DC based lights and fans

[digimart]

Hi
I am just working on assembling small DC based systems for small houses, and one/two rooms offices.
The basic idea is to have couple of LED DC bulbs, and DC fan , and all these to run on battery powered through appropriate size solar panels.
In this way, I be saved from losses incurred while DC-AC conversions, as well as Inveter's own power consumption too.

Example 1 :
Three (3) LED DC bulbs of 3W each to run for 8 hours. My calculation is that a panel of 15 Watts having 5 hours of sunlight, and a battery 12Volts battery of 9AH with 70% discharge, be able to run these for 8 Hours.

Example 2:
Three (3) LED DC bulbs of 5W each and 1 DC fan of 18 Watts to run for 8 hours. My calculation is that a panel of 60 Watts having 5 hours of sunlight, and a battery 12Volts battery of 30AH with 70% discharge, be able to run these for 8 Hours.

Such systems can be very beneficial for low-income households and small shops / offices.

Further, as per my understanding, in such cases, I just need a small electronic circuit to monitor battery charging and cut-off, so that battery is not over or under charged.

I like to have your comments on the above.

Regards.

Omar

[Mike90250]

You will have to factor in the system losses, and they generally run about 50%, so your 15w panel needs to be 30 watts.....

[Sunking]

Example 1 :
Three (3) LED DC bulbs of 3W each to run for 8 hours. My calculation is that a panel of 15 Watts having 5 hours of sunlight

Just where are you at? Very few places on earth recieve 5 Sun Hours minimum through a year. As Mike points out figure 50% losses.

[digimart]

Hello Mike90250 and Sunking

My location is Lahore, Pakistan
Latitude = 31.52058

As to my understanding the sunlight here is more than 7 hours even in winters, when a day's length is smallest. So would you agree that taking 5 hours of sunlight in my calculation takes into account the losses of Solar panels ?

And as there is no conversion being made from DC to AC, so i am saved from the PF of the inverter, as well as power consumption of the inverter too ?

Please advise,

[Mike90250]

here is a table for you:

http://www.nrel.gov/international/ra_pakistan.html

The closest city listed in PV watts, is New Delhi
"Station Identification"
"City:","New"
"State:","IND"
"Lat (deg N):", 28.58
"Long (deg W):", 77.20
"Elev (m): ", 216
"Weather Data:","IWEC"

"Month", "Solar Radiation (kWh/m^2/day)",
1, 5.56,
2, 5.90,
3, 6.65,
4, 7.01,
5, 6.91,
6, 6.34,
7, 5.28,
8, 5.25,
9, 5.89,
10, 6.17,
11, 5.74,
12, 5.56,
"Year", 6.02,


The longest day hours, is April, at 7.01 solar hours, the year average, is 6.02 hours. Local cloud cover may alter that, as you are some distance away from the reporting station.

[digimart]

Mike
thanks for the sunshine data, its great help.
OK as per the data on website avg per day sunshine is 6 hours.

I am taking sunshine based on 5 hours a day, so I guess that it be taking into account some of the losses.

Whats your opinion , that for say power usage of 200 Watts in 24 hours, I be needing panel of one 40 Watts ( 5 hours X 40 Watts = 200 Watts ), or I be needing a 80 watts panel for the same ?

Regards.

[Naptown]

With an inexpensive PWM charge controller I would go for twice the consumption or the 80W panel.
At low levels even the MPPT Charge controllers will go into a PWM mode. So that is money wasted.

[digimart]

Naptown

From your reply I understand that with a PWM controller in my quoted example ( reproduced below ), I be needing panel of about 80 Watts right ?


Example : "Whats your opinion , that for say power usage of 200 Watts in 24 hours, I be needing panel of one 40 Watts ( 5 hours X 40 Watts = 200 Watts ), or I be needing a 80 watts panel for the same ? "

[Naptown]

Naptown

From your reply I understand that with a PWM controller in my quoted example ( reproduced below ), I be needing panel of about 80 Watts right ?


Example : "Whats your opinion , that for say power usage of 200 Watts in 24 hours, I be needing panel of one 40 Watts ( 5 hours X 40 Watts = 200 Watts ), or I be needing a 80 watts panel for the same ? "

you have not taken charging losses into account. it takes 1.25 to 1.5 times the watts to replace what you use.