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Oversizing panel array

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Started 8 years ago by Shelb
Latest reply from Off-Grid

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TonyT
Member

Off-Grid said

" TonyT >>The optimum azimuth angle for Adelaide is 10deg west of north.

That seems odd, is the reason that it is cloudier in the morning than the afternoon, so you orient them to maximise face-on sun hours? "

Answer

The 10deg west of north figure is based only on trying different azimuth angles in
http://rredc.nrel.gov/solar/calculators/pvwatts/version1/
For Adelaide, the highest solar insolation value was calculated when I used an azimuth angle of about 10deg west of north.

Thanks for the info about Standard Testing Conditions, the solar input of 1,000W/sqm and the cloud edge effect.

Three questions:

Q1. Over 12 months, what additional % of kWh is obtained by using tracking equipment ?

Q2. Separated into "parts" and "installation labour", what is the cost for tracking equipment ?

Q3. If PV collector panels cost $1.50/watt, is it economic to use tracking ?

Posted Wednesday 6 Mar 2013 @ 8:41:26 am from IP #
Shelb
Member

Off-Grid - thanks for such detailed information. No, I was not thinking of oversizing when planning the installation. It was not even thought of, mentioned, in the margins at all. Dealers don't seem to be in the loop for that. All focus went on what type of panels, and what type of inverter and getting approval before cut off date. While it seemed that Sunpower panels were reported to be the most efficient of all, it was going to cost me an EXTRA $120 per panel to install on tiled roof (they halved that charge in a follow-up quote). Therefore the less panels the better, so 12 x 318watts fitted the bill rather than 20 x 190 watts or whatever. Also, do not have roofs facing east and west, so did not have different orientation choices. Although up here North seems to be considered optimal.

It seems to me, however, that having part of an array on east and west is 'self-clipping' in itself. Eastern orientation stops producing early, and Western orientation starts producing late. So compared to the clipping of an oversized array, it probably works out even in the end.

As I have 12 panels in one row across the roof (2 strings of 6), with the cabling from the far end 6 going under the panels of the 6 closest to the inverter, switching them to 2 x 5 and 1 x 6 may be costly. Perhaps the far 6 stay as they are, and 1 from the closest 6 becomes 1 + 4 new ones (in a second row) will do the trick. I hope to nail the dealer/installer tomorrow about it. They are very busy with new installs. Whether I go ahead or not will depend on all up cost.

The SB3800 specs read:
No. of MPP trackers / strings per MPP tracker = 1 / 3

TonyT - I searched pvoutput.org specifically for SA systems and did not find any that maxed out in my small search. Strange that Perth and Vic have systems that max out and not SA.

Greg - thanks for the heads up on Sunny Design. I did not think it was for free.

Thanks everyone for your input - all appreciated.

Posted Thursday 7 Mar 2013 @ 2:32:10 am from IP #
Off-Grid
Member

Shelb-
with that inverter you couldn't do 2X5 + 1X6 panels anyway, as your note on the specs says it only has 1 MPPT input internally. Unequal string lengths into one MPPT input mean none of hte panels can work at their maximum power point. Looks like it might have to be 2X7.
North facing arrays have traditionally been "optimal" due to high FiTs, especially when Gross, where people want the absolute maximum output from their fixed arrays. Now that FiTs are zero to minimal, you are better off not exporting anything, importing minimally and using as much as you can of your own production. The typical household usage pattern does not fit in well with north facing panel output! I have a thread on my Virtual Tracker idea on the Energy Matters forums.

TonyT-
I had a look at PVWatts and it seems to give a max annual energy return with arrays facing 5 or 6deg west of north. If it isn't due to some unusual cloud pattern, I'd suspect an error in their models. If it was sunny all day then I would expect (and this is what I see with my trackers) that greater output is generally to be had in the mornings, when the panels are cooler and more efficient.

1/ I reckon about 40-50% over fixed panels, although it does vary with latitude, and there are other factors to consider, especially for off-grid installations.

2/ I haven't checked prices lately, but there are a number of manufacturers and importers of trackers with websites, although the design of many of them leaves a lot to be desired. I design and build my own, based on years of experience building telescope mountings.

3/Probably not if you are purchasing one, but my Virtual Tracker idea will give a similar even output throughout the day, for less cost than a tracker, with PV costs as low as they are ATM. That may change in the future though, as PV prices are about to go upwards again.

Posted Thursday 7 Mar 2013 @ 3:40:58 am from IP #
TonyT
Member

Shelb

On PVoutput.org, how do you find systems that have collector panels with a total kW rating that is larger than the kW rating of the inverter ?

