The Vocabulary of Electrical Power Solar Under The Sun Solar School May 2010

` The purpose of this presentation is to review electrical terms such as volts, amps, and watts And to relate these terms to components in a solar power system

Picture of Four 6-volt batteries, Part-au-Prince50 amp and 20 amp circuit breakers Picture of Four 155 watt solar panels Archaie, Haiti Four 125 amp-hour batteries Archaie, Haiti

DC vs. AC electricity Photovoltaic (PV) panels and batteries are sources of DC power – In a DC system, current only flows in one direction Electric utilities, generators, and inverters are sources of AC power – In an AC system, current changes direction tens of times a second.

Water analogy for DC electricity Current is the flow of electrons in a circuit. – Units of current are amperes or amps – Think of current as the water flowing through a hose Voltage is the electrical potential – Units of voltage are volts – Think of voltage as the water pressure in a hose

Current Current can only flow when there is a complete loop – V = I*R, where R is resistance – If the load goes to 0 ohms resistance, this is called a short circuit + - LOAD current, I

Voltage Voltage exists even if there is no current When the resistance is infinite, is an open-circuit condition + - current, I = 0 12 volts

Power Power is the rate at which work is done Units of power are watts Power is the product of current and voltage P = V * I + - LOAD current, I V V

Power Examples A solar panel is outputting 4 amps at 25 volts. How much power is the solar panel producing? P = 4 amps * 25 volts = 100 watts A 150 watt solar panel operating at rated output provides 5 amps of current. What is the full-output voltage? P = V*I, so V = P/I = 150 watts/5 amps = 30 volts

Energy A photovoltaic panel converts solar energy (light) into electrical energy A battery stores energy and delivers energy Units of energy are watt-hours E = P * t, where t is time

Energy examples How much energy will a 155-watt PV panel produce when it operates at rated power for 5 hours? E = 155 watts * 5 hours = 775 watt-hours We will often refer to Energy in a particular time period – How many watt-hours will a solar array generate each day if it operates at rated output for 5 hours/day? E/day = 155 watts * 5 hours/ day = 775 watt- hours/day

How many solar panels? In a SUTS solar power system, the PV panels must provide enough watt-hours of energy each week to meet the watt-hour needs of the equipment and to keep the batteries at full charge. This calculation will normally be performed by a graduate of Solar 2

How many batteries? The batteries must be able to provide enough watt-hours of energy to meet the watt-hour requirements of the equipment for at least 3 days of no sun, while maintaining at least 50% of their total charge. This calculation will normally be performed by a graduate of Solar 2

Deep-cycle batteries Batteries for solar power systems should be “deep-cycle”. This means they are designed to provide a steady flow of power for an extended period of time Common sources of deep-cycle batteries are golf-cart batteries and wheelchair batteries

Batteries Batteries are characterized by two numbers – Their voltage (usually 6 or 12 volts) – Their amp-hour capacity Amp-hours are an indicator of how much charge a battery can store, and Amp-hours are an indicator of how many hours a battery can supply a given number of amps

How does this relate to Solar 1? Solar 1 graduates and Solar 2 graduates will complete the Solar Suitability Survey (SSS) during the partnership development visits with the operating partners

Solar Suitability Survey One component of the survey is determining what local or regional sources of solar equipment exist Where a network exists (like Haiti) a solar supplier will have already been identified

Camp Hopewell, CWU circa 2008 The initial system still used to test equipment and ideas DC Slo-pump replaced with Sun Pumps circulation pump AC pump tested and DC pumps adopted

Archaie, HaitiJuly, x 155-watt panels Water treatment system with UV disinfection Submersible pump Water fountains at school yard across the street Security lighting for water building

Institute Racine, Port-au-Prince, HaitiMarch watt solar panels Water treatment system with ozone disinfection Lighting for water building Outlets for charging computers and cell phones