Lunar sourcebook. A user's guide to the moon

This paper describes a new approach to online forecasting of power production from PV systems. The method is suited to online forecasting in many applications and in this paper it is used to predict hourly values of solar power for horizons of up to 36 h. The data used is 15-min observations of solar power from 21 PV systems located on rooftops in a small village in Denmark. The suggested method is a two-stage method where first a statistical normalization of the solar power is obtained using a clear sky model. The clear sky model is found using statistical smoothing techniques. Then forecasts of the normalized solar power are calculated using adaptive linear time series models. Both autoregressive (AR) and AR with exogenous input (ARX) models are evaluated, where the latter takes numerical weather predictions (NWPs) as input. The results indicate that for forecasts up to 2 h ahead the most important input is the available observations of solar power, while for longer horizons NWPs are the most important input. A root mean square error improvement of around 35% is achieved by the ARX model compared to a proposed reference model.

/pdf/online-short-term-solar-power-forecasting-1ljgpbshkb.pdf

Online Short-term Solar Power Forecasting

Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997); Int. J. Heat Mass Transfer, 40, 799 (1997)]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.

Constructal theory of generation of configuration in nature and engineering

The conceptual problems arising in the definition and measurement of temperature in non-equilibrium states are discussed in this paper in situations where the local-equilibrium hypothesis is no longer satisfactory. This is a necessary and urgent discussion because of the increasing interest in thermodynamic theories beyond local equilibrium, in computer simulations, in non-linear statistical mechanics, in new experiments, and in technological applications of nanoscale systems and material sciences. First, we briefly review the concept of temperature from the perspectives of equilibrium thermodynamics and statistical mechanics. Afterwards, we explore which of the equilibrium concepts may be extrapolated beyond local equilibrium and which of them should be modified, then we review several attempts to define temperature in non-equilibrium situations from macroscopic and microscopic bases. A wide review of proposals is offered on effective non-equilibrium temperatures and their application to ideal and real gases, electromagnetic radiation, nuclear collisions, granular systems, glasses, sheared fluids, amorphous semiconductors and turbulent fluids. The consistency between the different relativistic transformation laws for temperature is discussed in the new light gained from this perspective. A wide bibliography is provided in order to foster further research in this field.

/pdf/temperature-in-non-equilibrium-states-a-review-of-open-2vvmx2wgla.pdf

Temperature in non-equilibrium states: a review of open problems and current proposals

Endoreversible Thermodynamics of Solar Energy Conversion

Planck’s radiation formula is used to estimate the dimensionless efficiency of incandescent lamps as a function of filament temperature, with typical values of 2%–13%. Similarly, using the known spectral luminous efficiency of the eye, the efficacy of incandescent light bulbs is estimated as a function of temperature, showing values of 8–24 L W−1 for bulbs of 10–1000 W. The efficiency and efficacy results compare favorably with published data and enable estimation of the filament temperature for any lamp of known efficacy.

Efficiency and efficacy of incandescent lamps

Assuming that during the rated lifetime of a bulb roughly half of the radius of the filament evaporates, we can estimate the mean rate of evaporation. The filament's operating temperature can then be deduced from the Catalogue using linear interpolation. The probable reasons for the bulb's failure are also mentioned.

https://iopscience.iop.org/article/10.1088/0031-9120/33/1/023/pdf

Lifetime and temperature of incandescent lamps

The expression for the Stefan-Boltzmann constant in n-dimensions as obtained by Landsberg and De Vos is modified by the appropriate spin-degeneracy factor of the photon.

http://iopscience.iop.org/article/10.1088/0305-4470/31/3/021/pdf

Comment on 'the stefan-boltzmann constant in n-dimensional space'

An article by Leff1 on incandescent bulbs has been very successful in illuminating the minds of not only physics students but also teachers. It has also prompted many articles that explore various aspects of incandescent lamps.2–9 An interesting topic discussed by Leff concerns lifetime statistics of bulbs by drawing analogy from radioactive decay of nuclei. Leff obtained an empirical formula for the survival probability of commercial bulbs and also hinted at the approximate equality of the half-life, the average life, and the most probable life of the same. While teaching this topic over the past few years, we found that the students were confused about the precise link between the survival and decay probabilities, and were also unable to derive the said equality of different lives as this problem was left in Ref. 1 as an exercise. The aim of this paper is to clarify these ideas.

Lifetimes of Incandescent Bulbs

Exponent-rules are known to describe experimentally how the observables related to incandescent lamps alter with the change in the rated voltage. Pedagogical derivation of the rules for typical observables like the life, lumens, power, etc. in the case of vacuum bulbs is presented. This is achieved by assuming a steady-state operation of the bulb, parameterizing intrinsic properties of tungsten as suitable powers of temperature, and eliminating the temperature between those observables for which the exponent-rules are sought.

Dulli Chandra Agrawal

Papers

Efficiency and efficacy of incandescent lamps

Lifetime and temperature of incandescent lamps

Comment on 'the stefan-boltzmann constant in n-dimensional space'

Lifetimes of Incandescent Bulbs

Light bulb exponent-rules for the classroom