A 100 kW Commercial Solar System in the UK: Output, Roof Area and Grid
Updated 23 October 2026 · SEO Dons Editorial
What does 100 kW mean on a UK site?
On a commercial quote, "100 kW" can mean 100 kWp of panels, a 100 kW inverter or an agreed export capacity, and the three are not always equal. This page takes a 100 kW system to mean about 100 kWp of panels and works through what that means for panel count, roof area, output, inverters and the grid. The units are defined on the kWp, kW and kWh page.
How many panels make 100 kWp?
Divide 100,000 W by the module wattage and round up. The wattages are round examples; use the datasheet figure for the module quoted. Module surface assumes a 550 W module of 2.28 m by 1.13 m (2.58 m²), scaled for other wattages at the same watts per square metre.
| Module wattage | Panels | Resulting capacity | Module surface (illustrative) |
|---|---|---|---|
| 450 W | 223 | 100.35 kWp | 470 m² |
| 550 W | 182 | 100.10 kWp | 469 m² |
| 600 W | 167 | 100.20 kWp | 469 m² |
How much roof area does 100 kWp need?
The modules alone cover about 469 m². The roof needed is larger, and how much larger depends on layout. Flat east-west pairs sit close together because the two halves face away from each other. Tilted south-facing rows need a gap behind each row so it is not shaded by the one in front.
A strict test is to keep each row clear of the shadow of the next at midday on the winter solstice. The row pitch is then the module's sloping length multiplied by (cos tilt + sin tilt ÷ tan sun height), so the share of roof covered is 1 ÷ (cos tilt + sin tilt ÷ tan sun height). The PVGIS hourly series puts the sun 14.07 degrees above the horizon around midday on 21 December 2023 in Birmingham. That gives 60% coverage at a 10 degree tilt and 32% at 35 degrees. Sites further north need wider spacing, and designers accept some winter shading, so treat these as illustrations.
| Layout | Share of roof covered by modules | Roof needed for 100.1 kWp (182 modules of 550 W) | Annual output, Birmingham |
|---|---|---|---|
| East-west pairs, 10° tilt | 90% (assumed) | 521 m² | 80,100 kWh |
| South-facing rows, 10° tilt | 60% (calculated) | 787 m² | 87,600 kWh |
| South-facing rows, 35° tilt | 32% (calculated) | 1,457 m² | 96,900 kWh |
The roof figure is for the array alone. Class J keeps modules at least 1 m inside the roof edge, so, for example, a 40 m by 25 m flat roof (1,000 m²) leaves 874 m² before walkways, rooflights and plant come off. Per square metre of usable roof, east-west pairs carry about 2.8 times the capacity of 35 degree south racks. After the lower yield per kWp that is about 2.3 times the annual energy in this example: roughly 154,000 kWh from 1,000 m² against 66,000 kWh. Where demand rather than roof sets the size, the tilted rack can still be the better choice; the commercial PV systems guide sets out the order of those decisions.
How much does a 100 kWp system generate in a year?
Annual output is capacity multiplied by the PVGIS yield for the place and layout, with 14% losses. Figures are for 100 kWp and rounded to the nearest 100 kWh.
| Location | kWh per kWp, south 35° | kWh per kWp, east-west 10° | 100 kWp, south 35° | 100 kWp, east-west |
|---|---|---|---|---|
| Plymouth | 1,122 | 932 | 112,200 | 93,200 |
| London | 1,019 | 840 | 101,900 | 84,000 |
| Birmingham | 968 | 800 | 96,800 | 80,000 |
| Manchester | 886 | 741 | 88,600 | 74,100 |
| Edinburgh | 903 | 731 | 90,300 | 73,100 |
| Glasgow | 853 | 707 | 85,300 | 70,700 |
The range across these six places runs from about 70,700 kWh (east-west in Glasgow) to 112,200 kWh (south 35 degrees in Plymouth). The yield-by-region guide adds seven more locations and the south 10 degree layout, and the savings calculator turns generation into a bill estimate. PVGIS's 14% loss allowance already covers inverter losses.
What inverter arrangement suits a 100 kW system?
At this size the generator connects on three phases, and designers can weigh a small number of three-phase string inverters against one larger unit. One 100 kW unit, two 50 kW units or four 25 kW units all give 100 kW of AC capacity; the split changes how many array strings each inverter handles, how much of the system a single fault takes offline, and how many cable runs reach the plant room. The three-phase inverter guide covers the choice in detail.
