Parallel/Series combination of PV modules

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  • Thread starter DumpmeAdrenaline
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In summary, the parallel/series combination of photovoltaic (PV) modules refers to the configuration used to optimize the performance and output of solar energy systems. In a series connection, the voltage increases while the current remains the same, making it suitable for higher voltage applications. Conversely, in a parallel connection, the current increases while the voltage stays constant, which helps in maintaining performance under partial shading conditions. The choice between these configurations depends on factors such as desired voltage, current requirements, and the specific installation scenario, ultimately influencing the overall efficiency and effectiveness of the solar power system.
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DumpmeAdrenaline
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Homework Statement
You are to design a 24-volt, all-dc, stand-alone PV system to meet a 2.4 kWh/day demand for a small, isolated cabin. You want to size the PV array to meet the load in a month with average insolation equal to 5.0 kWh/m2-day. Your chosen PVs have their 1-sun maximum power point at VR = 18V and IR = 5A. Assume a 0.80 derate factor for dirt, wiring, module mismatch (i.e. 20% loss). You'll use 200-Ah, 12-V batteries with 100% Coulomb efficiency. How many PV modules are needed (you may need to round up or down)?
Relevant Equations
P=IV
The solar irradiance incident on the PV modules is 5 kwh/m^2-day.The current each module can provide is 5 A and the voltage due to the separation of charge carriers is 18 V under standard conditions (1 Sun=1000 W/m2) so we would have to connect two modules in series to exceed the voltage of the load. I am confused on the directions of current will current flow from the PV module flow to charge the battery or will it flow to the DC loads to meet the power demand of DC loads or both?
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  • #2
What work have you done towards solving this problem, so far?
 
  • #3
To charge the DC load, we would have to exceed 24 V. So, we connect 2 PV modules in series, thus producing 36 V. The power produced by the 2 PV modules is Power = IV * Derate factor = 36 * 5 * 0.8 = 144 W. Therefore, 144 * 5hr/day = 720 Wh/day = 0.72 kWh/day. The power demand is 2.4 kWh/day. So, we would need 6 modules (3 parallel * 2 in series arrangement) which would deliver a total of (36 * 15 * 5/1000) = 2.7 kWh/day. The extra 0.3 kWh/day would be used to charge the battery.
 
  • #4
Since it is a 24 volt system, you will need to limit it to 24 volt output, so the amount of current delivered should be multiplied by 24, correct?
 
  • #5
But how can we obtain 24 V from the PV modules when each module produces 18 V?
 
  • #6
A voltage regulator circuit can drop to the desired output voltage.

The simplest example would be a resistor in series with the load. Take the difference between source (solar panels) output voltage and desired voltage. You will need to start off with more than 24 volts, so two of the 18 volt panels in series will give 36 volts, then subtract for the losses.

Interesting note - I did an online search about dirty solar panels. Many of the links that I checked out talk about decreasing power output, but they don't specify whether it is a voltage decrease or current (or a combination).

For the moment, suppose the panel has circuitry to deliver constant voltage at a variety of lighting conditions, so the max current is reduced. To get a 12 volt drop (36-24), calculate the necessary series resistance at the required current load.

If two in series are not enough to provide the required current, then you need to add more pairs in parallel.
 
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  • #7
scottdave said:
Interesting note - I did an online search about dirty solar panels. Many of the links that I checked out talk about decreasing power output, but they don't specify whether it is a voltage decrease or current (or a combination).
For every 6 or so photons that hit the active material, 1 of those photons wil knock an electron loose. Current is a measure of how many of those electrons are flowing per second.

It follows then, that the fewer the number of photons that hit the active material (blocked by dirt), the lower the current.

Cheers,
Tom
 
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FAQ: Parallel/Series combination of PV modules

What is the difference between parallel and series combinations of PV modules?

In a series combination, PV modules are connected end-to-end, which increases the overall voltage while the current remains the same as that of a single module. In a parallel combination, the positive terminals are connected together and the negative terminals are connected together, which increases the overall current while the voltage remains the same as that of a single module.

How do parallel and series combinations affect the overall power output?

Both parallel and series combinations can be used to achieve the desired power output. In a series configuration, the voltage increases, which can be beneficial for systems requiring higher voltage. In a parallel configuration, the current increases, which can be advantageous for systems needing higher current. The total power output is the product of the total voltage and total current, so both configurations can be used to optimize the system based on the requirements.

What are the advantages and disadvantages of series connections of PV modules?

The main advantage of series connections is the increase in voltage, which can reduce the losses in the cables and make it easier to meet the voltage requirements of the inverter. However, a disadvantage is that if one module in the series string is shaded or fails, it can significantly reduce the current and thus the power output of the entire string.

What are the advantages and disadvantages of parallel connections of PV modules?

The main advantage of parallel connections is the increase in current, which can be useful for systems that need to supply more current to the load. Additionally, shading or failure of one module has less impact on the overall system performance compared to series connections. However, a disadvantage is that the system requires thicker cables to handle the increased current, which can increase the overall cost and complexity.

How do you determine the optimal combination of parallel and series connections for a PV system?

The optimal combination depends on several factors, including the voltage and current requirements of the load or inverter, the characteristics of the PV modules, and the environmental conditions. Generally, a balance between series and parallel connections is sought to maximize efficiency and minimize losses. System designers often use simulation software to model different configurations and select the one that provides the best performance while meeting all electrical and economic constraints.

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