Day 4 of 1415 minutes

Day 4: Solar, Tidal & Emerging Renewables

Solar PV, tidal energy, geothermal, and green hydrogen

Learning Objectives

  • Understand the scale and trajectory of solar PV deployment in the UK, including the rooftop vs. ground-mount debate.
  • Appreciate the UK's tidal energy potential and the current state of key projects.
  • Gain an overview of emerging renewable technologies — geothermal and green hydrogen — and their likely roles in the UK energy mix.

Solar Power: Quietly Booming

Wind dominates the UK renewables headlines, but solar PV has been growing rapidly and is now a significant part of the generation mix. As of 2024, the UK had approximately 16–17 GW of installed solar capacity. The government's ambition is to reach 70 GW of solar by 2035 — a roughly fourfold increase.

Solar's economics are compelling. The cost of solar panels has fallen by over 90% since 2010, making it one of the cheapest sources of new electricity globally. In the UK, solar is now cost-competitive with wind and significantly cheaper than gas or nuclear on a levelised cost basis.

There are two main categories: rooftop solar (installed on homes, commercial buildings, and warehouses) and ground-mounted solar farms. The UK has a growing portfolio of both. Rooftop installations have been driven by the Smart Export Guarantee (which pays households for surplus electricity exported to the grid) and by rising retail electricity prices, which improve the payback on self-generation. As of 2024, over a million UK homes had rooftop solar panels.

Ground-mounted solar farms have grown significantly, particularly in southern and eastern England where solar irradiance is highest. Several very large projects are in the planning pipeline: Sunnica Energy Farm in Cambridgeshire and Suffolk (up to 500 MW) and Botley West in Oxfordshire (up to 840 MW) are among the largest proposed in Europe.

However, solar farms face planning challenges. Local objections often focus on visual impact, loss of agricultural land, and biodiversity concerns. The designation of some solar projects as 'Nationally Significant Infrastructure Projects' (NSIPs) means they are decided centrally, bypassing some local authority constraints — but this doesn't remove the controversy.

Over one million UK homes now have rooftop solar panels, and the government's target is to reach 70 GW of total solar capacity by 2035 — roughly four times current levels.

The Solar Paradox: Daylight vs. Demand

Solar's great limitation in the UK is well known: it generates most power in summer, during the middle of the day, when demand is often at its lowest. On winter evenings — when UK electricity demand peaks — solar contributes almost nothing. This means solar is a valuable part of the mix but cannot, on its own, provide reliable baseload or peak power. It needs to be paired with storage (batteries, pumped hydro), other generation sources (wind, nuclear, gas backup), and demand flexibility.

This is not a fatal flaw — it's simply a system integration challenge. As battery storage costs continue to fall (as we'll explore on Day 6), the economics of storing midday solar surplus and discharging it in the evening are rapidly improving. The combination of solar plus batteries is increasingly attractive for both domestic and commercial installations.

Tidal Energy: The UK's Untapped Resource

The UK has some of the largest tidal ranges in the world — the Severn Estuary has the second-highest tidal range of any estuary globally. This makes tidal energy a perennial topic of interest, though progress has been far slower than wind or solar.

There are two main approaches:

Tidal stream technology uses underwater turbines placed in areas of strong tidal current — similar to underwater wind turbines. The leading UK project is MeyGen in the Pentland Firth, between mainland Scotland and Orkney. MeyGen has been generating electricity since 2017 and has planning consent for up to 398 MW, though only around 6 MW is currently operational. The technology works, but scaling it up and reducing costs remains a challenge.

Tidal range technology exploits the difference in water height between high and low tides, typically using barrages or lagoons. The most famous UK proposal was the Swansea Bay Tidal Lagoon, which would have generated approximately 320 MW. Despite receiving planning consent, the project was ultimately rejected by the UK Government in 2018 on cost grounds — a decision that remains controversial. Advocates argue tidal lagoons could provide predictable, long-duration power (tides are entirely predictable, unlike wind) and that costs would fall with subsequent projects.

Tidal energy's great advantage is its predictability — tides follow known cycles, making tidal power one of the few renewables that can be forecast with near-perfect accuracy years in advance. Its disadvantage is cost: it remains significantly more expensive per MWh than wind or solar.

Tidal energy is the most predictable of all renewable sources — tides can be forecast decades ahead — but high costs have so far prevented large-scale deployment in the UK.

