So, it has recently come to my attention that I know less than I thought (the lesson that life keeps on teachin' ?), and that some of what I thought I knew was wrong or incomplete (more on that in a future post. This took me down a rabbit hole of research, which led to many new questions and very few new answers (a situation I find myself in often?). As tempted as I am to just ask the scattershot of new questions now occupying my mind, I'm going to practice my deep breathing, slow down, and begin with the basics, so bear with me. This post is one part teaching, and one part learning through explaining, if you see anything that is wrong or inaccurate or incomplete, point it out. It is meant as a beginner friendly very basic introduction to PV arrays and wiring, and a lead up to a future intermediate level post on some of the complexities (where I will probably have more questions than answers).
Solar Arrays 101
A solar array is a grouping of solar panels, and a solar panel is made up of individual solar cells usually connected in series. Panels can be arranged in series, in parallel, or combination of series and parallel. Regardless of how you arrange your panels, power output (Watts) will be the same, but current, voltage, and performance in specific conditions will differ.
Simply put, with series there is one path for current to flow, while with parallel there are multiple current paths.
There are many factors that influence the best way to design and wire your array. Wiring efficiency, controller type (PWM, MPPT), controller limits (max input volts, amps), mppt optimization, partial shading, differences in irradiance or conditions across the array, or even mismatched panels. Covering these factors is beyond the scope of this post, but be aware of them.
Series
When panels are connected in series, voltage is multiplied by the number of panels in series, but the current stays the same. Panels connected in series are tolerant of differences in voltage, but intolerant of differences in currents. If one or more panels has a lower current, all panels in series will be reduced to the current of the panel outputting the lowest current. As you can see in the example below, panels are wired in series positive to negative and there is one path for current to flow.
Parallel
When panels are connected in parallel, current is multiplied by the number of panels in parallel, but the voltage stays the same. Panels connected in parallel are tolerant of different currents, but intolerant of different voltages. If there is a difference in voltage, all panels will be reduced to the voltage of the lowest voltage panel. As you can see in the example below, panels are wired by combining the positives and combining the negatives, and there are multiple parallel paths for current to flow.
Series-Parallel Combination
A third option is to first wire your cells into series connected groups called 'strings' or 'in-series' strings or pairs and then wire these strings in parallel. In this configuration voltage is multiplied by the number of panels in a series string and then current is multiplied by the number of strings in parallel. Each in-series string is tolerant to differences in voltage within the string, but intolerant to differences in current, and the parallel connected strings are tolerant to differences in current but intolerant to differences in voltage. In this configuration we get some but not all of the advantages and disadvantages of series and parallel connected arrays.
Technically there is a fourth option Parallel-Series Combination, but I'm not sure its ever used with PV arrays (with one possible exception being panels with half cut cells). It's basically the opposite of Series-Parallel, panels are first connected in parallel and then groups of parallel connected panels are connected in series. We sometimes do this with battery cells, but its not common with PV arrays. Does this arrangement exist? What do you think the pros/cons of this arrangement would be?
https://solarpanelsvenue.com/mixing-solar-panels/
Amps measure electrical current (flow) in a circuit. Volts are a unit of electrical potential or 'electrical pressure' and can be thought of as the 'pushing force' that causes electricity to flow. Resistance (measured in Ohms) opposes the flow of electricity in a circuit. Resistance can be useful or intentional (every device powered by electricity acts like a resistor) or non-useful and unavoidable in which case its just an inefficiency like resistance in a wire. Ohms law is the relationship between these three things: Voltage = Current x Resistance (which can also be represented as Current = Voltage / Resistance or Resistance = Voltage / Current).
If we imagine a water hose in a closed loop, with an inline pump, and an inline water turbine or constriction in the pipe. The rate of water flow through the hose is equivalent to 'current', the pump creates the pushing force, and the water turbine or constriction in the pipe are sources of resistance (a useful resistance in the case of the water turbine).
The practical takeaway for the purpose of this conversation is that because current is a rate of flow, like water flowing in a hose, if flow is restricted at any point in the circuit, the flow rate is lowered for the whole circuit.
If we imagine a water hose in a closed loop, with an inline pump, and an inline water turbine or constriction in the pipe. The rate of water flow through the hose is equivalent to 'current', the pump creates the pushing force, and the water turbine or constriction in the pipe are sources of resistance (a useful resistance in the case of the water turbine).
The practical takeaway for the purpose of this conversation is that because current is a rate of flow, like water flowing in a hose, if flow is restricted at any point in the circuit, the flow rate is lowered for the whole circuit.
Solar Arrays 101
A solar array is a grouping of solar panels, and a solar panel is made up of individual solar cells usually connected in series. Panels can be arranged in series, in parallel, or combination of series and parallel. Regardless of how you arrange your panels, power output (Watts) will be the same, but current, voltage, and performance in specific conditions will differ.
Simply put, with series there is one path for current to flow, while with parallel there are multiple current paths.
There are many factors that influence the best way to design and wire your array. Wiring efficiency, controller type (PWM, MPPT), controller limits (max input volts, amps), mppt optimization, partial shading, differences in irradiance or conditions across the array, or even mismatched panels. Covering these factors is beyond the scope of this post, but be aware of them.
Series
When panels are connected in series, voltage is multiplied by the number of panels in series, but the current stays the same. Panels connected in series are tolerant of differences in voltage, but intolerant of differences in currents. If one or more panels has a lower current, all panels in series will be reduced to the current of the panel outputting the lowest current. As you can see in the example below, panels are wired in series positive to negative and there is one path for current to flow.
Parallel
When panels are connected in parallel, current is multiplied by the number of panels in parallel, but the voltage stays the same. Panels connected in parallel are tolerant of different currents, but intolerant of different voltages. If there is a difference in voltage, all panels will be reduced to the voltage of the lowest voltage panel. As you can see in the example below, panels are wired by combining the positives and combining the negatives, and there are multiple parallel paths for current to flow.
Series-Parallel Combination
A third option is to first wire your cells into series connected groups called 'strings' or 'in-series' strings or pairs and then wire these strings in parallel. In this configuration voltage is multiplied by the number of panels in a series string and then current is multiplied by the number of strings in parallel. Each in-series string is tolerant to differences in voltage within the string, but intolerant to differences in current, and the parallel connected strings are tolerant to differences in current but intolerant to differences in voltage. In this configuration we get some but not all of the advantages and disadvantages of series and parallel connected arrays.
Technically there is a fourth option Parallel-Series Combination, but I'm not sure its ever used with PV arrays (with one possible exception being panels with half cut cells). It's basically the opposite of Series-Parallel, panels are first connected in parallel and then groups of parallel connected panels are connected in series. We sometimes do this with battery cells, but its not common with PV arrays. Does this arrangement exist? What do you think the pros/cons of this arrangement would be?
https://solarpanelsvenue.com/mixing-solar-panels/
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