I am currently working on a project that uses a 6v 4.5Ah battery and 12v solar panel. The battery is connected to a buck converter set to 5v and this powers an arduino and lcd screen directly. When running, the system draws about 60mA-100mA. The specs for the solar panel are
1260mW, charge rate: 70mA. These specs are from the manufacturer so I doubt they are real-world.

The solar panel was bought before the project was put together. Evidently that was a mistake since the panel is under powered. I have looked all over and I can't seem to find a calculation for determining the specs for the solar panel that I need.

Can someone provide a formula on how to calculate this?

 

Use the one you have to size the one you need. The alternative is to calculate the position of the sun in all seasons and all times of day, subtract clouds and tree shade, the angle of the panel east to west and above the horizon, dirt accumulation and cleaning schedule...

Get it? Take the easy way or the hard way. Your choice.

 

A simple method: http://www.solartechnology.co.uk/faqs/calculating-your-solar-requirments

I would over panel the project by 2X if you have the money and space for it.

 

A simple method: http://www.solartechnology.co.uk/faqs/calculating-your-solar-requirments

That was a great page for a UK resident, but it said little to nothing about Florida, Oregon, or wherever shutterb is, unless, by some serious luck, shutterb is in the UK.

ps, I am suddenly happy that I don't live in England. Not enough sunshine!!
All last week was rain here, and I feared I'd go all cabin fever.

 

That was a great page for a UK resident, but it said little to nothing about Florida, Oregon, or wherever shutterb is, unless, by some serious luck, shutterb is in the UK.

ps, I am suddenly happy that I don't live in England. Not enough sunshine!!
All last week was rain here, and I feared I'd go all cabin fever.

I picked it because it's close to worst case year round for a solar powered device. If he can make it work there it's good for just about anywhere easily. People new to solar almost always under-panel for the needed loads.

 

You can start with raw watts and work from there. Your 5 V load is 100 mA, for 0.5 W. Factor in 80% efficiency in the buck converter, and you're up to 0.625 W. To charge the battery at a reasonable pace you want the charging current to be 1/10 of the amp-hour rating, so that's 5.4 W at 12 V if you don't want to do another switching converter. So, 6 watts plus margin for solar cell efficiency, clouds, etc.

ak

 

I appreciate the help. Unfortunately the cost of the panel that I need is out of budget right this second. I am wondering if I could simply swap the solar panel out for a 6v battery float charger for the time being. Thoughts?

 

I appreciate the help. Unfortunately the cost of the panel that I need is out of budget right this second. I am wondering if I could simply swap the solar panel out for a 6v battery float charger for the time being. Thoughts?

Sure, if it's the proper charger for your battery type.

 

You can start with raw watts and work from there. Your 5 V load is 100 mA, for 0.5 W. Factor in 80% efficiency in the buck converter, and you're up to 0.625 W. To charge the battery at a reasonable pace you want the charging current to be 1/10 of the amp-hour rating, so that's 5.4 W at 12 V if you don't want to do another switching converter. So, 6 watts plus margin for solar cell efficiency, clouds, etc.

ak

So if I am understanding correctly, something like this http://www.ebay.com/itm/10W-12V-sol...224?pt=LH_DefaultDomain_0&hash=item5668cf7e60 should work?

 

So if I am understanding correctly, something like this http://www.ebay.com/itm/10W-12V-sol...224?pt=LH_DefaultDomain_0&hash=item5668cf7e60 should work?

Look for 6 volt ones.
http://www.ebay.com/itm/Solar-Panel...053?pt=LH_DefaultDomain_0&hash=item463b687495

 

I think this article will help to calculate everything:

http://www.homemade-circuits.com/2013/05/how-to-calculate-and-match-solar-panel.html