The UAE's Hybrid Solar Plant: Shams 1
As the portion of our power that comes from renewable energy continues to grow, these technologies will need to continue to evolve in order to mitigate some of their inherent infrastructural challenges–namely intermittency. Despite the fact that solar power has progressed leaps and bounds since its inception in terms of efficiency, it shouldn't be mistaken for a mature technology on par with things like the internal combustion engine. Solar still has plenty of room to grow and continue to make its inclusion into the grid more attractive to utilities and easier to integrate.
Part of my January excursion to the United Arab Emirates included a visit to the Shams 1 solar power plant. Heading out of Abu Dhabi on a bus, my fellow journalists and I headed out across the desert with promises of renewable energy production. On the approach, the plant slid of out the horizon in a somewhat unassuming way. Someone looking for a tall collection tower at the apex of hundreds of concentrated beams of reflected sunlight would have passed right by. Instead it was the hovering box of corrugated metal with large duct work connected to it that caught my eye–causing me to say to myself, "That looks like an bank of Air-Cooled Condensers," not unlike those used at Footprint Power's new plant in Salem, Massachusetts. Sure enough they were ACCs and we had arrived.
Built by a partnership of Masdar, Total and Abengoa with 100 MW of nameplate solar capacity, the Shams 1 power plant is the largest facility in the world of its kind–a unique system that helps take another step in how solar power can be more efficient for larger portions of the world. Nevada recently made news with its shiny new Ivanpah facility as it officially started producing power in mid-February. Covering over 5 square miles, the power plant is the largest concentrated solar power (CSP) plant in the world at 392 MW of capacity spread over three collection towers and over 300,000 mirrors. For those that are familiar with CSP, the power tower model is often the imagery that comes to mind, also made famous by the large facility in Seville, Spain.
But Shams 1 utilizes another CSP technology, the mirrored parabolic trough that tracks the movement of the sun to focus its rays on a suspended pipe filled with a petroleum-based fluid used to capture and transport heat (a.k.a. Heat Transfer Fluid, or HTF). When driving past the fields it was easy to see the brilliant white light illuminating the bottoms of the tubes that bring the HTF to 393° C. That heat is ultimately extracted via a heat-exchanger to boil water, make steam and turn a turbine. With miles of gleaming troughs, the plant occupies the area of 285 football fields within the desert landscape beneath the heat of the sun.
The parabolic troughs alone are not novel. We've seen them used before (showcased in the sunrise scene of Gattaca, for instance) but the rest of the plant puts a new spin on site-specific responses to the integration of solar polar. One example is the ACCs. After the steam produced by the plant leaves the turbine it needs to be cooled. Normally, power cooling is done by utilizing a water source (thermoelectric cooling is actually the largest use of water in the United States), but the United Arab Emirates isn't flush with fresh water. Instead, the plant is air cooled, using large fans to dissipate heat and return the steam to water within a closed loop. Overall, the ACCs save an estimated 200 million gallons of precious water a year.
Another surprising aspect of the CSP plant is that it's not actually fossil fuel free. Shams 1 has an integral natural gas component which is partly what makes it unique. About 80% of the heat used to make steam comes from the sun bringing the HTF to 393°, but in order maximize the efficiency of the steam turbine two supplemental natural gas heaters boost that temperature up to 542° that provides the other 20% of net power-producing energy. This configuration brings a number of side-effects, the first of which being that the facility can produce power at night at a maximum capacity of around 50 MW. In part, this came from a governmental requirement to be able to call for the plant to supply 25 – 50 MW of power at any time to help with grid stabilization. This means that the maximum capacity of the plant and the turbine is actually 125 MW including natural gas.
PV vs. CSP?
When I was at the plant, the operator pointed out that when construction on the plant began, CSP was more affordable than photovoltaics for comparable efficiencies. However, at after the crash of PV prices over the past couple years, the reverse is now true–underscoring how swiftly innovation and the economy can change the financial realities for young technologies. At the same time, there are advantages to building CSP capacity that PVs cannot yet match.
Perhaps the biggest difference is that CSP is much better for power storage. Given that the plant's major resource is heat, there are more ways to store that heat for later use like heated salt storage. CSP systems are also reportedly better at responding to cloud cover, resulting in a more steady stream of production in a wider array of weather conditions. Also, as this plant shows, CSP is better for hybrid facilities that are paired with combined-cycle plants–a configuration that may be increasingly popular given that utilities could be potentially more interested in power stations that can contribute to the reliability of base load power rather than the intermittent nature of most renewables.
Shams 1 ended up being an innovative solution to a series of site-specific conditions, including a harsh climate (if only more buildings in the developing world would undergo the same responsive design process). Many people have a tendency to think of solar power as a mature technology that is simply about deployment, but plants like this highlight the evolving process of renewable power production that may only add to its viability over the next decade. Energy pundit, Chris Nelder, had mentioned to me that too often when we are talking about natural gas as a 'bridging solution' to a more sustainable power grid we need to making sure that we are not building a bridge to nowhere. Eventually renewable sources need to be built to a capacity that makes their contribution material. Hybrid plants like Shams 1 could be one of the ways to make that transition more realistic.
For two hours on the bus I watched the rows of carefully planted trees pass by the window against a backdrop of a golden ocean of sand that met the sky in crests and troughs of rolling dunes. In a way it was a shame and perhaps the biggest drawback of the technologically innovative power station. Every mile that we drove away from the city was taking us closer to the point of power production, but farther away from the largest source of demand. The plant's operators explained that the siting of the facility was largely determined by access to existing natural gas infrastructure (also much like Footprint's plant). As a pilot project, I hope that we see more of its type spring up across the region.
Full Disclosure: Travel expenses to Sustainability Week were covered by Masdar
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