EE580 Solar Cells Todd J. Kaiser Lecture 09 Photovoltaic Systems Montana State University: Solar Cells Lecture 9: PV Systems 1 Several types of operating modes Centralized power plant Large PV system located in an optimum location, feeding into the grid Distributed Grid tied

Small residential type systems Stand Alone systems No grid connection needed or wanted Montana State University: Solar Cells Lecture 9: PV Systems 2 Residential Side Mounted You loose as much as 50% of the power if one cell is shadowed Could have future issues when the tree matures and shadows PV

system Montana State University: Solar Cells Lecture 9: PV Systems 3 Residential Stand Alone Montana State University: Solar Cells Lecture 9: PV Systems 4 Roof Mounted System National Center for

Appropriate Technology Headquarters (Butte, MT) 60 Shell SP75 modules each rated at 75 Watts Peak electrical output of system is 4.5 kilowatts 48 volt system connected to utility grid with inverter Provides 15% of building electrical consumption Montana State University: Solar Cells Lecture 9: PV Systems Hybrid System Montana State University: Solar Cells Lecture 9: PV Systems

6 Mobile Systems Montana State University: Solar Cells Lecture 9: PV Systems 7 Simple Stationary Montana State University: Solar Cells Lecture 9: PV Systems 8

Emergency Montana State University: Solar Cells Lecture 9: PV Systems 9 Temperature Dependence ? Solar Cells loose efficiency with the increase in temperature Colder is better Montana State University: Solar Cells Lecture 9: PV Systems 10

Solar Heating Solar heating (70-90%) is more efficient than photovoltaic (15%-20%) but electricity generally is more useful than heat. Montana State University: Solar Cells Lecture 9: PV Systems 11 Solar Cell Basics Photovoltaic Systems Cell Panel Array Balance of System (BOS) PV Panel ~

/ = Mounting Structures Storage Devices Power Conditioners Battery Load DC AC DC AC

DC Load AC Load Montana State University: Solar Cells Lecture 9: PV Systems Inverter Charge Regulator 12 Modularity: Solar Cell to Array Cell Module or Panel

Array Cell (c-Si 1010 cm2 =15% P=1.5Wp V=0.5V I=3A) Solar panel (36 c-Si cells P=54Wp I=3A V=18V ) Solar array Montana State University: Solar Cells Lecture 9: PV Systems 13 Specifications of PV Modules Type c:Si, a-Si:H, CdTe

Rated Power Max: Pmax (Wp) Rated Current: IMPP (A) Rated Voltage: VMPP (V) Short Circuit Current: ISC (A) Open Circuit Voltage: VOC (V) Configuration (V) Cells per Module (#) Dimensions (cm x cm) Warranty (years) Montana State University: Solar Cells

Lecture 9: PV Systems 14 Storage Devices (Batteries) Advantages Back up for night and cloudy days Disadvantages Decreases the efficiency of PV system Only 80% of energy stored retainable Adds to the expense of system Finite Lifetime ~ 5 - 10 years Added floor space, maintenance, safety concerns Montana State University: Solar Cells Lecture 9: PV Systems

15 Power Conditioners (Inverters) Limit Current and Voltage to Maximize Power Convert DC Power to AC Power Match AC Power to Utilities Network Protect Utility Workers during Repairs Montana State University: Solar Cells Lecture 9: PV Systems 16

Simple DC Direct Powering of Load No Energy Storage DC Montana State University: Solar Cells Lecture 9: PV Systems 17 Small DC Home and Recreational Use Charge Regulator DC

DC Load Single Panel Single Battery Montana State University: Solar Cells Lecture 9: PV Systems 18 Large DC Home and Recreational Use Industrial Use Charge Regulator DC DC Load Multiple Panels

Multiple Batteries Montana State University: Solar Cells Lecture 9: PV Systems 19 Large AC/DC Both AC and DC loads DC Charge Regulator DC Load ~ /

= Inverter AC AC Load Multiple Panels Multiple Batteries Montana State University: Solar Cells Lecture 9: PV Systems 20 Utility Grid Connected No On-Site Energy Storage

Inverter ~ / = AC AC Load Multiple Panels Electric Grid Montana State University: Solar Cells Lecture 9: PV Systems 21 Hybrid System

Supplement Generator DC Charge Regulator DC Load ~ / Inverter = AC AC Load AC Generator (Wind turbine)

Multiple Panels Multiple Batteries Montana State University: Solar Cells Lecture 9: PV Systems 22 PV System Design Rules 1. Determine the total load current and operational time 2. Add system losses 3. Determine the solar irradiation in daily equivalent sun hours (EHS) 4. Determine total solar array current requirements 5. Determine optimum module arrangement for solar array

6. Determine battery size for recommended reserve time Montana State University: Solar Cells Lecture 9: PV Systems 23 Determining Your Load The appliances and devices (TV's, computers, lights, water pumps etc.) that consume electrical power are called loads. Important : examine your power consumption and reduce your power needs as much as possible. Make a list of the appliances and/or loads you are going to run from your solar electric system. Find out how much power each item consumes while

operating. Most appliances have a label on the back which lists the Wattage. Specification sheets, local appliance dealers, and the product manufacturers are other sources of information. Power Consumption (DC) DC [W] Television 60 Refrigerator 60 Fan 15-30 Radio/tape 35 Lighting Bathroom 25-50 Bedroom 25-50 Dining room 70

Kitchen 75 Living room 75 Montana State University: Solar Cells Lecture 9: PV Systems 25 Power Consumption (AC) AC [W] AC [W] Television 175 Radio 15-80 Appliances

