfer fluid, isolation valves, cold reheat non-return check valves, and vent & drain valves (for more information on valves used in power generation see Power Generation: Understanding Valve Options by Hari Jinaga, CRANE Energy Flow Solutions). Control valves are particularly under the spotlight during the startup and shutdown procedures which occur every 24 hours as the sun rises and sets. They need to counter fluctuations in the power plant and operate exactly as required to maximise system efficiency.
But essentially, Concentrated Solar Power (CSP) technologies are similar to many other power plants - solar power is simply substituted for fossil fuels to generate energy for conversion to electricity. When I look up the twenty largest Concentrated Solar Plants in the world, most of the top ten are in the US (a lot in California) but 11 of the top 20 are located in Spain. Spanish suppliers have a wide offering of products for the CSP sector.
The advantage of CSP plants over PV plants is that they allow the provision of electricity hours after the sun has set. Solar often goes hand-in-hand with other industries such as desalination, which are often fueled by solar power. A sophisticated example is Qatar’s Sahara Forest Project, which exploits seawater to produce electricity and grow crops. Saltwater cools the greenhouses, while steam-driven turbines desalinate the water used to irrigate crops.
Now that sounds sustainable!
Header image: Part of the 354 MW SEGS solar complex in northern San Bernardino County, California.