Thread: How do you know what is a good solar panel.

So many variables of PV module application in many different levels of resource. How would you rate them?

Easy.
Just like the car manufacturers have been forced to be more honest.
How about rating in full sun in various places in Australia.
The information on radiance is easily available from the BOM and average of summer and winter could be given.
That would be a hell of a lot more realistic than now.
Regards PhilipA

Originally Posted by PhilipA

Warning ! boring for those not interested!
I have been trying to work out why nowadays that all solar panels seem to be over rated enormously.
I think I have the answer.
The manufacturers have a rating system based on an input of 1000watts per square metre.
It is printed on the panel as here.
Trouble is that the total input of sunlight is 1360watts per square metre at the edge of the atmosphere for a horizontal surface.

The ACTUAL daily watts input at Avoca Beach for a horizontal surface yesterday (source BOM at the Avoca Bowling club weather station) was 2800watts per square metre for the entire day midnight to midnight.

Seeing the main sunlight is for 6 hours lets assume , then the average watts per square metre are about 450watts per square metre.

So the output of any solar panel rated at say 200 watts will actually be less than half of that advertised if at Avoca Beach..

I really do not know how the industry got away with such a spurious set of claims .
Regards PhilipA

STC and panel rating is not used the way you have described it.

A layman description from me,

A (genuinely rated) 250 Watt panel for instance has simply being put in a lit testing room where 1000 Watts of light per square metre (and room temp is 25 degrees C) is hitting the panel, the panels physical size has being calculated based on it's cells conversion efficiency so it has enough surface area to produce 250 Watts of power in that testing environment.

The best panels to use (if you have permanent mounting space) are CEC certified (so you know the sticker output is accurate) house panels coupled with a high input voltage MPPT tracker/charger.

Polycrystalline cells improved considerably a few years ago and are virtually on par with mono efficiency.

I have never bothered with 12/24 volt panels they are under performing and over priced. I have always used 35 V (60 cell) to 40 plus V (72 cell) house panels.

If you don't have a genuine need (i.e. space constraints) for flexible or folding panels don't buy them coz every one else does, get some new or used house panels as previous posters have.

Hey Phillip,, if you now have a van, why are you worrying about flexible panels?
5 to 3 seems to be the ratio for Aus,, (watts to Amphrs)

Originally Posted by PhilipA

Easy.
Just like the car manufacturers have been forced to be more honest.
How about rating in full sun in various places in Australia.
The information on radiance is easily available from the BOM and average of summer and winter could be given.
That would be a hell of a lot more realistic than now.
Regards PhilipA

There is nothing duplicitous about the STC data. There is just misunderstanding outside of the industry of the meaning and intent of it. The data you allude to above is best provided by a local salesman not the manufacturer.

If that sales info is not forthcoming, all I can do is suggest you learn how to design and size a system using the manufacturers information at hand like everyone else in the solar industry has to and everything will make sense.

As a first approximation you could use the "Peak Sun Hours method". There are many iterations of this online. In essence, it builds on the STC (1000W/m2 - based) rating system and is good for first approximations - "back of the envelope" calculations.

If you wanted to stay on approximations but analyse a bit more of whole "balance of system" system performance in design, AS/NZS 4509.2 Stand alone power systems Part 2: system design - Appendix A & B has a good set of worksheets. Libraries sometimes have this standard in their reference section.

If you like computer modelling, you can use HOMER Pro (HOMER Pro - Microgrid Software for Designing Optimized Hybrid Microgrids) to get a more specific and optimised design that gives a system with lowest Net Present Cost. I use this alongside PVSyst (PVsyst – Logiciel Photovoltaique). I think both these computer-based modelling systems have a free trial period. These models are data hungry so be prepared to go searching for the relevant data to make them produce useful results. As the saying goes, "nonsense in, nonsense out".

What I am saying here is that the industry standard of rating module output while not perfect, has been adopted by the industry for good reasons to be able to compare modules like-for-like and design methods have been implemented using the STC data that can be applied globally across all manufactured modules. It allows a system engineer/designer to decide which of the vast array of module types, sizes and rated output on the marketplace best suits the given load, time of use, local shading conditions, space, solar resource, financial conditions, etc. So many variables.

I am not talking home systems but folding or suitcase solar panels sold on ebay and elsewhere.

I know that The installers have computer tools to track sunlight etc, but this does not help the shmuck trying to size a solar panel to recharge his fridge battery while camping.

Re the caravan. It is early days yet but my caravan has a 3 way fridge so low battery use. My 100AH Lithium and all LEDs should provide power for many days.

I have a link to the second battery of the car for my DC/DC charger which is relay controlled to work on "accessory"

I can therefore charge the van battery by charging my car second battery and passing through to the van battery via the DC/DC charger.

I have yet to try all this due to lockdown but that is the theory, and why I want a bigger output solar setup than my current 120W folding.
Regards PhilipA

Hey Phillip,, if you now have a van, why are you worrying about flexible panels?
5 to 3 seems to be the ratio for Aus,, (watts to Amphrs)

It is early days with the van. It is a poptop so I would not like too much weight on it, as I would have to replace struts etc.
We shall see as time goes on. Because of lockdown, I have not used the van yet . I should be in Queensland now but have had to reschedule twice so far.

My plan is as per the above post .

Regards PhilipA

Originally Posted by Pedro_The_Swift

Hey Phillip,, if you now have a van, why are you worrying about flexible panels?
5 to 3 seems to be the ratio for Aus,, (watts to Amphrs)

If you plan to spend any time in Victoria or Tassie over Winter I'd go 2 to 1 at least. I'm sure that works fine particularly up in the Sunnier States (Yes I'm jealous at the moment - it's a cold week down here in Melbourne.) There's only a few weeks of the year I sick of the cold and given we're about at the point of the coldest weekend I'm about there. It is supposed to be 18 next Tuesday though so a glimmer of hope. To all those with warmth and sunshine today - enjoy - we're heading for a heady top of 9 today...

Originally Posted by PhilipA

I am not talking home systems but folding or suitcase solar panels sold on ebay and elsewhere.

I know that The installers have computer tools to track sunlight etc, but this does not help the shmuck trying to size a solar panel to recharge his fridge battery while camping.

Re the caravan. It is early days yet but my caravan has a 3 way fridge so low battery use. My 100AH Lithium and all LEDs should provide power for many days.

I have a link to the second battery of the car for my DC/DC charger which is relay controlled to work on "accessory"

I can therefore charge the van battery by charging my car second battery and passing through to the van battery via the DC/DC charger.

I have yet to try all this due to lockdown but that is the theory, and why I want a bigger output solar setup than my current 120W folding.
Regards PhilipA

I don't know squat about pop tops and what can be put on the roof but a 250 Watt house panel ( CEC approved so you have confidence in the label ) weighs 18 kg and will give you about 30 odd volts and 8 amps output under ideal conditions (full sun).

If it is not certified by a testing authority, which most flexible folding suitcase panels don't seem to be, the sticker on the panel means squat which is why I am pushing for 'house' panels .

You don't need complicated formulas and precise interpretation of the testing conditions just 'rule of thumb' and a good idea of the total draw in watts of your loads.

Unless you are hell bent on flexible portable suitcase panels for storage/carrying reasons I would go a fixed roof panel if you are chasing cost effective power production.

Also the higher the voltage of the panel the earlier it will fire up the MPPT controller in the morning light and it will stay on later as the light fades eking out every little millwatt before shutdown at night.