Verification

Solar PV yield verification against SAP 10.3

Fixed worked examples run through MEPCalc's solar PV calculation, compared line by line with the equations and tables printed in SAP 10.3 Appendix M and Appendix U, and with the EREC G98 connection boundary.

Result: 25 of 25 checks pass
Cases: 13 worked examples
Version / published: v1.0 · 2026-09-03
Engine fingerprint: 190f0e73f425

Why we publish this

SAP 10.3 is the compliance method for PV in UK dwellings: Equation M1 gives the annual yield from the installed peak power, the annual solar radiation on the array and an overshading factor, and Appendix U gives that radiation for any region, orientation and tilt from its own tables. The expected radiation on every case below was derived by evaluating Equations U1 to U4 from the printed Table U3, U4 and U5 constants in a separate hand calculation, with the January working shown, so the check is against the printed method rather than against the calculation code itself.

What these calculations do not model

Other irradiance sources. The calculation can also take a weather-station dataset or a manually entered annual radiation, with a MEPCalc tilt correction on those paths. Neither is a SAP value, so only the Appendix U path and the bare Equation M1 case appear above.
Self-consumption, export and battery storage. These are an engineering estimate, not part of the Appendix M method, and are not asserted here. SAP's own treatment of the exported share is not implemented.
Additional system losses. Equation M1's 0.8 factor is all-in. An optional extra loss allowance exists for site-specific use; every case above has it at zero.
Independent datasets. A PVGIS cross-check of the UK-average south-facing case is kept in the calculation's own regression notes for context only. It is not a SAP value and is not an expected value here.

How to read the tables

Expected is the value printed in the standard, or a hand calculation from printed values. The working is shown under each quantity.
Tolerance is exact for tabulated values and selected sizes, and ±2 % for calculated quantities such as annual solar radiation on the array, annual yield, specific yield and inverter current.
Every check re-runs automatically whenever the calculation code changes, and this page is regenerated from those results. The engine fingerprint above identifies the calculation code the results came from.

Sources

EREC G98 Issue 2 (2025)
SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure

Printed page numbers refer to the editions above. Amendment 3:2024 to BS 7671 adds two definitions and one regulation on bidirectional protective devices and does not change any page cited here.

Worked examples

PV-01

10 kWp, south-facing at 35°, UK average (region 0), unshaded

Inputs

10 kWp array, south-facing, 35° tilt
SAP region 0 (UK average): Table U4 latitude 53.5°
Overshading: none or very little (Table M1, Z_PV = 1)

Checks for case PV-01
Quantity	Expected	Source	MEPCalc	Tolerance	Result
Overshading factor, Z_PV	1	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Table M1, printed p93 (none or very little, < 10 %)	1	exact	Pass
Annual solar radiation on the array, S South column k1…k9 with sin(17.5°) = 0.3007: A = 0.8535, B = −2.1603, C = 2.2169; January: cos(53.5° − (−20.7°)) = 0.2723 → R = 1.6920, S = 26 × 1.6920 = 44.0 W/m² → 0.024 × 31 × 44.0 = 32.7 kWh/m²; summed over twelve months S = 1081.4 kWh/m²	1081.4kWh/m²	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix U, Tables U3–U5 and Equations U1–U4, printed p127–129	1081.4kWh/m²	±2 %	Pass
Annual electricity produced, E_PV E_PV = 0.8 × 10 × 1081.4 × 1 = 8651 kWh/yr	8651.2kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	8651.4kWh/yr	±2 %	Pass
Specific yield 8651 ÷ 10 = 865 kWh/kWp, inside SAP's printed 720–940 band	865.1kWh/kWp	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92 (the 720 to 940 kWh per kWp band)	865.1kWh/kWp	±2 %	Pass

PV-02

8 kWp, east-facing at 15°, UK average (region 0), unshaded

Inputs

8 kWp array, east-facing, 15° tilt
SAP region 0 (UK average)
Overshading: none or very little

