Design of Small Photovoltaic (PV) Solar-Powered Water Pump Syste

Technical Note No. 28
PORTLAND, OREGON
Design of Small Photovoltaic (PV)
Solar-Powered Water Pump Systems
Natural Resources Conservation Service
October 2010
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 ii
Issued October 2010
Cover photo courtesy of Nicholle Kovach, Basin Engineer, USDA NRCS.
Trade names mentioned are for specific information and do not constitute a guarantee or warranty of the product by the Department of Agriculture or an endorsement by the Department over other products not mentioned.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, re-prisal, or because all or a part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720–2600 (voice and TDD).
To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW., Washington, DC 20250–9410, or call (800) 795–3272 (voice) or (202) 720–6382 (TDD). USDA is an equal opportunity provider and employer.
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 iii
ACKNOWLEDGEMENTS
This technical note was written by Teresa D. Morales, Oregon State Design Engineer, United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), Portland, Oregon, and John Busch, Oregon State Irrigation Engineer, USDA NRCS, Baker City, Oregon.
Drawings by Kristi Yasumiishi, Civil Engineering Technician, USDA NRCS, Portland, Oregon.
Reviewed by Dave Dishman, Oregon State Engineer, USDA NRCS, Portland, Oregon; Stefanie Aschmann, Leader of Energy Technology Development Team, NRCS West National Technology Support Center (WNTSC), Portland, Oregon; Peter Robinson, Water Management Engineer, NRCS WNTSC, Portland, Oregon; Clarence Prestwich, Irrigation Engineer, NRCS WNTSC, Portland, Oregon; Kip Yasumiishi, Civil Engineer, NRCS WNTSC, Portland, Oregon; Kelly Albers, Basin Engineer, USDA NRCS, Tangent, Oregon; Ginny Cairo, Basin Engineer, USDA NRCS, Roseburg, Oregon; Bill Cronin, Basin Engineer, USDA NRCS, Medford, Oregon; Kevin Shaw, Basin Engineer, USDA NRCS, Baker City, Oregon.
Edited by Erin McDuff, Administrative Assistant, USDA NRCS, Portland, Oregon.
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 iv
PREFACE
The intent of this technical publication is to provide general guidance on the design of small solar-powered water pump systems for use with livestock operations or irrigation systems. This document provides a review of the basic elements of electricity, a description of the different components of solar-powered water pump systems, important planning considerations, and general guidance on designing a solar-powered water pump system. This publication also provides design examples for typical design scenarios and standard drawings for use by the reader. However, this technical note is not intended to be used as a standalone document. Instead, users are encouraged to consult the NRCS National Engineering Manual (NEH 210) on hydraulics and irrigation engineering for additional assistance in the design of water delivery systems.
All sources used in the development of this technical note are provided in the References section at the back of the document.
