Solar Calculator or basic Math?

[van-gogh]

Solar Calculators:

I have some basic understanding of math skills. I did a forum search and found nothing relating to "Solar Calculator(s)"

So some simple questions as to the best and most accurate method to arrive at an answer? (Meaning how would anyone know the output watts stated on a panel are factual readings for the watts shown?)

Anyone have a mathematical formula for converting Solar watts into basic outputs of AMPS, VOLTS, etc.

A real handheld calculator?

A website link?

pencel and paper math?

So that anyone wanting to know what they are getting from a solar panel output?

And without going too far out into cyberspace is they're a method to knowing the real watts coming from a solar panel?

Thanks.

[LJowdy]

Knowing the """exact""" output isn't going to make things better. I'd just trust your meter and go by what it says. If it ain't broke don't fix it.

[Winterbagoal]

https://www.wholesalesolar.com/solar...rid-calculator

https://www.gogreensolar.com/pages/h...nels-do-i-need

https://pvwatts.nrel.gov

https://www.altestore.com/store/calc...id_calculator/

This is what I searched on....there are plenty of these types of estimators....
https://www.google.com/search?source...sclient=psy-ab

Most are for off grid homes and so on, but a panel is a panel, watts are watts, amps are amps, and so on.

I've seen threads that do the watts to amps to volts conversions on several forums.
Maybe this search will help?
https://www.google.com/search?source...sclient=psy-ab

[van-gogh]

Originally Posted by LJowdy

Knowing the """exact""" output isn't going to make things better. I'd just trust your meter and go by what it says. If it ain't broke don't fix it.

Sorry, did I say I had a meter? No, I have no meter.

[van-gogh]

Originally Posted by Winterbagoal

https://www.wholesalesolar.com/solar...rid-calculator

https://www.gogreensolar.com/pages/h...nels-do-i-need

https://pvwatts.nrel.gov

https://www.altestore.com/store/calc...id_calculator/

This is what I searched on....there are plenty of these types of estimators....
https://www.google.com/search?source...sclient=psy-ab

Most are for off grid homes and so on, but a panel is a panel, watts are watts, amps are amps, and so on.

I've seen threads that do the watts to amps to volts conversions on several forums.
Maybe this search will help?
https://www.google.com/search?source...sclient=psy-ab

I have seen all but 2 of the above websites for "HOMES Solar and maybe I was not clear when asking about the math formula used to calculate the math. I understand 2+2, but 200 x 240-mins =48,000 watts or time I have no idea as his video says time and time again on and off-grid, a true salesman at work. But no MATH?

I do understand you are trying to help. BUT I DO NOT KNOW HOW TO BE MORE CLEAR THAN I WAS about the "MATH" Thanks I know you're trying to be helpful, as I am only looking for the math side of solar as I stated above. Thanks for your help.

[van-gogh]

Thanks to everyone I found this searching the web for the STATE of Florida:

https://sunshineworks.com/pages/sola...-power-systems

Watts to Amps calculatorlogy:
https://www.calculatorology.com/watt...ps-calculator/

[RVingNow]

The math is pretty simple but it probably won't help much. Watts = Volts x Amps. So a 100 watt panel will produce 8.3a at 12v or as your battery nears capacity 7.1a at 14v. But remember the 100 watt rating is best case conditions usually found in labs, so your mileage will vary. The biggest issue is exposure including angle to the sun, height of the sun, latitude, altitude, clouds...

A simple solution to know what's happening with you solar output, which fits well with the example above, is a cheap meter like this from ebay $3.
1pc DC 100V 10A Voltmeter Ammeter Blue+Red LED Dual Digital Volt Amp Meter Gauge ( I would have posted the link but it was really long)

No other parts needed since the meter includes the shunt to handle up to 10amps. When wired correctly this can monitor both the voltage and amperage the panel produces.