Checks for case PV-02
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Annual solar radiation on the array, S East/West column with sin(7.5°) = 0.1305: A = 0.1027, B = −0.1830, C = 1.0647; January R = 1.0225, S = 26.6 W/m²; summed S = 940.6 kWh/m²	940.6kWh/m²	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix U, Tables U3–U5 and Equations U1–U4, printed p127–129	940.6kWh/m²	0.00 %	±2 %	Pass
Annual electricity produced, E_PV 0.8 × 8 × 940.6 × 1 = 6020 kWh/yr	6020kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	6020kWh/yr	0.00 %	±2 %	Pass

PV-03

30 kWp flat roof, south-facing at 10°, UK average (region 0), unshaded

Inputs

30 kWp array, south-facing, 10° tilt
SAP region 0 (UK average)
Overshading: none or very little

Checks for case PV-03
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Annual solar radiation on the array, S South column with sin(5°) = 0.0872: A = 0.2541, B = −0.6454, C = 1.3907; January R = 1.2338, S = 32.1 W/m²; summed S = 1015.1 kWh/m²	1015.1kWh/m²	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix U, Tables U3–U5 and Equations U1–U4, printed p127–129	1015.1kWh/m²	0.00 %	±2 %	Pass
Annual electricity produced, E_PV 0.8 × 30 × 1015.1 × 1 = 24 362 kWh/yr	24362kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	24362kWh/yr	0.00 %	±2 %	Pass

PV-04

4 kWp, south-facing at 35°, Southern England (region 3), unshaded

Inputs

4 kWp array, south-facing, 35° tilt
SAP region 3 (Southern England): Table U3 row 35 62 109 172 209 235 217 185 138 80 44 27 W/m², Table U4 latitude 50.9°
Overshading: none or very little

Checks for case PV-04
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Annual solar radiation on the array, S A, B, C as PV-01 (same orientation and tilt); January: cos(50.9° + 20.7°) = 0.3156 → R = 1.6201, S = 35 × 1.6201 = 56.7 W/m²; summed S = 1233.3 kWh/m²	1233.3kWh/m²	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix U, Tables U3–U5 and Equations U1–U4, printed p127–129	1233.3kWh/m²	0.00 %	±2 %	Pass
Annual electricity produced, E_PV 0.8 × 4 × 1233.3 × 1 = 3947 kWh/yr	3946.7kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	3946.7kWh/yr	0.00 %	±2 %	Pass

PV-05

6 kWp, south-west at 40°, Highland (region 17), unshaded

Inputs

6 kWp array, south-west facing, 40° tilt
SAP region 17 (Highland): Table U3 row 17 43 85 145 189 185 170 139 98 51 22 12 W/m², Table U4 latitude 57.5°
Overshading: none or very little

Checks for case PV-05
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Annual solar radiation on the array, S SE/SW column with sin(20°) = 0.3420: A = 0.6202, B = −1.6511, C = 1.9119; January: cos(57.5° + 20.7°) = 0.2045 → R = 1.6002, S = 17 × 1.6002 = 27.2 W/m²; summed S = 927.3 kWh/m²	927.3kWh/m²	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix U, Tables U3–U5 and Equations U1–U4, printed p127–129	927.3kWh/m²	0.00 %	±2 %	Pass
Annual electricity produced, E_PV 0.8 × 6 × 927.3 × 1 = 4451 kWh/yr	4450.9kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	4450.9kWh/yr	0.00 %	±2 %	Pass

PV-06

5 kWp, north-facing at 30°, Shetland (region 20), unshaded

Inputs

5 kWp array, north-facing, 30° tilt
SAP region 20 (Shetland): Table U3 row 12 34 79 135 196 190 168 144 90 46 16 7 W/m², Table U4 latitude 60.1°
Overshading: none or very little

A north-facing array in Shetland yields 464 kWh/kWp, below SAP's 720–940 band for favourable orientations, and the calculation warns accordingly.

