Quick Maths for watts and cost and effort

Pho3nix

The Legend
Joined
Jul 31, 2009
Messages
27,559
Hi,

Have about 40 gu10 10w lights. Considering changing these to the 3.5w variety but trying to get my maths right.

New ones = 40 * 3.5w = 140w
Old ones = 40 * 10w = 400w

If charged at the tariff of R1.1858 per kwh then would the cost difference be R46 odd?

(5 Hours a day of 3w = (140w*5) = 0.7kwh * 1.1858) = R0.83006 = R24.9018
(5 Hours a day of 10w = (400w*5) = 2kwh * 1.1858) = R2.3716 * 30 days = R71.148

40 lights is a cost of R800 odd so ROI in a year an a half. Worth the effort?
 

alqassam

Expert Member
Joined
Aug 11, 2014
Messages
2,684
Hi,

Have about 40 gu10 10w lights. Considering changing these to the 3.5w variety but trying to get my maths right.

New ones = 40 * 3.5w = 140w
Old ones = 40 * 10w = 400w

If charged at the tariff of R1.1858 per kwh then would the cost difference be R46 odd?

(5 Hours a day of 3w = (140w*5) = 0.7kwh * 1.1858) = R0.83006 = R24.9018
(5 Hours a day of 10w = (400w*5) = 2kwh * 1.1858) = R2.3716 * 30 days = R71.148

40 lights is a cost of R800 odd so ROI in a year an a half. Worth the effort?
Should be because they will last way longer than 1.5yrs.

Also 1.18 kWh is cheap where do you live in a power station?
 

Pho3nix

The Legend
Joined
Jul 31, 2009
Messages
27,559
Should be because they will last way longer than 1.5yrs.

Also 1.18 kWh is cheap where do you live in a power station?
Apparently what we are paying within the estate if I am to believe the invoices I’m looking at
 

alqassam

Expert Member
Joined
Aug 11, 2014
Messages
2,684
Makro has osram 3w for 6 for 100 on special spend 700 and get 42.

Just wait for the special and buy then

You Payback faster
 

alqassam

Expert Member
Joined
Aug 11, 2014
Messages
2,684
Also if you start going low power on everything it makes it easier to move onto solar when you have extra funds.

Now you only need 1 X 320w panel to run your lights
 

Pho3nix

The Legend
Joined
Jul 31, 2009
Messages
27,559
Also if you start going low power on everything it makes it easier to move onto solar when you have extra funds.

Now you only need 1 X 320w panel to run your lights
Didn’t consider this. Part of the eventual plan
 
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