Watts needed
I have read where folks suggest any where from 1 to 2 watts of solar per ah of battery. My question, is this based on battery rating (ie 215 AH) or is it based on useable amp hours(105)? All reply...
Forum Discussion
1W per 1 AH is a very broad guideline. There is no such thing as too much solar.
Geographic location matters. Also, how big is your battery bank relatively to your daily energy needs.
Flat 100W solar would harvest ~35 AH on an average day in June at latitude of Portland OR. More in San Diego, less in Seattle. Tilted panel (ex. portable solar suitcase) will harvest more than flat panel. If your 100 AH battery is discharged 50%, you need ~55 AH solar harvest because of all the losses, so flat 100W solar won't cut it. Even 150W might not cut it because the last 20 AH will go in slowly.
It is easier to get away with less solar wattage if your energy use is low and battery bank is bigger than you need, for example your energy use is the same 50 AH a day and you have 200 AH battery bank. Then you won't need more than flat 150W solar because you'll start the day with battery 75% full and in a few minutes it will slow down and won't need more than a few amps.
When you're using energy mostly in daytime, having more solar than, say, 1.5W per 1 AH helps "better" because solar is feeding both loads and the battery, so it's less important that the battery is slow on those last 20% of SOC. Whatever solar energy battery can't take, loads will.
Geographic location matters. Also, how big is your battery bank relatively to your daily energy needs.
Flat 100W solar would harvest ~35 AH on an average day in June at latitude of Portland OR. More in San Diego, less in Seattle. Tilted panel (ex. portable solar suitcase) will harvest more than flat panel. If your 100 AH battery is discharged 50%, you need ~55 AH solar harvest because of all the losses, so flat 100W solar won't cut it. Even 150W might not cut it because the last 20 AH will go in slowly.
It is easier to get away with less solar wattage if your energy use is low and battery bank is bigger than you need, for example your energy use is the same 50 AH a day and you have 200 AH battery bank. Then you won't need more than flat 150W solar because you'll start the day with battery 75% full and in a few minutes it will slow down and won't need more than a few amps.
When you're using energy mostly in daytime, having more solar than, say, 1.5W per 1 AH helps "better" because solar is feeding both loads and the battery, so it's less important that the battery is slow on those last 20% of SOC. Whatever solar energy battery can't take, loads will.
