Paul Gauché

Initial review and analysis of the direct environmental impacts of CSP in the northern Cape, South Africa

The Integrated Resource Plan (IRP) of 2010 and the IRP Update provide the most recent guidance to the electricity generation future of South Africa (SA) and both plans include an increased proportion of renewable energy generation capacity. Given that SA has abundant renewable energy resource potential, this inclusion is welcome. Only 600 MW of the capacity allocated to concentrating solar power (CSP) has been committed to projects in the Northern Cape and represents roughly a fifth of the capacity that has been included in the IRP. Although CSP is particularly new in the electricity generation system of the country, the abundant solar resources of the region with annual DNI values of above 2900 kWh/m2 across the arid Savannah and Nama-Karoo biomes offer a promising future for the development of CSP in South Africa. These areas have largely been left untouched by technological development activities and thus renewable energy projects present a variety of possible direct and indirect environmental, social ...

Use of MEMs and optical sensors for closed loop heliostat control

The Helio 100 project at STERG (Stellenbosch Solar Thermal Research Group) aims to help reduce the cost of Concentrated Solar Thermal plants by deploying large numbers of small (1x2 m) low cost heliostats. One of the methods employed to reduce the cost of the heliostat field is to have a field that requires no site preparation (grading, leveling, vegetation clearance) and no expensive foundations or concrete pouring for each individual heliostat base. This implies that the heliostat pod frames and vertical mounts might be slightly out of vertical, and the normal method of dead reckoning using accurately surveyed and aligned heliostat bases cannot be used. This paper describes a combination of MEMs and optical sensors on the back of the heliostat, that together with a simple machine learning approach, give accurate and reproducible azimuth and elevation information for the heliostat plane. Initial experiments were done with an android phone mounted on the back of a heliostat as it was a readily available p...

Developing a competitive concentrating solar power industry in South Africa: Current gaps and recommended next steps

The paper provides an overview of the attractiveness of the global concentrating solar power (CSP) industry, analyses South Africas current capabilities in developing a CSP manufacturing capacity, and then makes recommendations regarding policy measures and an associated industry roadmap for developing a competitive CSP industry in South Africa. The analyses highlight that cost reduction is currently the most important stumbling block for the large-scale rollout of CSP. From a supply, or technology-push, perspective, changes such as cost-effective production methods, improved products through directed research and development, and reductions in operating and installation costs could be implemented. From a demand, or technology-pull, perspective, more ambitious targets need to be incorporated into the current South African policies with reliable support schemes to ensure long-term investment security for CSP systems. Recommendations are made accordingly. Specifically, South Africa should continue to promote strategic collaborations with potential CSP investors to access funding possibilities for projects.

CSP scenarios in South Africa: Benefits of CSP and the lessons learned

The dispatchibility potential of CSP in South Africa was investigated in the previous study. This was done by proposing a virtual hybrid system including the planned Open Cycle Gas Turbines and an optimized fleet of CSP plants. The study revealed a number of benefits; mitigates costs of capital, incrementally reduces fuel dependency, adds reserve margin and leads to a lower LCOE of the system. The subsequent paper to that, investigated the effects of the two-tier tariff structure, introduced in the Independent Power Producer Programme of the Department of Energy, which has on the proposed 3 300 MW capacity of CSP plants that is proposed as a peaking CSP system. The former study showed that the proposed CSP system generates 29 % less revenue under the two-tier tariff. However, when the CSP system is optimized for the two-tier tariff, it becomes profitable – with a smaller storage capacity of 5 hours.This report investigates and presents the results and beneficial strategies from the previous reports. In ad...

CSP opportunity and challenges in a national system: The WWF renewable vision for a 2030 South African electricity mix

The WWF proposes a renewable energy vision scenario for South Africa as an alternative to the currently mandated policy which favors additional nuclear in reducing greenhouse gas emissions. Current policy also blends additional coal, hydropower, renewables and gas turbine (open and combined cycle) capacity. We validated and refined the WWF scenario showing that a renewable favored scenario potentially leads to the lowest cost system while also demonstrating better resilience. This paper focusses on the role that CSP plays within the WWF scenario. For the WWF scenario to lead to a low cost and reliable system, significant CSP capacity was needed and the optimal storage rating was high (avg. 12 hours). Through initial sensitivity analysis of the WWF scenario, we try to understand this role. Our findings suggest that provided CSP capacity is planned well, it indeed can play a pivotal role in our future. Not just in justifying a renewable path, but as essential in the best solution for South Africa in the per...

