solar system that charges batteries in 4 is impossibe ?

[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

[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.

[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.)

[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.

[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.

[gendil]

hi people

looks like i am lucky with this one ....one of my batteries i saw it cleary as shown in picture ...it was AGM that mean now i can do the following


i do have 2 100A12V total of 200 12 volt batteries

currently charging them with a 250 watt panel and the rule of 10 hours still holds


but i am happy that they can accept 500 watt panel ...that will allow me to charge them IN 5 hours time since 500*5 is 2500 watt

and that is the amount of power in my 200*12 =2400 watt batteries


5 hours time is really accpetable

[gendil]

here is the sticker of my panel which shows it abilities power is 250 ....now all i have to do is to buy another one and change my controller to mppt which pretty sure will draw

almost all 250 watt of each panel ...total will be 500 watt and high current will pass to my batteries

they will charge in 5 hours of time

the nice side of this is that if my betteries are full charged and out there there is nice sun >>>>>(plenty of sun in libya ...but plenty of black outs ..country in war ...that is

why i am concerned with fully charging my batteries in quick time ......we are in situation of LIFE ON ISLAND where we have to manage our power need on our own )>>>>>>>.



back to subject ...if we have good sun i can run many loads that are under the 500 watt since batteries will not be discharged because most of the charge is coming directly from sun


that willl do alot to me and my difficult life ....like running clothe washing machine some time running the refrigerator as long as sun is strong ...this will freeze the foods

in my fridge-freeze ....will keep the food in good condition till the next day ...next sun shine and ....5 hours of batteries charge

once they are full ... i can then use fridges etc rest of the day depending on solar power ....batteries will only be used as BUFFER

WHERE clould can pass temporarily and solar energy generation reduced a bit ....


am i Right on this thoughts ? ....thanks for help...need more help ....i am in LIFE ON ISLAND situation where i must make "MOST " of my system


thanks for all



(note : we do have around 7 hour of sun in winter and more than 10 hours of sun in summer ...the concern is to harvest it quickly ..charge batteires quickly ...and enjoy 2 hours of free sun power in winter 7-5 =2 hours and enjoy 5 hours of free power in summer 10-5 =5 hours ....the 5 hour is the charging time ...)

[ButchDeal]

hi people

looks like i am lucky with this one ....one of my batteries i saw it cleary as shown in picture ...it was AGM that mean now i can do the following


i do have 2 100A12V total of 200 12 volt batteries

currently charging them with a 250 watt panel and the rule of 10 hours still holds


but i am happy that they can accept 500 watt panel ...that will allow me to charge them IN 5 hours time since 500*5 is 2500 watt

and that is the amount of power in my 200*12 =2400 watt batteries


5 hours time is really accpetable

So you expect a 250 watt module to generate 250 watt/hours every hour for 5 hours every day.
thats cute.

[jflorey2]

almost all 250 watt of each panel ...total will be 500 watt and high current will pass to my batteries

1) You won't get 500 watts out of that system. You will be fortunate to get 400 watts in direct sun.
2) You won't get 400 watts for much of the day. Power will vary as the angle changes. Below is an example. Note at the peak they are getting about 70% of the rated power of the system, and only for an hour or so.

[Brian53713]

In Desperate conditions, where your life depends on it you're going to want those panels ground-mounted, easily moved to track all of the available hours of Sun. My best day last summer 200 watts of panel, 1.8 kilowatt, therefore 9 hours of sun it seems like.

[bcroe]

why i am concerned with fully charging my batteries in quick time ......we are in situation of
LIFE ON ISLAND where we have to manage our power need on our own )>>>>>>>.

(note : we do have around 7 hour of sun in winter and more than 10 hours of sun in summer ...
the concern is to harvest it quickly ..charge batteires quickly ...and enjoy 2 hours of free sun
power in winter 7-5 =2 hours and enjoy 5 hours of free power in summer 10-5 =5 hours ....the
5 hour is the charging time ..

Instead of moving your panels all day every day, you might put in parallel some panels facing
east and some facing west. With some adjustment of the angle, you can have full charging
current over extra hours, instead of a big peak you can't use at noon. Here is a curve from
this summer at 42 degrees latitude of 3 panels. Note that 2 E-W panels added equal a single S
panel current at noon, but over a much broader number of hours.
PVm17Jn16.jpg

Haze and clouds will of course drastically drop these levels. It is possible to use more panels to partly compensate for this, but your charge
controller will need to limit charging current on sunny days. Bruce Roe

[gendil]

a research done by the nothinghamm university in uk shows that libya can produce 5 times money in solar than in oil
and it has the incridible 7 kwh a day per squar meter on flat panel

the research is here mr butche dealer

http://www.csers.ly/en/news/30-libyan-solar

so it seems that 250 watt panel can produce 300 watt hehehe

thanks mr brian for your more PRODUCTIVE answer

...on the same research they mention the word "7kwh per day in square meter in flat panel"

can that mean flating my solar panel??

looks like it the same trick you already mention to me mr brian ? flating the panel will allow me to harvest alot of power


thanks bcroe ...seem good solution a ABIT risky due to increase in charging current

[SunEagle]

a research done by the nothinghamm university in uk shows that libya can produce 5 times money in solar than in oil
and it has the incridible 7 kwh a day per squar meter on flat panel

the research is here mr butche dealer

http://www.csers.ly/en/news/30-libyan-solar

so it seems that 250 watt panel can produce 300 watt hehehe

thanks mr brian for your more PRODUCTIVE answer

...on the same research they mention the word "7kwh per day in square meter in flat panel"

can that mean flating my solar panel??

looks like it the same trick you already mention to me mr brian ? flating the panel will allow me to harvest alot of power


thanks bcroe ...seem good solution a ABIT risky due to increase in charging current

You would need a pretty big extension cord from Libya to charge your batteries.

[gendil]

i am living in the middle of libya hehehe

[SunEagle]

i am living in the middle of libya hehehe

Then you are ahead of the game with a lot of great sunlight for pv.