Updated June 2016

How much solar energy is available depends on locality, cloud cover and season. This article explains its measurement, and how to know exactly for free.


This map shows average yearly global solar input. Solar power is totally feasible in all areas where input exceeds about 2-2.5 kWh/m2. Pic: courtesy of SolarGIS.

Right now (2016) there is about 7000 times more solar than is needed to supply the world’s energy needs. Around midday, countries in latitudes like Australia, the north of New Zealand, and South Africa have 800-1000 watts of solar energy falling on each flat square metre. Currently, affordable solar panels are 14% to 20.5% efficient so solar reality (what you have to use) is about 120 to 140 watts per square metre.

How much solar energy is available – how it is measured

Technically, solar energy is shown as above (in watts per square metre). The solar industry however has simplified this for non-technical readers. It likens the sun’s energy to daily rainfall – and (apart from calling it ‘insolation’) expresses it in a similar way.

In effect it captures sunlight (much as rain in a rain-gauge) by using what in effect is a standard-sized ‘light bucket’.When ‘full’ that amount of energy is is equivalent to 1000 watts per square metre. That amount is also known by the industry as one Peak Sun Hour – and usually abbreviated to PSH.

In areas like central Australian or Arizona etc that bucket typically fills 5-6 times a day (for much of the year). There is thus 6000-7000 watt hours (6-7) PSH). In areas such as a Melbourne or Madrid mid-winter, solar input may be as low as 1000-1500 watts per square metre (1-1.5 PSH).

For exact and full data,  first establish your geographic coordinates (via Google or a good map). Then go to https:[email protected]gov and enter that data. This will  bring up more information than you probably need to know. The Tables you need relate to Radiation on an Equator-pointed Tilted Surface kWh/m2/day. (By Equator NASA means solar modules facing South in the northern hemisphere and North in the southern hemisphere.) The data is based on a running ten-year averaged basis and thus correct for local and global changes. As will be seen exactly-correct solar module orientation is not needed. Five to ten degrees difference in tilt and direction makes only minor change.

The tables also shows that you can tilt the solar modules to obtain more input in winter – at the expense of summer, (and vice versa). Some people thus have them adjustable. 

How much solar energy is available –  the energy that’s actually usable

Because solar modules are far from efficient the electrical output from the solar modules (i.e that which you can actually use) is likely to be 12%-21.5% of your solar insolation. This increases slightly from year to year as solar module technology evolves and the various ways that you employ to optimise your system. Solar capacity however is now cheap (and becomes cheaper year by year). 

How and where to go from here?

This article explains how to establish (totally reliably and independently) the minimum and most solar input you can, on average, capture for your desired location. In effect, whether or not it worthwhile going ahead with your solar energy plans. How and where to go from here cannot be covered in article form.

Every aspect of designing and installing your own solar system, is covered in my two globally-selling solar books. We promise that their price will be covered many times over by the massive savings that they show you how to readily achieve

As with this article and my other articles, my books are written in plain down-to-earth English, but technically correct throughout. My bio is at: http://www.successfulsolarbooks.com/collyn-rivers/

Full details of every aspect of the use, purchase, design, making and installation of solar in homes and properties is in my book Solar Success. That for camper trailers, caravans and motor homes is in my associated books  Solar That Really Works! and Caravan & Motorhome Electrics. See also Our all solar house

If you are interested also in solar in RVs – please do also see our associated website: caravanandmotorhomebooks.com