500watt vs 1000watt solar...... difference?

[jenevers]

Apologies in advance to whoever took all the trouble to produce this spreadsheet - I kept it bit did not keep a note of the author.

 

It is an excellent piece of work for calculations regarding solar requirements.

 

1) Do your electrical usage audit, entering the information on the left of the table.

2) Enter your battery bank size

3) Enter the size of your solar array

4) Enter your location

 

The spreadsheet will tell you

1) How many months the solar will supply your usage

3) Alternative solar requirements.

 

Thanks for this info.

I downloaded sheet 1 but can't get any further with the spreadsheet to enter battery size etc

Any suggestions?

[WotEver]

Someone with better knowledge may come along and correct me but the wattage isn't the important part of the equation, it's the amps.

 

Sure, I'll disagree with you wholeheartedly because you are wrong.

 

The power of the panel (wattage) is absolutely the most important part of the equation. The higher the power output the higher the maximum current at charging voltage and the more months that you will produce usable energy.

 

Obviously, as has been pointed out to you by Phil (which you argued with), it is important to match the controller to the panels. Taking an example of 1000W of panels with a maximum voltage of 100V feeding a 12V bank you'd want a 90A MPPT controller with a maximum input voltage >120V. There's nothing special about that, it's simply a case of using the appropriate controller for the panels which you have chosen.

 

Tony

[Alan de Enfield]

Thanks for this info.

I downloaded sheet 1 but can't get any further with the spreadsheet to enter battery size etc

Any suggestions?

 

Enter you battery bank size (sheet 1) under "battery fitted"

Choose latitude - click on the box and then choose 55 from the drop down box

Under the 'enter max power' put in your proposed solar size (500, 1000 or whatever)

 

Try this version.

Solar Panel Calculator.xls

[MarkHez]

And I'm now understanding why I've read this forum for several years and refrained from posting on it!

Because when you do post, you give out bad advice that can cause damage to solar charge controllers?

[Paul C]

Because when you do post, you give out bad advice that can cause damage to solar charge controllers?

 

In fairness, I think I know what he means and there's a school of thought which says you can save money by installing a controller which is "too small" for the panels. The controller won't blow up, but it will limit its output to (actually slightly above) its max rated current.

 

The reason you might do this is this: Let us take an example of a 1000W array of solar panels, but a controller which is only 50A, in other words it can only do 12x50 = 600W of power. In summer, you have the 1000W array capable of generating............1000W.....but you don't need all that power except for the very start of battery charging a flat bank where its in bulk phase. Charging takes a bit longer, but you have all day to do it....etc

 

Now in winter, those 1000W panels can only generate 100W (assuming a reasonable 10% of summer output guideline). Had we sized the solar panels based on a summertime, we'd have probably only fitted 600W or less - but we oversized the array so that in wintertime it can generate 100W instead of 60W.

 

Of course, there will be times when you might say "I wish I had a bigger MPPT controller" and indeed if it were bigger, it would charge the batteries quicker or provide more available amps for something. Those times are probably in the spring and autumn. But there is a cost saving in not having that bigger controller. So its a balance to weigh up.

Edited April 21, 2016 by Paul C

[WotEver]

 

In fairness, I think I know what he means and there's a school of thought which says you can save money by installing a controller which is "too small" for the panels. The controller won't blow up, but it will limit its output to (actually slightly above) its max rated current.

 

For max current, sure. But not max Voc - that is the route to escaping magic smoke.

 

Tony

Edited April 21, 2016 by WotEver

[jenevers]

Enter you battery bank size (sheet 1) under "battery fitted"

Choose latitude - click on the box and then choose 55 from the drop down box

Under the 'enter max power' put in your proposed solar size (500, 1000 or whatever)

 

Try this version.

Nope! Can't enter anything at all. Can't even see "battery fitted"!!

[WotEver]

Nope! Can't enter anything at all. Can't even see "battery fitted"!!

 

Works for me on both Open Office and MS Office (Excell).

 

Did you download it and run it from your PC?

 

Tony

[Alan de Enfield]

Nope! Can't enter anything at all. Can't even see "battery fitted"!!

 

How odd !

There is only one sheet so

Sheet 1, line 39 column c/d fill in line 39 column e

Edited April 21, 2016 by Alan de Enfield

[jenevers]

How odd !

There is only one sheet so

Sheet 1, line 39 column c/d fill in line 39 column e

This is what I'm getting on my iPad.

