Anyway, as most PV system owners are aware of, there are a couple of online resources you can use to see what your roof looks like and even measuring tools to get an idea of how many panels you could get up there.

The first is Nearmap (free for personal use). I believe they use aerial photos taken from planes and give very good resolution if you’re in a populated area. They update their views every month or so and have this neat feature where you can go back in time to see the same area or house as it was the previous times they took photos there (historical view). There’s only a couple of downsides to Nearmap – outside of built-up areas their coverage is fairly poor and if you’re searching for a particular address you’re out of luck. There’s a lot of street names missing from their search facility and no house numbers. So it’s OK if you know what you’re looking for but if you only have an address then what you need is Google Maps.

Google Maps is great in that you can search for a particular address and most of the time it comes up with the goods (although I have been on one or two wild goose chases following roads I thought were thoroughfares only to find out they were dead-ends). It also has

> the intuitive Google way of trying to guess your address which can be useful if you don’t know the suburb or exact spelling of the street etc. Sometimes you need to turn off the satellite view and just look at the map view to check the property boundaries with respect to the house numbers as they can get a little out of alignment. And there’s also Streetview to give you an idea of what the house looks like from the road.

Google Maps has greater

coverage than Nearmap, especially in the regional areas, but the resolution is usually not as good and their maps are not updated nearly as often as Nearmap. Also, if you need to use measuring tools you need to switch to Google Earth.

Note that maps for both these sites face true north, the optimal orientation for solar panels, so you’ll get a good idea of what panel orientations are possible on your roof.

There’s been a bit of flack (and rightly so) around some solar installation companies not doing a site inspection before they install the PV system, they’ll try to use Nearmap and/or Google Maps to check the roof area and work out what size system will fit. This might be convenient for the solar company but apart from it not complying with the CEC guidelines (meaning they’re not strictly eligible to claim the RECs/STCs) it also means they’re missing out on so much information relevant to whoever has to actually do this installation.

Aerial views won’t give you any information about the compliance of your meter box, shading effects of nearby vegetation (overhead images only give you shading info for one time of the day), any cable run issues and so on. So if you’re thinking of getting solar installed make sure the company sends somebody around to check the site and take photos (either an installer or trained technician or even a trained salesman if there is such a beast). Software is great to get an overview of what’s possible but is no substitute for a site visit.

Any other sites out there that show aerial views? Drop a note in the comments.

The first is a new publication written by Trevor Berrill and published by Which Energy. Trevor has many years experience involved in solar and taught at Tafes here in Queensland as well as being involved in public education and policy. This is the most comprehensive guide I’ve seen and is well worth reading by system designers as well as current system owners and those thinking of installing solar. It’s available for the low price of $10 at most newsagents (no, I’m not on commission). There’s a sample of the guide available here with a list of subjects covered. 

The other consumer guide that I’m aware of is put out by the Clean Energy Council available here. This guide gets updated every few weeks (not sure if it’s because they add in new information or they keep finding mistakes that need correcting

:) but also has some useful information in it. It’s free but not as comprehensive as the one above.

There may also be a Choice solar guide but as I’m not a subscriber I’m not sure about this. Some of the bigger solar companies also have varying degrees of info on their websites (see Energy Matters for example) but they usually try to steer you towards buying their own particular brand of panels etc.

If you know of any other (impartial) sources of solar info put a link in the comments. Thanks.

Power is measured in watts (W) and is instantaneous i.e. for a typical PV system it’s constantly changing. It will start at zero in the morning before the inverter switches on, then on a clear day it will approximately follow a curve which peaks around midday and starts to tail off into the late afternoon.

A lot of inverters will show this curve on an LCD screen and also show

the power production at that particular time as a wattage reading.

Energy is measured in kWh (for electrical applications – also measured in joules J for thermal systems). Energy is measured over time and is equal to power x time. This you can see from the units: kW x h.

1 kWh is the amount of energy a 100 W bulb uses if it’s on for ten hours, or a 1000 W toaster used for 1 hour. It’s what your electricity bills are measured in and how we pay for the power we use.

So a PV system outputs power which goes up and down during the day depending on many factors – the season, the time of day, the weather, shading on panels etc. What you should be interested in is the amount of energy a system produces over a day (kWh/day) or a month or an average year as this is the figure you use to determine how much your electricity bill will be reduced by or how much excess you’ll have to feed into the grid.

The kWh figure is also used when you compare systems. For example if you’re talking with a neighbour who also has a PV system (not necessarily the same size) it’s easy to compare outputs if you divide the kWh you generate over a day and divide it by your system size. If both systems are working properly (and similar orientation & pitch) then the figures should generally be similar.

So no more talk of kW per hour or day – this just doesn’t make sense. If it’s instantaneous use W or kW, if it’s over time use kWh and the solar gods will be appeased.

The pitch of the panel is also usually determined by the roof pitch. Brackets that tilt the panels up or skew the panels around to a different orientation generally look kind of ugly and introduce wind loading issues. You’ll pay extra for them too.

Normal roof pitches are between 15 & 25 degrees which work fine here in SE Qld.

A lot of people think that panels should ideally be pitched at the latitude angle (about 26 degrees on the Sunshine Coast) as this is the angle where the sun is perpendicular to the panels at the March & September equinox i.e. the sun spends half of the year below this angle and half the year higher. This only makes sense if the amount of sunlight was the same in winter as in summer but mainly because the days are longer in summer it’s better to lower the angle of panel pitch to maximise the summer gains.

For a grid-connect system you’re looking to maximise solar generation over the year so a pitch angle of about 10 degrees less than latitude

is what you’re aiming for (but 5 to 10 degrees either side of this doesn’t make a lot of difference when you look at the figures). This assumes the panels face north (-ish).

Of course for a stand-alone solar system (SAPS) you need to work out when you require more energy – winter or summer – and adjust panel pitch accordingly. This can only be decided when you do a detailed energy audit or load analysis of what the proposed SAPS is supposed to run.

It’s also recommended to keep the panel pitch to at least 10 degrees so the rain washes any crud off the panels. If you don’t mind getting up on your roof every so often then maybe this isn’t a big deal if you have a good reason to want to lay your panels flatter than this.

I’ve been working for a grid-connect solar power company here on the Sunshine Coast (Queensland) for the last few years

and learnt a thing or two along the way.

Now that I’ve been retrenched (a victim of the gummint I tells ya :), I have a bit of time to share some of this information with anybody who may be interested.

Enjoy. And give feedback if you want.