Good Luck

[MN_Traveler]

Dog man - are you concerned about the issue that panels appear to be rated in watts ... and controllers appear to be rated in amps ... and how do you compare the two?

[AnotherMike]

Originally Posted by Dogman635UT

Anyone have a mathematical formula for converting Solar watts into basic outputs of AMPS, VOLTS, etc.

(snip)

And without going too far out into cyberspace is they're a method to knowing the real watts coming from a solar panel?

The biggest problem is that a solar panel puts out variable power. It's not like shore power or a generator. As such you are not gong to power your MH from it, you are going to run the MH on batteries and the solar is used as a battery charger.

I acquired my first solar panels - four "12 volt" panels - over 40 years ago. When set up in my back yard I was seeing anything from 6 to 17 volts at up to 2 amps per panel. Naturally anything approaching the rated power was only at solar noon on a clear day in mid-summer.

Another variable that you have to consider is the panel mounting method... Most RVs with solar panels have them mounted flat to the roof. You will see some that have tiltable mounts (especially boondockers). They park their RV broadside to the sun in a location where they can tilt the panels to better present the face of the panel to the sun... Tiltable panels can increase the power level by a large amount...

Personal experience: my four panels wired in parallel and in the homebrew mount would produce a peak of a little more than 8 amps with the sun directly overhead. I saw only about 40% to 50% with the morning or evening sun.

Now to answer your question:
To properly size a system to you needs you need to FIRST quantify your needs... find out how much power you actually use... and you only get those numbers by installing a shunt-based battery monitor on your house battery bank... and logging that info for a worst-case month.

Next figure out what you can do to reduce your needs. Obviously use LEDs instead of incandescent lighting. Maybe play snowbird and go north for the summer to reduce your air conditioning needs.

One friend commented that a 100-watt panel can produce about 25-30 amp-hours per summer day, so if you know what your needs are you have a starting guess as to how much solar generation you need.
If you are going to be a fulltimer year-round person you will need to size your solar system for the shorter winter day. That will need more solar panels than someone who stores his RV for half of the year and only uses it in the summer.

To calculate the size of your solar photovoltaic system you need to:

1) Determine your kWh energy requirement. You an get that from your battery monitor, it's measured in WattHours or KilloWattHours. Call that number EU for Energy Used. Keeping a logbook for 3-4 months and averaging them will result in more accurate numbers.
Look here: http: // www.jenericramblings.com/2017/03/30/battery-meters-an-rv-must-have/

2) Determine how many solar hours you get per day. Call it SH for Solar Hours.
And as said above a winter day will have much less solar production than a summer day.

3) Divide your EU by SH to get the panel output you need. So you are dividing KilloWattHours by Hours and getting KilloWatts. Call that ER for Energy Required.

Then divide the ER by the Panel Watts rating to get the total number of solar panels for your system.

However that ER number is an constant for every hour of the solar day, and it's not constant! Because you don't have full sunlight for the morning and evening you will have to pad that panel count. And because the panels will be flat to the roof you will have to pad the panel count some more. And unless you park in full sun all the time you will have to pad it even more.

Here is a very basic calculation page intended for a sticks-and-bricks home but the concepts and techniques are the same:
https: // www.solarpowerauthority.com/how-to-size-a-solar-pv-system-for-your-home/

However the panel watts numbers you see on solar panel spec sheets or advertisements is naturally for an ideal situation: flat facing the sun (i.e. directly overhead) in the summer. Those numbers are peak numbers that are only useful to marketing weenies do write brochures from. And they always round the numbers up. I always discount spec sheets by 40% to 50%.
The following link if for a 6-times-a-year magazine that was devoted to home-made power. They went under recently but the index and all of their back issues are available for download.
There is a tremendous amount of information on solar systems here. Some is dated however.
https: // www.homepower.com

Before you start laying out $$$ you should learn about solar charge controllers (PWM or MPPT), low voltage disconnects, state of charge, how wire size can make or break a system, and a lot more.

