Performance and Cost Discussion Plant Performance

Increasing the performance of the solar collectors and power plant are one of the primary opportunities for reducin g the cost of trough technology. Collector performance improvements can come from developing new more efficien t collector technologies and components but often also by improving the reliability and lifetime of existing components. Table 4 shows the annual performance and net solar-to-electric efficiency of each of the technology cases describe d above.

The 1997 baseline case performance represents the actual 1996 performance of the 30 MW SEGS VI plant (its 8th year of operation). During 1996, the SEGS VI plant had an annual net solar-to-electric efficiency of 10.7% [10,18]. Thi s performance was somewhat reduced by the high level of HCE breakage at the plant (5% with broken glass and 1% with lost vacuum). Since the HCE problems at SEGS VI are due to a design error that was later corrected, we assume that HCE breakage at future plants should remain below 1%, a number consistent with the experience at the SEGS V plant. The SEGS VI plant was selected as the baseline system because substantially more cost and performance data i s available and more analysis of plant performance has been completed than at either of the existing 80 MW SEG S plants. Note, even though only 25% of the annual energy input to the plant comes from natural gas, since this energ y is converted only at the highest turbine cycle efficiency, 34% of the annual electric output from the plant comes fro m gas energy.

The year 2000 technology shows a 20% improvement in net solar to electric efficiency over the 1997 baseline syste m performance. This is achieved by using current technologies and designs, by reducing HCE heat losses and electri c parasitics. New HCEs have an improved selective surface with a higher absorptance and a 50% lower emittance. This helps reduce trough receiver heat losses by one third. The ball joint assemblies and the reduced number of SCAs pe r collector loop (6 for LS-3 versus 16 for LS-2 collectors) will reduce HTF pumping parasitics. Adjusting for reduce d parasitics, improved HCE selective surface, and lower HCE breakage, a new 80 MW plant would be expected to have a net solar-to-electric efficiency of 12.9%.

The 2005 technology shows a 7% increase in efficiency primarily as a result of adding thermal storage. Therma l storage elimin ates dumping of solar energy during power plant start-up and during peak solar conditions when sola r field thermal delivery is greater than power plant capacity. Thermal storage also allows the power plant to operate independently of the solar field. This allows the power plant to operate near full load efficiency more often, improving the annual average power block efficiency. The thermal storage system is assumed to have an 85% round-tri p efficiency. Minor performance improvements also result from scaling the plant up to 160 MW from 80 MW. Annual net solar-to-electric efficiency increases to 13.8% [1].

The 2010 technology shows a 6% increase in net solar-to-electric efficiency primarily due to the use of the tilte d collector. Power plant efficiency improves slightly due to larger size of the 320 MW power plant. Thermal storag e has been increased to 10 hours and the solar field size increased to allow the plant to operate up to a 50% annual capacity factor. As a result, more solar energy must be stored before it can be used to generate electricity, thus the 85% round-trip efficiency of the thermal storage system tends to have a larger impact on annual plant performance. Th e resulting annual net solar-to-electric efficiency increases to 14.6%.

The 2020 and 2030 technologies show 5% and 10% improvements in performance over the 2010 trough technology . The is due to the introduction of the direct steam generation trough collector technology. DSG improves the efficiency in the solar field and reduces equipment costs by eliminating the HTF system. Power cycle efficiency is assumed t o improve due to higher solar steam temperatures. Solar parasitics are reduced through elimination of HTF pumps . Although feedwater must still be pumped through the solar field, it is pumped at a much lower mass flow rate. Thi s design also assumes that a low cost thermal storage system with an 85% round-trip efficiency is developed for use with the DSG solar field. Conversion to the DSG collector system could allow the net solar-to-electric efficiency to increase to over 16% by 2030. The changes between 2020 and 2030 are assumed to be evolutionary improvements and fin e tuning of the DSG technology.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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