Warehouse Solar vs Factory Solar: What Actually Differs

Warehouse solar and factory solar are not the same problem

On paper, a distribution shed and a manufacturing plant look like the same solar job. Both are big single-storey buildings with acres of flat or low-pitch roof, both pay too much for grid electricity, and both are chasing the same 3 to 6 year payback. Put the two projects side by side, though, and the economics diverge in one place that matters more than any other: the load profile. How much electricity the building draws, and when, decides how much of your generation you actually keep. That single number drives the return.

This guide compares the two honestly. It is written for warehouse and logistics operators, but if you run a factory it is just as useful, because seeing the contrast makes your own numbers clearer. For factory-specific detail on process load, multi-shift patterns and heat demand, our sister site solarpanelsforfactories.co.uk goes deeper on that side. Here, we stay on the fault line between the two.

Why load profile is the whole game

Commercial solar earns its return from self-consumption, not from export. Every kilowatt-hour you generate and use on site displaces a unit you would have bought at 25 to 40p. Every unit you export earns only the Smart Export Guarantee (SEG) rate your supplier chooses to offer, which is a fraction of the import price and is not guaranteed to be generous. So the question that decides payback is simple: of the solar you generate on a bright day, how much does the building swallow, and how much spills to the grid?

That is where warehouses and factories part ways.

The warehouse pattern: low, flat, and daytime

A modern ambient warehouse, LED-lit, running order-picking and dispatch, has a surprisingly gentle electricity profile. The base-load is lighting, small power, battery chargers for materials handling equipment (MHE), and IT. It is low and flat across the working day, with modest bumps around order peaks. There is very little heavy rotating plant. Because that base-load sits squarely in daylight hours, solar lines up well with demand: for a site running roughly 06:00 to 18:00, self-consumption of 90% or more is realistic. Across mixed shift patterns, 60 to 75% is typical.

The catch is scale. That flat base-load is often small relative to the enormous roof. Cover the whole roof and you generate far more at midday than the shed can use, and the surplus exports at the poor SEG rate, dragging the return down. The winning move for a warehouse is to size to the load, not to the roof, then grow the load into the spare roof over time (more on that below).

The factory pattern: higher, continuous, multi-shift

A manufacturing plant is a different animal. Motors, compressors, extraction, ovens, curing, process heating and heavy HVAC create a higher and more continuous load, and many factories run two or three shifts. That demand does not switch off at 18:00. A bigger array can therefore be self-consumed directly, because there is genuine demand to soak up midday generation and often into the evening. The constraint flips: a factory’s roof may be small relative to its demand, so the limit is how many panels fit, not how much load there is to serve. A factory rarely has a self-consumption problem; it has a “can I fit enough generation” problem.

Roof: warehouses have the space, factories have the demand

Warehouse roofs are vast, but do not assume every square metre is usable. Rooflights, plant, walkways, safety zones, structural limits and shading typically leave only 40 to 60% of the gross roof area available for panels. A survey of the roof structure and its load capacity is not optional, especially on older or lightweight sheds.

Factory roofs are frequently more cluttered still, broken up by extraction stacks, service runs and rooftop plant, and are smaller relative to the electrical demand underneath them. The practical result: a warehouse usually has more roof than it needs and must be careful not to over-size; a factory usually wants more roof than it has.

Sizing: same maths, opposite starting point

The sizing arithmetic is identical for both buildings. As a rule of thumb, expect around 100 to 140 kWp per 1,000 m2 of usable roof, and in UK conditions each kWp yields roughly 750 to 1,050 kWh a year depending on orientation, pitch and region. Costs are the same for warehouse and factory alike: indicatively £850 to £1,100 per kWp at around 100 kW, falling to £650 to £850 per kWp at 1 MW as scale kicks in.

What differs is the input you size from. For both, you must start from 12 months of half-hourly (HH) consumption data, not the roof area and not last year’s total kWh bill. But the HH data is telling you different things:

• Warehouse: the HH curve reveals a low, flat plateau. Size the array to sit under that plateau so most generation is self-consumed, then plan to grow the base-load.
• Factory: the HH curve reveals a high, sustained draw. Size the array as large as the roof and grid connection allow, because the demand to absorb it is already there.