 

Solar Data

LOADS Current Wattage Hours run Watt Hours

per day per day Sun hours Horizontal 1kW/m²

Lights Fluorescent 1,300 15,60 4 62,4 Month 51ºN 55ºN 59ºN

Light Toilet 1,050 12,60 1 12,6 Jan 0,8065 0,4516 0,25

Light Bedside 4,300 51,60 0,5 25,8 Feb 1,6140 1,0526 0,69

Toilet Flush 0,00 0,01 0 Mar 2,4839 1,9355 1,51

Toilet Full light 0,005 0,06 0 Apr 4,2333 3,2000 2,42

Water Pump 0,00 0,25 0 May 5,0968 4,0968 3,29

Fridge standby 0,060 0,72 24 17,28 Jun 5,3000 4,4667 3,76

Fridge running 3,620 43,44 2,4 104,26 Jul 5,2258 4,1290 3,26

TV standby 0,013 0,16 24 3,744 Aug 4,5161 3,3871 2,54

TV on 4,000 48,00 1 48 Sep 3,1667 2,2667 1,62

0,00 0 Oct 1,9032 1,2581 0,83

0,00 0 Nov 1,0667 0,6333 0,38

0,00 0 Dec 0,6452 0,3548 0,20

0,00 0 1 2 3 4 2

0,00 0

0,00 0 Choose design month Mar

0,00 0

0,00 0 Choose Latitude 51ºN

0,00 0

0,00 0 Enter Max Power 50 W Derate for ageing 90%

0,00 0 Derate for Guaranteed 95%

Modules required 3,3 Derate for climate 100%

Total Watt hours/day 0.00 01

Total Amp Hr/day 0.00 7257600020 Modules to be fitted 2

 

Round trip efficiency 80% Energy Balance

Replacement AmpHr/day 0.00 4752000013

Degrade for ageing 90,00% Sunhours Wh per Day Wh req Day Daily Balance

Allowance for retaining charge 90,00% Jan 0,8065 55,2 274,08 -218,9

Feb 1,6140 110,4 274,08 -163,7

Autonomy in Days 2 Mar 2,4839 169,9 274,08 -104,2

Apr 4,2333 289,6 274,08 15,5_

BATTERY SIZE 0 4266666711 May 5,0968 348,6 274,08 74,5_

Jun 5,3000 362,5 274,08 88,4_

BATTERY FITTED 0 00 Jul 5,2258 357,4 274,08 83,4_

Aug 4,5161 308,9 274,08 34,8_

Sep 3,1667 216,6 274,08 -57,5

Oct 1,9032 130,2 274,08 -143,9

Nov 1,0667 73,0 274,08 -201,1

Dec 0,6452 44,1 274,08 -230,0

 

Equivalent derated Wh of Battery 544,32

Reserve

Days % surplus

Jan -2,5

Feb -3,3

Mar -5,2

Apr 3%

May 14%

Jun 16%

Jul 15%

Aug 6%

[Alan de Enfield]

You do have Microsoft office software don't you ? (or even 'open office' will do)

[jenevers]

You do have Microsoft office software don't you ? (or even 'open office' will do)

Err. No!

[Paul C]

Does it load okay on Google Sheeps?

[Alan de Enfield]

Err. No!

 

That may be the reason you cannot read it.

 

I didn't think there was anyone, anywhere in the world that didn't use MS Office.

You can buy the full unlocked software in the markets in Cambodia for US $1

Does it load okay on Google Sheeps?

 

Baaaa

Sheep are too stupid to use MS Office

[jenevers]

didnt know you could have Microsoft on iPads

Edited April 21, 2016 by jenevers

[WotEver]

didnt know you could have Microsoft on iPads

 

https://itunes.apple.com/gb/app/microsoft-excel/id586683407?mt=8

 

Tony

[Alan de Enfield]

didnt know you could have Microsoft on iPads

 

Many (most ?) travelling business men are using iPads (from what I have seen at airports) and Office is the international 'standard' for business communications.

I know my No1 Son definitely uses Office on his iPad.

[WotEver]

 

Many (most ?) travelling business men are using iPads (from what I have seen at airports) and Office is the international 'standard' for business communications.

I know my No1 Son definitely uses Office on his iPad.

 

https://products.office.com/en-gb/mobile/office-ipad

 

Tony

[Robbo]

didnt know you could have Microsoft on iPads

 

The mobile (ie tablet and phone) version of Microsoft Office is actually better on the Apple devices than the Windows Mobile devices! Microsoft have changed in recent years and are become a service company rather than "MS Windows". You can now get MS-SQL on Linux and they just announced running the bash shell and SSH directly in Windows.

