PV Grid Connect System Sizing

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Solar PV Panels In SEN SOL 50 On Roof Mounting SystemSee also:
Measuring Power Consumption
Off Grid Sizing

The limiting factors for a grid connected solar PV system are usually the maximum available sunny area for the siting of a PV array combined with the budget available! Since all energy can be used (surplus going to the grid if necessary) and all needs met (shortfall coming from the grid as required) sizing based on critical load patterns is not necessary. Instead, comparison of potential energy generation (kWh) can be made with energy usage - found on one’s electricity bill (1 unit = 1 kWh).

  • In common with off-grid systems - energy conservation and efficiency is a pre-requisite step to obtaining energy self-sufficiency. Once electricity requirements have been reduced through efficiency, it is much easier (and cheaper) to meet those requirements through on-site PV generation.
  • 8 m² allows ~ 1kWp (Kilowatts peak) of PV system.
  • For most of the UK there are on average approx. 4-5 peak sun hours in summer going down to an average of 1 hour in winter.
  • For well sited grid connected PV arrays - 1kWp will produce ~ 800kWh (units) per year.
  • Installed cost for 3-4kWp PV system is approx. £6-8,000.00.

If mounting a PV array on a roof then the first step is to determine how many and which type of PV module fits into the available roof space. 

It is important to avoid any areas that are shaded by obstructions such as chimneys, other parts of the building or trees & aerials. (at any time of the year).
The Solmetric SunEye and the Solar Horizon Estimator are useful tools in assessing this.

A margin should be allowed around the PV array to reduce wind loadings and to enable access. Once the PV array area has been determined, then the number of modules is matched to inverters and mounting frame dimensions, to decide upon the most cost effective and efficient system.

Output

Information MapPerformance can vary according to geographical area and orientation. In order to estimate approximate yearly output:

  1. Find the peak power (kWp) of the array to be installed,
  2. Identify your location on the solar radiation map and it’s annual energy production (kWh/kWp).
  3. Identify the Correction Factor for required orientation.

Total Annual Energy Production = (1) x (2) x (3)

Approx. annual energy production in kWh for a 1kWp PV system. South facing, unshaded & 35º tilt

 

Tilt AnglesAverage Irradiation Correction Factor For Different Tilt & Orientation (Azimuth)
Orientation from South ( Azimuth Angle in º )
( º )0 (South)102030405060708090 (East/West)
0-10 90.1% 90.1% 90% 89.7% 89.3% 88.9% 88.4% 87.9% 87.3% 86.6%
11-20 96.5% 96.3% 95.7% 95% 93.7% 92.4% 90.7% 88.8% 86.8% 84.8%
21-30 99.2% 99% 98.3% 97.1% 95.5% 93.4% 91% 88.3% 85.4% 82.5%
31-40 100% 99.7% 98.8% 97.4% 95.4% 92.9% 90% 86.7% 83.2% 79.4%
41-50 99% 98.7% 97.7% 96.1% 94% 91.4% 88.2% 84.6% 80.9% 76.8%
51-60 94.2% 93.9% 93% 91.4% 89.1% 86.2% 82.8% 79% 75% 70.7%
61-70 88.5% 88.3% 87.3% 86% 83.6% 80.9% 77.5% 73.8% 69.8% 65.7%
71-80 81.1% 80.9% 80.5% 78.8% 77.3% 73.8% 71.2% 67.8% 64.1% 60.1%
81-90 72.3% 72.1% 71.6% 70.5% 68.9% 66.7% 64.1% 61% 57.6% 54.3%


A useful tool for estimating monthly output using sunlight data for anywhere in Europe and Africa is available here.