If you want the step-by-step method for reading a warehouse HH file, we cover it in how to size warehouse solar from half-hourly data.

The warehouse trump card: growing load into the roof

Here is where the warehouse story gets more interesting than the factory one. That surplus roof is not dead weight, it is optionality. Over the next few years, most logistics operators are electrifying the things that currently burn diesel or run on grid import:

• Forklift and MHE charging shifting from opportunity charging to planned daytime charging that soaks up solar.
• Last-mile and yard EV vans charging on site during the day.
• HGV charging as fleets electrify, which turns a modest warehouse into a serious electrical load.

Each of these lets you convert exported surplus into self-consumed value, and each improves the return on solar you have already installed. A factory has less of this headroom; its load is already high and its roof is already the binding constraint. So the honest framing is: a warehouse can design for tomorrow’s load today, sizing generously and letting electrification fill the gap. For deeper vertical detail see ambient and general storage and 3PL and contract logistics, where lease length and tenant mix change the calculus.

Side by side

	Warehouse / Logistics	Factory / Manufacturing
Typical load profile	Low, flat daytime base-load (lighting, chargers, small power) with peaks around order flow	Higher, more continuous process load (motors, compressors, ovens, HVAC), often multi-shift
Self-consumption potential	60 to 75% typical; 90%+ for 06:00 to 18:00 ops, if sized to load not roof	High and steady; a larger array is absorbed directly by continuous demand
Roof area vs demand	Huge roof, often more than needed; only ~40 to 60% usable	Roof often small relative to demand; the binding constraint
Sizing approach	Size to the flat base-load, then grow load into the roof over time	Size as large as roof and grid allow; demand is already there
Typical payback driver	Sizing discipline plus future load growth (MHE, EV vans, HGV)	High base self-consumption from existing continuous load
Key risk	Over-sizing to the roof and exporting surplus at poor SEG rates	Roof or grid connection caps generation below what demand could use

Which pays back faster? Honestly, it depends

Neither building is universally the better solar bet. Both target the same headline range: roughly 3 to 6 years to payback when self-funded, with the best-configured sites landing 2.5 to 4 years. What moves you within that range is different for each.

A factory often reaches strong self-consumption immediately because the continuous load is already there to absorb generation. If the roof is big enough and the grid connection allows it, the return can be excellent from day one, with little reliance on future changes.

A warehouse that is sized carelessly to the roof will disappoint, because midday surplus exports cheaply. But a warehouse that is sized to its base-load and then deliberately grows that load through forklift charging and EV fleets can end up with an outstanding return, and it does so with a far larger asset in place ready to serve future demand. In other words: a factory tends to be strong out of the gate; a warehouse rewards discipline now and gets better over time.

Tax and grid: identical rules for both

Whatever the building, the fiscal and connection rules are the same, and worth getting right.

• Capital allowances. The Annual Investment Allowance (AIA) gives 100% first-year relief up to £1m of qualifying spend. Above that cap, solar sits in the special-rate pool, so full expensing does not apply; expenditure above the AIA attracts the 50% first-year allowance instead. Take advice on how your total capital plan interacts with the £1m cap.
• VAT. There is no 0% VAT on commercial solar. You pay 20%, but a VAT-registered business can normally reclaim it, so it is a cash-flow timing point, not a permanent cost.
• Grid connection. Any project above roughly 1 MW typically faces a 12 to 24 month DNO connection timeline, and where export is constrained you may need G100 export limitation or a battery to proceed. Factories hitting the roof-limited ceiling and large logistics parks alike should start the DNO conversation early, because the connection, not the panels, is often the long pole.

For definitions of the terms used here, from SEG to G100 to special-rate pool, see the glossary.

Getting the numbers right for your building

The comparison matters, but your decision comes down to your own HH data, your own roof survey and your own electrification roadmap. A warehouse operator in Leeds with a big ambient shed and an EV fleet on the horizon should reach a very different design to a two-shift factory next door, even with the same roof and the same budget. Both can be excellent investments; both fail when sized to the roof instead of the load.

If you would like an indicative sizing and payback figure built from your actual consumption profile rather than a rule of thumb, see our cost guide for how the numbers are put together, then request a tailored assessment.

Ready to compare your options with real figures? Get a free, no-obligation quote and we will size it to your load, not your roof.