Daily PV panel output

I'm looking for websites/software where I lookup all sorts of info about solar panels.
- Historical  kWh output.
- Output forecast.
- Optimal orientation of the panels (throughout the day)
- Nice graphs.

I once found such a site. Free. I allowed me to configure all sorts of things like the location were I live, how many panels I have etc.
I lost the link, and that's why I'm here to ask if anyone knows about a website and/or software that provides such data.
Must be Windows software or work in a browser. I'm not really interested in anything that only works on a phone.

The average for USA is 4hr per day (5hrs in the summer and 3hrs in the winter).
So if you installed a 10,000W solar array you would produce:
Summer Production = 10KW x 5Hr = 50KWHr per day
Avg Production = 10KW x 4Hr = 40KWHr per day
Winter Production = 10KW x 3Hr = 30KWHr per day

It's usually cheaper and better to just install more solar panels on the roof vs fussing about tilt angle or worse solar tracking. A 10degree tilt angle is enough for the solar panel to be self-cleaning.

Price = $20,000
$6,000 Solar Array 10,000W (1,200KWHr/month)
$1,500 Solar Array Support
$6,000 ChargeController/Inverter 12KW SolArk
$6,000 Battery Bank (LiFePO4) 12KWHr
Self-Labor + $500 for electrician stamp/double check

BuildItSolar has a list of sites here: https://builditsolar.com/References/SunChartRS.htm one of those might have some info for you.

There are sites like https://unboundsolar.com/solar-information/sun-hours-us-map which give some general numbers for the annual average hours per day. I would think that it really depends if you are doing this on-grid or off-grid though, as on-grid it's usually about generating the most power on average and filling in with grid power otherwise.

Off-grid on the other hand, it's usually about having enough power during the shortest winter days while staying above the minimum charge levels of your battery system. A site that gets say 4 hours of average annual daily sun may get 1-1.5 hours on a winter day, and some locations have mostly clear winter days while others are almost always overcast which causes a big drop in power production. There you might find pitching your panels perpendicular to the winter solstice or near that works best, again depending when you normally have a lot of overcast days.

As to the cost, to compare to the above values I'm taken the "conservation first" approach and my power use is usually under 3kwh/day, and my solar setup is 1200w in panels and about 5.2kwh of storage (2.6kwh usable, used lead acid batteries). All the parts including cabling cost me just under $2000US after taxes. It's not grid tied which saves a lot.

S Bengi wrote:
It's usually cheaper and better to just install more solar panels on the roof vs fussing about tilt angle or worse solar tracking.

I'm not planning on tracking but I might optimize for a certain season.
Or I may do 'tracking' by manually changing the angle 2 or 4 times a year.

A 10degree tilt angle is enough for the solar panel to be self-cleaning.

Once found an app with its location always defaulting to Spain. The all around optimum angel it gave was horizontal, all year around. Great output but also a lot of cleaning.
According to this site solar tracking is vastly overrated. Not just because it's expensive, but also because minimal yield differences.
He starts with saying most calculations are only true when you live on a planet without an atmosphere. Refraction, diffusion, pollution, clouds, etc all change the optimum.
His conclusion:

For example, when I set my tilt angle to 25° - a pretty large deviation from the optimal tilt - it results in only a 1% reduction in overall annual power generation.

Why is this? Buffalo is often fairly cloudy, which means that diffuse light plays a large role in the power generation for my system. Because the light is diffuse, it doesn’t matter as much if the panels are perpendicular to the sun.

His optimal tilt is 33° and a 8° deviation only gives 1% difference.
This is likely old info for most around here but not for me. I own exactly 0 kW in solar panels.
I'm researching a bit to make the best choice for my situation.





https://www.thesolarnerd.com/blog/optimal-solar-panel-tilt-most-calculators-are-wrong/

Mark Brunnr wrote:BuildItSolar has a list of sites here: https://builditsolar.com/References/SunChartRS.htm one of those might have some info for you.

