Two brothers’ quest for accessible clean energy

Two brothers with a shared passion for socially responsible entrepreneurship and sustainable development set up a business that is shaking things up in the biogas industry. Sanne and Mirik Castro founded SimGas in 2009, with the idea to design and bring to market a highly scalable biogas digester that provides clean energy and fertilizer for millions of rural households. The SimGas biogas system was launched: a groundbreaking product that is mass produced, easily installed, and customized to best fit consumer needs – three unique selling points that enable supply to meet the increasing demand for domestic biogas in Africa and Asia.

The SimGas biogas system is a fully integrated farm solution: manure from livestock goes in, biogas and organic slurry come out. Biogas is primarily used to replace wood, charcoal and kerosene as cooking fuel. Using biogas thereby lowers household energy expenditures and makes households independent of unreliable or non-existent power grids.

Alleviating dependence on wood fuel or charcoal not only takes away the health hazards of indoor air pollution, it also saves time: about two to four hours a day. Slurry that has been fully digested exits the system through a pipe, onto the farmer’s land where it is used as an organic fertilizer to grow crops and cow fodder. The improved crop yield is consumed by the household or sold at the local market, increasing income. The improved cow fodder is fed to the cows, which in turn will produce more milk and manure. The cycle repeats itself, every day.

Save costs and live healthy with SimGas

One of our customers in Tanzania, Mama Alinda Massawe, who owns a six-cubic metre SimGas biogas system, best explains the benefits: “I’ve told just about all my neighbors how great and helpful the biogas system is. It has helped me to save costs and there is no more firewood smoke. The slurry is very helpful for my banana plants. They look better than ever, I am even planning on selling them. The SimGas biogas system is what we all need.”


Since 2009, SimGas is growing fast: a joint venture in Tanzania (est. 2011), three daughter companies in Tanzania (est. 2011), Kenya (est. 2013) and Rwanda (est. 2015), and a production facility in Tanzania (est. 2014).

While its daughter companies handle local production and implementation in East Africa, SimGas’s headquarters in The Hague specializes in design and research, engineering, and business development. By working closely with customers and partners, we identify needs beyond clean cooking, such as safe sanitation to prevent diseases, innovative financing models (e.g. lease-to-own or pay-as-you go) to make our products more affordable, collecting live performance data to measure impact, and cooling milk to increase our customers’ milk sales.

A collaboration between organizations

Our latest product – which is being developed together with SNV Netherlands Development Organization, Mueller BV, and BoP Innovation Center –  is the world’s first off-grid, biogas-powered milk chiller at the farm level that helps small dairy farmers (with up to 10 dairy cows) to reduce milk losses and meet international quality standards required to access the formal market. The amount of manure generated by a cow creates enough biogas to refrigerate her own milk.

Here is a call to all do-gooders within the ImpactCity network: if you feel as excited as we do about developing groundbreaking products and services that empower people in East Africa and South Asia, find out what we’re working on at and let us know what we could do in cooperation with you.