Saturday, 23 October 2010

Solar Panels ... Setting the Angle

In November 2009 I posted an article containing information about our remote power supply setup. Systems such as ours are more commonly known as Stand Alone Power Systems or SAPS.

When Central West Solar installed our system they set the angle of the fixed solar panels on the shed at approximately 43 degrees ... being latitude (34 degrees south of the equator) plus 10 degrees. From this I assumed that the ideal 'rule of thumb' for all solar panels would be the same as ours i.e. latitude plus 10 degrees.

A farming family we know who live south of Grenfell recently had a 10 kW grid-connect solar system installed, with the panels attached to the roof of one of their sheds. The panels have been attached directly to the roof without angle-adjustment frames and thus are at the same angle as the roof pitch. The pitch of this roof is very low ... at a guess around 5 degrees. My initial reaction was that they would most likely be missing out on quite a bit of potential energy capture at this angle.

I've been in contact with Robert at Central West Solar to get some clarification on the solar panel angle conventions and now understand that the angle can and should be set differently depending on the goal of the solar panel installation. Robert advises that "Generally peoples power consumption in this region over winter is approx the same as summer. If you dont take bias of array to suit loads in different seasons then the rule of thumb is: 
  • For the best all year round yield: Angle should be equal to the latitude
  • For the best summer yield: Angle should be latitude MINUS 10 to 15 degrees
  • For the best winter yield: Angle should be latitude PLUS 10 to 15 degrees"
In our own case, given we have a SAPS (and cannot sell surplus or externally source shortfalls), our goal is to maximise the winter yield as this is naturally a low capture part of the year due to shorter day length, less intense light, and higher probability of cloud and fog cover. Thus 43 degrees is spot on for us.

For those who are on grid connect systems where the primarily goal is to reduce the year round power bill (or maximise year round revenue) then the appropriate angle would be equal to latitude. Letting the mind wander creatively for a moment (and assuming all things being equal ... which they are not) people with this goal:
  • Living on the equator could install panels directly on to flat roofs
  • Living on the south pole could install panels directly on to north facing walls
  • With a 20 degree north facing pitch roof living at one of the following places in Australia could affix panels directly to their roof: Camooweal, Charters Towers or Bowen in Queensland; Tanumi or Avon Downs in the Northern Territory; or Port Hedland in Western Australia
What I have not investigated and thus don't have a feel for is what the yield reduction is for each degree the panels are not at the ideal setting. This is the type of information I reckon anyone with a grid connect system should find out as it would allow for cost benefit analysis to be carried out to assess the return from spending money on frames and structures that alter the angle of the panels from the pitch of the roof or for 'follow the sun' moving solar panel support structures.

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