There are sites like https://unboundsolar.com/solar-information/sun-hours-us-map which give some general numbers for the annual average hours per day. I would think that it really depends if you are doing this on-grid or off-grid though, as on-grid it's usually about generating the most power on average and filling in with grid power otherwise.

Those links are like a treasure chest for me...


Few links I've collected:
TILT:
http://www.solarelectricityhandbook.com/solar-angle-calculator.html
https://footprinthero.com/solar-panel-tilt-angle-calculator
https://solarsena.com/solar-panel-tilt-angle-calculator/
http://www.solarelectricityhandbook.com/solar-angle-calculator.html

https://www.thesolarnerd.com/blog/optimal-solar-panel-tilt-most-calculators-are-wrong/
https://www.thesolarnerd.com/calculator/

kWh forecast

Forecast Solar - Extremely basic
https://forecast.solar/
https://doc.forecast.solar/doku.php?id=api:estimate

https://api.forecast.solar/estimate/:lat/:lon/:dec/:az/:kwp
https://api.forecast.solar/estimate/45.67890/4.56789/123

SOLAR ATLAS - Best
https://globalsolaratlas.info/map?s=45.67890,4.56789&m=site

PVWatts® Calculator - Good
https://pvwatts.nrel.gov/pvwatts.php
https://www.energy.gov/eere/solar/sunshot-2030

I'm a bit confused about what the voltage of the panel is.
The warning states "Solar module has full voltage even in very low light"
I guess that's the  Voc of 21.0V.
The working voltage is 17.5 Vmp when under full load (100 Watt)

Does that mean if I connect a 50Wattt load the voltage is about halfway open and full load voltage?

My main question is this. Suppose I permanently connect a 200 Watt, 24V heater directly to the panel without any regulating electronics in between.
Will it damage the panel because it will be in constant overload?
Will the minimum voltage be 17.5V even when overloaded (or short circuited)?
Will the panel deliver between 0-100W to the heater depending on the strength of the sun?


PS. I'm aware a 200W, 24V heater will have a lower rating at 17.5V. I just don't want to overcomplicate my question

17.5V x 5.8A=101.5W
As soon as you apply any load to the solar panel it pretty much drop to 17.5V immediately.

This 100W or 17.5V solar panel is what we would call a 12v solar panel.
So it is recommended that you connect a 12v heater/load/battery and not a 24v heater/load/battery.
The panel will vary rarely produce 100W instead it will look closer to this:
6am-10am(25W/hour)
10am-2pm(75W/hour)
2pm-6pm (25W/hour)
So a 75W heater is probably better.

Will the output voltage always be stable at 16.5 volt but the current depends on the brightness of the sun?

If yes, does it really matter how big the load is?
To put this to the extreme, if I would connect a 12v, 2kW heater would it just heat between 0-100Watt depending the brightness of the sun?
Or will that damage the panel.

Tony Masterson wrote:Will the output voltage always be stable at 16.5 volt but the current depends on the brightness of the sun?

If yes, does it really matter how big the load is?
To put this to the extreme, if I would connect a 12v, 2kW heater would it just heat between 0-100Watt depending the brightness of the sun?
Or will that damage the panel.

you will not damage the panel by shorting it through a heater.ake sure the heater is made for the load and it does not have any kind of fan which would be voltage sensitive. Always remover your power math : voltage is just potential it's not power. So power (in watts) is voltage x current.
As for tilt angle it depends where you are. For southern Ontario we start with latitude for optimum angle and adjust seasonally. So 45 degrees is the base and we use that for spring and fall, in the suer we subtract 15 to degrees and in the winter we add 15 degrees. Depending on when you want to maximize you could build a fixed angle as well...
Cheers, David

Overloading a solar panel with a load higher than what it is rated for, will not give you max power production unfortunately. But your solar panel will not be damaged, some electronics/motors might have some problems but with the "dumb" resistive heater that you gave as an example it too would be fine. In general it's a not the best idea to purposely overload a solar panel/circuit.