Shota Furuya

Pieces日本語版

Can renewables supply all our energy with today's technology?

Mention a “100% renewable society” and the reply is still that it is a fantasy, or idealism. To answer the question squarely, though, we first have to be clear about what “all our energy” means. Electricity alone? Or total final energy consumption, including vehicle fuel, heating, steelmaking and aviation? The maturity of the technology and the scale of deployment involved are quite different in the two cases.

The short answer: (1) for electricity, 100% renewables is already technically possible with combinations of existing technology, and several regions and countries demonstrate it; (2) for total final energy including heat, transport and industry, the known technology portfolio can reach close to 100% by 2050, which is the common conclusion of the major scenarios from IRENA, the IEA and the Jacobson group at Stanford; and (3) the hard-to-abate sectors — steel, cement, aviation, shipping — need ten to twenty years to scale green hydrogen, synthetic fuels and electrification commercially, and that is the greatest obstacle. What follows separates what the technology can do from where its limits lie.

First, break “all energy” apart

Energy statistics have two layers: primary energy supply, counting oil, coal, gas, uranium and renewables at the resource stage, and final energy consumption, counted where it reaches households, transport and industry. Japan’s final energy consumption is about 12,500 PJ a year on METI’s 2024 energy white paper, roughly 45% industry, 23% transport and 32% commercial and residential. Electricity is only about 27% of that. The other 73% is fuel burned directly — petrol in cars, coal in steelmaking, heavy oil in boilers, gas in homes.

Supplying all energy from renewables therefore takes more than a 100% renewable power sector. It means electrifying what now burns fossil fuel directly (or switching it to hydrogen or synthetic fuels) and supplying that electricity from renewables — a two-stage problem known as sector coupling. Which has a useful consequence: the more electrification proceeds, the smaller total final energy becomes. An EV is three to four times as efficient as an internal combustion car and a heat pump three to five times as efficient as a gas boiler, so IRENA’s 1.5°C scenario has final energy consumption in 2050 about 30% below 2020.

Electricity: countries and regions that already run on 100% renewables

For electricity, 100% renewable supply is not a hypothesis but an accomplished fact. Iceland runs on geothermal and hydro at 100% renewable, and Norway is about 99%, mostly hydro. Costa Rica has run more than 300 days a year on renewables since 2015, and about 99.6% of its electricity across 2024 was renewable (Costa Rica ICE, 2025). Albania, Paraguay and Ethiopia are effectively 100% on hydro.

Cases are multiplying where there is no great hydro resource either. Denmark met demand in 2024 with 59% wind and more than 9% solar; Portugal ran on 100% renewables for 149 days in 2024, including six consecutive days (REN, 2025). South Australia reached 74% renewables on a 12-month average in December 2024 and has 100% by 2027 as an official target (AEMO, 2025). These are achievements without the vast natural battery of hydro, and they demonstrate that a grid can be operated stably on variable renewables combined with storage and demand response.

The technology portfolio rests on: (a) geographical and temporal spread of solar and wind, (b) storage through pumped hydro, grid batteries and hydrogen, (c) the demand side through demand response and virtual power plants, and (d) stronger interregional links. On cost, new utility-scale solar is at US$0.043/kWh (about ¥6.5/kWh) and onshore wind at US$0.034/kWh (about ¥5.1/kWh), 41–53% below the cheapest fossil generation on average (IRENA, 2025) — economically the rational choice as well.

Heat, transport and industry: sector coupling with electricity and hydrogen

Everything outside electricity is the real work. Across the major scenarios, transport is assumed to electrify to more than 95% of passenger cars by 2050 through EVs, fuel cell vehicles and electric buses (IEA Net Zero, 2023). For heating in homes and buildings, heat pumps take the lead: Europe expects 60 million units by 2030, and Japan ships some 600,000 a year. Water heating moves to heat-pump systems and cooking to induction. All of these are mature technologies you can buy today; no further breakthrough is required.

Low- and medium-temperature industrial heat (below 150°C: food, textiles, pulp and paper) can be served by industrial heat pumps and electric boilers; the European heat pump association expects up to a million industrial units by 2030. Japan’s green growth strategy likewise treats electrification of low- and medium-temperature heat in the 2030s as a central measure.