[Jambo]

But generally the mobile versions of Excel are lacking a fair bit of important functionality so use with caution! Better to upload this spreadsheet to google sheets imo as it's pretty capable and should be usable by all (including mobile devices).

[Punk Stig]

Yep, Paul c understands me, sorry for not being articulate enough for you guys, I have to simplify things in my head to understand them, hence the simple way of calling a solar charge controller a 'charger' and then that's how I try to explain - so again, as it's been mentioned several times, and to clarify- check yourself that your system or the system you are buying has the required safety components so that if your panels are rated higher than the controller it won't go puff!

 

With regards to wattage, and this is the whole reason why I started the post with 'correct me if I'm wrong' because I'm happy to have it explained to me-

We have numerous choices in what panels to buy and use, from my investigation before purchasing I have the following figures to work on

100w panel on average has a maximum output of just over 5 amps

250w panel has on average a maximum output of just over 8amps

(by average I mean as a comparison between manufacturers)

In my simplistic mind I see that as 5x100w panels capable of providing a maximum of 25 amps, whereas 2x250w panels can only provide a maximum of 16 amps

Is my view of this incorrect please?

[Paul C]

Yep, Paul c understands me, sorry for not being articulate enough for you guys, I have to simplify things in my head to understand them, hence the simple way of calling a solar charge controller a 'charger' and then that's how I try to explain - so again, as it's been mentioned several times, and to clarify- check yourself that your system or the system you are buying has the required safety components so that if your panels are rated higher than the controller it won't go puff!

 

With regards to wattage, and this is the whole reason why I started the post with 'correct me if I'm wrong' because I'm happy to have it explained to me-

We have numerous choices in what panels to buy and use, from my investigation before purchasing I have the following figures to work on

100w panel on average has a maximum output of just over 5 amps

250w panel has on average a maximum output of just over 8amps

(by average I mean as a comparison between manufacturers)

In my simplistic mind I see that as 5x100w panels capable of providing a maximum of 25 amps, whereas 2x250w panels can only provide a maximum of 16 amps

Is my view of this incorrect please?

 

Basically what you'd do is rigidly follow the rule never to exceed the V_oc of the controller. This means that you might choose to wire panels up in parallel instead of series; or choose a different set of panels, or different controller, so they match. Put simply: match the controller to the panels.

 

Don't worry about whether 5x100W or 2x250W are better - they both equate to 500W

 

Once you've ascertained that the controller is appropriate for the panels, don't worry about volts and amps on the "solar" side - the MPPT controller will worry about this, vary it, and find the best voltage/amps for the given situation. After all, that's what MPPT controllers are good at.

 

Your system (ie the batteries....and the electrical devices) will still be 12V (or 24V...or whatever) irrespective of what's screwed onto the roof. So, with a given amount of sunshine, and a given total power generated by them panels (lets say its a lovely sunny day and the batteries are flat, so they are able to run at their max of 500W) the current input into the batteries (minus that consumed by loads) will be:

 

P = V x I

 

rearranged......

 

I = P / V

[WotEver]

Is my view of this incorrect please?

 

Yep.

 

a 100W panel can supply 8A at 12V.

a 250W panel can supply 21A at 12V.

 

The current you are quoting is at whatever the panel voltage happens to be. It's important to know the panel voltage simply because that's how you choose a suitable controller - the Voc must never exceed the maximum controller input voltage - but neither the Voc nor the quoted current at that voltage is particularly relevant. The most important figure by far is the power - the Wattage.

 

Another consideration is that higher voltage panels have the advantage that a suitable MPPT controller has a better ability to track the ideal power point.

 

Tony

 

ETA - Paul beat me to it with another explanation of the Power Law which explains more of what I've written above. Read his post and mine and between the two it will hopefully explain things to you.

Edited April 21, 2016 by WotEver

[Punk Stig]

Thankyou- I had no idea the quoted maximum power outputs of panels from their spec sheets could be exceeded and thus everything I said before me was based on those quoted amps and not panel wattages!

We got there in the end, right?

And also the precise reason I had a pro fit mine instead of diy!

[WotEver]

Thankyou- I had no idea the quoted maximum power outputs of panels from their spec sheets could be exceeded...

It's not exceeding the specs, it's just applying those specs correctly.

 

Tony