How to determine whether solar energy is right for your site EE80S: Sustainability Engineering and Practice Fall 2007

PV System Components PV generates electrical current from solar radiation Nuclear fusion generates photons Controls charging of batteries Energy storage Converts direct current (DC) to alternating current (AC)

Insolation Zone Map

Calculating Electricity Bill Savings for a Net-Metered PV System Determine the system's size in kilowatts (kW). A reasonable range is from1 to 5 kW. This value is the “kW of PV” input for the equations below. Based on your geographic location, select the energy production factor from the map below for the “kWh/kW-year” input for the equations. Energy from the PV system = (kW of PV) x (kWh/kW-year) = kWh/year Divide this number by 12 if you want to determine your monthly energy reduction. Energy bills savings = (kWh/year) x (Residential Rate)/ 100 = $/year saved (Residential Rate in this above equation should be in dollars per kWh; for example, a rate of 10 cents per kWh is input as $0.10/kWh.) For example, a 2-kW system in Denver, CO, at a residential energy rate of $0.07/kWh will save about $266 per year: 1,900 kWh/kW-year x $0.07/kWhx 2 kW = $266/year.

Energy Production Factor

Required Area for PV’s

Roof Mounting Systems

Ground Mounting Systems

Photovoltaic Cell

Tilt Angle To capture the maximum amount of solar radiation over a year, the solar array should be tilted at an angle approximately equal to a site's latitude, and facing within 15º of due south. (Santa Cruz North Latitude) To optimize winter performance, the solar array can be tilted 15º more than the latitude angle, and to optimize summer performance, 15º less than the latitude angle. At any given instant, the array will output maximum available power when pointed directly at the sun.

System Configurations

Grid Connected PV System

On-Grid

Off-Grid Keewaydin Island, Gulf of Mexico

Off-Grid

Power Requirements

Technical Specifications System Overview System type: Off-grid battery-based PV system Location: Keewaydin Island, Florida Solar resource: 5.5 average daily peak sun hours Production: 400 AC KWH average per month Photovoltaics Modules: 12 RWE Schott, ASE 300-DGF/17, 300 W STC, 17.0 Vmp, 12 VDC nominal Array: Six, two-module series strings, 3,600 W STC total, 34 Vmp, 24 VDC nominal Array combiner box: Two OutBack PSPV, 30 A breakers Array disconnects: 60 A breakers in DC250 and PSDC-175 enclosures Array installation: Custom aluminum rails, SSW orientation, 30-degree tilt Energy Storage Batteries: Four HuP Solar-One, SO , 12 VDC nominal, 1,270 AH at 20-hour rate, flooded lead-acid Battery pack: 24 VDC nominal, 2,540 AH total, 48.8 KWH total at 80% DOD Battery/inverter disconnects: Xantrex DC250, two 250 A breakers; OutBack PSDC-175, two 175 A breakers and one 250 A breaker Balance of System Charge controllers: Three Xantrex C40s, 40 A, PWM Inverters: Two Xantrex SW4024, 4,000 W each, 8,000 W total, 24 VDC nominal input, series stacked for 120/240 VAC output; one Trace SW4024, 4,000 W, 24 VDC nominal input, and two OutBack FX2024, 2,000 W each, 8,000 W total, 24 VDC nominal input, series stacked for 120/240 VAC output Engine generator: Onan GGDB 20 KW watercooled, propane-fired, remote electric start, 240 VAC output; average yearly run time is 200 to 300 hours System performance metering: Xantrex TM500A AH Meter, OutBack MATE, PC with RightHand Engineering software

Kyocera Solar Modules

Batteries Four large, industrial quality, deep-cycle batteries provide energy storage for the island home.

Batteries Flooded Lead Acid Absorbed Glass Mat Sealed Lead Acid (AGM) Gelled Electrolyte Sealed Lead Acid

Batteries

System Cost

Cost of Iraq War $460,491,648,  7% of the number of homes in the US (2006)

Boulder Creek Site

Mercey Hot Springs Mercey’s electrical system is comprised of: 1 kW (kilowatt) solar array 3 kW wind powered generator 15 kW diesel generator (waste vegetable oil) (2) - 5 kW Inverters 1,350 amp hours of battery storage

Solar Water Heaters