The AC figure need not equal the panel kWp. With a DC:AC ratio of 1.2, 100 kWp of panels sits behind an inverter of about 83 kW. In the PVGIS hourly series for a south-facing 35 degree array in Birmingham in 2023, a ratio of 1.2 clipped 0.03% of annual energy, and a ratio of 1.3 clipped 0.36%; the kWp page shows the full table. National Grid Electricity Distribution (NGED) sizes a solar connection from the inverter's continuous steady state output, so the ratio can also decide which side of the 50 kW line a design sits on. State it in the quote.
What is the grid route at 100 kW?
Above 3.68 kW per phase (11.04 kW across three phases) the Energy Networks Association (ENA) says G99 applies, so 100 kW is a G99 connection. NGED separates generation with an aggregate capacity of 50 kW or less on three phases, which has a simplified application, from capacity above that, which uses the standard application form; its table puts generation "Greater than 50kW & less than 1MW" in the Type A band. SSEN adds that for generation above 50 kilowatts the customer's account manager provides the export MPAN, where smaller systems go through a supplier or network planner.
Before committing to an inverter count, screen the site against the operator's capacity map (the heat maps guide lists each one). Network operators publish generation of 50 kW and over in their Embedded Capacity Register, so the register shows what is already connected or accepted nearby. This page does not explain how to apply; that is the installer's task.
What changes between 50 kW and 100 kW?
| Question | Array of 50 kW or less | Array of about 100 kW |
|---|---|---|
| Roof planning in England | Class J(b), microgeneration solar PV on a building | Class J(c), other solar PV on a roof: apply to the planning authority for a prior-approval determination first, with glare the named concern, then wait for the answer or 56 days |
| Grid application (NGED) | Simplified process | Standard application form |
| Export MPAN (SSEN) | Supplier under 30 kW; network planner from 30 to 50 kW | Account manager |
| Embedded Capacity Register | Listing starts at 50 kW | Listed once connected or accepted |
| Smart Export Guarantee | Eligible up to 5 MW of total installed capacity | Eligible on the same basis; certification evidence is covered on the MCS page |
Class J(c) makes glare a design input, so orientation and tilt should be tested against neighbouring land and buildings before the layout is fixed. The glint and glare guide covers glare assessment, the planning guide the other Class J limits, and the 50 kW page the thresholds from the smaller side. You can send an enquiry through the site's form for a contractor to check a roof against these lines.
Sources
- Energy Act 2004, section 82, legislation.gov.uk, legislation.gov.uk, checked 22 October 2026.
- Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 14, Class J, legislation.gov.uk, legislation.gov.uk, checked 22 October 2026.
- Connecting commercial generation to the electricity networks, Energy Networks Association, energynetworks.org, checked 22 October 2026.
- G99 connection procedures, National Grid Electricity Distribution, connections.nationalgrid.co.uk, checked 22 October 2026.
- Embedded capacity register, National Grid Electricity Distribution, commercial.nationalgrid.co.uk, checked 22 October 2026.
- Embedded capacity register, SP Electricity North West, enwl.co.uk, checked 22 October 2026.
- Large scale microgeneration (installations above 3.68kW per phase, but 50kW or less), Scottish and Southern Electricity Networks, ssen.co.uk, checked 22 October 2026.
- Smart Export Guarantee (SEG) - Generators, Ofgem, ofgem.gov.uk, checked 22 October 2026.
- PVGIS 5.3 PVcalc runs (PVGIS-SARAH3, crystalline silicon, 1 kWp, 14% losses; south at 35 degrees, east and west at 10 degrees), European Commission Joint Research Centre, checked 22 October 2026: Plymouth south, east, west; London south, east, west; Birmingham south, flat south, east, west; Manchester south, east, west; Edinburgh south, east, west; Glasgow south, east, west; the PVGIS user manual; and the Birmingham 2023 hourly series: south, east, west.
Common questions
How many solar panels do I need for 100 kW?
With 550 W modules, 182 panels make 100.1 kWp. With 450 W modules it takes 223 panels and with 600 W modules 167.
What roof area does a 100 kWp array take up?
It depends on layout. On the page's assumptions, east-west pairs need about 521 m², south-facing rows at 10 degrees about 787 m² and rows at 35 degrees about 1,457 m², before edge zones, walkways and plant.
Is a 100 kW solar system a G99 connection?
Yes. The Energy Networks Association says G99 applies to a generator with a capacity greater than 3.68 kW per phase. NGED also uses a standard application for aggregate capacity above 50 kW on three phases. The network operator decides the terms for the specific site.
What size inverter does 100 kWp of panels need?
There is no single answer. A DC:AC ratio of 1.0 means a 100 kW inverter, and a ratio of 1.2 means about 83 kW. Because NGED sizes the connection from the inverter's output, the choice affects the grid route as well as clipping, so the quote should state panel kWp and inverter kW separately.