# DIY Solar 1 Light System Calculations



## classradiance (Oct 13, 2012)

How to calculate a Single Light System

1. Add up the hours that the 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
1 Zone
1 x LED FLOOD @ 15W
on for (SEE CHART) hours per night
...................
-Watt/Hour Winter Chart- - Only ever use 12 volt LED light -
1 Zone - 15W on when required daily average use -- 4pm until 10pm - 6 hours x 15 Watts = 90wh
Total usage per night in Winter = 90wh/d 
-----------------------------------------------------------------------------------------

-Load and Battery - 

House Lights Consumption = 90Wh 
90 watt-hours divided by 12 volts = 7.5 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 7.5 amps x 2 = 15 amp hours.

I want my system to be reliable if we have four consecutive days of cloudy weather,
4 days of autonomy x 15 Amps = 60 amp hours for the battery. = 60 + amp hour battery 
(Required Battery Bank = 1 x 60 Ah minimum - True Deep Cycle

cost so far = £15 for LED light + £50 Battery = £65
-------------------------------------------------------------------------------------------
-Charging Battery from Panel-
This installation is in a location that gets 4 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 15 amps in 5 hours = 15 / 5 = 3 Amps every hour 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. 3 A / 0.8 = 3.75 Amps. 

A single 70W solar array that has an Impp (amps maximum power point) of 3.9A would be suitable
Based on (Model - CS6D - 70P / Manufacturer - Canadian Solar Inc.)
cost of PV Array = £80
------------------------------------------------------------------------------------------

-Charge Controller Rating in AMPS-
The 70W solar array has a short circuit amp rating (Isc) of 4.21A 4.21A x 1.25 = 5.3A
use a 5.3A or larger charge controller with this array to charge the battery.

Cheap example - 10A Unit
For best efficiency to charge use an MPPT Type = £30
------------------------------------------------------------------------------------------
- estimated Cost of mentioned Materials over 20 years = £200. \ 240 months = £0.83 month = £0.20 per week 

Have seen 100w poly panel on Net for £100 inc delivery
Have seen 60Ah Varta Leisure Battery 12V 60Ah for around £50 inc delivery
20A Charge controller £10 - £30 - mppt prefered of course
1 QUALITY External (For in or out & VERY BRIGHT) LED Light 1 x 15w = £15
100m of .75mm twin and earth from wholesalers = $30
Mounting Bracket for Panel = $20

Estimated Total = £200ish

Also required - Fuse box / switches / bits .. 


-----------------------------------------------------------------------------------------
-Solar Panel specification-
CS6D - 70P..... manufactured by Canadian Solar
Related power
70W
Open circuit voltage Voc(V)
22.1V
Short-circuit current Isc(A)
4.21A
Optimum operation voltage Vmp(V)
17.8V
Optimum operation current Imp(A)
3.93A
.......................
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-


----------



## classradiance (Oct 13, 2012)

-------------------------------------------------------------------------
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.
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


-------------------------------------------------------------------------------------------

-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 ....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 .. 


-----------------------------------------------------------------------------------------
-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
.......................


----------



## LincTex (Apr 1, 2011)

I buy 10 watt LED floodlights for less than US$15 on eBay. 

At 900 lumen, they are WAY too bright to use indoors (generally).


----------