Posted Thursday 7 Mar 2013 @ 5:18:16 am from IP #
Shelb
Member

TonyT - tediously! Running the cursor down the system size column, looking for an inverter size that is smaller than system size. Sometimes I am tricked by the inverter size which might say 3000, but after clicking on the system for more detail, I discover there are actually 2 of them. Sometimes an unusual system size is a clue. Maybe there is another way but I have not discovered it yet. Search Tips provide good info but not for that. Perhaps another column with full inverter size would be helpful. If you have a system size in mind, try inputting that in search field, e.g. if you would like to see 7000kW systems, you are likely to strike some with 5kw inverters.

Off-Grid - yep, looks like 2x7. That should get me over the air-con hump without being greedy.

Posted Thursday 7 Mar 2013 @ 10:11:10 am from IP #
TonyT
Member

Thanks Shelb

There must be some way of searching without the tedium but I have not found it !

Posted Thursday 7 Mar 2013 @ 10:18:25 pm from IP #
johnmath
Member

Tony have you thought about contacting the site owner through the "About" tab? I would think this would be a worthwhile embellishment to the site.

Posted Friday 8 Mar 2013 @ 12:08:42 am from IP #
Shelb
Member

I will also - the more who do, the more successful we will be. So we are asking for another column which identifies the TOTAL inverter size, or at least a means to quickly search and identify those systems which are larger than the inverter size (trying to keep it non-negative and not using oversizing, over-clocking and over-driving words), in order to observe the benefits of such a system.

Posted Friday 8 Mar 2013 @ 12:46:45 am from IP #
TonyT
Member

johnmath

Good idea: will do !

Posted Friday 8 Mar 2013 @ 3:50:45 am from IP #
ubhat892
Member

What are the effects on inverter and PV panels in a grid tied system when AC power is curtailed ?

Posted Saturday 17 Sep 2016 @ 11:23:31 am from IP #
Bushwalker
Member

ubhat892 said:
What are the effects on inverter and PV panels in a grid tied system when AC power is curtailed ?

A standard Inverter shuts down when mains power is dropped.

Posted Saturday 17 Sep 2016 @ 10:43:01 pm from IP #
ubhat892
Member

That's OK, but I am asking when grid is not able to consume all the power generated by the inverter so in that case what are the effects of that residual power on the inverter or PV modules ?

Posted Sunday 18 Sep 2016 @ 8:32:45 am from IP #
Off-Grid
Member

That's not a situation that arises in practice, the grid takes it all.
In the case of a 5kW export limit imposed by the electricity company, with a larger inverter and PV array, some inverters can be configured to limit exports, and they just raise the voltage (above the maximum power point) at which the panels are normally operated (which reduces output power) until their output matches local load + output.

Posted Sunday 18 Sep 2016 @ 10:44:21 pm from IP #
ubhat892
Member

So whether this process in any way badly effects our solar modules or not ?

Posted Monday 19 Sep 2016 @ 4:50:44 am from IP #
Bushwalker
Member

Maybe explain your situation?

Posted Monday 19 Sep 2016 @ 5:24:10 am from IP #
Off-Grid
Member

I'm not entirely clear about what process you are referring to... the grid going down?

That will have no bad effects on panels.

Posted Monday 19 Sep 2016 @ 5:42:47 am from IP #
APR
Member

ubhat892 said:
...I am asking when grid is not able to consume all the power generated by the inverter so in that case what are the effects of that residual power on the inverter or PV modules ?

At this point in time the grid should be able to take all residential solar generated energy. However, if there is more solar energy being generated and sent to the grid than the local grid is designed to handle, you will find the grid voltage rising. Inverters have a maximum voltage at which they are designed to keep working, and so if the grid voltage rises above that voltage the inverter will shut down. The panels will be OK, and inverters are designed to handle voltages above the shutdown voltage without damage.

Posted Monday 19 Sep 2016 @ 7:14:47 am from IP #
ubhat892
Member

Like if my solar farm is generating 1 MW and load dispatch centre tells to curtail my solar farm output from 1 MW to 500 kW so in this case I will limit my inverter's output to 500 kW. I am asking now whether this throttling of inverter will adversely affect my inverter or PV module in any way ?

Posted Monday 19 Sep 2016 @ 10:16:28 am from IP #
Off-Grid
Member

Bushwalker>> Maybe explain your situation?

ubhat892>> Like if my solar farm is generating 1 MW...

I'm pretty sure that anyone with a 1MW solar power station knows that it isn't a problem, nor will it be a problem if you expand to 10MW

Anyway, it is unlikely you'd be using a 1MW inverter, much more likely to have a number of smaller inverters, some of which you could turn off.

Posted Monday 19 Sep 2016 @ 10:44:51 pm from IP #

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