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Old 09-23-12, 06:21 PM   #7
Join Date: Sep 2012
Location: England
Posts: 28
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Default Solar Pad - estimate your setup - lights on time

1.Add up the hours that each light will be on for to get the Total of Energy Consumed.
2.From that you can Calculate everything you need IE: Solar Panel / Battery / Regulator

My Calculations
3 Zones
1 X LED SPOT @ 10W + 2 x LED FLOOD @ 15W
on for (SEE CHART) hours per night

-Watt/Hour Chart- - Only ever use 12 volt LED lights -

3 Room scenario

kitchen/Diner 15W on when required daily average use -- 3 hours = 45wh
Bedroom 10W on when required daily average use - 2 hours = 20wh
front Room 15W on when required daily average use - 8 hours = 120wh

Total usage per night in Winter = 185wh/d

-Load and Battery -

House Lights Consumption = 185Wh
185 watt-hours divided by 12 volts = 15.42 amphours taken from system in 1 night

Because we can only use half the energy in a lead acid battery without harming the battery,
the minimum battery size is 15.42 amps x 2 = 30.84 amp hours.

I want my system to be reliable if we have four consecutive days of cloudy weather,
4 days of autonomy x 30.84 = 123.36 amp hours for the battery. = 124 + amp hour battery
(Required Battery Bank = 1 x 130 Ah True Deep Cycle


-Charging Battery from Panel-
This installation is in a location that gets 5 hours of full sun per day.
Check the charts for this depending on the month in the Season.
To recharge the battery for one day of use we need 30.84 amps in 5 hours = 30.84 / 5 = 6.17 amps from a 12 volt solar panel array.

-Solar Panel -
Most load calculations include a discount factor for the inefficiency of recharging the battery.
20% is typical. 6.17 / 0.8 = 7.71 amps.

A single 140W solar array that has an Impp (amps maximum power point) of 7.7A would be suitable


-Charge Controller Rating in AMPS-
The 140W solar array has a short circuit amp rating (Isc) of 8.2A 8.2A x 1.25 = 10.25A
use a 10.3A or larger charge controller with this array to charge the battery.

Cheap example - 20A Unit
For best efficiency to charge use an MPPT Type.

- estimated Cost of mentioned Materials - 20 years / $450. = $500./240 months = 2.08 month = .52 per week

Have seen 140w poly panel on Net for $170 inc delivery
Have seen 130Ah Varta Leisure Battery 12V 130Ah for around $150 inc delivery
20A Charge controller $20 - $60 - mppt prefered of course
3 QUALITY External (For in or out & VERY BRIGHT) LED Lights 2 x 15w/1 x 10w = $60
100m of .75mm twin and earth from wholesalers = $30
Mounting Bracket for Panel = $20

Estimated Total = $500ish

Also required - Fuse box / switches / bits ..

-Solar Panel specification-
STK-140P6-A ...... manufactured by 3E
Related power
Open circuit voltage Voc(V)
Short-circuit current Isc(A)
Optimum operation voltage Vmp(V)
Optimum operation current Imp(A)

Thanks to everyone who places information out there so I could put all this up
Hope the above can inspire you, cause the Bills r going up !!
Not mentioned above are Switches, Inverters, Distribution, Heating, Health & Safety,
etc ... Caution -12V Batteries can Cause Fire if not Fused or Stored Correctly-

- Battery info -

Deep cycle batteries are designed to be discharged down as much as 80% time after time,
and have much thicker plates. The major difference between a true deep cycle battery
and others is that the plates are SOLID Lead plates - not sponge. This gives less surface
area, thus less "instant" power like starting batteries need. Although these can be cycled
down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about
50% discharge.

Battery life is directly related to how deep the battery is cycled each time.
If a battery is discharged to 50% every day, it will last about twice as long
as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times
as long as one cycled to 50%. Obviously, there are some practical limitations on this
- you don't usually want to have a 5 ton pile of batteries sitting there just to reduce
the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean
you cannot go to 80% once in a while. It's just that when designing a system when you have
some idea of the loads, you should figure on an average DOD of around 50% for the best storage
vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less
will usually not last as long as one cycled down 10%. This happens because at very shallow cycles,
the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

If this has helped you in any way, let me know . . good luck
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