In addition to its role as engineering, procurement and construction contractor, ABB will also supply the electrical and control equipment for the plant and provide the connection to the power grid.
South African connection
FG Emvelo – a joint venture between Germany’s FG.de and South Africa’s Emvelo Projects – recently acquired a 340 square km site at the Karoshoek Solar Valley in Northern Cape province. Together with partners it is developing a pipeline of CSP and concentrating PV projects in the valley. The site has been chosen because it exhibits high DNI (direct normal irradiance). In February it was announced that the CSP plants will use ABB-Novatec packaged solar technology. ABB recently completed South Africa’s first PV power plants for Eskom, the national energy company.
The packaged plant is said to be extremely quick, easy and cost effective to build and operate. Based on Novatec Solar’s patented Fresnel-based CSP technology, the power units should use 70% less material, require 40% less land and consume 80% less water per megawatt generated compared to conventional parabolic trough designs. This is of some significance in the Northern Cape, which is South Africa’s largest and most arid region.
This performance is achieved mainly through a boiler design for direct steam generation that is based on linear Fresnel collector technology (see panel) combined with Novatec’s vacuum tube absorber. Instead of the curved mirrors of a parabolic trough, the collectors use flat glass mirrors to reflect solar energy onto a receiver in which water is vaporised directly to produce superheated steam at temperatures of up to 500 deg C and a pressure of 100 bar. The direct steam technology operates without thermal oil or any other toxic heat transfer medium.
The cost of building and operating the plants is kept very low, a feature that offer huge potential for global deployment, by bringing into play a number of factors including the use of standard materials such as sheet steel and flat glass mirrors, the automated mass production of key components in locally erected production facilities, what the manufacturer describes as a fast and accurate assembly process, highly efficient land use, and a robotic cleaning system that uses very little water. Applications include standalone or hybrid power plants, and as fuel savers in existing power plants, in desalination and district cooling plants, and in industrial processes that require steam such as enhanced oil recovery.
This collaboration with Novatec adds to an ABB portfolio that already includes EPC contracting of conventional photovoltaic power plants, in which area it has successfully delivered 26 plants with a combined capacity of more than 120 MW in the past nine months. And in December it completed the set with the acquisition of a strategic stake in US-based GreenVolts, paying $20 million for a substantial minority stake. GreenVolts is a provider of turnkey concentrating photovoltaic (CPV) systems.
Through the investment ABB gains access to GreenVolts’ proprietary technology and can now offer its CPV turnkey solutions. GreenVolts’ CPV system is claimed to be more efficient than conventional PV and thin-film modules, a claim it says arises from the use of high-performance components such as proprietary optics and tracking technology optimised and integrated into a complete system, and delivers energy yields that can be 30 to 40% higher than other panel-based systems.
Novatec’s linear Fresnel technology has been demonstrated with a 1.4 MWe plant, Puerto Errado 1, (PE1) located in Murcia and connected to the Spanish grid since March 2009. Next to the site and currently under construction is the first commercial installation of the technology, PE2, a 30 MWe solar thermal power plant that was started in 2010 and is scheduled to start generating power for the grid in 2012.
A third plant is located in Liddell, Australia. When completed in mid-2012 the 9.3 MWt facility will be, says Novatec, the world’s first solar boiler contributing steam to drive turbines and help reduce carbon emissions.
The Murcia plant passed a landmark in September last year when it succeeded in generating superheated steam at temperatures above 500 deg C by implementing a receiver design that incorporated the Fresnel technology and vacuum absorber tubes, allowing the supply of steam to superheated steam turbines, achieving higher cycle efficiency and therefore a significant reduction in the cost of generation.
‘Using vacuum receivers, the heat losses can be reduced by 50% compared to the Nova1 (Novatec’s earlier technology),’ said Dr Max Mertins, head of Novatec R&D. The German Aerospace Centre (DLR) has since been engaged as an independent certifying body to carry out performance tests on the plant.
Novatec Solar’s patented solar steam generator is a linear-focused solar power system that generates steam with temperatures in the range 270-500 deg C.
The generator is in modular form and utilises Fresnel collector mirrors. This is a development of the familiar parabolic system, but using flat glass mirrors in place of parabolically curved mirrors to focus the sun’s heat. Fresnel mirrors work in a similar way to Fresnel lenses – in which a series of narrow flat glass elements imitates the action of a single curved surface. Such a lens or mirror does not possess the high resolution of a curved optic, but for this kind of application it is not required to, and it is much cheaper and easier to make. It has the advantage also that all the surfaces, suitably angled so that the optical result is a crude parabola, can be brought into a single plane, reducing the weight and bulk of the resulting mirror. These principles are shown in the figures above. Flat mirrors permit a simpler solar field array.
In this case 16 parallel lines of mirrors reflect solar energy onto a receiver in which water is vaporised. The steam can be directed to a steam turbine for power generation or used for seawater desalination, solar cooling, and other industrial heat applications.
The basic module consists of 16 rows of 8 primary reflector units, 128 in all, with a total mirror surface area of 513.6 m? and 8 receiver units, and can be arranged longitudinally to form a collector row. Rows of 5 modules, 224m in length, or up to 22 modules, 985.6m in length, can be arranged in parallel to form a solar array of any size.
The solar boiler package contains all the components necessary for direct steam generation. Other than the foundations and supporting structure these are the primary reflectors, radiation receivers, and systems that control primary reflector tracking and solar array output.
The unit’s strength is its simplicity, leading to low cost, rapid construction in remote locations and low susceptibility to damage. Its built-in quality control is made possible by industrial robot manufacturing processes.