Shedding light on solar technologies
We’ve summarized the Solyndra saga and discussed photovoltaic technology. With its economies at small scale, PV is widely deployed and visible on rooftops everywhere from homes to factories.Developers are working to scale PV technology up to power plant-size applications, but whether PV is viable for such large-scale applications remains a question. Consequently, a competing approach known as concentrated solar power has gained traction.The complexities of concentrated solar power or CSP are difficult to explain in layman’s terms. CSP uses mirrors to concentrate sunlight onto a pipe or equivalent that contains a liquid which, when heated, creates steam that runs a steam generator. As I said, it’s extremely complex.Though the basic theory is simplistic, there are myriad inherent intricacies. Four uniquely different CSP architectures are being pursued — parabolic trough, parabolic dish, tower systems, and linear fresnel.The market leader — parabolic trough — generates steam by using single axis tracking U-shaped mirrors. Single axis tracking means that the mirrors only follow the sun in one direction – east to west. Oil is typically used as the heat transfer fluid. The main disadvantage of parabolic trough is that its relatively low temperatures are less efficient.Tower systems use large arrays of TV satellite dish-like mirrors called heliostats. For greater flexibility in following the sun, tower systems deploy a two-axis tracking system. Instead of a pipe, a tower is used to create a single point of concentration that can generate temperatures exceeding 1000o F. The latest designs use molten salt that can be stored to generate electricity at night.Parabolic dish — Stirling engine systems focus light on a Stirling engine that directly generates electricity without steam. This approach produces the highest temperatures (approximately 1450o F) and claims the highest efficiencies.Linear fresnel is the least proven technology. By using flat single-axis mirrors, its big advantage is construction and maintenance cost savings.Costs and complexityGiven their simplicity, why aren’t these systems widely deployed? Glad you asked. Because fossil fuels remain less expensive. How can fossil fuels be cheaper than bunch of mirrors and some pipe?Here’s the Cliffs Notes version of why solar isn’t ubiquitous: • Solar’s power generation is limited to daylight hours because, at this point, storing energy for later use is too complex and costly. More problematic is that these systems require a specific quality of sunlight as measured by its direct normal insolation, or DNI. Unfortunately, there are limited geographies that possess the requisite DNI of 5 or higher — namely deserts. Needless to say, deserts pose construction and maintenance challenges. For example, having to keep thousands of mirrors constantly clean from dusty wind storms — without a ready supply of water. Then there’s the small matter of being far removed from the electrical grid. • The need not just for sunlight, but for “quality” sunlight is a major reason solar is unlikely to be the singular answer to the world’s renewable energy needs. In some geographies, wind is better suited. One such “wind corridor” exists from the Canadian border to West Texas. This is one reason — along with natural gas — wind is a component of T. Boone Pickens’ plan to eliminate our dependence on foreign oil. And geographically independent biofuels may also contribute.Notwithstanding connecting to the grid, and despite the free source of fuel, the costs of construction and the complexity of maintenance cause the key measure of price competitiveness — levelized cost of energy, or LCOE — to be unattractive for solar compared to fossil fuels. Thus subsidies remain integral to advancing the technology.Author, professor, entrepreneur, radio and TV commentator, Tony Paradiso of Wilton is a marketing, management and macroeconomic expert. His website is at tonyparadiso.com.