Ultra-compact, linear, solar-thermal steam generator

Abstract

Direct solar thermal steam generator with an ultra-compact linear Fresnel reflector field that has “travel and turn” capability by means of independent linear and rotational motion of reflectors.Method of positioning and orienting the reflectors of the traveling field such that the reflected energy of the field is maximized at all timesCrescent like rotational support rail of the reflector with its gravitational center in the center of the crescent. The curvature of the reflector is customized for each row of the fieldUltra-light, collector-absorber structure, with cable suspended arch-like tubular absorber, wide aperture, and secondary reflector with optimized light entrapmentFlow distribution and control method of the large horizontal solar thermal steam generation field.

Description

TECHNICAL FIELD[0001]The present application relates generally to solar thermal energy collectors and more particularly relates to direct solar thermal steam generation.BACKGROUND OF THE INVENTION[0002]The type of solar thermal collectors referred as “Linear Fresnel Reflectors” (LFR) are known and used for their simplicity and cost effectiveness. These are fields of flat or quasi-flat reflector “strips” (long and narrow bands) arranged in parallel rows and oriented to a common collector located at a certain height above the reflector field. The collector is also a strip-like, long and narrow structure, aligned in parallel with the rows of reflectors designed to collect the energy from the reflector field. One collector collects the reflected energy from multiple reflector rows on each of its sides. For discussion purposes the basic unit of the field is defined as two adjacent collectors and the reflectors between them. In theory any reflector can serve either of the two collectors. ...

AI Technical Summary

Benefits of technology

[0006]The present application thus describes a “traveling” ultra-compact reflector field, where the reflector rows have a new, additional degree of freedom of horizontal mobility, perpendicular to the longitudinal axis of the rows. The traveling rows have the ability to adjust and optimize their position between two collectors such that the reflected sunlight from the field as a whole is maximized throughout the day and throughout the year.

[0007]The present application further describes the carriage apparatus of the traveling reflectors. This device provides the linear and rotational mobility of the reflector structure as well as the tracking and positioning required for maximizing the reflected energy of the BFU.

[0008]The present application further describes the ultra-light, high-efficiency collector-absorber structure. The assembly has a simple construction, advantageous for manufacturing and field erection. The features of the collector are: wide aperture, optimized curvature of the secondary reflector surface, arch-like absorber, rolling-bead cable suspension of absorber, pre-stressed cable-bridge support structure, light-gauge, bent sheet metal enclosure, and flat-plane glass cover.

Problems solved by technology

The Pro-Solar rows have typically less exposed normal surface, thus they are less effective.

The trade-off of such design is the higher convectional heat loss of the absorbers.

1) Large space requirement or limited reflector surface-to-ground surface ratio. This is typical for systems that are designed to minimize the overlapping-shadowing effect (blocking off either the incident or reflected sunlight) of adjacent reflectors. The distance between the reflector rows and their orientation may be optimized for a specific position of the Sun on the sky that occurs only once (twice for equinox) a year. In order to make the highest use of the reflector surfaces, the rows are spaced with considerable gaps between them. This way the extent of the field required for a given thermal output becomes large. Large field then results in extensive and costly piping and other service infrastructures.

2) Limited reflected energy per unit of linear length of the mirror. This is typical for systems that are designed to minimize the area of reflector field. In this case the reflector rows are often spaced evenly, close to each other. These systems have low reflector area utilization because the above described blocking-shadowing effect.

3) Limited seasonal energy. This is typical for all known systems, including the floating rotating “Solar-Island” concept. This disadvantage comes from the fixed position of the reflectors in relation to the collectors. This anchored position of the mirrors, even if it is optimized, it is ideal only for a single hour of the year, however for the rest of the year the mirrors would require a different optimized distribution between the collectors.

4) Limited collector efficiency. The known collector systems either have high heat losses or poor radiation capturing efficiency. Heat losses are caused by the high surface temperature and high incident radiation flux. The root cause of poor collection efficiency is the inaccuracy of focusing of quasi-flat (slightly curved) mirrors over relatively large distances to the absorber. On one hand the active absorber surface of the collector must be limited (to an optimum value), on the other hand the collector aperture (the opening of the collector) receiving the reflected radiation needs to stay large to be able to capture the somewhat scattered sunlight.

5) Limited hydraulic stability, poor turndown ratio and insufficient controllability of the water and steam loop systems. As a consequence of horizontal feedwater and evaporator-tubing, extended over large areas and distances, the known systems have very large pressure losses, poor control over the stability of heat transfer and the quality of steam. They have limited or no freeze protection and are prone to high velocity water-hammer—stemming from plug-type fluid flow.

6) High cost and complexity of construction. While the LFR technologies in general and the Compact LFR in particular is the simplest and most cost effective compared to other technologies, its installation cost is still considerable and leaves room for significant improvements.

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