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 v
CONTENTS
1. INTRODUCTION ............................................................................................................................................ 1
1.0 ELECTRICITY BASICS .............................................................................................................................................. 2
1.1 THE PHOTOELECTRIC EFFECT .................................................................................................................................. 2
2. SOLAR RADIATION, SOLAR IRRADIANCE, AND SOLAR INSOLATION .............................................................. 3
2.0 SEASONAL AND LATITUDE VARIATION ....................................................................................................................... 5
2.1 CLOUD COVER ..................................................................................................................................................... 5
3. PHOTOVOLTAIC (PV) PANELS ........................................................................................................................ 6
3.0 PV PANEL ELECTRICAL CHARACTERISTICS .................................................................................................................. 6
3.1 PV PANEL ORIENTATION AND TRACKING .................................................................................................................. 7
3.2 ENVIRONMENTAL FACTORS .................................................................................................................................... 8
4.0 STRUCTURE AND FOUNDATION CONSIDERATIONS ....................................................................................... 8
4.0 STRUCTURAL SUPPORTS FOR PV PANELS ................................................................................................................... 8
4.1 MOUNTING POSTS ............................................................................................................................................... 8
4.2 EMBEDMENT CONSIDERATIONS FOR MOUNTING POSTS ............................................................................................... 9
4.3 CORROSION PROTECTION ....................................................................................................................................... 9
5.0 ELECTRICAL CONTROLLERS ......................................................................................................................... 10
6.0 SOLAR-POWERED PUMPS ........................................................................................................................... 11
6.0 PUMP SELECTION AND SYSTEM DESIGN .................................................................................................................. 11
6.1 SOLAR-POWERED PUMP CHARACTERISTICS ............................................................................................................. 13
7. DESIGN PROCESS ........................................................................................................................................ 14
7.0 STEP 1 – WATER REQUIREMENT ........................................................................................................................... 14
7.1 STEP 2 – WATER SOURCE .................................................................................................................................... 14
7.2 STEP 3 – SYSTEM LAYOUT .................................................................................................................................... 15
7.3 STEP 4 – WATER STORAGE .................................................................................................................................. 17
7.4 STEP 5 – SOLAR INSOLATION AND PV PANEL LOCATION............................................................................................. 17
7.5 STEP 6 – DESIGN FLOW RATE FOR THE PUMP .......................................................................................................... 17
7.6 STEP 7 – TOTAL DYNAMIC HEAD (TDH) FOR THE PUMP ............................................................................................ 18
7.7 STEP 8 – PUMP SELECTION AND ASSOCIATED POWER REQUIREMENT ........................................................................... 18
7.8 STEP 9 – PV PANEL SELECTION AND ARRAY LAYOUT ................................................................................................. 18
7.9 STEP 10 – PV ARRAY MOUNTING AND FOUNDATION REQUIREMENTS .......................................................................... 18
7.10 STEP 11 – WATER FLOW RATES AND DELIVERY POINT PRESSURE ................................................................................ 19
7.11 STEP 12 – SUMMARY DESCRIPTION OF THE SYSTEM .................................................................................................. 19
8. ADDITIONAL CONSIDERATIONS .................................................................................................................. 19
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 vi
APPENDIXES
APPENDIX A: REFERENCES ............................................................................................................................. 20
APPENDIX B: ADDITIONAL RESOURCES .......................................................................................................... 21
APPENDIX C: DESIGN EXAMPLES ................................................................................................................... 22
DESIGN EXAMPLE 1: SOLAR-POWERED WATER PUMP SYSTEM USING SURFACE WATER (A STREAM) AS A WATER SOURCE ..... 22
DESIGN EXAMPLE 2: SOLAR-POWERED WATER PUMP SYSTEM USING SUBSURFACE WATER (A WELL) AS A WATER SOURCE ... 28
APPENDIX D: SOLAR INSOLATION VALUES FOR OREGON .............................................................................. 36
