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Bitang,

Your numbers are theoretical from some source, are they not? Are you sure the source is accurate?

Smurf gave a real life example of theeast string running at 80% while the north srting was running at 10% at 9 am.

I am wondering if the 'tilt' angles you are using are the same for east and west, ie the east string, 22" tilt to the east, or the east string tilted 22" to the north. Or the east and west strings tilted to the north-east and north west?

Several years ago, we put in 5kw and recieved the high feed-in tariffs after I had been involved in lots of discussion on the CFU thread, which convinced me of the worth of solar. We spent over $15k on our system facing north.

I am about to add another completely separate system andit will be east west for the reasons Smurf mentions.
Another aspect not yet mentioned is that you could probably put 3kw facing east and 3kw facing west, with 30" tilts(to the east and west) and use a 5 kw inverter, to spread maximum power throughout the day.

Smurf, your thoughts on N/E and N/W tilts for east and west facing panels please?
 
Hi

I'm in Perth with a 2 storey home with a steep roof. I have just commenced enquiries about solar panels. The first company contacted declined to quote as they don't install on steep roofs.

Any recommendations appreciated.

Thank you.
 
Sorry to go back to an old post Pixel... but as we're both in Perth...

After my post above I went for a walk and met a chap who had installed panels back when the rebate as 47c. He was very dubious as to whether there is any financial merit in installing them now.

However I gather the general view is that installation is still a proposition worth considering.

If you, or others, have a view on this I would be grateful for comments.

Also if anyone is comfortable recommending a supplier with whom they were pleased I'd be grateful for the company name.

With thanks

Muschu [Rick in a previous time]

 
Systems were more expensive then, in particular large systems.

With the feed in tariff now much less than the usage tariff, the greatest benefit is obviously for those who would directly use most of the electricity generated from the panels. Subject to all other things being equal, a small system installed on a high usage household makes the greatest sense in terms of return on investment.

Advertisements I see showing rates of returns on solar panel installs assume the most generous scenario of a household using all the electricity directly from the panels and none being fed in to the grid. This is obviously unrealistic for many domestic situations and even more so with larger capacity systems.
 

Many thanks DrS and very interesting.

Regards
 

My source of numbers are as follows:
Global horizontal radiation (GHR) at a specified location comes from the NASA SSE (Surface Meteorological Solar Energy) world data base. For Smurf's Sydney location I used latitude 33.85 South and longitude 151.2 East.
GHR is converted to radiation incident on the solar array using the array's azimuth angle (i.e. orientation north, east or west) and tilt angle which in this case is 22 degrees from the horizontal for all orientations considered.



Yes all calculations used for designing solar installations are theoretical as is the case with any kind of engineering design. But that is the nature of design and it remains the basis for decision making.
As for Smurf's real life data, if it is consistently like that I would get the entire system checked. There could be an imbalance in the system such as some modules in the northern array being partly shaded or soiled.
 
Bitang,

Thanks for that. As Smurf works in the electricity industry, I am not going to question his numbers.

However as you have the ability to draw those graphs for east and west, I was wondering if you could please do me a favor and show the output for east and west facing panels at several different tilts. We have those for 22". Could you generate some graphs for 30" and 40" please as I'd like to see the output for different angles for the system I'm planning (off grid, where late afternoon generation in summer will really count) lat 38.5 south long 143.5 east.

Thanks in advance
 

I'm using Sunny Design, PV Watts and the real world experience of myself and others. But overall we both seem to be using "legitimate" sources of data.

My actual location is Hobart, but I've used Sydney for calculations since it's more relevant to where most Australians actually live (and near enough to Melbourne and Brisbane to not be a huge difference there). But I included Darwin and Hobart to show the range of possibilities.

As for Smurf's real life data, if it is consistently like that I would get the entire system checked. There could be an imbalance in the system such as some modules in the northern array being partly shaded or soiled.
Click to expand...

