Charging duration

[misango]

hi there, I am just asking how long will it take for 15w solar pannel to charge a 100amphrs battery. If any one knows how to calculate this please help me cause i'm knew to this things

[Mike90250]

It can't, and it won't.
Who is selling these 15w money pits?


So the story:

100AH battery has 1% self discharge just sitting That's 1 amp every day, lost.


15watt STC spec panel, when in sun, heated up, only produces 80% of spec: 12W
If this is the amorphous panel, power will reduce to 7W in 6 months.
Amorphous panels (rows of parallel hairlines across the array) are subject to about 5% degradation per year after initial degradation.

12W max expected output, for a well aimed, fixed panel, 5 hours of usable sunlight
12 * 5 = 60WH converted to amps @ 12V = 5 amp hours per day, of which only 80% gets actually stored, battery charging losses. leaves us with 4AH actually stored into the battery, per sunny day.

And I haven't added losses (3%) in for the charge controller. - You could wire directly to battery, but I doubt the panels have a blocking diode, which means at night, the power you put in daytime, runs back out and thru the panel at night. Neat-O !

So while you have a gain of 3 amp hours, that in actuality, is just barely enough to keep the battery trickle charged, but if you use any power, you will deplete the battery, and need weeks to recharge it.

Attached photo comparison is of a Sun120W panel, and a trio of HF 15watt. Photo credit to RussellJ

[suneguy]

Ok newbie here. So your saying that amorphous panels are not worth the money compared to poly panels? I have 2 sharp 80 watters model NE-80EJEA that need to be returned right away if this is the case. Panels were $469 retail each at a local hardware chain.

[Mike90250]

Ok newbie here. So your saying that amorphous panels are not worth the money compared to poly panels? I have 2 sharp 80 watters model NE-80EJEA that need to be returned right away if this is the case. Panels were $469 retail each at a local hardware chain.

That's my take on it. I did not even know Sharp made amorphous panels.
The way to tell for sure, is look at the warranty.

If it's Rated power -10% after 20 years, you should be OK.

If its only a 2 or 3 year warranty,or -5% every year (after 20 years you have 0) then return it.

AFIK, amorphous panels are quite a bit larger, as they are less efficient.

For $469, picked up, you should be getting a lot more power.
130W, $434 + shipping http://store.solar-electric.com/kykc130wasop.html
How do the dimensions of that 130 W (16% eff) 56.1 x 25.7 inches, 27 lbs
compare to your 90 ? That will be a clue as to how efficient the panels are.

[suneguy]

Hi Mike,
The warranty reads as follows: Limited warranty for power. The warranty period with respect to power output continues for a total of 25 years from date of purchase by the consumer, the first 10 years at 90% minimum rated power output and the balance of 15 years at 80% minimum rated power output. The warranty is transferable when product remains installed at the original location at the time of product warranty registration. Is this acceptable?

[suneguy]

Mike,
BTW, these are 80 watters. So if the charge controller uses 2% and the inverter uses 5%? then after the 10th year they may only make 2/3rds what they made new right?

[suneguy]

Mike,
Sorry I forgot to list the size. It is 45" X 20".

[Mike90250]

Well, the warranty looks OK, efficiency is there
45x20 = 900si @ 90W = 10W:si
56x26 = 1456si @130W = 11W:si
Must be a new sales pitch on amphourus. Let us know how they work out in 10 years

[suneguy]

Ok, will do! hahahaha.