Lighting Bathroom 75 Bedroom 75 Dining room 100 Kitchen 100 Living room 75 Tools Saw circular 800-1200 Saw table 800-950

Drill 240 Refrigerator 350 Freezer 350-600 Microwave oven 3001450 Toaster 1100-1250 Washing machine 375550 Coffee maker 850-1500 Air conditioner 30004000 Montana State University: Solar Cells Lecture 9: PV Systems 26 Determining your Loads II Calculate your AC loads (and DC if necessary)

List all AC loads, wattage and hours of use per week (Hrs/Wk). Multiply Watts by Hrs/Wk to get Watt-hours per week (WH/Wk). Add all the watt hours per week to determine AC Watt Hours Per Week. Divide by 1000 to get kW-hrs/week Determining the Batteries Decide how much storage you would like your battery bank to provide (you may need 0 if grid tied) expressed as "days of autonomy" because it is based on the number of days you expect your system to provide power without receiving an input charge from the solar panels or the grid.

Also consider usage pattern and critical nature of your application. If you are installing a system for a weekend home, you might want to consider a larger battery bank because your system will have all week to charge and store energy. Alternatively, if you are adding a solar panel array as a supplement to a generator based system, your battery bank can be slightly undersized since the generator can be operated in needed for recharging. Batteries II Once you have determined your storage capacity, you are ready to consider the following key parameters: Amp hours, temperature multiplier, battery size

and number To get Amp hours you need: 1. daily Amp hours 2. number of days of storage capacity typically 5 days no input ) 1 x 2 = A-hrs needed Note: For grid tied inverter losses ( Temperature Multiplier

Temp oF 80 F 70 F 60 F 50 F 40 F 30 F 20 F Temp oC 26.7 C 21.2 C 15.6 C 10.0 C 4.4 C -1.1 C -6.7 C

Multiplier 1.00 1.04 1.11 1.19 1.30 1.40 1.59 Select the closest multiplier for the average ambient winter temperature your batteries will experience. Determining Battery Size Determine the discharge limit for the batteries ( between 0.2 - 0.8 )

Deep-cycle lead acid batteries should never be completely discharged, an acceptable discharge average is 50% or a discharge limit of 0.5 Divide A-hrs/week by discharge limit and multiply by temperature multiplier Then determine A-hrs of battery and # of batteries needed - Round off to the next highest number. This is the number of batteries wired in parallel needed. Total Number of Batteries Wired in Series Divide system voltage ( typically 12, 24 or 48 ) by battery voltage. This is the number of batteries wired in series needed.

Multiply the number of batteries in parallel by the number in series This is the total number of batteries needed. Determining the Number of PV Modules First find the Solar Irradiance in your area Irradiance is the amount of solar power striking a given area and is a measure of the intensity of the sunshine. PV engineers use units of Watts (or kiloWatts) per square meter (W/m2) for irradiance. For detailed Solar Radiation data available for your area in the US: http://rredc.nrel.gov/solar/old_data/nsrdb/

How Much Solar Irradiance Do You Get? Calculating Energy Output of a PV Array Determine total A-hrs/day and increase by 20% for battery losses then divide by 1 sun hours to get total Amps needed for array Then divide your Amps by the Peak Amps produced by your solar module You can determine peak amperage if you divide the module's wattage by the peak power point voltage Determine the number of modules in each series string needed to supply necessary DC battery Voltage

Then multiply the number (for A and for V) together to get the amount of power you need P=IV [W]=[A]x[V] Charge Controller Charge controllers are included in most PV systems to protect the batteries from overcharge and/or excessive discharge. The minimum function of the controller is to disconnect the array when the battery is fully charged and keep the battery fully charged without damage. The charging routine is not the same for all batteries: a charge controller designed for lead-acid batteries should not be used to control NiCd batteries. Size by determining total Amp max for your array Wiring

Selecting the correct size and type of wire will enhance the performance and reliability of your PV system. The size of the wire must be large enough to carry the maximum current expected without undue voltage losses. All wire has a certain amount of resistance to the flow of current. This resistance causes a drop in the voltage from the source to the load. Voltage drops cause inefficiencies, especially in low voltage systems ( 12V or less ). See wire size charts here: www.solarexpert.com/Photowiring.html Inverters

For AC grid-tied systems you do not need a battery or charge controller if you do not need back up power just the inverter. The Inverter changes the DC current stored in the batteries or directly from your PV into usable AC current. To size increase the Watts expected to be used by your AC loads running simultaneously by 20% Inverters For AC grid-tied systems you do not need a battery or

charge controller if you do not need back up power just the inverter. The Inverter changes the DC current stored in the batteries or directly from your PV into usable AC current. To size increase the Watts expected to be used by your AC loads running simultaneously by 20% Books for the DIYer If you want to do everything yourself also consider these resources: Richard J. Komp, and John

Perlin, Practical Photovoltaics: Electricity from Solar Cells, Aatec Pub., 3.1 edition, 2002. (A laymans treatment). Roger Messenger and Jerry Ventre, Photovoltaic Systems Engineering, CRC Press, 1999. (Comprehensive specialized engineering of PV systems). Photovoltaics Design and Installation Manual Photovoltaics: Design &

Installation Manual by SEI Solar Energy International, 2004 A manual on how to design, install and maintain a photovoltaic (PV) system. This manual offers an overview of photovoltaic electricity, and a detailed description of PV system components, including PV modules, batteries, controllers and inverters. Electrical loads are also addressed, including lighting systems, refrigeration, water pumping, tools and appliances.