On-site or off-site renewable energy supply options? Life cycle cost analysis of a Net Zero Energy Building in Denmark

The concept of a Net Zero Energy Building (Net ZEB) encompasses two options of supplying renewable energy, which can offset energy use of a building, in particular on-site or off-site renewable energy supply. Currently, the on-site options are much more popular than the off-site; however, taking into consideration the limited area of roof and/or façade, primarily in the dense city areas, the Danish weather conditions, the growing interest and number of wind turbine co-ops, the off-site renewable energy supply options could become a meaningful solution for reaching ‘zero’ energy goal in the Danish context. Therefore, this paper deploys the life cycle cost analysis and takes the private economy perspective to investigate the life cycle cost of different renewable energy supply options, and to identify the cost-optimal combination between energy efficiency and renewable energy generation. The analysis includes five technologies, i.e., two on-site options: (1) photovoltaic, (2) micro combined heat and power, and three off-site options: (1) off-site windmill, (2) share of a windmill farm and (3) purchase of green energy from the 100% renewable utility grid. The results indicate that in case of the on-site renewable supply options, the energy efficiency should be the first priority in order to design a cost-optimal Net ZEB. However, the results are opposite for the off-site renewable supply options, and thus it is more cost-effective to invest in renewable energy technologies than in energy efficiency. ► We model Net ZEB with 10 renewable energy systems and estimate corresponding life cycle cost. ► We examine cost-optimal combination of energy efficiency and renewable energy generation. ► Focussing only on up-font investments leads to a non-cost-optimal building design. ► Increasing energy efficiency decreases life cycle cost of Net ZEB with on-site RES. ► Increasing energy efficiency increases life cycle cost of Net ZEB with off-site RES.