Concentrating solar power: Improving electricity cost and security of supply, and other economic benefits

The South African solar resource is vast. By utilising this resource effectively, concentrating solar power (CSP) offers the ability to efficiently store thermal energy until needed for electricity generation. This technology can therefore assist the total electricity system to link demand and supply. Nevertheless, CSP is still entering the commercialisation phase and, as the learning rate sets in, the cost is expected to decrease significantly; thus providing a dispatchable renewable energy option that is competitive with conventional options. A major dilemma needs to be overcome. Until sufficient CSP capacity is installed each year, the localisation potential, and the overall economic benefit for the country, will not materialise. This in turn could stall the technology. This paper presents a techno-economic scenario to show that a CSP industry can be established now that exceeds the threshold for setting up economies of scale, reduces the cost of electricity, and increases energy security.

Techno-economic sensitivity study of heliostat field parameters for micro-gas turbine CSP

Concentrating solar power systems based on micro-gas turbines potentially offer numerous benefits should they become commercially viable. Heliostat fields for such systems have unique requirements in that the number of heliostats and the focal ratios are typically much lower than conventional central receiver systems. This paper presents a techno-economic sensitivity study of heliostat field parameters for a micro-gas turbine central receiver system. A 100 kWe minitower system is considered for the base case and a one-at-a-time strategy is used to investigate parameter sensitivities. Increasing heliostat focal ratios are found to have significant optical performance benefits due to both a reduction in astigmatic aberrations and a reduction in the number of facet focal lengths required; confirming the hypothesis that smaller heliostats offer a techno-economic advantage. Fixed Horizontal Axis tracking mechanism is shown to outperform the conventional Azimuth Zenith tracking mechanism in high density heliostat fields. Although several improvements to heliostat field performance are discussed, the capex fraction of the heliostat field for such system is shown to be almost half that of a conventional central receiver system and optimum utilization of the higher capex components, namely; the receiver and turbine subsystems, are more rewarding than that of the heliostat field.Concentrating solar power systems based on micro-gas turbines potentially offer numerous benefits should they become commercially viable. Heliostat fields for such systems have unique requirements in that the number of heliostats and the focal ratios are typically much lower than conventional central receiver systems. This paper presents a techno-economic sensitivity study of heliostat field parameters for a micro-gas turbine central receiver system. A 100 kWe minitower system is considered for the base case and a one-at-a-time strategy is used to investigate parameter sensitivities. Increasing heliostat focal ratios are found to have significant optical performance benefits due to both a reduction in astigmatic aberrations and a reduction in the number of facet focal lengths required; confirming the hypothesis that smaller heliostats offer a techno-economic advantage. Fixed Horizontal Axis tracking mechanism is shown to outperform the conventional Azimuth Zenith tracking mechanism in high density heliost...

The hybrid pressurized air receiver (HPAR) in the SUNDISC cycle

Tubular metallic pressurized air solar receivers face challenges in terms of temperature distribution on the absorber tubes and the limited sustainable solar influx. The HPAR concept aims at mitigating these problems through a macro-volumetric design and a secondary non-pressurized air flow around the absorber elements. Here, a 360◦ manifestation of this concept for implementation in the dual-pressure SUNDISC cycle is presented. Computationally inexpensive models for the numerous heat flows were developed for use in parametric studies of a receiver’s geometric layout. Initial findings are presented on the optical penetration of concentrated solar radiation into the absorber structure, blocking of thermal radiation from hot surfaces and the influence of the flow path through the heated tubes. In the basic design the heat transfer to the non-pressurized air stream is found to be insufficient and possible measures for its improvement are given. Their effect will be examined in more detailed models of externa...

Rock bed thermal storage: Concepts and costs

Thermal storage enables concentrating solar power (CSP) plants to provide baseload or dispatchable power. Currently CSP plants use two-tank molten salt thermal storage, with estimated capital costs of about 22-30

Gaussian mixture models as flux prediction method for central receivers

/kWhth. In the interests of reducing CSP costs, alternative storage concepts have been proposed. In particular, packed rock beds with air as the heat transfer fluid offer the potential of lower cost storage because of the low cost and abundance of rock. Two rock bed storage concepts which have been formulated for use at temperatures up to at least 600 °C are presented and a brief analysis and cost estimate is given. The cost estimate shows that both concepts are capable of capital costs less than 15