solar system that charges batteries in 4 is impossibe ?

[PNPmacnab]

One more point. It is easy to think, what moron designed a 18V panel to use on a 12V battery. Panels produce less voltage the higher the temperature gets. Something black in the sun can get really hot and a panel may not make much more than 15V under load. That considers rated load current, aged cells and resistances. In that case a PWM controller is not that bad. As there is some justice in the world, higher voltages are made in the winter when days are shorter. At that season a MPPT makes some sense even at 12V. Voltage/power is rated at 25C, an unlikely temperature that will only be seen in the winter.

[littleharbor]

With a PWM controller your panels MUST be 12 volt nominal (18 volt) for you to get any decent charging power from your panels. 200+ watt panels are higher voltage and all that higher voltage will be wasted as you will only get 13-14.5 volts @ the panels rated amperage. Best use MPPT controller. The extra cost of the controller will be offset by the cheaper large panels.

[jflorey2]

now comes the tricky part ...the panel ....we have got 2000 watt ...that needed to be collected ....hopefully in one hour ...but that is impossible because 2000 watt panel will produce large currents that will destroy the battery

If you have very limited sun hours and your battery seems "too small" to handle that current - increase the size of the battery. Or change the type of the battery. AGM's can handle C/4. LiFePO4 can handle even more; the Iron Edison pack, for example, can handle C/2. (The CALB cell datasheet claims 10C but I would take that with a HUGE grain of salt.)

SOLAR PANEL THAT HAS POWER RATING THAT IS 1/10 OF THE BATTERY WATT

For flooded cells that's a reasonable starting point. (Although to be technically correct, you want an array that will provide 1/10 of the current of the amp-hour rating of the battery. That is pretty close to your statement though.)

[inetdog]

Well, first correct your figures to plan for only a 20% discharge of the battery bank daily. That allows for long battery life and up to 2.5 days without charging (bad weather, etc.) before the batteries are at 50%.
Second, take that 20% discharge and multiply by the C/12 or C/10 rate and you get a full recharge in only about two hours of full direct sun.
That, however, is not realistic, since the batteries will only accept recharge at that rate until they get to about 90% charged or lower and the remaining time will be spent in a decreasing current pattern together making up the Absorb and Float stages of charging.

If you add more panel power, up to say twice the battery AH at 12V, you will not be able to charge any faster with FLA batteries, but may be able to keep a decent charge rate later in the day or with scattered clouds. But the current should still be limited to C/8 at most.

Now if you ever get down to 50% charge, that means that you will not be able to get back to full charge in just one day, or maybe even not in two days while running your normal loads.
For that you need to have a generator available.

Now if you must charge your battery bank at more than C/8, maybe because of the reduced sun time on the panels in winter, it may be worthwhile to use AGM sealed batteries that can be charged at C/4 or even higher, depending on the construction details and manufacturer's recommendations.

Think about that for awhile and see if you have more questions.

By the way, the rule of thumb that we normally use is that the wattage of the panel array should be at least equal to the battery AH for 12V batteries, which gives us C/12 instead of C/10 for the peak current.

[gendil]

i am fully a ware of how to calculate and install solar system for home uses ....we first start by determing our loads in hour fashion

for example one lamp 100 watt for 10 hours means 1000 watt /hour amount of energy is needed

which means that we need battery that hold this amount of power which will be 1000/12 that is 83 amper battery doubling its capacity wont harm since this wont allow battery to

be "completely discharge"

83*2=160 amper 12 volt battery

160*12=around 2000 watt


now comes the tricky part ...the panel ....we have got 2000 watt ...that needed to be collected ....hopefully in one hour ...but that is impossible because 2000 watt panel will produce large currents that will destroy the battery


many suggest the "GOLDEN RATE " of c/10 where c is battery capacity now we do have 160 amper battery /10 that is 16 amper

so we have to buy that panel that gives 12 volt at 16 amper and we have achieved that "golden rate"

panels that charge 12 volt batteries are not 12 volt panles ...they are 18 volt vmp panels .....vmp is the maximum power voltage ..

so we need 18vmp panel at 16 amper ....despite the fact that 18 panel @16 amper panel is a 290 watt panel ...but because we use a pwm controller in this design

18volt @16 amper is never a 290 ...because pwm controller will only use 13.5 at 16 a and toss the extra voltage

which will "DRAW' only 216 watt out of 290 watt panel ....


even designing this system with mppt is ok .. that will allow us to buy panel that has 18 volt at lower current than 16 ...

the extra lost voltages that pwm tosses mppt convert to current and thus

we wont lose money by buying large panel that we only draw little watt out of it

...sorry for this long prelude but in a nutshell by following "solar bibles" we find our self with a

SOLAR PANEL THAT HAS POWER RATING THAT IS 1/10 OF THE BATTERY WATT

IN our case 2000 watt battery (12 volt *160) and the panel is 290 watt (from which we get only 216 watt due to pwm controller) or 200 watt panel

18 at 11 amper panel if we use mppt ....despite the fact that the mppt will charge battery at 13.5 but turn the lost voltage into current

which will crank up current into 16 amper again


so how some system manage to charge batteries in 4 hours time if we follow the rules we only find our self with panel that 1/10

of battery wattage which will force the harsh fact that our panels will collect our needed power in 10 hours time


very very long and perfectly impractical even in the middle east countries (libyan man here )


thanks every body please share your thought with me