Advances in solar thermal electricity technology

Abstract

Various advanced solar thermal electricity technologies are reviewed with an emphasis on new technology and new market approaches.

In single-axis tracking technology, the conventional parabolic trough collector is the mainstream established technology and is under continued development but is soon to face competition from two linear Fresnel reflector (LFR) technologies, the CLFR and Solarmundo. A Solarmundo prototype has been built in Belgium, and a CLFR prototype is awaiting presale of electricity as a commercial plant before it can be constructed in Queensland. In two-axis tracking technologies, dish/Stirling technologies are faced with high Stirling engine costs and emphasism may shift to solarised gas micro-turbines, which are adapted from the small stationary gas turbine market and will be available shortly at a price in the US$1 ppW range. ANU dish technology, in which steam is collected across the field and run through large steam turbines, has not been commercialised. Emphasis in solar thermal electricity applications in two-axis tracking systems seems to be shifting to tower technology. Two central receiver towers are planned for Spain, and one for Israel. Our own multi-tower solar array (MTSA) technology has gained Australian Research Council funding for an initial single tower prototype in Australia of approximately 150 kW(e) and will use combined microturbine and PV receivers. Non-tracking systems are described of two diverse types, Chimney and evacuated tubes. Solar chimney technology is being proposed for Australia based upon German technology. Air is heated underneath a large glass structure of about 5 km in diameter, and passes up a large chimney through a wind turbine near the base as it rises. A company Enviromission Ltd. has been listed in Australia to commercialise the concept. Evacuated tubes are growing rapidly for domestic hot water heating in Europe and organic rankine cycle engines such as the Freepower 6 kW are being considered for operation with thermal energy developed by evacuated tube and trough systems. These may replace some PV in medium sized applications as they offer potential for inexpensive pressurised water storage for 24 h operation, and backup by fuels instead of generators. In the medium term there is a clear trend to creation of smaller sized systems which can operate on a retail electricity cost offset basis near urban and industrial installations. In the longer term large low cost plants will be necessary for large scale electricity and fuels production. Retrofit central generation solar plants offer a cost effective transition market which allows increased production rates and gradual cost reduction for large solar thermal plant. In the paper the author describes current funding systems in Europe, Australia, and the USA, and makes suggestions for more effective programmes of support.

Introduction

Solar thermal electricity may be defined as the result of a process by which directly collected solar energy is converted to electricity through the use of some sort of heat to electricity conversion device. Mostly this is a heat engine, but there are other options such as a thermoelectric pile converter or a fan converter as in solar chimneys.

Solar thermal electricity on grid was not achieved until the 1980s, although the basic technology for the production of mechanical energy (which could be converted to electricity using a conventional generator) had been under development for about 140 years, beginning with Mouchot and Pifre (Pifre, 1882) in France, and continued by extraordinary pioneers such as Ericsson (1888), Eneas (1901), Shuman (1913), and Francia, 1961, Francia, 1968. In the 1980s, the first large trough, dish and tower arrays were installed in response to the challenges of the 1970s oil crises, and one of these, the Luz LS3 trough collector technology, was installed in several large successful 80 MW arrays. These are still operating.

Solar thermal power has probably the greatest potential of any single renewable energy area, but has been delayed in market development since the 1980s because of market resistance to large plant sizes and poor political and financial support from incentive programmes. However, at this time there is rapid development occurring both in the basic technology and the market strategy, and prospects for rapid growth appear now to be very bright for newer approaches.

In this paper, an overview of the current technologies which are available, or are being developed, is given together with an assessment of their market prospects. There will be a stress on new developments and technologies. Our group is active in fixed collectors and both basic types of tracking strategy development. I will describe our own approaches in some detail but will also stress the most recent activity of other groups.