HELP With Incorrectly Positioned Solar Panels - Sydney

Our solar panels were installed on west-facing roof of our house, which faces WSW at 260 degrees (does that make sense ?).

However, they weren't installed on frames which would have allowed them to face north (as advised by Rheem themselves). The installer said that it wasn't necessary. That we'd get enough sun. This does NOT make sense to us !

We are waiting for a 2nd response from Rheem, but I'd really like to hear from our Homeone energy gurus, please !

Was the installer correct or was he making excuses ?


PS. It is an offpeak electrically boosted HWS.

Solar north is ideal

+/- 45 deg - 90% of maximum possible output

> +/- 45 deg - 80% or less

See this to get an idea:

http://www.yourhome.gov.au/technical/fs67.html#siting

Every where I read it always says point the collectors solar north.

I found this for you.

http://www.rheem.com.au/dimensions.asp? ... stallation

It's pretty obvious that your collectors are not going to run efficiently.

Southies,

You're telling us that the panels were mounted closer to south than north? That is, 10 degrees south of due west?

Unfortunately, the link given by dynomite69 is for photovoltaics, where the objective is to maximise overall yearly lighting. For a hot water system, it's winter that matters. The sun is lower in the sky so your roof pitch will come into the equation.

I wouldn't be happy with the positioning. Rotated clockwise 90 degrees and you would have had (almost) the ideal positioning.

Cheers,
Casa

The link is related to photovoltaics but the principles are the same - the further away from solar north the less available solar energy. Once you go past 45 degrees you compromise heating winter, autumn or summer. As Casa2 points out, altitude (tilt) is also important to achieve load leveling. Here is some modeling done.

http://forums.envirotalk.com.au/index.p ... st&p=26835

If we understand this correctly dymonite69, our solar hws will be 85% efficient situated as it is now facing WSW. and that the installer was correct in advising that we don't need a frame to situate the panels to face north.

You are understanding correctly.

The general recommendation is to have the collector tilted to the horizontal at least equal to the latitude of your location e.g. Sydney 33' 51'' .


http://www.yourhome.gov.au/technical/fs ... ositioning

You may wish to lift it even higher to get more winter heating (low sun) and minimise boiling over in summer. The reason that this isn't conventionally done is usually due to aesthetics. The perfect system will actually track the sun's path so that sunlight is always at right angles to the collector.

The requirement for a frame will also depend on the original pitch of your roof.

I'm concerned about the azimuth (east/west rotation) positioning of the hot water panels. I tried to find something on the net, but the closest I can come up with is http://www.pasolar.ncat.org/lesson03.php.

Performance degradation with azimuth rotation for photovoltaics is different than for hot water.

From the referenced website, we see that having solar panels facing due west results in the following degradation:

Yearly average degradation: 14%
Summer degradation: 1%
Winter degradation: 31%

Now, for photovoltaics, the objective is to maximise yearly power. It doesn’t really mater how it's distributed (unless you're working self sufficient and working off batteries).

For hot water panels, you want to maximise winter performance. By putting the panels due west you loose one-third of your solar energy. Add another 10 degrees to the south ad it's looking very bad.

I hope this all makes sense. The key thing to remember is that the degradation for solar hot water and solar photovoltaics with increased azimuth rotation from true north is very different.

Hi Southies, I probably can't help much here. For my panels, the positions are shown on the plans that were submitted to council. I thought council requires to know this as this affects the exterior appearance. Have you checked if they are on you plan??

Correct conclusion but wrong reason. Yearly degradation is the important figure, not winter degradation.

This sound counter-intuitive but the net yearly energy gain is predominantly determined by the efficiency of the 'shoulder seasons' e.g. spring and autumn. The best solution is to optimise for that period of the year.

Summer is easy - there is more insolation than you probably need and even an inefficient set up is going to churn out enough hot water for your needs.

Winter will be a struggle no matter how well the system is set up. There is about a third less sun. The collectors also work less efficiently due to heat loss to the cold air (unless you have an evacuated tube collector). At the best you can only heat about 1/4 to 1/5 of your tank before needing boosting. In other words, fiddling around here is going to get you small gains - maybe 25 extra litres of hot water per day.

Where you are going to get your biggest benefit is by increasing spring or autum efficiency. There is more sun and the air temperatures won't challenge the collector.The earlier in the season you can start producing all your hot water needs, the greater the net annual gain. Smaller changes in % efficiency during this season will yield higher absolute gains.

So a 50% loss of winter efficiency is easily made up by a 25% gain in efficiency in spring or autumn.

Southies.

This document might help.

http://www.resourcesmart.vic.gov.au/documents/SHW_performance_req.pdf

thankyou dymonite69 & Yak_Chat, after having studied the info you have both provided, we think that the installer was right.

In other words, the aspect is not ideal but it is reasonable.