Solar Energy Conversion Systems

Jeffrey R. S. Brownson

• Publisher: Academic Press
• Year: 2013
• ISBN:
  9780123973153
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Solar energy conversion requires a different mind-set from traditional energy engineering in order to assess distribution, scales of use, systems design, predictive economic models for fluctuating solar resources, and planning to address transient cycles and social adoption. Solar Energy Conversion Systems examines solar energy conversion as an integrative design process, applying systems thinking methods to a solid knowledge base for creators of solar energy systems. This approach permits different levels of access for the emerging broad audience of scientists, engineers, architects, planners, and economists. Traditional texts in solar energy engineering have often emerged from mechanical or chemical engineering fields. Instead, Solar Energy Conversion Systems approaches solar energy conversion from the perspectives of integrative design, environmental technology, sustainability science, and materials science in the wake of amazing new thin films, polymers, and glasses developed by the optoelectronics and semiconductor industries. This is a new solar text for the new generation of green job designers and developers. It's highlighted with vignettes that break down solar conversion into useful stories and provides common points of reference, as well as techniques, for effective estimation of evolving technologies.

• Contextualizes solar conversion for systems design and implementation in practical applications
• Provides a complete understanding of solar power, from underlying science to essential economic outcomes
• Analytical approach emphasizes systems simulations from measured irradiance and weather data rather than estimations from "rules of thumb"
• Emphasizes integrative design and solar utility, where trans-disciplinary teams can develop sustainable solar solutions that increase client well-being and ecosystems services for a given locale

Chapter 06

Sun-Earth Geometry

Abstract

Just like navigation for a naval ship or airplane, we observe that time and space relations are linked together, and can be represented and communicated as geographic information. In this chapter we describe how to manipulate that geographic information in terms of angles, and use key relations from spherical trigonometry to make time and space relations easy to calculate with a computer. For our purposes: angles are coordinates in space and time. We describe the spatial and temporal relationships of the Sun relative to the Earth and for an Observer on the surface of Earth relative to the Sun at any given time. These angular relationships are then used to describe in detail the relative orientation of a Solar Energy Conversion System (SECS) surface relative to the moving Sun, while identifying the times that local shadows might obscure our SECS.

Keywords

Declination; Hour angle; Analemma; Altitude angle; Tilt; Azimuth

[Harrison’s “equation of time”] table enabled the clock’s user to rectify the difference between solar, or “true” time (as shown on a sundial) with the artificial but more regular “mean” time (as measured by clocks that strike noon every twenty-four hours). The disparity between solar noon and mean noon widens and narrows as the seasons change, on a sliding scale. We take no note of solar time today, relying solely on Greenwich mean time as our standard, but in Harrison’s era sundials still enjoyed wide use.

Dave Sobel’s Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time (2007).

Diunior et excellentior sit Triangulorum sphæricorum cognitio, quam fas sit eius mysteria omnibus propalare.—The nature of comprehending spherical triangles is so divine and elevated that it is not appropriate to share these mysteries with everyone.

Tycho Brahe De Nova Stella (1573)

THINK, before watches and computers were synchronizing time via satellite, in accordance with an international standard set by atomic clocks in national laboratories across the globe, our cultures had powerful thought and design invested in the linkage between astronomy, place, and time. We can surmise from an informal poll that our contemporaries in science and engineering (and science writing) no longer view solar time as relevant to “modern” society, even though solar time is equivalent to the sequencing of diurnal events that we observe. In solar design we require that our concepts transition into a solar time frame of reference. For the solar design professional, it is far easier to just find solutions first in solar time, and then correct our answers back to mean time for the public.

After completing this chapter, we wish you congratulations and bid you welcome to the club of mysteries that Tycho Brahe referred to.

We have established that time and space are essential relations in solar resource assessment, and we have argued that in keeping with a sustainability ethic for design in SECS, the precepts of sustainability science should be in our minds to ensure that our solving for patterns are tied to critical self-reflection of our diverse scientific approaches and our underlying assumptions. Again, among other factors sustainability science is developed in reference to the locale and the local nature of solutions as well as coordinating our solutions for ecosystems services (like provisioning and regulating services) with respect to time. One cannot develop a strong design project for SECS without holding in mind the locale and the relative positioning of the Sun and Aperture with respect to time.

Sustainability in design and systems thinking has enormous potential to lift up society and our supporting ecosystems. You will likely spend your entire careers developing sustainability as an integral ethic to your design principles.

Now consider the topic of communication. As solar energy design is a part of sustainability science and environmental technology, we must communicate our work across many disciplines, and we must be able to bridge the communication among science and society.¹ So how do we “orient” ourselves in both language and coordinates such that we can communicate across disciplines and audiences regarding:

• our position on Earth relative to others,

• the orientation of our SECS relative to the Sun,

• the time of day relative to the Prime Meridian,

• the times of shadowing from the beam irradiation relative to surrounding trees and buildings, and

• the animation and tracking of our SECS with respect to the Sun?

These are all relevant and challenging, and each is within our grasp to learn and then hone to become strong career skills as professionals in the solar industry.

Given the goal of solar design, we will have three tools that we can leverage to affect the solar utility for a client in a given locale:

1. Reduce the angle of incidence on ...