Procurement

A practical deep dive into multipurchase contracts for UK businesses

Multipurchase contracts let UK firms with 1‑5 GWh annual demand lock in price bands while retaining flexibility to trade volume across periods. This article explains period choices, tranche design, caps, triggers and the optimal moment to fix non‑commodity components, ending with a realistic worked example.

By TUS Trade Desk — Commercial Energy Consultants•Published 23 September 2026•6 min read

Why multipurchase contracts matter

For a business that consumes between 1 and 5 GWh a year, the volatility of the wholesale market can swing the annual electricity bill by tens of thousands of pounds. A multipurchase (or "flex‑purchase") contract offers a hybrid approach: a core volume is purchased at a negotiated price, while the remainder can be sourced on the spot market or via short‑term contracts. The result is a predictable cost base that still captures upside when market prices fall.

Core structure of a multipurchase deal

A typical multipurchase agreement is built around three pillars – the period cadence, the tranche allocation and the price protection mechanisms.

Period choices

The contract can be sliced into monthly, quarterly or seasonal windows. Monthly periods give the finest granularity and align with most energy invoices, but they increase administrative overhead. Quarterly periods match the Ofgem Settlement period and are common for businesses that report under the Streamlined Energy and Carbon Reporting (SECR) framework. Seasonal periods (e.g., winter vs summer) are useful when demand is strongly weather‑driven and when the business can tolerate broader price swings.

Tranches and volume allocation

A tranche is a pre‑agreed block of energy (in MWh) that the buyer commits to purchase at the contract price. For a 3 GWh portfolio a typical split might be:

30 % (900 MWh) as a fixed‑price tranche covering baseline demand.
40 % (1 200 MWh) as a flexible tranche with a price band and volume caps.
30 % (900 MWh) left open for spot market purchases. The flexible tranche can be re‑balanced each period, allowing the buyer to shift volume between months or quarters based on actual consumption.

Caps, triggers and price floors

Two price‑control tools protect both parties:

Cap – the maximum price the buyer will pay for the flexible tranche. If the market price exceeds the cap, the supplier absorbs the excess.
Trigger (or floor) – the minimum price at which the supplier can sell the tranche. If the market price falls below the trigger, the buyer benefits from the lower price, but the supplier receives a pre‑agreed floor to cover costs. Typical caps for 2024‑25 range from £80/MWh to £120/MWh depending on the risk appetite, while triggers sit 5‑10 % below the cap.

Timing the non‑commodity components

A multipurchase contract is not just about the commodity price. It also bundles:

Transmission and Distribution Use of System (TNUoS/DuoS) charges – fixed per‑kWh rates set by Ofgem.
Capacity market payments – relevant for large users that need to demonstrate demand response capability.
Renewables Obligation (RO) and Contracts for Difference (CfD) pass‑throughs – affect the overall price composition. Best practice is to lock these non‑commodity components at the start of the contract term, typically a 12‑month horizon, because they are regulated and change infrequently. Fixing them early removes a layer of uncertainty and aligns the contract with SECR reporting periods.

Worked example

Assumptions

Annual demand: 3 GWh (3 000 MWh).
Period: quarterly (4 periods).
Tranche split: 30 % fixed, 40 % flexible, 30 % spot.
Fixed‑price tranche: £85/MWh (incl. TNUoS/DuoS).
Flexible tranche cap: £110/MWh, trigger: £95/MWh.
Spot market average forecast for 2024‑25: £100/MWh with a volatility band of ±£20.
Non‑commodity charges fixed at £12/MWh (TNUoS) and £6/MWh (DuoS).
Discount rate for NPV: 5 %.

Step‑by‑step calculation

Fixed tranche cost – 900 MWh × (£85 + £12 + £6) = £103,500.
Flexible tranche – quarter 1 – actual market price £78/MWh (below trigger). Buyer pays trigger £95/MWh. Cost: 1 200 MWh × (£95 + £12 + £6) = £123,600.
Flexible tranche – quarter 2 – market price £115/MWh (above cap). Supplier absorbs excess; buyer pays cap £110/MWh. Cost: 1 200 MWh × (£110 + £12 + £6) = £148,800.
Flexible tranche – quarter 3 – market price £102/MWh (within band). Buyer pays market price. Cost: 1 200 MWh × (£102 + £12 + £6) = £144,000.
Flexible tranche – quarter 4 – market price £88/MWh (below trigger). Buyer pays trigger £95/MWh. Cost: 1 200 MWh × (£95 + £12 + £6) = £123,600.
Spot tranche – assume average market price £100/MWh for the remaining 900 MWh. Cost: 900 MWh × (£100 + £12 + £6) = £103,800.

Total annual cost = £103,500 + £123,600 + £148,800 + £144,000 + £123,600 + £103,800 = £747,300.

Comparison with pure spot exposure If the business bought the full 3 000 MWh on the spot market at the same average price (£100/MWh) the cost would be 3 000 MWh × (£100 + £12 + £6) = £354,000. However, the spot price volatility could swing the bill by ±£60,000 (±£20/MWh × 3 000 MWh). The multipurchase structure caps the downside at £110/MWh for 40 % of volume, delivering a predictable ceiling of £747,300 while still allowing upside when prices fall below the trigger.

Payback of the contract design Assuming the business could have achieved a 5 % reduction in energy spend through internal efficiency measures, the multipurchase contract delivers a comparable risk‑adjusted saving. Over a 3‑year horizon, the net present value of the avoided price spikes (estimated at £30,000 per year) is roughly £82,000, comfortably covering the typical transaction fee of 0.5 % of annual spend.

Risks and mitigation

Volume mismatch – If actual consumption deviates significantly from the tranche allocation, the business may incur excess fixed‑price volume. Mitigate by building a 5‑10 % buffer into the flexible tranche.
Regulatory change – Adjustments to TNUoS/DuoS or the capacity market can affect the total cost. A clause that allows annual price review linked to Ofgem tariffs protects both parties.
Supplier credit risk – With caps and triggers, the supplier bears price risk. Selecting a supplier from TUS's 30+ panel, which has collectively delivered 150+ GWh under flex management and beat supplier projections by 20 % in the last 12 months, reduces this risk.

Bottom line

Multipurchase contracts give UK businesses with 1‑5 GWh portfolios a pragmatic blend of price certainty and market participation. By choosing the right period cadence, allocating tranches wisely, and fixing non‑commodity components early, a finance director can shield the balance sheet from wholesale spikes while still benefiting from lower prices when the market softens. The worked example shows how caps and triggers translate into a predictable cost ceiling, and the risk‑mitigation steps ensure the structure remains robust under regulatory or consumption changes.