Checks for case PV-06
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Annual solar radiation on the array, S North column with sin(15°) = 0.2588: A = 1.7075, B = −1.5373, C = 0.9380; January: cos(60.1° + 20.7°) = 0.1599 → R = 0.7359, S = 12 × 0.7359 = 8.8 W/m²; summed S = 580.6 kWh/m²	580.6kWh/m²	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix U, Tables U3–U5 and Equations U1–U4, printed p127–129	580.6kWh/m²	0.00 %	±2 %	Pass
Annual electricity produced, E_PV 0.8 × 5 × 580.6 × 1 = 2322 kWh/yr	2322.4kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	2322.4kWh/yr	0.00 %	±2 %	Pass

PV-07

Equation M1 alone — the PV-01 radiation entered directly

Inputs

10 kWp array, annual radiation on the array entered as 1081.4 kWh/m² (the PV-01 value)
Overshading: none or very little

Isolates Equation M1 from Appendix U: with the radiation fixed, only the 0.8 factor and Z_PV are in play.

Checks for case PV-07
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Annual electricity produced, E_PV E_PV = 0.8 × kWp × S × Z_PV = 0.8 × 10 × 1081.4 × 1 = 8651 kWh/yr	8651.2kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	8651.2kWh/yr	0.00 %	±2 %	Pass

PV-08

Overshading — 12 % of the southern sky blocked (Table M1 modest band)

Inputs

As PV-01, with 12 % of the southern sky blocked by obstructions

Checks for case PV-08
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Overshading factor, Z_PV	0.8	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Table M1, printed p93 (modest, 10 % – 25 %)	0.8	0.00 %	exact	Pass
Annual electricity produced, E_PV 0.8 × 10 × 1081.4 × 0.8 = 6921 kWh/yr	6921kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	6921.1kWh/yr	0.00 %	±2 %	Pass

PV-09

Overshading — exactly 25 % blocked, the shared edge of two Table M1 bands

Inputs

As PV-01, with 25 % of the southern sky blocked

Table M1 prints 25 % in both the modest and significant bands; the lower factor is applied.

Checks for case PV-09
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Overshading factor, Z_PV	0.5	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Table M1, printed p93 (significant, 25 % – 60 %)	0.5	0.00 %	exact	Pass
Annual electricity produced, E_PV 0.8 × 10 × 1081.4 × 0.5 = 4326 kWh/yr	4325.6kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	4325.7kWh/yr	0.00 %	±2 %	Pass

PV-10

Overshading — heavy (Table M1 tier chosen directly)

Inputs

As PV-01, overshading tier: heavy (> 60 % – 80 % of the southern sky blocked)

Checks for case PV-10
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Overshading factor, Z_PV	0.35	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Table M1, printed p93 (heavy)	0.35	0.00 %	exact	Pass
Annual electricity produced, E_PV 0.8 × 10 × 1081.4 × 0.35 = 3028 kWh/yr	3027.9kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	3028kWh/yr	0.00 %	±2 %	Pass

PV-11

Overshading — 100 % blocked (Table M1 severe band)

Inputs

As PV-01, with the whole southern sky blocked

Checks for case PV-11
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Overshading factor, Z_PV	0.2	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Table M1, printed p93 (severe, > 80 %)	0.2	0.00 %	exact	Pass
Annual electricity produced, E_PV 0.8 × 10 × 1081.4 × 0.2 = 1730 kWh/yr	1730.2kWh/yr	SAP 10.3 (13-01-2026), The Government's Standard Assessment Procedure Appendix M, Equation M1, printed p92	1730.3kWh/yr	0.01 %	±2 %	Pass

PV-12

EREC G98 boundary — 3.68 kW single-phase is exactly 16 A per phase

Inputs

3.68 kWp array on a single-phase 230 V connection

Checks for case PV-12
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Inverter output current per phase 3680 W ÷ 230 V = 16.0 A — the G98 registered-capacity limit	16A	EREC G98 Issue 2 (2025) §2.8, printed p11	16A	0.00 %	±2 %	Pass

PV-13

EREC G98 boundary — 11.04 kW three-phase is exactly 16 A per phase

Inputs

11.04 kWp array on a three-phase 400/230 V connection

Checks for case PV-13
Quantity	Expected	Source	MEPCalc	Δ	Tolerance	Result
Inverter output current per phase 11 040 W ÷ (3 × 230 V) = 16.0 A per phase — the G98 registered-capacity limit	16A	EREC G98 Issue 2 (2025) §2.8, printed p11	16A	0.00 %	±2 %	Pass