Step into the sun, step into the light

The problems I've had with our solar installer prompted me to do the math on the actual difference between installing a solar system on roofs facing different directions....

Taking the system I've had installed for example, its basically a 5kW system using 20 250W panels and a 5kW inverter.

When installing panels there are basically two parameters to take into consideration azimuth and pitch

Azimuth is basically the compass direction the panel is facing,

Pitch is the angle of the panels from horizontal, at the equator this would be horizontal, increasing as you move north/south away from the equator.

Ideally the pitch and angle should be selected to maximize the panels exposure to the sun, and if you were going to go for the gold standard then you would be looking at a system with a tracking frame that constantly adjusted the azimuth and pitch.

OK, so, all of this is pretty basic understanding, but whats not so well understood is the effects of making the compromises we all make when installing a solar system.

Using my system as an example, were I to use a full tracking frame then I could expect a annual energy Yield of 10550kWh

Full tracking frames are expensive and need a lot of space, so generally most systems are a fixed system, but it represents the maximum power that can be generated from a given hardware setup, as for pitch well the ideal pitch at the Brisbane Latitude is 27 degrees, and since our roof pitch is actually 25 degrees we go with that.

Full tracking 10550kWh per year
North Facing 25 degrees pitch 8205kWh/year
North East/West 25 degrees pitch 7950kWh/year
East/West Facing 25 degrees pitch 7235kWh/year
South East/West 25 degrees pitch 6390kWh/year
South Facing 25 degrees pitch 6000kWh/year

Generally there is little difference between east and west, however an east facing system may be warmer at midday (the peak generation period), so it may be a little less efficient, and a West facing system will probably generate more power when its actually needed, as opposed to when everybody is at work, so given an equal choice west is generally preferred over East and north west over North East etc.

Because our North West roof is too small for the system we split it over the North East/West roofs, with 6 panels and the solar hot water on the North West roof and the other 14 panels on the North East roof, this should have given us a projected yield of 7950kWh/year, which given its 97% of the projected yield for an ideal north facing system we felt was pretty good.

So, where did our installer go wrong, well firstly nobody gave them the installation drawings I supplied to the solar company!, so without these the installer used the west over east preference rational to believe that installing the panels on the South West roof was preferable to the North East..WRONG South west is only preferable over South East or South.

Had we left the system as installed then our projected Yield would have been reduced to 6850kWh/Year, that's a loss of 1100kWh/Year