And think about this: What will you do if you have a solid week of overcast days? Or even two weeks? You may want to keep your generator...

One useful writeup: "The 12 volt side of life".
There is 2 versions out there - one long PDF and a pair titled "Part 1" and "Part 2".
Part 1: www.marxrv.com/12volt/12volt.htm
Part 2: www.marxrv.com/12volt/12volta.htm

Then there's the HandyBob writeups... well worth reading:
https://handybobsolar.wordpress.com

Mike

[van-gogh]

Originally Posted by MN_Traveler

Dog man - are you concerned about the issue that panels appear to be rated in watts ... and controllers appear to be rated in amps ... and how do you compare the two?

NO sir, just trying to focus on the math to better understand its relationship of power following through each piece of equipment.

[van-gogh]

Originally Posted by AnotherMike

The biggest problem is that a solar panel puts out variable power. It's not like shore power or a generator. As such you are not gong to power your MH from it, you are going to run the MH on batteries and the solar is used as a battery charger. {This I do UNDERSTAND and Thanks}

I acquired my first solar panels - four "12 volt" panels - over 40 years ago. When set up in my back yard I was seeing anything from 6 to 17 volts at up to 2 amps per panel. Naturally anything approaching the rated power was only at solar noon on a clear day in mid-summer.{I'm impressed with time under solar and all the helpful links. I do understand that panels don't always put out as stated. I'm trying to focus on the MATH between the equipment parts}

Another variable that you have to consider is the panel mounting method... Most RVs with solar panels have them mounted flat to the roof. You will see some that have tiltable mounts (especially boondockers). They park their RV broadside to the sun in a location where they can tilt the panels to better present the face of the panel to the sun... Tiltable panels can increase the power level by a large amount... {YES, This I fully understand, thanks as some reading may not}

Personal experience: my four panels wired in parallel and in the homebrew mount would produce a peak of a little more than 8 amps with the sun directly overhead. I saw only about 40% to 50% with the morning or evening sun.

Now to answer your question:
To properly size a system to you needs you need to FIRST quantify your needs... find out how much power you actually use... and you only get those numbers by installing a shunt-based battery monitor on your house battery bank... and logging that info for a worst-case month.

Next figure out what you can do to reduce your needs. Obviously use LEDs instead of incandescent lighting. Maybe play snowbird and go north for the summer to reduce your air conditioning needs.

One friend commented that a 100-watt panel can produce about 25-30 amp-hours per summer day, so if you know what your needs are you have a starting guess as to how much solar generation you need.
If you are going to be a fulltimer year-round person you will need to size your solar system for the shorter winter day. That will need more solar panels than someone who stores his RV for half of the year and only uses it in the summer.

To calculate the size of your solar photovoltaic system you need to:

1) Determine your kWh energy requirement. You an get that from your battery monitor, it's measured in WattHours or KilloWattHours. Call that number EU for Energy Used. Keeping a logbook for 3-4 months and averaging them will result in more accurate numbers.
Look here: http: // www.jenericramblings.com/2017/03/30/battery-meters-an-rv-must-have/

2) Determine how many solar hours you get per day. Call it SH for Solar Hours.
And as said above a winter day will have much less solar production than a summer day.

3) Divide your EU by SH to get the panel output you need. So you are dividing KilloWattHours by Hours and getting KilloWatts. Call that ER for Energy Required.

Then divide the ER by the Panel Watts rating to get the total number of solar panels for your system.

