System Sizing

What is Sizing?

Sizing is simply the process of designin a solar electric system to
meet the required operating loads based on the total wattage of all appliances in the system.

For instance in you are using a tv set that consumes about 65 watts of
power, you  need to put into consideration how many hours a day you
intend to use the tv as it will help u calculate your total wattage in watt hour.

A lot of things needs to be put into consideration when  calculating the cost
 of setting up a solar generator.

First and foremost, you must consider the period of usable sunlight available
at your location

 For some of us who stay  close to the equator, we get about 7 to 8 hours
or more of sunlight during dry season, “this is just a just a rough estimate”

how to determine the size of solar panel needed for your project?

The power consumption of appliances is given in Watts hence To calculate
 the energy you will use over time, You  have to multiply the total power
consumption by the hours of usage.

Assuming I  have 100W tv set which I want to use for 8hrs,  20W dvd
player for the same period, and maybe  a 60W bulb for 5 hours.

To calculate the total power in watts hours, follow the following steps

The energy for each appliance is Watts x time (hours) = Wh

The energy used up by the tv in watt = 100 x 8 = 800Wh (watt hours)


The energy used dvd player = 25 x 8 = 200 Wh


the energy used bulb will be = 60 x 5 = 300Wh

 next we need to add up the total wattage consumed by the all the appliances
appliances

that would be  800+200+300=1,300 watt hour

This implies that the solar panel will need to supply 1,300 watt hours of energy
 to your batteries each day to cover the total power required by these appliances.

Since no system is 100 percent efficient as there are bound to be energy losses,
we have to take the losses into consideration by  multiplying  the result by 1.2
(this factor allows for natural system losses, and assumes an  85% efficiency).
Therefore, we will assume the panels will actually need to be able to supply a
 total of
1300 x 1.2 = 1560Wh

to be able to determine  the  solar panel capable of giving out 1560wh of energy we assume
to receive 7 hours of sunlight

The power rating of our needed solar panel will be = 1560Wh / 6 h = 260W

This means you will need a solar panel of not less than 260 watts.


Now assuming we have a Solar panel with a power rating of 200watts, we'll have
 to first apply  th 85% efficiency rule, and because of that it  means the panel will
only be able to deliver 200 x 0.85= 170 watts

Battery Sizing

Based of the calculations above,Your battery should be able to store
1560Wh of energy.
Since batteries capacities are rated in Ah (Ampere Hours) you need to multiply Ah by
the Volt rating to know the Watt Hour. Power(W) = Voltage (V) x Current (I) ;
Watt hour = V x I x Hour
We’ll make I the subject of the formula.

Therefore Ah (which is I x h) = Wh / V = 1560 / 12 (the number 12 represents
a 12v battery)= 130 Ah

This  means you will need not less than an 130Ah, 12V battery (deep-cycle batteries,
 not ordinary car batteries) to do the job.

This implies that the battery can supply a 260watt appliance for 1560/70 = 22 hours