Everything's working fine, of that I am certain. The only issue with the Northern array is the neighbour's growing tree which thus year has become tall enough to start casting a shadow over the panels late in the afternoon at least during Autumn (and will be the same in Spring). I suspect that it won't (yet) be an issue in Summer or Winter however due to its' location.

The explanation for high output from East panels early in the morning versus low output from North facing panels is simply the location of sunrise. Eg in December the sun in Hobart rises at 5:26am, rising 34 degrees south of true east, such that there's no direct radiation onto north-facing panels for quite some time until the sun is higher in the sky. Meanwhile there's direct sun onto the East panels, which at that time of day will also be quite cool thus assisting their output.

The concept of E - W versus N is an interesting one. The data I have, based on real world experiences, shows an almost flat (on a chart) level of production from early in the morning until not long before sunset for an E - W system versus the definite bell curve for a N facing system. This doesn't seem to match your calculated data however, which is interesting.

Think I'll have to investigate this a bit further.....
 

Smurf, are you able to share some plots of your actual data for E-W vs N as I am also curious?
In preparing my charts I have not examined seasonal differences, which of course get more extreme further from the equator - or maybe in your case I should say closer to the south pole

A little bit of shading on even one module can have a big impact on performance as the whole series of modules gets 'dragged down' by the lowest performer. But you say there is only possibility of shade in the afternoon so that doesn't explain the morning phenomenon around 9:00am. Here are my charts for your actual location .... which I happen to know very well as I am originally from Hobart myself.

I recalibrated my calculations for the 22deg tilt North array to get the same annual AC output as you calculated for Hobart i.e. 1267 kWh/yr per 1kW PV (STC). With the same efficiency factors I get 1085 for the E-W configuration versus your 1089. So in terms of total annual output our results are the same. The only difference is the shape of the daily output curve. I am also curious to know how your real world annual output compares to these theoretical estimates.



 

brty that's a fair bit of work but I'll see what I can do. I caution though that the charts I have been showing do not examine seasonal differences. They are averages for the entire year, i.e. the power output plotted for each hour of the day is the average of the power output at the same time of day on each day of the year.
 
brty said:
Bitang,

Could you generate some graphs for 30" and 40" please as I'd like to see the output for different angles for the system I'm planning (off grid, where late afternoon generation in summer will really count) lat 38.5 south long 143.5 east.
Click to expand...

brty,
I began by looking up your location on Google Earth. Looks to me like you have quite a few trees there which might cause you a shading problem, in which case your PV output could look something like the red line on the following chart



The charts that follow apply to a more 'treeless' landscape.

First is for an east facing 1kWp array at tilt angles 22/30/40. The second is a west facing 1kWp array at the same set of tilt angles. For interest, I have also included in these two charts the estimated output for a 1 kWp array that has continuous azimuth tracking.




If you are going to use east and/or west facing arrays the lower tilt angle of 22 deg is marginally better. This is not the case for a north facing array for which the annual array ouptut would be maximised with a tilt angle of around 35 deg - but again the difference is marginal because total annual output is more sensitive to azimuth angle than tilt angle.

Continuous azimuth tracking can give you 40% more output but such systems are not cheap. But this theoretical comparison between the fixed arrays and the tracking array is interesting.

The last chart once again examines the idea of mixed East-West arrays but here I have plotted the output of 22 deg tilt east and west arrays, which are each 0.5 kWp. Their combination gives the total system output for 1kWp which is the dark blue curve. Theoretically the ideal installation would have azimuth tracking. Two 1kWp arrays, one facing east and one facing west would approximate the azimuth tracking array but at the cost of twice as many PV modules. But if the prices of PV modules continue to come down that might not be a silly idea.

 
Thankyou Bintang,

That is exactly what I was after, and despite it being a yearly average, for when I need it, summer, it tells me that I can get away with just putting more panels on and give good performance throughout the day.

BTW, the lat and long were not exact, but close enough. I believe that to be about 10-15k from my location, didn't want to be exact.

