Original Presentation by J. M. Pearce 2006 Email profpearce_at_gmail.com 2 Outline Part I
What is a photovoltaic system
Cell Module and Array
PV System Design Basics
3 The Cell The Module and The Array 4 Balance of System (BOS)
The BOS typically contains
Structures for mounting the PV arrays or modules
Power conditioning equipment that massages and converts the do electricity to the proper form and magnitude required by an alternating current (ac) load.
Sometimes also storage devices such as batteries for storing PV generated electricity during cloudy days and at night.
5 Three Types of Systems
Stand-alone systems - those systems which use photovoltaics technology only and are not connected to a utility grid.
Hybrid systems - those systems which use photovoltaics and some other form of energy such as diesel generation or wind.
Grid-tied systems - those systems which are connected to a utility grid.
6 Stand Alone PV System
7 Examples of Stand Alone PV Systems
PV panel on a water pump in Thailand
PV powers stock water pumps in remote locations in Wyoming
8 Examples of Stand Alone PV Systems
Communications facilities can be powered by solar technologies even in remote rugged terrain. Also if a natural or human-caused disaster disables the utility grid solar technologies can maintain power to critical operations
9 Examples of Stand Alone PV Systems
This exhibit dubbed Solar Independence is a 4-kW system used for mobile emergency power.
while the workhorse batteries that can store up to 51 kW-hrs of electricity are housed in a portable trailer behind the flag.
The system is the largest mobile power unit ever built
10 Examples of Stand Alone PV Systems
Smiling child stands in front of Tibetan home that uses 20 W PV panel for electricity
PV panel on rooftop of rural residence
11 Hybrid PV System 12 Examples of Hybrid PV Systems
Ranching the Sun project in Hawaii generates 175 kW of PVpower and 50 kW of wind power from the five Bergey 10 kW wind turbines
13 Examples of Hybrid PV Systems
A fleet of small turbines PV panels in the foreground
14 Examples of Hybrid PV Systems
PV / diesel hybrid power system - 12 kW PV array 20 kW diesel genset
This system serves as the master site for the top gun Tactical Air Combat Training System (TACTS) on the U.S. Navys Fallon Range.
15 Grid-Tied PV System 16 Examples of Grid Tied Systems
National Center for Appropriate Technology Headquarters
17 Examples of Grid Tied Systems
The worlds largest residential PV project
18 Designing a PV System
Determine the load (energy not power)
You should think of the load as being supplied by the stored energy device usually the battery and of the photovoltaic system as a battery charger. Initial steps in the process include
Calculating the battery size if one is needed
Calculate the number of photovoltaic modules required
Assessing the need for any back-up energy of flexibility for load growth
Stand-Alone Photovoltaic Systems A Handbook of Recommended Design Practices details the design of complete photovoltaic systems.
19 Determining Your Load
The appliances and devices (TVs 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.
20 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
21 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.
22 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
daily Amp hours
number of days of storage capacity ( typically 5 days no input )
1 x 2 A-hrs needed
Note For grid tied inverter losses
23 Temperature Multiplier
Temp oF80 F70 F60 F50 F40 F30 F20 F
Temp oC26.7 C21.2 C15.6 C10.0 C4.4 C-1.1 C-6.7 C Multiplier1.001.041.111.191.301.401.59 Select the closest multiplier for the average ambient winter temperature your batteries will experience. 24 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.
25 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.
26 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/o ld_data/nsrdb/
27 How Much Solar Irradiance Do You Get 28 Solar Radiation
On any given day the solar radiation varies continuously from sunup to sundown and depends on cloud cover sun position and content and turbidity of the atmosphere.
The maximum irradiance is available at solar noon which is defined as the midpoint in time between sunrise and sunset.
Insolation (now commonly referred as irradiation) differs from irradiance because of the inclusion of time. Insolation is the amount of solar energy received on a given area over time measured in kilowatt-hours per square meter squared (kW-hrs/m2) - this value is equivalent to peak sun hours.
29 Peak Sun Hours
Peak sun hours is defined as the equivalent number of hours per day with solar irradiance equaling 1000 W/m2 that gives the same energy received from sunrise to sundown.
Peak sun hours only make sense because PV panel power output is rated with a radiation level of 1000W/m2.
Many tables of solar data are often presented as an average daily value of peak sun hours (kW-hrs/m2) for each month.
30 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 modules 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
31 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
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
VIR or R V/I 33 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
34 Books for Designing a PV System
Steven J. Strong and William G. Scheller The Solar Electric House Energy for the Environmentally- Responsive Energy-Independent Home by Chelsea Green Pub Co 2nd edition 1994.
This book will help with the initial design and contacting a certified installer.
35 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).
36 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.
37 Solar Photovoltaics is the Future 38 Acknowledgements
This is the second in a series of presentations created for the solar energy community to assist in the dissemination of information about solar photovoltaics.
This work was supported from a grant from the Pennsylvania State System of Higher Education.
The author would like to acknowledge assistance in creation of this presentation from Heather Zielonka Scott Horengic and Jennifer Rockage.
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