How to select your solar power system

A skilled solar installer can provide you with advice and a proposal, but will it be the right system for your site and worth the investment? Here are some steps to follow when choosing your solar power system.
A grid connected solar power system with an average daily output up to the average daily electricity usage of the premises where it is connected can be expected to produce a reasonable return on investment, despite the low prices currently paid for electricity fed to the grid by new systems. The steps outlined below can be followed to assess a suitable size for a solar PV system.
 PictureFitting PV panels to available roof area

Electricty usage

Solar power output
Work out the average daily electricity usage. This is often shown on each quarterly bill on a graph as Kilowatt hours per day.  Otherwise divide the total usage for one year by 365 days. 

Decide whether to aim to match this average usage (eg. zero net electricity) or some higher or lower goal.

With a grid connected solar power system sized to match the average daily electricity usage, a typical household could expect a payback period in the order of 10 years.
Next work out what size system would supply the average daily usage. 

In Sydney, the average daily output per 1 kW of optimally oriented panels is 3.8 kWh/day. So divide the average daily electricity usage by 3.8 to get the nominal PV power system which would produce that amount of electricity. 
Divide the system size by any correction factor needed for tilt and orientation as shown below.

Round the system size to the nearest inverter size. Typically in steps of 500 Watts. eg 2kWatt, 2.5 kW, 3.0 kWatt

Solar panel array size

Locate the largest unshaded roof area facing the northern half of the sky. Google earth or Sixmaps (NSW) both have tools to measure distance in their aerial photos.

Solar panels are typically 1.0m x 1.6 m.
Work out how many panels will fit - they are typically mounted in rows - either portrait or landscape.

The rated output of a  typical solar panel is 250 Watts but higher rated panels are available. Four such panels would be required per 1.0 kWatt of array.
PicturePV power output compared to optimum - Sydney

Solar panel tilt and orientation

Not all roofs face north. The diagram on the left shows the proportion of annual output compared with output for optimum orientation and tilt.  

It shows that even low pitched south facing panels can result in annual output of over 80% compared to optimum. Note there will be very low winter output with such an orientation.

Power utilities may in the future provide better rates for PV systems which provide more of their output during the late afternoon - i.e. west facing systems.

For you chosen array, adjust the average daily output by the correct proportion for the proposed orientation and tilt angle.
To find out how we can help reduce your energy bills call  John 0418 262706 or email info@ecologicaldesign.com.au 

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