However that ER number is an constant for every hour of the solar day, and it's not constant! Because you don't have full sunlight for the morning and evening you will have to pad that panel count. And because the panels will be flat to the roof you will have to pad the panel count some more. And unless you park in full sun all the time you will have to pad it even more.{Very informative and keeping a logbook is a great idea and all of the above is helpful thanks for sharing}

Here is a very basic calculation page intended for a sticks-and-bricks home but the concepts and techniques are the same:
https: // www.solarpowerauthority.com/how-to-size-a-solar-pv-system-for-your-home/

However the panel watts numbers you see on solar panel spec sheets or advertisements is naturally for an ideal situation: flat facing the sun (i.e. directly overhead) in the summer. Those numbers are peak numbers that are only useful to marketing weenies do write brochures from. And they always round the numbers up. I always discount spec sheets by 40% to 50%.
The following link if for a 6-times-a-year magazine that was devoted to home-made power. They went under recently but the index and all of their back issues are available for download.
There is a tremendous amount of information on solar systems here. Some is dated however.
https: // www.homepower.com

Before you start laying out $$$ you should learn about solar charge controllers (PWM or MPPT), low voltage disconnects, state of charge, how wire size can make or break a system, and a lot more.

And think about this: What will you do if you have a solid week of overcast days? Or even two weeks? You may want to keep your generator...

One useful writeup: "The 12 volt side of life".
There is 2 versions out there - one long PDF and a pair titled "Part 1" and "Part 2".
Part 1: www.marxrv.com/12volt/12volt.htm
Part 2: www.marxrv.com/12volt/12volta.htm

Then there's the HandyBob writeups... well worth reading:
https://handybobsolar.wordpress.com

Mike

Mike,
I very much enjoyed reading and will review the links and will create a link from this post to my group in this forum to help others. A little more of a background story about me. I have never owned anything SOLAR and soon we will be jumping into a complete 2021 Class B with no stand-alone generator. I do know solar is not the only place power will come into the van from. I have set about learning and understand each component and how they all work in relationship/concert to one another. This kind of RV is new to me, but I enjoy learning and looking forward to this new adventure. I am looking forward to a night out in the woods or RV park with little or no noise from us, but from nature and would be incredible if a deer should walk up unannounced. My question was to understand the math. but your post has been eye-opening and informative, thanks for sharing.

[van-gogh]

Originally Posted by RVingNow

The math is pretty simple but it probably won't help much. Watts = Volts x Amps. So a 100 watt panel will produce 8.3a at 12v or as your battery nears capacity 7.1a at 14v. But remember the 100 watt rating is best case conditions usually found in labs, so your mileage will vary. The biggest issue is exposure including angle to the sun, height of the sun, latitude, altitude, clouds...

A simple solution to know what's happening with you solar output, which fits well with the example above, is a cheap meter like this from ebay $3.
1pc DC 100V 10A Voltmeter Ammeter Blue+Red LED Dual Digital Volt Amp Meter Gauge ( I would have posted the link but it was really long)

No other parts needed since the meter includes the shunt to handle up to 10amps. When wired correctly this can monitor both the voltage and amperage the panel produces.

Good Luck

Thanks I happen to have one which I had used for other things. But found how to test and here is one of the long links. https://www.bing.com/videos/search?q...6FORM%3DVDVVXX

[KanzKran]

Originally Posted by RVingNow

No other parts needed since the meter includes the shunt to handle up to 10amps. When wired correctly this can monitor both the voltage and amperage the panel produces.

Just a friendly warning to those not used to working with multimeters - units like the Flukes have an 11A fuse in there that's a little pricey. If you forget that it's set for current instead of voltage, with the red lead in the "10A" port, and stick the probes into something with unlimited current like a 120V receptacle, it'll cost you another fuse, or worse. I'm sure they all have a fuse of some sort; I'm just familiar with Fluke and a couple of cheap-o's.

Even after half a century of using multimeters, I still do that every once in a while.

[AnotherMike]

> ...units like the Flukes have an 11A fuse in there that's a little pricey.

Not only are they pricey, they're hard to find. I now have the local McMaster-Carr and Grainger stores in my phone contacts list... they are the only ones that stock the Fluke fuses in my area.... I now have 3 sets of Fluke fuses in a baggie in my Fluke meter case.


Mike