Inverter-sizing Calculator              Backup Time Calculator        Solar-panel-sizing calculator    

 

MORE ON SOLAR POWER SYSTEMS

How solar cells work
A solar panel
Solar panel calculation
Solar panel installation
Solar panel pricing

How solar cells work
Another name for a solar cell is photovoltaic (PV) cell,photo meaning “light” and voltaic meaning “electricity or relating to electricity”. A major material or component of  solar cells is the semiconductor like silicon or germanium.Silicon is still more widely used as a major semiconductor material in solar cells.When sunlight strikes a solar cell,some of its energy is absorbed by the semiconductor material as photons.These absorbed  photons impact on some electrons of the semiconductor material,thereby  breaking loose from their atoms,resulting in a free flow of electrons in the semiconductor.The semiconductor has an  inherent electric field by its design, which forces these loose electrons to flow in a certain direction,resulting in an electric current(flow of electrons).By placing metal contacts at the top and bottom of the cell,current is therefore drawn for some external use. This current which is drawn and the cell’s voltage defines the power capacity of the solar cell. The process of how a solar cell works is much more complex than we have explained,but this brief explanation suffices for the purpose intended here.Today,solar cells can also be made by the process of screen printing, reducing the cost of production,though it is doubtful whether solar cells made this way are as durable as the ones made by the conventional sophisticated process of solar cell manufacturing. 

A solar cell

Top of Page

A solar panel
A solar panel is essentially an aggregate number of solar cells interconnected accordingly and arranged neatly in a frame,covered with a smooth glass ,providing a higher current flow and volatge, in effect higher power capacity.The details of how this is done is beyond the scope of this article and can be found in a number of websites on the internet. Solar panels come in different capacities/ratings including: 12V/50W,12V/75W, 12V/80W, 12V/100W, 12V/125W, 12V/140W. The major set back for the wide use of solar energy systems as an alternative source of enery is its cost. Though this cost has been dropping over the years,however,it is still outside the reach of the common man. Cost is usually in the range of N700 to N1000 per watt. Thus a 100Watt solar panel would cost in the range of N70,000 to N100,000 depending on manufacturer,though prices are a little bit higher in our Nigerian market. German,US and Japan solar panels are known to last very long(up to 25 years) and are usually more expensive than others.A few Chinese solar panels are also good.12-volts solar panels output voltage are usually between 16V to 20V,therefore solar panels are usually sold with charge controllers which regulate the charging voltage from the solar panel, ensuring the 12V batteries are not overcharged and damaged.   Usually,you may need more than one solar panel to meet your electricty need,so you would have more than one solar panel connected together.This arrangement of a connection of solar panels together is called a solar array or solar panel array.

solar panel

A solar panel-an aggregate number of solar cells connected accordingly
 

solar array

Solar array-an aggregate number of solar panels connected together Top of Page

Solar-panel-sizing calculator

This calculator is for sizing the right 12Volt-Solar Panel array to fully charge your battery bank during the day;for use during the night or otherwise,whether it is for street LED lighting , DC fridge,inverter or other appliances running directly off a rechargeable battery.Average of 12hour daily sunlight is assumed. Battery depth of discharge is usually between 70 to 90%.

Input DC Voltage of Appliance(e.g Inverter,LED bulb,DC fridge)
(A multiple of 12 e.g 12 or 24 or 36 or 48...480 or 720 e.t.c)
No of 12Volts Batteries Connected
Each Battery Capacity(AmpH)
Each Battery Depth of Discharge(%)
 
All entries must be numbers and cannot be empty or zero!

 

Example: A 4 x 3 of 75Watt solar panel array is described as 3 parallel connections of (4 solar panels connected in series).There are 12 of 75Watts solar panels in this array.

Solar panel installation
Solar panels can be installed on different roof types. It is best to install solar panel mounting frame while a home is being roofed for the following adavantages:

  1. This will usually eliminate the chances of roof leakages.However, this is no issue with super roof sealants of nowadays.
  2. It is also much easier to locate rafters when the roof has not been fixed. All mounting frames for the solar panels need to be fixed onto the roof with stainless steel bolts firmly fastened  into the roof rafters.
  3.  It is also less expensive to provide these mounting points for the solar panel frame while the building is yet to be roofed. The cost of removing the roof and fixing these mounts would then have been avoided.

However,solar panels can always be mounted even on already finished roof .There are materials and facilities to be used that would ensure a leakage proof installation. Solar panel installation on tile roofs can however be such a daunting task,as one must be very careful not to damage these tiles,especially when they have aged.
Solar panels can be flush mounted or tilted upwards.

photovoltaic solar energy array

Flush-mounted solar panel array

8 Siemens SP-75's

Upward-tilted solar panel array Top of Page

Solar angle and Positioning

Especially for temperate regions of the world,where sunlight can be a scarce resource for very long periods of the year,it is necessary to correctly position the solar panel to face the right direction where most of the sun's energy would be captured for most part of the year.Some people also use a solar tracking device which keeps tracking the movement of the sun in order to capture most of the sun's energy per time.This however comes with a cost and adds more work to managing the entire system. A general rule without bothering with exact calculations of solar angles is to have your solar panles face south if you are in the north and face north if you are in the south.


STEP 1.

Calculate how many solar panels required for your installation and determine from these the dimensions of the mounting frame that will hold these panels on the roof. You may require from your design,to have two or more separate mounting frames on the roof due to the dimensions involved,but all connected together after the panels are mounted.

STEP 2.
Locate the rafters on the roof and mark the positions on the rafters, where you will fix the solar panel mounting posts.Be sure that these marked positions are in straight lines so that the metal rail on which the solar panels will be fixed,will easily fit on the mounting posts.You can use a chalk to draw a line to be sure they are in straight lines. Pre-drill these marked positions with a drill bit to avoid splitting the wooden rafters. Note that flush mounted solar panels must allow enough space,say a minimum of 10cm,between them and the roof for free flow of air.This is important to avoid the undesirable build up of heat under the panels.

STEP 3.
Fasten the mounting posts to the roof with stainless steel lag bolts through these pre-drilled marked positions.

Fast Jack

A mounting post on a roof
STEP 4.
Place metal flashings over these mounts and and apply water-proof sealants around the  the mounts.Secure the metal  rails  to the mounting posts with half-inch stainless steel bolts.

rails secured

Two metal rails fixed on both rows of the mounting posts(the mounting posts need to be in straight lines to allow the metal rails fit very well. )
STEP 5.
Next, install the solar panels by fixing them to the metal rails accordingly using the provided pre-drilled holes on them.

panels are mounted

Solar panels fixed on the metal rails
STEP 6.
Finally, run the correct cables from the solar panel array to connect the panels to the inverter or as may be required.

40 Siemens solar modules

Three groups of solar array are mounted on this roof,and are all connected together to the inverter to provide the required designed capacity Top of Page

Solar panel pricing

Solar panel prices  vary widely from manufacturer to manufacturer and also the the type of panels in question. Generally,pure crystalline solar panels are much more expensive than the amorphous types and they last much longer.Some makes include Suntech,Solar world,Sharp,Trika,BP solar panels and many others.

Here below is the  price range of  common solar panels available today

SN

CAPACITY(Watts)

PRICE RANGE(N)
K=1000

1

50

30k to 60k

2

75

60k to 80k

3

80

75k to 90k

4

100

90k to 110k

5

125

120k to 140k

6

140

130k to 150k

Top of Page