The energy targets of the Sustainable Development Goals (SDGs) call for both a reduction of total energy use and an increase in the share of renewables as part of the total consumed energy. With the emergence of Renewable Energy Systems (RES) on a local scale there is still little research on the efficiency of actual micro-grids on building scale, let alone on how their functioning relates to reaching the energy targets of the SDGs. Here it is shown how an expected degree of decrease in renewable energy generation from solar panels, combined with a failure to anticipate intensifying building energy needs, can impede reaching the SDGs’ energy targets on the local level. When examining a building scale micro-grid, not only had solar panel performance decreased by twice the expected average, but building energy use had doubled by 156-203%, and thereby the share of renewable energy of total energy use has decreased by 29-47%, depending on the season. This indicates that in order to reach the SDG energy targets, it is important that newly designed building, as well as community Energy Management Systems, do not merely account for current energy users, but accommodate increasing RES concurrent to increasing energy demand.