APPENDIX E: NREL APPROACH TO DETERMINING SOLAR INSOLATION VALUES ............................................ 46
APPENDIX F: STANDARD DRAWINGS............................................................................................................. 50
APPENDIX G: FRICTION HEAD LOSS FOR SCHEDULE 40 PVC PLASTIC PIPE ...................................................... 56
APPENDIX H: SAMPLE WELL LOG ................................................................................................................... 57
APPENDIX I: OREGON DEPARTMENT OF FISH AND WILDLIFE FISH SCREENING CRITERIA .............................. 58
APPENDIX J: SOLAR PANEL WIRING .............................................................................................................. 60
APPENDIX K: GLOSSARY OF SOLAR-POWERED WATER PUMP TERMS ............................................................ 61
LIST OF FIGURES
FIGURE 1 – A TYPICAL SOLAR-POWERED WATER PUMP SYSTEM, WHICH INCLUDES A SOLAR ARRAY, CONTROLLER, PUMP, AND STORAGE TANK. (SOURCE: “THE MONTANA AGSOLAR PROJECT – EXPANDING THE AGRICULTURAL USES OF SOLAR ENERGY IN MONTANA.”) 1
FIGURE 2 – THE PHOTOELECTRIC EFFECT AND SUBSEQUENT ELECTRON MOTION. (IMAGE INSPIRED BY ................................................. 3
FIGURE 3 – SOLAR IRRADIANCE AND PEAK SUN HOURS. .............................................................................................................. 4
FIGURE 4 – EXAMPLE SUMMER AND WINTER SUN ELEVATION AND ANGLE. (SOURCE: “RENEWABLE ENERGY PRIMER-SOLAR.”) ............... 5
FIGURE 5 – SOLAR CELL, PV SOLAR PANEL, AND PV PANEL ARRAY. (SOURCE: “GUIDE TO SOLAR POWERED WATER ............................... 6
FIGURE 6 – SOLAR PANEL TILT ANGLES: WINTER TILT WITH MORE ANGLE FROM HORIZONTAL [LEFT] AND SUMMER TILT WITH LESS............. 8
FIGURE 7 – PV SOLAR ARRAY WITH STORAGE TANK AND STOCK. ................................................................................................. 11
FIGURE 8 – TYPICAL SURFACE INSTALLATION WITH PERTINENT PARAMETERS. ................................................................................ 12
FIGURE 9 – TYPICAL WELL INSTALLATION WITH PERTINENT PARAMETERS...................................................................................... 12
FIGURE 10 – EXAMPLE SOLAR-POWERED PUMP PERFORMANCE CURVES FOR A POSITIVE DISPLACEMENT PUMP. ................................... 13
FIGURE 11 – EXAMPLE SOLAR-POWERED PUMP PERFORMANCE CURVES FOR A CENTRIFUGAL PUMP. ................................................. 13
FIGURE 12 – A PLAN OF AN EXAMPLE WATERING SYSTEM WITH A STORAGE TANK AND PV ARRAY. .................................................... 16
FIGURE 13 – ELEMENTS OF A TYPICAL INSTALLATION SUPPLIED BY A SURFACE WATER SOURCE. ......................................................... 16
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 vii
LIST OF TABLES
TABLE 1 – ELECTRICITY FOR NON-ELECTRICAL ......................................................................................................................... 2
TABLE 2 – SOLAR RADIATION FOR FLAT-PLATE COLLECTORS FACING SOUTH AT A FIXED TILT OF 43° FOR NORTH BEND, OR ................ 4
TABLE 3 – EXAMPLE PV SOLAR PANEL ELECTRICAL .................................................................................................................. 6
TABLE 4 – TYPICAL WATER USE REQUIREMENTS ................................................................................................................... 14
LIST OF EQUATIONS
EQUATION 1...................................................................................................................................................................... 2
EQUATION 2...................................................................................................................................................................... 2
EQUATION 3.................................................................................................................................................................... 18
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 1
1. INTRODUCTION
Photovoltaic (PV) panels are often used for agricultural operations, especially in remote areas or where the use of an alternative energy source is desired. In particular, they have been demonstrated time and time again to reliably produce sufficient electricity directly from solar radiation (sunlight) to power livestock and irrigation watering systems.
A benefit of using solar energy to power agricultural water pump systems is that increased water requirements for livestock and irrigation tend to coincide with the seasonal increase of incoming solar energy. When properly designed, these PV systems can also result in significant long-term cost savings and a smaller environmental footprint compared to conventional power systems.
The volume of water pumped by a solar-powered system in a given interval depends on the total amount of solar energy available in that time period. Specifically, the flow rate of the water pumped is determined by both the intensity of the solar energy available and the size of the PV array used to convert that solar energy into direct current (DC) electricity.
The principle components in a solar-powered water pump system (shown in Figure 1, right) include:
• The PV array and its support structure,
• An electrical controller, and
• An electric-powered pump.
It is important that the components be designed as part of an integrated system to ensure that all the equipment is compatible and that the system operates as intended. It is therefore recommended that all components be obtained from a single supplier to ensure their compatibility.
The following information is required to design a PV-powered pump:
• The site-specific solar energy available (referred to as “solar insolation”).
