It is said that just 100 square miles of Solar Panels could deliver enough Electricity to meet Global demand !!
Here is the Math for a system if you ever need it, for your own needs as a family.
Start out with just 1 Light when calculating and then add more later when you get used to what you are actually doing.
Basic Electronics Theory is required along with knowledge of Safe Battery Storage and Handling.
Remember that a 12V Car Battery can cause fire if not handled correctly, study safe practice first to easily avoid problems.
The same principles as charging a car battery whilst driving where instead of an Alternator you have a Solar Panel.
The Solar Panel cables go into a small box called a Charge Controller, which supplies the correct Power to the Battery and then allows an LED Light circuit to go active when the Sun Light drops.
Calculations for Home / Boat / Caravan / Shed
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
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My Calculations
3 Zones (ROOMS)
1 X LED SPOT @ 10W + 2 x LED FLOOD @ 15W
on for (SEE CHART) hours per night
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-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
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-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.
the minimum battery size is 15.42 amps x 2 = 30.84 amp hours
or 15.42ah / .5(50%) = 30.84ah or 15.42ah / .3 (30%) = 51.4ah or 15.42ah / .2 (20%) = 77.1ah, choose what calculation will be best for your battery !!
10% discharge
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
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-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.
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-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
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-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.
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- estimated Cost of mentioned Materials - 20 years / $450. = $500./240 months = £2.08 month = .52 per week ....wow
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 ..
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-Solar Panel specification-
STK-140P6-A ...... manufactured by 3E
Related power
140W
Open circuit voltage Voc(V)
23V
Short-circuit current Isc(A)
8.2A
Optimum operation voltage Vmp(V)
18.3V
Optimum operation current Imp(A)
7.7A
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Thanks to everyone who places information out there on the WEB
Hope the above can inspire you.
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.
Sizing a system
In sizing a system correctly, the aim is to balance the power going in from the solar panel
with the power going out of the battery over a period of days or weeks (depending on how
it is being used). A 10W panel will give 10W (0.6A @ 16.5V) over an hour under standard
test conditions (1000W/m sq and 25oC – equivalent to one hour of 'peak' sunshine). In the
UK we expect around 4 hours equivalent sunshine in summer and 1 hour in winter. Thus in
Winter a 10W panel will give 10W over a whole day, whereas in summer it will give 40W.
These are fairly conservative figures – some companies use up to 6 hours in summer, but
of course whatever figure you use the panels will perform the same in real life. You can do
the same calculations with the Amps.
Let me know if this has helped you or given you an interest in Solar Light Systems - This is free advice and I want nothing for it.
The information above is taken from many books/videos/web sites and my own angle on it all is above where I have built and tested my own Hardware.
But more to the point is if in a Catastrophe you required a means to Light the Dark nights without Flame, then the above may help or inspire you to look into the Science of Solar Power.