“Zero-energy” buildings and self-contained buildings: a plausible prospect on a large scale?

Perfectly! The building of the future can be seen as a kind of power plant that can produce more energy than it consumes. Technical solutions for zero-energy buildings already exist on the market. Their multiplication thus does not depend on hypothetical technological developments, but only on political will and economic issues.

The term “zero-energy” applies to comfortable buildings which produce more primary energy on site from renewable energy sources and, on average, over the year than they consume (annual balance in terms of primary energy). We also refer to “positive-energy” buildings. This does not necessarily mean that they are fully autonomous. The term “self-contained building” applies to buildings that produce more primary energy on site over the course of the year than they consume.

Already today, Switzerland has nearly 40,000 very low-energy buildings meeting the Minergie® standards, including more than 550 Minergie® A buildings, which are heated exclusively with renewable energy sources. Construction standards are changing rapidly, and it is expected that by 2020 a majority of new buildings will have a positive overall energy balance.

In 2007, California was the first state to formulate a “Zero Net Energy Buildings” goal for all new residential buildings by 2020 – as early as 2030 for commercial buildings. The European Union, a little less ambitious, has developed the concept of “near zero energy” by 2020.

Switzerland, a pioneer (along with Germany) of energy-efficient buildings, is also beginning to talk about a “zero-energy” standard for new construction as early as 2020, under the guidance of the cantons, since the energy performance of buildings falls within their jurisdiction. In terms of investment, it is estimated that a zero-energy building today costs around 10 to 15% more to construct than a standard energy-efficient building. This additional cost, which is expected to decrease with the commercial maturity of the materials and technologies used, would pay for itself after 25-30 years.

The cantons go even further, referring to the possibility of “energy self-sufficiency” or “self-sufficient” (or “autarkic”) buildings. In contrast to a zero-energy building, which aims to balance its energy over the year by making up an energy deficit in the winter with a surplus of production in the summer, a self-sufficient building will have to generate all of its (entirely renewable) energy itself throughout the year. This major challenge will require the development of seasonal storage, which consists of conserving excess heat and electricity accumulated in summer (in a large underground water tank and batteries, for example) to be recovered during the cold season, and storing excess cold in winter to help air-condition the building in summer [→ Q77].

Technically feasible, such buildings are likely to remain the exception, given the still prohibitive cost of seasonal storage facilities. Nevertheless, several self-sufficient buildings for heating already exist in Switzerland and the European Union.

One solution for the future is likely to be producing hydrogen from surplus solar energy in the summer. This hydrogen fuel can be stored until the following winter to power a fuel cell that can provide heat and electricity [→ Q28].