Flat-plate solar-collector performance evaluation with a solar simulator as a basis for collector selection and performance prediction

Simon, F. F.

doi:10.1016/0038-092x(76)90012-8

Cited by 42 publications

(7 citation statements)

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“…In actual operation, on the other hand, the incidence angle on any collector with less than full two-axis tracking varies over the course of the day and the year. In most collectors the efficiency varies with incidence angle and one must take this variation into account to predict correctly long term energy delivery (1)(2)(3)(4).…”

Section: I~itroduc':'ionmentioning

confidence: 99%

“…For example, if the receiver has an overhang r on the east side and no overhang on the west side, one must use Eq. (2)(3)(4)(5)(6) for negative 6 (morning) and Eq. (2)(3)(4)(5)(6)(7) for positive 6 (afternoon).…”

Section: Collec!or Parametersmentioning

confidence: 99%

“…Since the incidence angle affects only the optical ter:n in Eq. [2][3][4], it is best to measure '1( 6) at or near ambient temperature to Minimize the heat loss correction. If this is not possible, the heat loss term F'UAT/I :nust be added to 11 (9) to isolate the optical term ::''11 0 (9 • 0) K(e) r'(S).…”

Section: Collec!or Parametersmentioning

confidence: 99%

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Incidence-Angle Modifier and Average Optical Efficiency of Parabolic Trough Collectors

Gaul

Rabl

1980

Journal of Solar Energy Engineering

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The incidence-angle modifier for parabolic troughs is investigated in order to clarify the connection between collector tests and prediction of long-term energy delivery by collector arrays. The optical efficiency of a parabolic trough collector decreases with incidence angle for several reasons: the decreased transmission of the glazing and the absorption of the absorber; the increased width of the solar image on the receiver; and the spillover of the radiation from troughs of finite length. In order to be able to apply test results from a short collector module to collector arrays of arbitrary length, it is necessary to separate analytically the end loss from the first two effects. This analysis is applied to several collectors that have been tested at Sandia Laboratories and at the Solar Energy Research Institute (SERI). The measurements of the incidence-angle modifier at SERI were, carried out at low temperature with an open water test loop for improved accuracy. The results are presented in two forms: as a polynomial fit to the data; and as a single number, the all-day average optical efficiency for typical operating conditions.

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Section: I~itroduc':'ionmentioning

confidence: 99%

Section: Collec!or Parametersmentioning

confidence: 99%

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Incidence-Angle Modifier and Average Optical Efficiency of Parabolic Trough Collectors

Gaul

Rabl

1980

Journal of Solar Energy Engineering

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“…For very low temperatures (e.g., < 100 °C), convective and radiative losses are small, so maximizing absorptance is the most important concern, and good efficiencies can be achieved using a simple black surface (Simon, 1976). For temperatures in the range of 100-300 °C convective losses become more important, but can be eliminated through the use of an evacuated transparent enclosure as mentioned earlier (Bermel et al, 2012;Mills, 2004).…”

Section: Introductionmentioning

confidence: 99%

Optical cavity for improved performance of solar receivers in solar-thermal systems

et al. 2014

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Abstract:A principal loss mechanism for solar receivers in solar-thermal systems is radiation from the absorbing surface. This loss can be reduced by using the concept of directional selectivity in which radiation is suppressed at angles larger than the incident angle of the sunlight striking the absorber. Directional selectivity can achieve efficiencies similar to high solar concentration, without the drawbacks associated with large heat fluxes. A specularly reflective hemispherical cavity placed over the absorber can reflect emitted radiation back to the absorber, effectively suppressing emission losses. An aperture in the cavity will still allow sunlight to reach the absorber surface when used with point focus concentrating systems. In this paper the reduction in radiative losses through the use of a hemispherical cavity is predicted using ray tracing simulations, and the effects of cavity size and absorber alignment are investigated. Simulated results are validated with proof of concept experiments that show reductions in radiative losses of more than 75% from a near blackbody absorber surface. The demonstrated cavity system is shown to be capable of achieving receiver efficiencies comparable to idealized spectrally selective absorbers across a wide range of operating temperatures. Highlights:-A specularly reflective cavity placed over a solar absorber reduces radiative losses -Cavity performance is sensitive to cavity size and cavity-absorber alignment -Radiative loss reduction validated with proof of concept experiments -Losses from near blackbody absorber reduced by over 75% -Receiver efficiency shown to be comparable to idealized wavelength selective absorber

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“…Simplified models such as the equation shown on the top righthand side of Fig. 5.14 (Hill et al 1977;Simon 1975;Gillet and Moon 1985) permit a satisfactory long-term prediction of collector's performance under transient conditions to be obtained. They have used extensively to produce expressions for various characteristics of a solar-energy collector, such as the response period (Hill et al 1977) and the effective thermal capacitance (Simon 1975).…”

Section: Water Heating Flat-plate Collectorsmentioning

confidence: 99%

Flat-Plate and Evacuated Tube Collectors

Norton¹

2013

Lecture Notes in Energy

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The sun has got his hat on Hip hip hip hooray! The sun has got his hat on, and he's coming out to play Gay and Butler (1932) 5.1 Overview Solar-energy collectors are devices employed to gain useful heat energy from the incident solar radiation. They can be of the concentrating or the flat-plate type. A simple flat-plate solar energy collector consists basically of an absorbing surface which absorbs the insolation and transmit it in form of heat to a working fluid commonly air or water. A general steady-state analysis for flat-plate collectors is shown in Fig. 5.1.Instantaneous efficiencies are plotted against (T fii ÀT a )/I and the intercept and the slope determined (7.1.5). The long-term performance of many solar heating collectors can be characterized by a thus determined intercept and slope as shown by the illustrative examples for different collector types given in Fig. 5.2. These parameters are not constant but depend on temperature and wind speed. Heat removed is also a weak function of overall heat loss. To account for these effects non-linear equations have been developed and together with an angular dependent "incident angle modifier" are used in various versions as the basis for rating tests. These are shown in Fig. 5.3.The absorber material in a flat-plate collector, in addition to having a high absorbance of the incident radiation should also have a low emissivity, good thermal conductivity, and be stable thermally under temperatures encountered during operation and stagnation. It should also be durable, have low weight per unit area and, most importantly, be cheap. Black coated metal sheets (in air heater) and fins in water heaters are used frequently as absorbers due to their effectiveness, ease of use, availability and relatively low cost. Wisely or not, a multitude of

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Flat-plate solar-collector performance evaluation with a solar simulator as a basis for collector selection and performance prediction

Cited by 42 publications

References 1 publication

Incidence-Angle Modifier and Average Optical Efficiency of Parabolic Trough Collectors

Incidence-Angle Modifier and Average Optical Efficiency of Parabolic Trough Collectors

Optical cavity for improved performance of solar receivers in solar-thermal systems

Flat-Plate and Evacuated Tube Collectors

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