• The volume of water required in a given period of time for livestock or irrigation purposes, as well as for storage. (A storage volume equal to a three-day water requirement is normally recommended for livestock operations as a backup for the system’s safety features and cloudy days.)
• The total dynamic head (TDH) for the pump.
• The quantity and quality of available water.
• The system’s proposed layout and hydraulic criteria.
The following sections will first provide an introduction to the basic concepts involved in solar-powered pump systems, then descriptions of and design considerations for the previously mentioned, individual system components. (See Appendix K: Glossary of Solar-Powered Water Pump Terms for definitions of the technical terms and abbreviations used.)
Figure 1 – A typical solar-powered water pump system, which includes a solar array, controller, pump, and storage tank. (Source: “The Montana Agsolar Project – Expanding the Agricultural Uses of Solar Energy in Montana.”)
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 2
1.0 Electricity Basics
It is important to be familiar with fundamental electrical concepts, such as energy, voltage, amperage, and resistance, before you begin to design a solar-powered water pump system.
Voltage is the electrical potential (i.e. the pressure) in the solar-powered system. It is measured in units of Volts (V).
Amperage refers to the movement or flow of electrons (i.e. the electrical current) through the system. It is measured in units of Amps (A).
Voltage multiplied by amperage is the power produced. It is measured in units of watts (Pw), as shown in Equation 1:
Electrical energy is the amount of power generated over a period of time. Energy is typically measured in kilowatt-hours (kWh).
Lastly, resistance is a measure of a material’s resistance to the flow of electrons across it. It is measured in Ohms (Ω).
A good analogy to help describe the flow of electrons in a wire is the flow of water through a pressurized line. In order to illustrate this analogy, Table 1 (right) compares the flow of electricity through a circuit with the flow of water through a pipe.
As with water flowing through a pipe, resistance (friction, in the case of water) in the electrical line results in an energy loss in the system. It is influenced by the length, size, and type of wire conductor. Specifically, resistance is proportional to the length of the wire and inversely proportional to the cross-sectional area of the wire. In other words, the longer the wire, the greater the loss and the larger the wire diameter, the less the loss. The energy
Table 1 – Electricity for Non-Electrical
Engineers
Electricity in a Wire
Water in a Pipe
Amp
(flow of electrons)
Q
(flow rate of water)
Volts
(energy potential)
Pressure
(energy potential)
Watts (power)
= Amps x Volts
Hydraulic/Water Power = Q x Pressure
Resistance
Friction + Minor Losses
High Voltage, Small Wire = High Amps, High Resistive losses, Heat and Fires
High Pressure, Small Pipe = High Velocity, High Friction Losses, Blown Pipe
loss is also influenced by the wire material: a good conductor, such as copper, has a low resistance and will result in less energy loss.
Another effective way to reduce electrical losses in a system is to decrease the current flow. Power losses in an electrical circuit are proportional to the square of the current, as shown in Equation 2:
Consequently, as indicated in Equations 1 and 2, increasing the voltage while reducing the current will result in the same power transmission, but with less power loss. Therefore, higher voltage pumps tend to be more efficient than lower voltage pumps, assuming all other properties are similar.
1.1 The Photoelectric Effect
PV systems harness the sun’s energy by converting it into electricity via the photoelectric effect. This occurs when incoming photons interact with a conductive surface, such as a silicon cell or metal film, and electrons in the material become excited and jump from one conductive layer to the other, as shown in Figure 2, on the following page.
Power Loss = Current2 x Resistance
Equation 2
Watts = Volts x Amps
Equation 1
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 3
In this figure, the excitation of electrons and their movement from the p-layer to the n-layer results in a voltage differential across the electrical circuit, causing electrons to flow through the rest of the circuit to maintain a charge balance. The system is designed so that there is an electrical load in the external circuit, permitting the current flow to perform a useful function. In other words, the behavior of electrons in the solar cell creates a voltage that can be utilized to, for example, operate a water pump system.
