AN OVERVIEW OF PHOTOVOLTAIC SYSTEM DESIGN FOR THE BEGINNERORHOW TO INSTALL SOLAR PANELS

PURPOSETO PROVIDE AN EASY TO DIGEST RESOURCE TO HELP INTRODUCTORY STUDENTS UNDERSTAND PHOTOVOLTAIC SYSTEM DESIGN.

EXPLAIN/DEFINE

Explain what a photovoltaic system and identifying its key components. Defining the crucial terms needed to understand a basic system

DEMONSTRATE

Demonstrate the crucial equations needed for the design process. Demonstrate how to turn the answers to the equations into the basic plan of a system

CONTENTS

Basic Terms

Components

Equations

Fitting it Together

Each section is color coded to help you skip to the Information you need.

BASIC TERMS

Watt- A common unit of electrical power. It is important to remember that power is always measured over time. (W) When divided by volts it gives amps.

Volt – A common unit used to measure electrical potential to do work. (V) When multiplied by amps it gives watts.

Amp- A common unit used to quantify the strength of an electric current. (A) When multiplied by volts it gives watts.

BASIC TERMS

Load-The amount of watts a powered device is demanding from a Photovoltaic system. Forms the starting point for the system design.

Efficiency – A number with no units that describes how much of an electrical input to a module is produced as output. It is represented By this symbol and is most easy to think of in a percentage term.

COMPONENTS

Photovoltaic ModuleBetter know as a “solar panel”. It converts electromagnetic energy from the sun into D/C current that can be used to power a device or stored for later use in a battery. The modules are rated by watts, which refers to the watts produced for every FULL hour of DIRECT sunlight. This number can be located on the PVWatts website.

BatteryThe device used to store electricity generated by

the photovoltaic module. Rated in “amp-hours”, that is, drawing one amp from

it an hour how many hours of charge can the battery

hold.

COMPONENTS

Inverter – Converts D/C current to A/C current. Rated by maximum wattage

InverterThe inverter converts the D/C current coming our of the batteries to A/C current. It is rated for a maximum wattage and multiples could be necessary depending on the load.

Charge ControllerIt’s job is to regulate the rate at which the batteries charge, and once they are at capacity cut off the charge to them to prevent damage. Also, when the state of charge in the battery gets low, it stops drawing on it so as to not weaken it by draining it completely. Has a maximum amp rating and multiples may be needed

EQUATIONS

To Find: Input to inverter

Take the output of the inverter ( the load) and divide it by the efficiency of the inverter. Output(W)/

To Find : Amperage output of the charge controller. • Since we know

the output of the charge controller in watts we simply divide by the voltage of the system ( normal is 12V)

To Find: Kilowatt hours used per day by the load.

Take the output of inverter and divide by 1000. Then multiply by hours of use per day

EQUATIONS To Find: Solar Panels Needed

Go to the website for PVWatts(rredc.nrel.gov/solar/calculations/PVWATTS/version1/

Look up the geographic region your system is in. Take the average hours of max sun per day provided there. Multiply that number by the watt output of one of your solar panels. Divide this result by 1000 to convert to kilowatts.

Then divide kilowatt hours per day of your load by the kilowatts one solar panel provides per day. Remember to round up as you cant have a fraction of panel, whole numbers only, and what you know have after rounding is how many solar panels you will need.

EQUATIONS

How to : Determine number of batteries needed to provide backup power for “x” days in case of clouds or other system failure.Determine days you want to run on battery power for. Next multiply that number by the Kwh/day of your load. Convert this to kiloamp hours by dividing by the voltage of your system (12 is standard remember). Last divide by 1000 to convert to amphours. Divide this number by the amphour rating of a single battery in your system and as usual remember to round up.

First determine the input load to your inverter. Divide the out put load by the efficiency of the inverter. Divide your inverters max wattage rating, rounding up, to determine how many inverters you need.

Next determine the amperage of the charge controller. Divide the inverter input by the voltage of the system (standard is 12V). Divide the controllers max amp rating by this number, rounding up, to determine how many controllers you need.

Determine Kwh/day by multiplying the load by hours it runs per day, then divide by 1000.

Fitting it together

Page1/2

To find the number of solar panels utilize PVwatts for the avg hours of max sun in you location per day. Multiply by the watt output of your solar panel. Now divide by 1000. And divide this number into the Kwh/day of your load. Round up as always.

Determine how many batteries you need. Multiply your days of battery operations by the Kwh/day of your load. Divide this number by the voltage of your system (common to be 12V), now divide by 1000 to convert to amp hours. Divide this number by the amp hour rating of one of your batteries, round up and this is how many batteries you need.

Fitting it together

Page2/2