SOLA2540 Chap.2 Solar Resource and PV Array Sizing
Solar Resource and PV Array Sizing
PV array sizing connects a seasonal service requirement to the solar resource on the proposed plane of array. The process begins with site analysis: location, orientation, tilt, shading, available area, access and environmental exposure.
Monthly load and resource cases identify the design month, which is the period with the most demanding useful-solar-input relationship rather than automatically the month with the lowest irradiation. Module nameplate power is then derated for manufacturing tolerance, effective cell temperature and soiling.
The array count follows from design daily energy, tilted-plane peak-sun hours, subsystem efficiency and any stated oversupply decision. Rounding up the energy count is only the first closing step; the selected number must form series and parallel strings that remain inside controller voltage and current limits across temperature.
What this chapter covers
- 01
Site analysis records plane orientation, tilt, shading, available area, access and environmental conditions
- 02
The design month is chosen by comparing seasonal load with the matching useful solar resource
- 03
Peak-sun hours represent daily irradiation on the plane of array for energy calculations
- 04
Standard-test-condition module power is adjusted with named manufacturing, temperature and soiling factors
- 05
Independent loss factors are multiplied rather than added as one vague percentage
- 06
Subsystem efficiency follows the selected energy path through cables, controller and storage
- 07
Module count is rounded up after the energy calculation
- 08
Series voltage, parallel current and MPPT limits can require a different feasible configuration from the energy minimum
Worked example · free
Size an original MPPT array
- +1Derated module power is 390 × 0.98 × 0.89 × 0.96 = 326.6 W.
- +1Useful daily energy per module is 326.6 × 4.1 × 0.85 = 1,138.1 Wh/day.
- +1Required design energy with oversupply is 6,300 × 1.10 = 6,930 Wh/day, so the quotient is 6,930/1,138.1 = 6.09.
- +1Round up to seven modules, then verify that a feasible seven-module series-parallel arrangement satisfies the controller's hot and cold voltage and current limits.
Key terms
- Plane-of-array irradiation
- Solar energy received on the actual tilted and oriented array plane. It differs from a horizontal resource value and is the relevant input for array energy calculations.
- Peak-sun hours
- Daily irradiation expressed as equivalent hours at one kilowatt per square metre. Multiplying by derated power gives a daily-energy estimate before downstream losses.
- Design month
- The seasonal case whose useful resource is most demanding relative to the required service after load and site adjustments are considered together.
- Temperature derating
- The reduction in module output associated with effective cell temperature relative to the standard test temperature, using the applicable power temperature coefficient.
- Subsystem efficiency
- The combined energy efficiency of the actual path between the array and the selected energy boundary, such as cables, regulator and battery.
- MPPT window
- The controller voltage range within which maximum-power-point tracking can operate. String voltage must remain compatible across expected module temperatures.
Solar Resource and PV Array Sizing FAQ
Why not size the array from annual average sunshine?
A stand-alone design must serve the controlling seasonal case. Annual averages can hide a month with weak irradiation, strong demand or both. Compare monthly or seasonal load with resource on the proposed array plane, then justify the selected design month. If backup generation or planned shedding changes the service during that period, include the operational rule rather than assuming unlimited support.
Why is module nameplate power derated?
Nameplate power is measured under standard test conditions. Field output changes with manufacturing tolerance, effective cell temperature and soiling, and energy then passes through cables, a controller and possibly storage. Applying named factors creates a traceable design value. One unexplained loss percentage is harder to audit and can conceal double counting or the use of a factor from an unrelated module or climate.
When should module count be rounded?
Complete the energy calculation with unrounded intermediate values and round the final module count up to a whole number. Then perform electrical configuration checks. Series count must satisfy cold maximum voltage and hot operating voltage constraints; parallel count must satisfy current limits.
A controller's permitted string structure can force a larger array or a different controller than the energy quotient alone suggests.
How should uncertain shading be treated?
Do not invent a precise shading percentage from a broad description. Record the obstruction, season and affected hours, model a transparent range if necessary, and identify the survey or measurement that would resolve it. Keep site shading distinct from weather variability and ordinary soiling so each loss can be investigated and updated without changing unrelated assumptions.
Assessment move
Practise the array calculation as a sequence of named transformations. Begin with the design-month load and draw the energy boundary. Record the tilted-plane peak-sun hours and the basis for the site adjustment. Derate module power by multiplying tolerance, temperature and soiling factors, then calculate daily module energy.
Apply downstream subsystem efficiency once, multiply the required load by any stated oversupply coefficient, divide and round up. After that arithmetic, change modes: sketch the series-parallel arrangement and check cold open-circuit voltage, hot operating voltage, controller MPPT range and maximum current.
Create an adverse sensitivity case by lowering resource or increasing cell temperature until the module count crosses an integer boundary; explain the cost and controller consequences. For conceptual questions, distinguish annual average from design month, ambient from effective cell temperature, and energy sufficiency from electrical compatibility.
A strong final sentence identifies which assumption controls the module count and which field measurement would most improve confidence.
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