TESDA Photovoltaic NC II Method · PEC 2017 Design Margins

Solar PV Sizing Calculator

Work through the same five-step method used in Philippine PV installer training — load analysis, panel sizing, inverter sizing, battery bank, and charge controller — for off-grid, on-grid, or hybrid systems.

System Settings

Sun Peak Hours (PSH)

4.0 hrs/day

Philippines average is ~4–4.5 PSH (lower in rainy season / Luzon north, higher in Mindanao). Adjust to your site's solar resource data.

System DC Voltage

Higher bus voltage = lower current = smaller conductors, per PEC ampacity rules.

Loss / Safety Factor

1.3× array oversize

Covers wiring, temperature, dust, and inverter conversion losses — consistent with PEC's continuous-duty margin (conductors/OCPD sized ≥125% of load).

Roof / Site Dimensions

Checks whether the physical roof can actually fit the number of panels each mode recommends — not just the electrical sizing.

Roof Length (m) Roof Width (m)

Fire / Access Setback (m)

Clear pathway kept along ridges, hips, and eaves for fire access and maintenance — ~0.9m (3 ft) is a common minimum per fire code and TESDA rooftop-mounting practice.

Usable Roof Area

— m² usable

of — m² total roof area

System Wiring Diagram — Single Line

PV → charge controller → battery bank → inverter → main distribution panel. No utility connection.

DC AC Battery link

Breaker and SPD ratings shown are sized at 125% of calculated current, per PEC continuous-duty practice — verify against manufacturer datasheets before installation.

01Load Analysis

List every appliance the off-grid system must run daily.

Load	Qty	Watts	Hrs/day	Type		Daily Wh

Non-motor ×1.3Motor ×2/×3

Total Daily Consumption0 Wh

03Inverter Sizing (Surge)

Motor loads (fans, fridge, aircon, pumps) draw 2–3× their rated watts on start-up.

05Charge Controller

Panel Voc (V)

Panel Isc (A)

Controller Vmax (V)

Controller Type

02PV Panel Sizing

Panel Rating (W)

Panel Length (m)

Panel Width (m)

04Battery Bank

Battery Chemistry

Battery Rating (Ah)

Battery Voltage (V)

Array oversize / loss factor (1.3×) mirrors the continuous-duty design margin used throughout Philippine electrical practice — PEC 2017 requires conductors and overcurrent devices for continuous loads (PV included) to be sized with headroom above nameplate current, rather than at exactly 100%.
Sun Peak Hours (PSH) should be based on actual site irradiance data (PAGASA solar maps or a pyranometer study) where available — 4.0 PSH is a conservative planning default used in TESDA PV NC II training.
Motor starting multipliers (2–3×) account for locked-rotor / inrush current of fans, compressors, and pumps when selecting inverter surge capacity — undersizing here is the most common cause of inverter nuisance trips.
Battery depth-of-discharge (DOD) limits protect cycle life — 50% is standard for flooded lead-acid, while lithium LiFePO4 tolerates 80–90% DOD, directly reducing the number of battery strings required.
String voltage (Voc × series count) must stay below the charge controller / inverter's maximum DC input voltage at all times, including at low ambient temperature when Voc rises — always re-check against the manufacturer's temperature coefficient before final design.
DC and AC wire sizes shown in the wiring diagrams are picked from PEC 2017 Part 1's allowable-ampacity table for insulated copper conductors (60°C column for terminations ≤100A, 75°C above that) and the standard single-strand DC solar cable ampacity reference — breakers are rounded up to the nearest standard PEC AC fuse/breaker or DC breaker rating, both sized at 125% of calculated current.
Roof / site dimensions are checked against the recommended panel count using each panel's actual footprint, after subtracting a clear perimeter pathway (default 0.9m / 3 ft) for fire access and maintenance along ridges, hips, and eaves — a real physical constraint on top of the electrical sizing, and one TESDA rooftop-mounting training flags as commonly overlooked.
All DC and AC disconnects, grounding/bonding, conductor ampacity, and labeling should follow PEC 2017 Article 690 (Solar Photovoltaic Systems) and be reviewed by a PEC-licensed electrical engineer prior to installation and utility interconnection.

This calculator reproduces the standard load-analysis → panel → inverter → battery → charge-controller sizing sequence taught in TESDA's Photovoltaic Systems Design and Installation curriculum, for preliminary estimation and training purposes only. It is not a substitute for a licensed engineer's system design, permit drawings, or manufacturer datasheet verification.

Design references & notes

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