Solar Lighting System

Solar Home lighting Systems are powered by solar energy using solar cells that convert solar energy (sunlight) directly to electricity. The electricity is stored in batteries and used for the purpose of lighting whenever required. These systems are useful in non-electrified rural areas and as reliable emergency lighting system for important domestic, commercial and industrial applications. The SPV systems have found important application in the dairy industry for lighting milk collection/ chilling centers mostly located in rural areas.

The Solar Home Lighting system is a fixed installation designed for domestic application. The system comprises of Solar PV Module (Solar Cells), charge controller, battery and lighting system (lamps & fans). The schematic of the HLS is given below. The solar module is installed in the open on roof/terrace - exposed to sunlight and the charge controller and battery are kept inside a protected place in the house. The solar module requires periodic dusting for effective performance.

 

 

 Building Your Solar Photovoltaic (PV) System
 

Solar PV systems vary in complexity. Some systems are referred to as "stand-alone" or "off-grid", which means they are the only source of power to a home. Off grid systems can be designed to run with or without battery backup depending on the usage. Off-grid home power systems usually have some form of storage to store the energy generated during the day for use at night. Typically this would be a battery bank.

Off-grid systems are very cost-effective when compared to alternatives such as grid utility connections.

Grid-connected systems where the amount of energy generated exceeds the energy used and is exported (sold) back to the electricity provider.  Energy can also be drawn from the electricity grid when the energy from the PV system is insufficient to power the load of the building.  Naturally, you have to have an agreement with your electricity provider to be able to export excess energy to the electricity grid.

Grid Connected systems are very cost-effective when compared to alternatives such as grid utility connections.

Regardless of the system chosen each will require specific components besides the solar PV modules. To generate alternating current (AC) an inverter is required.  Battery storage requires special batteries (AGM or GEL) depending upon the application and a battery charge controller.

The final cost of any solar PV system depends upon the size of the array, the battery bank size, and other additional components, such as inverters, PV mounting frames etc.

Estimating the size and cost of the Solar Photovoltaic (PV) Modules

Step 1

Determine load, available sunlight, pv array and battery bank size

1. a. Determine the Load - The best way to approach this is to anticipate your daily load requirements.

Appliance	AC or DC Watts (The Load)		Hours Used By Each  Appliance Per Day		Watt Hours  Per Day
Coffee Maker	600	x	0.5	=	300
Clothes Dryer	4,500	x	1.0	=	4,500
Cooker (Electric)	5,000	x	2.0	=	10,000
Computer	75	x	3.0	=	225
Computer Monitor	150	x	3.0	=	450
Dishwasher	1,500	x	0.45	=	675
Lights	4 x 20w	x	6.0	=	480
Microwave Oven	1,400	x	0.5	=	700
Radio	80	x	2.0	=	160
Refrigerator	650	x	9.0	=	5,850
Television	300	x	6.0	=	1,800
Vacuum Cleaner	600	x	0.30	=	180
Video	40	x	1.0	=	40
Washing Machine	400	x	1.0	=	400
Total					25,760 Wh

Table showing typical household (daily load) appliances and use. 

Note: the table and the figures provided should only be used as a guide and should not be taken as the wattage of your actual appliance.  Always check your appliance details.

Before you can install an array (one or more solar pv panels) you do need to estimate all the different loads used in your house on a typical day.  The above table shows how to calculate the watt-hours (Wh).

Of course it is very difficult to estimate each and every single load.  Some appliances draw power even when they are turned off, e.g., electric clocks, stereo's TVs etc. Because of this it is always recommended that the estimated daily load is multiplied by "fudge factor" of 1.5. 

1. a. Determine the available sunlight.

The amount of available sunlight should be determined from an average day in the worst month of the year.  This is known as the "isolation value". Using the worst month of the year will ensure that the system will operate year-round. The isolation value can be interpreted as the kilowatt-hours per day of sunlight energy that falls on each square meter of solar panels at a tilt latitude.

1. b. Determine Battery Bank Size

We recommend that batteries are shallow cycled and never deep cycled - requiring lots of charging and discharging.  Daily discharge should be about 20% of the capacity of the battery and deep cycling can be saved for those crucial days.

A 20% discharge figure suggests that the capacity of the battery bank system should be about five times the daily load.  This also suggests that your battery bank storage should be able to provide power