Feed-in Tariff Changes 2026: What the RPI to CPI Switch Really Means for Solar Owners

I remember when the Feed-in Tariff first launched felt like a gold miner in the mid west! For many businesses and homeowners, it wasn’t just about going green — it was about locking in predictable, inflation-linked income for 20 years. Solar panels became more than an environmental decision. They became a financial asset. From 2026, the inflation mechanism behind those payments will change. UK Feed-in Tariff (FIT) payments will move from RPI indexation to CPI. This is not a headline-grabbing policy shift. It isn’t a reduction in tariff rates. But over the remaining life of many agreements, it will influence projected returns. For commercial property owners, agricultural estates and legacy FIT holders, it is worth understanding properly.

What Was the Feed-in Tariff Designed to Do? The UK Feed-in Tariff scheme, introduced in 2010 and closed to new applicants in 2019, was designed to accelerate adoption of small-scale renewable electricity generation. Under the scheme, system owners received: A generation tariff (for every kWh produced) An export payment (for electricity exported to the grid) Crucially, both elements were linked to inflation. This provided long-term income certainty and protected returns against the impact of rising prices. For many commercial installations and agricultural estates, FIT income became a predictable secondary revenue stream — often modelled conservatively but relied upon confidently.

What Is Changing in 2026? From 2026 onward, the inflation index applied to Feed-in Tariff payments will switch from: RPI (Retail Price Index) to CPI (Consumer Price Index) The tariff rates themselves are not being reduced. The structure of payments remains in place. The duration of agreements is not being shortened. What changes is how those payments increase each year. And that distinction matters.

Understanding RPI vs CPI (In Practical Terms) Both RPI and CPI measure inflation — but they are calculated differently. RPI includes housing costs such as mortgage interest and typically produces higher figures. CPI excludes certain housing components and uses a different statistical formula, generally resulting in lower reported inflation. Historically, CPI has averaged around 0.5–1.0 percentage points lower than RPI over long periods. That difference may appear modest in a single year. Over 10–15 years of compounded indexation, however, it becomes more meaningful.

Why CPI Is Typically Lower There are structural reasons: CPI uses a calculation method that dampens price swings more than RPI. CPI excludes mortgage interest costs. Government policy over the last decade has increasingly aligned public payments and bonds with CPI rather than RPI. This reflects a broader international trend. Across several countries, long-term public financial instruments — including pensions and infrastructure-linked payments — have shifted toward CPI-style indices as governments standardise inflation measures and manage long-term liabilities. The UK adjustment sits within that wider pattern.

Is This a Tariff Cut? Technically, no. The base tariff rates remain unchanged. System owners will continue to receive payments under their original contract terms. However, because CPI generally grows more slowly than RPI, the future escalation of those payments will be lower than under the previous mechanism. It is not a reduction of today’s entitlement. It is a change in the pace at which that entitlement increases. That nuance is important.

What Does This Mean Financially? The practical impact depends on: Remaining years on your FIT agreement System size Original tariff rate Assumed long-term inflation differential For a commercial array with 10–15 years remaining, a 0.7% average annual difference between RPI and CPI could result in: Lower cumulative lifetime revenue A modest adjustment to projected internal rate of return (IRR) Revised long-term cashflow assumptions This does not render legacy systems unviable. It does mean that financial models created years ago may now rely on outdated escalation assumptions. When energy infrastructure is treated as a financial asset, assumptions deserve periodic review.

The Wider Framework: Smart Export Guarantee It is also important to separate legacy FIT systems from the current policy environment. New solar systems no longer operate under the Feed-in Tariff. They fall under the Smart Export Guarantee (SEG), introduced in 2020, which requires suppliers to pay for exported electricity — but at market-based rates rather than fixed, index-linked tariffs. This represents a structural shift: FIT = long-term fixed tariff, inflation-linked SEG = variable export rate, supplier-set The RPI to CPI change reflects the broader evolution of UK solar policy — from subsidy-led deployment to market-integrated generation. For owners of older systems, that reinforces a key point: Your installation operates under a legacy structure. And legacy structures evolve.

What Should Existing Solar Owners Review? This is not a moment for alarm. It is a moment for reassessment. Asset owners may wish to review: Remaining FIT term with updated CPI projections Revised long-term income forecasts System performance against original yield modelling Maintenance and inverter replacement timelines Whether optimisation upgrades or battery storage improve total returns Many commercial and agricultural solar arrays installed in the early 2010s are now mature assets. Regulatory adjustments provide a natural checkpoint for reviewing performance and financial projections.

Energy Infrastructure Is a Financial Asset Over the past decade, solar has shifted from being viewed purely as a sustainability initiative to being recognised as infrastructure. Infrastructure appears on the balance sheet. When regulatory assumptions change — even incrementally — responsible asset management means revisiting forecasts. The RPI to CPI switch beginning in 2026 does not undermine the value of legacy systems. It does adjust the projected growth rate of income. Over time, that shapes total return.

Final Perspective Regulatory shifts rarely dominate headlines. Yet they often influence long-term asset performance. The move from RPI to CPI indexation is technical and policy-driven — not dramatic. For legacy FIT holders, the appropriate response is not concerning. It is clarity and updated modelling.

Review Your Solar Income Forecast If you own a commercial, agricultural or legacy FIT solar system and would like an updated CPI-based income projection, we can provide an independent asset performance review. Energy infrastructure should be reviewed when assumptions change. And inflation assumptions have now changed.

Justin Dring www.independentsolarconsultants.com