10 Biggest ASX Renewable Energy and Sustainability Stocks in 2025

1. Rio Tinto (ASX:RIO,NYSE:RIO,LSE:RIO)

Market cap: AU$159.48 billion
Share price: AU$115.59

Rio Tinto is a major global miner focused on metals vital to the cleantech sector, including copper, lithium and aluminum.

The company has been increasing its focus on supporting clean technologies, exploring carbon-free technology for aluminum smelting through the ELYSIS joint venture. Using the ELYSIS technology, Rio Tinto's Arvida smelter in Québec, Canada, will produce the world's first greenhouse gas free aluminum.

Additionally, Rio Tinto's acquisition of Arcadium Lithium in March 2025 places it in the heart of the electric vehicle and battery supply chain, while its efforts to decarbonize its operations reflect its evolving role in the global energy transition.

2. Meridian Energy (ASX:MEZ,OTC Pink:MDDNF)

Market cap: AU$13.93 billion
Share price: AU$5.11

Renewable energy stock Meridian Energy is New Zealand’s largest electricity generator, with five wind farms, seven hydro power stations and commercial solar arrays. The company's Harapaki wind farm project reached completion in July 2024 and now stands as the second-largest in New Zealand.

The company also designed and built the Ross Island wind farm, which is located in Antarctica.

3. Reece (ASX:REH,OTC Pink:REECF)

Market cap: AU$10.48 billion
Share price: AU$16.16

Reece is a global leader in wholesale, import and distribution for plumbing, waterworks and HVAC-R products in Australia, New Zealand and the US. Through the Reece Foundation, the company helps connect the trade sector to communities that are in need of clean water and sanitation.

4. Mercury (ASX:MCY,OTC Pink:MGHTF)

Market cap: AU$7.65 billion
Share price: AU$5.27

Mercury is a New Zealand-based gas, renewable electricity and internet provider. The company's electricity generation comes from a variety of renewable energy sources, including wind, hydro and geothermal.

Mercury's nine hydro stations are responsible for an average of 10 percent of New Zealand’s annual electricity supply. It also operates five geothermal plants and four wind farms, including the country's largest. Construction of a fifth wind farm is expected to be completed by the end of 2026.

5. Contact Energy (ASX:CEN,OTC Pink:COENF)

Market cap: AU$6.78 billion
Share price: AU$7.89

Contact Energy provides electricity, natural gas, broadband, solar and renewable energy. It owns and operates 11 power stations and produces 80 to 85 percent of its electricity from its renewable hydro and geothermal stations. Construction of its new 101 megawatt plant, Te Mihi Stage 2, is expected to be completed by Q3 2027.

The company was the highest of five New Zealand firms to land on the 2023 Dow Jones Sustainability Index Asia-Pacific. It was also the winner of Deloitte's sustainability leadership award in 2023 for leading decarbonisation efforts through its Contact26 strategy, which includes more than NZ$1.2 billion in investments in renewable generation projects.

6. Cleanaway Waste Management (ASX:CWY,OTC Pink:TSPCF)

Market cap: AU$5.87 billion
Share price: AU$2.64

One of the biggest companies in Australia's waste sector, Cleanaway Waste is an end-to-end e-waste recycler with 250 branches nationwide.

Cleanaway Waste is well positioned to offer solutions to the country’s plastic waste challenge, as well as its need to become waste self-sufficient after China’s ban on recycling material from Australia in 2021.

7. Pilbara Minerals (ASX:PLS,OTC Pink:PILBF)

Market cap: AU$4.76 billion
Share price: AU$1.48

Pilbara Minerals is one of Australia's largest lithium companies by market cap. Its flagship asset is the Pilgangoora project — located in the Pilbara region of Western Australia, it produces spodumene and tantalite concentrate.

Pilbara Minerals' P1000 project, a significant expansion of its Pilgangoora lithium operation, was completed ahead of schedule and achieved its first ore production in January 2025.

The company has long-term agreements with China’s Ganfeng Lithium (OTC Pink:GNENF,SZSE:002460), Great Wall Motor Company (OTC Pink:GWLLF,HKEX:2333), Yibin Tianyi and General Lithium.

8. Reliance Worldwide (ASX:RWC,OTC Pink:RLLWF)

Market cap: AU$3.2 billion
Share price: AU$4.09

Reliance Worldwide designs, manufactures and supplies high-efficiency water flow and control products. The company is also a global leader in the manufacturing of push-to-connect behind-the-wall plumbing fittings.

As its name suggests, Reliance's footprint is worldwide, with 29 distribution hubs, 14 manufacturing plants and five innovation centres across the Americas, Asia-Pacific, Europe, the Middle East and Africa.

9. Sims (ASX:SGM,OTC Pink:SMUPF)

Market cap: AU$2.86 billion
Share price: AU$14.78

Sims Metal, a business division of Sims, has established itself as an integral part of the circular economy through buying and recycling scrap metal, including ferrous and non-ferrous metals. The company has more than 130 processing facilities across the US, the United Kingdom and Australasia.

10. Nanosonics (ASX:NAN,OTC Pink:NNCSF)

Market cap: AU$1.48 billion
Share price: AU$4.73

Nanosonics is an infection-prevention company that has commercialised automated disinfection technology. Its Trophon technology, which includes an ultrasound probe high-level disinfection device, is primarily sold to hospitals. The device breaks the remaining chemicals from the process into oxygen and water.

Nanosonics is currently working to bring CORIS, its new endoscope reprocessing platform, to market. The CORIS technology platform seeks to address one of the biggest unmet needs: the reprocessing of flexible endoscopes. It was approved by the US Food and Drug Administration in March 2025.