Realistic decarbonisation plan: how to build it and cut energy costs

A realistic decarbonisation plan is built in four moves: measure Scope 1, 2 and 3 emissions, rank the measures by cost per tonne avoided, start with the ones that pay for themselves through energy savings, and leave structural investment for later. Cutting the bill and cutting emissions overlap more than people expect, but not completely.

This guide explains how to build that plan with a financial lens: which levers exist, what each does to cost, how to prioritise them with an abatement curve and how the work spreads across three years.

What should a decarbonisation plan contain?

Decarbonisation is the process of reducing the greenhouse gas emissions linked to an organisation's activity. The plan is the document that turns it into budgeted decisions. A plan that survives an audit and a board meeting contains:

• An emissions inventory with a declared base year and explicit organisational boundaries.
• A quantified target against that base year, with a horizon and an intensity ratio.
• A portfolio of measures with estimated tonnes avoided, capital cost, annual saving and an owner.
• A timetable and a monitoring mechanism based on data, not impressions.
• An explicit energy price assumption, because the whole financial case rests on it.

Without the inventory there is no plan. If you do not have one yet, start by delimiting Scope 1, 2 and 3 emissions and identifying where your critical mass sits.

Which reduction levers actually cut energy costs?

Not every decarbonisation measure saves money, and it is better to say so before presenting the plan. The table ranks the common levers by their real effect on cost.

Two caveats. First, Spain's Energy Saving Certificates scheme, set up by Royal Decree 36/2023, turns verified energy savings into a tradable asset, which improves the return on efficiency measures. Second, offsetting is not a reduction lever: it applies to the residual and always adds cost.

How do you prioritise measures by abatement cost?

The marginal abatement cost of a measure is its net annualised cost divided by the tonnes of CO₂ equivalent it avoids each year. The formula is simple: annualise the investment, subtract the annual energy saving, divide by the tonnes avoided.

When the saving exceeds the annualised cost, the result is negative and the measure pays for itself. Sorting the portfolio from lowest to highest abatement cost produces the curve that lets you decide on financial grounds and defend the plan to the finance team.

Four criteria complete the ranking:

1. Cost per tonne. Negative first, then cheap, then expensive.
2. Available volume. A very cheap measure that only avoids fifty tonnes will not move the target.
3. Lead time and third-party dependency. Anything that depends on a supplier or a permit takes longer than planned.
4. Regulatory risk. ETS2 for buildings and road transport, CBAM on imports and workplace mobility plans change the return on some measures sooner than a static analysis suggests.

The abatement curve has a known limit: it is sensitive to the assumed energy price and it does not capture benefits that are hard to monetise, such as access to customers who demand footprint data. Run it with a high-price and a low-price scenario before closing the budget. You can cross-check it with our analysis of the impact of energy costs on businesses.

A realistic three-year sequence

Most plans fail because they try to do everything in year one. This sequence spreads effort and budget in a way that holds.

If your goal includes Spain's Reduzco seal, bear in mind it requires four consecutive years of data with identical boundaries and methodology. The detail is in our guide to the MITECO carbon footprint registry and its seals.

How to build the plan step by step

1. Measure the carbon footprint

Without a reliable inventory there are no defensible targets. The calculation should cover Scope 1, 2 and 3 following the GHG Protocol and ISO 14064-1. Scope 3 usually concentrates most of the footprint, even if it is not where the immediate financial saving sits.

2. Set the target

Quantified target, base year and horizon. The recommended route is to align it with science through science-based targets, separating the 2030 goal from long-term neutrality in 2050.

3. Build the portfolio of measures

Every measure needs an owner, a timeline, an investment figure, an estimated annual saving and the tonnes avoided. Without those five fields you cannot calculate abatement cost or defend the budget line.

4. Execute with frequent monitoring

An annual plan reviewed once a year is always late. Continuous monitoring of carbon footprint data lets you check whether a measure is delivering the expected saving while you can still correct it.

5. Report and verify

External verification of the inventory and, where relevant, registration with MITECO give the plan credibility and keep greenwashing accusations away. For measures and targets, lean on our guide to carbon footprint reduction plans.

What regulation requires a plan?

• Royal Decree 214/2025. Companies that report non-financial information must calculate their Scope 1 and 2 footprint and draw up and publish a reduction plan with a quantified target and a minimum five-year horizon, within six months of the end of the financial year. The reference year is 2025.
• CSRD after Directive (EU) 2026/470. Scope has narrowed to companies with more than 1,000 employees and more than 450 million euros in net turnover, with financial year 2027 as the first reporting year. The standalone obligation to put the climate transition plan into effect disappears, but the plan remains disclosure content for companies in scope. We cover it in Manglai's CSRD solution.
• Spain's PNIEC 2023-2030. The update approved on 25 September 2024 sets, for 2030, a 32% cut in emissions against 1990, 48% renewables in final energy consumption, 81% renewable electricity generation and a 43% improvement in energy efficiency.
• Law 7/2021 on climate change and energy transition. It sets climate neutrality in Spain no later than 2050 and gives legal cover to the obligations above.
• ETS2. The new European emissions trading regime for buildings and road transport fuels starts with auctions in 2027 and will be fully operational in 2028, with a direct effect on diesel and gas costs.

Mistakes that sink a decarbonisation plan

• Setting the target before the inventory exists, which forces a rewrite when forgotten sources appear.
• Mixing reduction and offsetting in a single figure.
• Not declaring the energy price assumption, which makes the return unauditable.
• Changing organisational boundaries without a comparability adjustment, which breaks the historical series.
• Leaving Scope 3 out of the plan until a large customer demands it contractually.

Frequently asked questions about the decarbonisation plan

Does a decarbonisation plan save money or cost money?

Both, at different moments. Management and efficiency measures usually have a negative abatement cost and generate cash from year one. Process and fleet electrification and offsetting the residual carry a positive cost. A well-sequenced plan uses the savings from the first group to fund the second.

How do you calculate a measure's abatement cost?

Annualise the investment over its useful life, subtract the annual energy saving, and divide the result by the tonnes of CO₂ equivalent avoided per year. A negative value means the measure pays for itself.

Is a decarbonisation plan mandatory in Spain?

For companies required to report non-financial information, yes: Royal Decree 214/2025 requires them to draw up and publish a reduction plan. It is also a requirement to register the footprint with MITECO. For everyone else it is voluntary, although customers and lenders increasingly ask for it.

How long before it shows up on the bill?

Operational measures show within weeks. Light-investment efficiency measures show within the same financial year. Self-consumption and thermal electrification work on multi-year horizons and their return depends on energy prices.

What is the difference between a decarbonisation strategy and a plan?

The decarbonisation strategy sets the long-term vision and objectives. The plan specifies measures, owners, budget and deadlines to get there.

Where do I start if my data is not structured?

With the last twelve months of energy and fuel invoices and a supplier list ranked by spend. That is enough to build a first inventory with documented estimates and to see where refinement pays off.

To measure, prioritise and track the plan with the same data a verifier will later ask for, you can rely on Manglai's carbon footprint platform.