Emerging Technologies: Geothermal and Green Hydrogen

Geothermal energy uses heat from deep underground. The UK has limited high-temperature geothermal resources compared to countries like Iceland or New Zealand, but there is growing interest in lower-temperature geothermal for district heating. The United Downs Deep Geothermal Power project in Cornwall is testing a 5 MW scheme that would be the UK's first geothermal electricity plant. Abandoned mine workings — of which the UK has many — are also being explored for mine water geothermal heating, where water warmed by the Earth's heat is pumped up to heat nearby buildings. The Seaham Garden Village project in County Durham is a leading example.

Green hydrogen — produced by splitting water using renewable electricity — is attracting enormous policy attention. The UK Hydrogen Strategy, published in 2021, set an ambition of 10 GW of low-carbon hydrogen production capacity by 2030. Hydrogen could play a role in decarbonising sectors that are hard to electrify directly: heavy industry (steel, chemicals), long-distance freight, and potentially some heating applications. However, green hydrogen is currently expensive, and the infrastructure to produce, store, and distribute it at scale does not yet exist. There is vigorous debate about which applications truly need hydrogen versus those where direct electrification would be more efficient — a topic we'll touch on again in Day 7 when we discuss heating.

Key Takeaway

Solar PV is booming and tidal energy offers predictable power in a country blessed with enormous tidal resources — but both require system-level solutions (storage, grid flexibility) and, in tidal's case, significant cost reduction to fulfil their potential alongside wind.

Quick-Fire Recap

  • The UK has approximately 16–17 GW of installed solar capacity, with a 70 GW target for 2035.
  • Over one million UK homes have rooftop solar panels.
  • Solar generates most power in summer daytime, creating a seasonal mismatch with peak winter demand.
  • MeyGen in Scotland's Pentland Firth is the UK's leading tidal stream project; the Swansea Bay Tidal Lagoon was rejected in 2018 on cost grounds.
  • Green hydrogen is being pursued for hard-to-electrify sectors, with a 10 GW production target for 2030, but remains expensive.

Reflection Prompt

If you owned a home with a south-facing roof, what would you want to know before deciding whether to install solar panels — and what kind of tool or service would help you make that decision?

Sources & Further Reading

  1. Department for Energy Security and Net Zero, "Solar Photovoltaics Deployment", DESNZ, 2024. https://www.gov.uk/government/statistics/solar-photovoltaics-deployment
  2. Solar Energy UK, "Solar Energy UK Briefing", Solar Energy UK, 2024. https://solarenergyuk.org/
  3. UK Government, "British Energy Security Strategy", HM Government, April 2022.
  4. SAE Renewables / Simec Atlantis, "MeyGen Tidal Energy Project", 2024. https://simecatlantis.com/meygen/
  5. UK Government, "UK Hydrogen Strategy", HM Government, August 2021. https://www.gov.uk/government/publications/uk-hydrogen-strategy
  6. Geothermal Engineering Ltd, "United Downs Deep Geothermal Power Project", 2024. https://www.uniteddownsgeothermal.co.uk/
  7. Climate Change Committee, "Sixth Carbon Budget – The UK's Path to Net Zero", CCC, December 2020.
  8. Carbon Brief, "Solar Power in the UK: An In-Depth Q&A", Carbon Brief, 2023. https://www.carbonbrief.org/

Through a Product Designer's Lens

The reflection prompt for today is itself a design challenge. Deciding whether to install rooftop solar involves navigating a bewildering array of variables: roof orientation, shading, panel efficiency, local electricity tariffs, export rates, battery costs, planning rules, and payback periods. Yet for most consumers, the decision-making tools are rudimentary — basic online calculators that don't account for real-world conditions.

There's a clear UX/UI opportunity for a product that uses satellite imagery, weather data, and smart meter information to give homeowners a personalised, trustworthy solar assessment — showing expected generation, payback period, and carbon savings, with a clear path to trusted installers. Companies like Sunsure and Solar Together are making progress here, but the user experience still lags behind what's technically possible.

From a product strategy angle, the solar-plus-battery combination is creating a new category of consumer energy products. Companies like Givenergy and Tesla (Powerwall) sell domestic batteries, but the market is fragmented and confusing for consumers. A product that simplifies the entire journey — from assessment through installation to ongoing optimisation — could capture significant value as the market scales toward 70 GW. The behavioural nudge angle matters too: showing a household their real-time self-consumption rate and how much they're earning from exports can reinforce the investment decision and shift usage patterns to maximise self-consumption.

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