Posts Tagged 'PV'

Where is the sun? (sun path diagram, solar iPhone apps, and more)

Ever wondered how to calculate the exact position of the sun at a given date and time? Not something everyone worries about – but maybe you’ve thought about how to best shade an overheated room… or where to install solar panels on your roof for the best outcome.

As you have probably gathered, this is actually quite tricky to work out! I’ve been asked this question a few times so I thought I’d post the options I know of here.

1. Use a Sun-path Diagram

The easiest way that I can think of is to use a sunpath diagram. This will tell you where the sun will be on any given date and time for a given locality. A sunpath diagram for Sydney, Australia (latitude of about 33 degrees South, longitude about 151 degrees East)  is shown below (click to enlarge).

How to read it for 5pm on the 1st January (as an example):

Follow the solid line for the 1st January up from bottom left of the chart till you hit ’16’ for 4pm (because we’re in Daylight Savings Time). You will come to a point with an ‘Azimuth’ of (very roughly) 265 degrees from North and an ‘Elevation’ or ‘Altitude’ of 35 degrees.

Source: Photovoltaics CD ROM, Honsberg and Bowden.

2. Use a pre-developed calculator

Another more accurate and probably even easier way is to use a pre-developed calculator. It’s important to understand the fundamentals first though, otherwise you won’t appreciate what you are looking at. A great free tool is provided here:

This calculator works really well, but it is important to note that the Azimuth referred to here is not the same as the standard definition as used on the sunpath diagram above. This might be because the tool was developed for the Northern Hemisphere. Choose Azimuth Zero = North and you should be able to work out what the results mean (if not, click the names for their definition).

UPDATE: Or you can simply use an application on your phone. See the comments section below about available iPhone applications.

3. Crunch the numbers!

Not for the faint hearted, but if you like numbers and want to appreciate all the goings-on in these and other solar equations I suggest you buy a book such as ‘Applied Photovoltaics’ (authors: Stuart R. Wenham, Martin A. Green, Muriel E. Watt, Richard Corkish).

Steplight plug-in appliance power meter


A brief introduction to photovoltaics

Photovoltaic cells generate electricity from sunlight, typically by means of a p-n junction semiconductor material. Their ability to generate energy from a free fuel, using no moving parts, creating no noise or on-site emissions, with minimal maintenance in a highly predictable and reliable fashion, is unparalleled. Application of the technology is modularised and deployment can take place where energy is most valuable: at the point of use. In a world of widespread energy inequality, dominated by unbalanced and typically centralised energy systems, photovoltaics’ time has come.

Knowledge of photovoltaic technology has progressed rapidly over the last half-century. Although the photovoltaic effect was discovered in the 1800’s, the silicon solar cell was first developed in a useful form by the Bell Telephone Laboratories in 1954. This wafer-based silicon cell has become the mainstay of the solar industry since that time and has certainly led the charge to production levels of a giga-watt per annum scale (reached in 2004). The global bottleneck in supply of high purity solar grade silicon experienced in recent years highlighted the point that this technology is not likely to lead the charge to a world with a terra-watt of installed photovoltaic capacity.

Photovoltaics is, however, not without its limits. Just as the amount of oil left in the earth’s crust is limited, there is only a finite amount of energy available from sunlight. Thankfully, unlike oil and other fossil fuels, this amount of energy is highly predictable, enormous on a global scale and quite obviously, constantly replenished.

This is an edited excerpt from Opportunities for Vehicle Integrated Photovoltaics.

If you are interested in buying an in-depth book on the topic I suggest Applied Photovoltaics from Amazon.

Energy Efficiency Tips:

- Get expert advice with a Home Energy Audit or Business Energy Audit.

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- Use these innovative Energy Saving Devices.