2. SOLAR RADIATION, SOLAR IRRADIANCE, AND SOLAR INSOLATION
To design a solar-powered water pump system, you will need to quantify the available solar energy. It is therefore important for you to be familiar with the definitions and distinctions between the three related terms “solar
radiation,” “solar irradiance,” and “solar insolation.”
Solar radiation is the energy from the sun that reaches the earth. It is commonly expressed in units of kilowatts per square meter (kW/m2). The earth receives a nearly constant 1.36 kW/m2 of solar radiation at its outer atmosphere. However, by the time this energy reaches the earth’s surface, the total amount of solar radiation is reduced to approximately 1 kW/m2.
The intensity of sunshine (i.e. solar radiation) varies based on geographic location. A good analogy to describe this variation is the different conditions that can be found on the north slope of a mountain versus its south slope.
The intensity of sunlight also varies based on the time of day because the sun’s energy must
Figure 2 – The photoelectric effect and subsequent electron motion. (Image inspired by
Merriam-Webster, 2006.)
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 4
pass through different amounts of the earth's atmosphere as the incident angle of the sun changes. Solar intensity is greatest when the sun is straight overhead (also known as solar noon) and light is passing through the least amount of atmosphere. Conversely, solar intensity is least during the early morning and late afternoon hours when the sunlight passes through the greatest amount of atmosphere. In most areas, the most productive hours of sunlight (when solar radiation levels approach 1 kW/m2) are from 9:00 a.m. to 3:00 p.m. Outside of this time range, solar power might still be produced, but at much lower levels.
Solar irradiance, on the other hand, is the amount of solar energy received by or projected onto a specific surface. Solar irradiance is also expressed in units of kW/m2 and is measured at the surface of the material. In the case of a PV-powered system, this surface is the solar panel.
Finally, solar insolation is the amount of solar irradiance measured over a given period of time. It is typically quantified in peak sun hours, which are the equivalent number of hours per day when solar irradiance averages 1 kW/m2. It is important to note that although the sun may be above the horizon for 14 hours in a given day, it may only generate energy equivalent to 6 peak sun hours.
Figure 3, right, demonstrates how peak sun hours are determined for any particular day. The entire amount of solar irradiance (indicated by the blue arc) is divided by 1 kW/m2, which equals the total number of peak sun hours for that day (indicated by the white rectangle).
Another term that is synonymous with peak sun hours (solar insolation) is “equivalent full sun
hours.” Occasionally, the term “solar radiation” can also be used to describe equivalent full sun hours (in addition to the definition above), as in Appendix D.
Two important considerations when determining solar insolation values are the latitude of the project site and the proposed tilt angle of the PV array. (The tilt angle, which is discussed in Section 3.1, is the angle of the panel relative to horizontal where 0° is horizontal and 90° is vertical. Latitude is discussed in Section 2.0). An example of monthly solar insolation values for North Bend, Oregon (latitude 43 degrees) for a fixed tilt angle is shown in Table 2, below. Additional solar insolation (solar radiation) values are provided in Appendix D for nine locations in Oregon. (Data for Boise, Idaho, are also included in Appendix D due to its proximity to eastern Oregon.)
An approach for determining solar insolation values for locations not listed in these solar
Table 2 – Solar Radiation for Flat-Plate Collectors Facing South at a Fixed Tilt of 43° for North Bend, OR
(kWh/m2/day), Uncertainty +/-9%
North Bend, OR Latitude - 15° =
43 – 15 = 28°
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
2.4
3.0
4.1
5.1
6.8
6.1
6.5
6.5
6.0
5.4
4.0
2.6
4.4
Figure 3 – Solar irradiance and peak sun hours.
(Source: “Renewable Energy Primer-Solar.”)
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 5
tables has been developed by researchers at the U.S. Department of Energy’s National Renewable Energy Lab (DOE-NREL). NREL has developed two software packages (PVWATTS v. 1 and PVWATTS v. 2) that can determine solar insolation values, as well as cost estimates for different types of solar-powered systems. A simple introduction to how to use PVWATTS v.2 (Beta) FlexViewer is provided in Appendix E.