The difficulty is high-temperature heat above 500°C and chemical reduction. Steel, cement, petrochemicals and glass need coal as coke for reduction reactions, and firing at 1,400°C, which simple electrification cannot replace. This is where green hydrogen — made by electrolysing water with renewable electricity — comes in. Sweden’s HYBRIT project delivered the world’s first hydrogen-reduced steel commercially in 2021, and SSAB plans production of a million tonnes a year from 2026. Nippon Steel has published a roadmap for demonstration in 2030 and commercialisation in the 2040s. For aviation and shipping the candidates are synthetic fuels and green ammonia; Mitsui O.S.K. Lines and NYK plan to put ammonia-fuelled vessels into service in 2026–27.

Cost and scale-up are the wall here. Green hydrogen costs US$4–8/kg to produce today, two to four times the US$1–2/kg of grey hydrogen from fossil fuels. BloombergNEF expects electrolyser costs to halve by 2030 and hydrogen-reduced steel to compete with blast furnaces in the 2040s, but mass production over the next ten to twenty years is the shared task. The accurate description of the present is: the technology exists; it is not yet cheap enough.

Japan’s potential: physically, there is plenty

Narrowing to Japan, “we have no resources” is also an outdated premise. The environment ministry’s 2022 study of renewable potential estimates Japan’s technical potential at about 2,930 GW of solar (utility and residential combined), 285 GW of onshore wind, 1,120 GW of offshore wind, 14 GW of geothermal and 14 GW of small hydro. Against annual electricity consumption of about 950 TWh in FY2024, solar alone could physically generate more than 3,800 TWh a year at a 15% capacity factor — four times demand.

The problem is the institutions and the social acceptance needed to draw that physical potential into the real world. Forest clearance for large solar farms, conversion of farmland, coordination with fishing rights, agreement with residents — these constrain how much of the potential is realised. The key is combining approaches with little competition for land: agrivoltaics, thorough use of roofs, offshore wind, plug-in solar.

Full decarbonisation in a country with Japan’s seasonal swings also needs long-duration storage. Summer cooling peaks, winter heating demand, and the particular climate of the rainy season and weak winter sun on the Japan Sea coast cannot be absorbed by lithium batteries alone, which work over hours to a day. Underground storage of hydrogen and ammonia, synthetic methane, and stronger interregional links are needed in layers.

Objections and limits: “100%” is a social question, not an engineering one

The scientific answer to whether 100% renewables is technically possible has converged over the past decade. The Jacobson group at Stanford published scenarios for 145 countries running on wind, water and solar and concluded that it is technically achievable by 2050 (Jacobson et al., 2022). Joint work by LUT University and the Energy Watch Group reaches the same conclusion, and IRENA’s World Energy Transitions Outlook 2024 sets out a scenario in which renewables supply 77% of final energy in 2050.

There is a wide gap, though, between “100% is impossible right now” and “100% will be impossible in 2050”. The first is a fact; the second is pessimism with no scientific basis left. The real constraints are not engineering but social and economic: (1) the stranded-asset exposure and political resistance of incumbents — utilities and the fossil industry, (2) allocating investment to large grid reinforcement and to replacing appliances and equipment, (3) the 30–50 year replacement cycles of steel and chemical plants, (4) social acceptance and siting conflicts, and (5) the geopolitics of international supply chains for critical minerals.

Which is to say: now that technical limits are no longer the bottleneck, the argument has moved to policy design and social agreement. “How far can today’s technology go?” has stopped being a reason for delay and become a question about what to invest in and legislate for first.

Summary

  • “All energy” means electricity (27% of final energy) plus heat, transport and industry (73%); the latter is addressed through electrification, hydrogen and synthetic fuels.
  • 100% renewable electricity is already implemented: Iceland, Costa Rica at 99.6%, Portugal at 100% for 149 days a year, South Australia at 74%.
  • The electrification technologies for heat and transport — heat pumps, EVs — are mature and on the market; no further breakthrough is needed.
  • Steel, cement, aviation and shipping have technical answers in green hydrogen and synthetic fuels, but commercial scale-up runs into the 2030s and 2040s.
  • Japan’s technical renewable potential is four times demand (Ministry of the Environment, 2022). The constraint is institutions, acceptance and the allocation of investment, not physics.
  • The major scenarios — IRENA, IEA, Jacobson — all conclude that close to 100% renewable final energy is technically possible by 2050.

“100% renewables is impossible with current technology” is a premise from more than a decade ago, one that overlooks what has happened in the power sector and in sector coupling. The real question is not whether it can be done, but how fast, at whose cost, and under what social arrangements.

References and data sources

International scenarios and reports

100% renewable electricity in practice

Batteries and LCOE

Industrial decarbonisation and hydrogen

Japan’s potential and statistics

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