# Solar Analysis

Articles about solar position, photovoltaics and all aspects of solar radiation.

## Solar Availability in Cities

Dense urban environments provide a complex environment, where solar and daylight availability can become a scarce commodity, especially since buildings become increasingly taller. This is manly due to the complex dynamic overshadowing effects present on building surfaces. Accurately quantifying these effects is key in predicting reductions in solar availability. These in turn, can significantly affect daylight and thermal performance of buildings, as well as potential for PVs and other renewables. It is therefore necessary to use simulation tools to predict these complex effects.

## Comparing Solar Position Data

I have had a couple of occasions recently where I needed to directly compare different solar position algorithms, as well as predicted versus recorded position data. This sounds pretty simple, but there are actually some interesting little quirks where even datasets that are so close as to be virtually identical will still throw up spuriously large differences in individual values. I thought these might be worth documenting and discussing.

## ECOTECT and the Average Energy Year

When you perform solar and thermal calculations in Ecotect, it does not do these for any specific year, but rather a standard 'average' energy year. This is true of nearly all thermal and energy analysis tools. Even the weather files used for solar and energy analysis are usually averaged to better represent long-term conditions. This article explains the basic assumptions behind the 'average' energy year and why this approach is more appropriate than using any particular year.

## Averaging Solar Radiation

For the most part, the mathematics of solar radiation is pretty straightforward. However, there are a couple of situations that are less intuitive than they first appear. This is definitely true in the calculation of average hourly incident solar radiation (insolation).

## Why Do Shading Calculations Take so Long?

Calculating detailed solar shading and overshadowing is a problem for most building analysis tools, ECOTECT included. It is important to a whole range of building performance criteria, from thermal and daylighting analysis through to solar access and rights-to-light. However, to do it properly can take a frustratingly long time. This article explains exactly what is happening during these calculations and offers tips on how to optimise the process and make best use of your existing shading data.

## Solar Shading Potential

Not all parts of a solar shading device are equally effective or even necessary. Techniques have been developed in ECOTECT to visually map variations in effectiveness over the actual geometry of a modelled shading device. These same techniques can be used during the design process to map shading potential over a proposed device or even to determine the best location for shading. This article explains the concepts behind these techniques and how they may be best applied.

## An Optimised Shading Example

A number of people have recently requested information on how to complete an overshadowing exercise I set some Masters students at a couple of different Universities. As a result, I have added some more descriptive text and reformatted the original answer sheet to describe both the exercise problem and an example method that can be used to generate the answer.

## The Thermal Effects of Solar Gain

In many building regulations and simplified analysis methods, solar effects on buildings are characterised only by the exposed apperture area and the average solar transmittance of the glazing used. However, the true impact of solar radiation on the internal conditions within a space are often much more complex than this simple relationship would suggest. To explain the problem, this article tracks solar radiation as it enters through a window and looks at the various factors that govern its resultant effects.

## Domes and Solar Radiation

Domed roofs have great structural advantages, but also some significant thermal advantages due to their response to incident solar radiation. This article presents a quick outline of this response when compared to flat or inclined roofs.

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