2.0 Seasonal and Latitude Variation
In addition to the variation of sunlight intensity on any given day, the seasonal variation of intensity must also be considered when planning for a solar-powered system. In the northern hemisphere, the least amount of sunlight occurs in the winter because the days are shorter and the sun is lower in the sky, as shown in Figure 4, below. In Oregon specifically, there is also typically increased cloud cover in many regions during the winter months (which is discussed further in the following section). Therefore, sunlight intensity is least during December and greatest during mid-summer in the June – July period.
Adjusting the tilt angle of the PV array to account for seasonal variations in the sun’s elevation can result in increased electrical power output from the array. Additional information on adjusting for tilt angle is provided in Section 3.1.
2.1 Cloud Cover
Clouds, fog, and overcast skies are common weather events that occur throughout the year across Oregon, but particularly in the western part of the state during the winter months. Their effects are reflected in the solar insolation data shown in Appendix D. The tables include maximum, minimum, and average values with a ±9 percent uncertainty. Reduction or adjustment of the solar insolation values (equivalent full sun hours) is not needed as the effects of cloud cover are already accounted for. Instead, it is recommended that the designer use the average values included in these tables unless local conditions (such as for sites located under heavy vegetation or in unusual geological features) warrant otherwise.
Figure 4 – Example summer and winter sun elevation and angle. (Source: “Renewable Energy Primer-Solar.”)
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 6
3. PHOTOVOLTAIC (PV) PANELS
PV panels are made up of a series of solar cells, as shown in Figure 5, below. Each solar cell has two or more specially prepared layers of semiconductor material that produce DC electricity when exposed to sunlight. A single, typical solar cell can generate approximately 3 watts of energy in full sunlight.
The semiconductor layers can be either crystalline or thin film. Crystalline solar cells are generally constructed out of silicon and have an efficiency of approximately 15%. Solar cells that are constructed out of thin films, which can consist of a variety of different metals, have efficiencies of approximately 8% to 11%. They are not as durable as silicon solar cells, but they are lighter and considerably less expensive.
PV panels may be arranged in arrays and connected by electrical wiring to deliver power to a pump (see Section 3.0 for more details).
PV panels must meet all NRCS required specifications, both for power production and structural integrity (including resistance to hail), as described in the following sections.
3.0 PV Panel Electrical Characteristics
PV panels are rated according to their output, which is based on an incoming solar irradiance of 1 kW/m2 at a specified temperature. Panel output data include peak power (Watts [Pw]), voltage (Volts [V]), and current (Amps [A]). Under conditions of reduced solar radiation, the current produced is decreased accordingly, but the voltage is reduced only slightly. Example electrical characteristics for a solar panel are shown in Table 3.
Multiple panel arrays should be wired in a series and/or parallel so that the resulting voltage and current are compatible with the controller and pump motor requirements.
Table 3 – Example PV Solar Panel Electrical
Characteristics
Characteristic
Value
Units
Peak Power
117
Watt [Pw]
Power Tolerance
±5
%
Max Power Voltage
35.5
Volts [V]
Max Power Current
3.3
Amps [A]
Open Circuit Voltage
40.0
Volts [V]
Short Circuit Current
3.5
Amps [A]
Figure 5 – Solar cell, PV solar panel, and PV panel array. (Source: “Guide to Solar Powered Water
Pumping Systems in New York State.”)
PV Solar Panel
Array of PV Solar Panels
PV Solar Cell
Design of Small Photovoltaic (PV) Solar-Powered Water Pump Systems
Technical Note No. 28, October 2010 Page 7
When multiple panels are wired in a series, the total output voltage is the sum of the individual panel output voltages; the total current stays the same. Conversely, when panels are wired in parallel, the voltage stays the same while the resultant total current is the sum of the individual panel current inputs. The total power output from a PV panel array is determined by multiplying the total output voltage by the total output current. (Basic PV panel wiring diagrams are shown in