Another question for either yourelf or Smurf (or anybody else who knows for that matter). Is it better to have panels direct coupled to a grid connect inverter, then a stand alone inverter (thinking SMA + sunny island) to run directly off 240v, with excess power going into a battery bank for cloudy periods, or better to run straight into batteries via a regulator, then to a sunny island for ac power? I hope the question makes sense.
I'm talking about an off-grid system that is mainly for the sunshine hours during summer, therefore small battery bank requirement.
TIA.
 

Actually I figured you hadn't given me exact co-ordinates but I couldn't resist making a joke. (First rule for the prospective PV system installer ... Do a careful site analysis).

By the way, given a fixed number of modules/budget etc I personally would still face all of the modules north (rather than half east and half west) if my specific site situation would allow me to do so. (see below the last of my previous charts with a performance profile added for a 1 kWp north facing array).

However, if Smurf can show us some real world data which demonstrates that over an annual period the combo east + west arrays give better cumulative performance than the north array and that it is not due to system imbalance, then I might change my mind.



For your battery question you are now talking about a system which is grid-tied with battery back-up. Such systems are more complex and costly than a simple grid-direct system. You are going to need a battery bank with its own charge controller and a specialised inverter and you will probably also need a separate sub-panel for back-up loads. So then I have to ask you what do you mean by 'better'? If the answer is better economically I think the answer will be no. Battery storage is worth considering if your location is off-grid and getting connected to the grid is impossible or too costly but otherwise every time I have considered a grid-tied with battery back-up system the economics don't make sense. Nonetheless I am planning at some stage to install such a system but only as a 'hobby' project rather than for any economic objective. In this context 'better' for me means 'doing it for the hell of it and having some fun'.
 
Bintang,

Again, thankyou, but you missed this bit....

I'm talking about an off-grid system that is mainly for the sunshine hours during summer, therefore small battery bank requirement.
Click to expand...

This is a separate system to anything grid tied. However in an off grid situation you can use an SMA grid-tied inverter with an SMA sunny island inverter. They speak to each other.

My question/situation is not about getting the maximum amount of power, but a distributed amount throughout the day, especially later in the afternoon.
 
I don't have the hourly data for individual strings, only for the total of the whole system, but I'll take some measurements soon (over Easter if the weather is suitable).
 

Sorry brty, indeed I missed it. Must have been too busy multi-tasking. If you are putting in a completely off-grid system with some battery back-up and using SMA equipment, the configuration would be array connected to a Sunny Island charger and the battery bank would be connected to a Sunny Island battery inverter.
I don't think you can use a grid connect inverter.
 
A bit later than promised due to weather, but here are some measurements.

Location = Hobart.

Time = 8:30am Thursday 24th April 2014.

Weather = 10 degrees, clear sky to the east, overcast to the west.

Output from East facing panels (8 x 195W) = 751W (481W per kW)

Output from North facing panels (8 x 170W) = 338 W (248W per kW)

Both are AC power measurements using an identical inverter.

Both systems are producing daily and annual outputs which suggest they are working correctly.

No shade on either system at this time of day.

Based on the above, I conclude that east-facing panels do generate more power prior to 9am (ie when household usage is typically higher) than do north-facing panels. At least they do at my house in Hobart. If I measured at a different time of day or different time of year the results would be different, but these are the actual figures for today.
 
Hi Smurf,

Those figures of yours almost completely back up Bintangs arguments.

For instance if both sets of panels were the same (I note you do have the w/kw figure), and you had half the number facing east(with the other half facing west) as that facing north, then the outputs would be nearly the same for 8.30am.

From those numbers, it appears that there is no advantage in facing 1/2 panels east and 1/2 west instead of all north, to get a better spread of power output, without the mid-day peak . Interesting, or is it a time of year issue?
 
Someday ago, I read an article on Chinese Solar Panels. Personally I'm not interested to Chinese products as they are so much cheap,available and non branded products. You can goggling
 
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