Renewable Energy Integration and Nearly Zero-Energy Buildings
NZEB concept
A nearly zero-energy building has very high energy performance, with the low remaining demand covered to a significant extent by renewable energy, including on-site or nearby sources. Bulgarian requirements apply to new public buildings first, then all new buildings, with defined thresholds. The logic: reduce demand first (envelope, efficient systems, heat recovery), then supply renewables, then manage the remainder.
Renewable technologies
Solar thermal (DHW, space heating), photovoltaics (on-site electricity, self-consumption vs. export), heat pumps (aerothermal/geothermal - counted as renewable under defined conditions), biomass boilers, and district renewable heat. Know the concepts of self-consumption, load matching, storage, and the difference between on-site, nearby, and off-site renewable supply.
Traps in questions
- Treating a heat pump as automatically renewable regardless of performance/conditions.
- Adding renewables without reducing demand - NZEB requires both.
- Confusing installed capacity (kWp) with annual yield (kWh); yield depends on irradiation, orientation, shading, and performance ratio.
- Ignoring grid interaction and export limits.
- Assuming PV output equals nameplate × hours; use specific yield (kWh/kWp/yr).
Worked example
A building needs 60,000 kWh/yr heating after efficiency measures. A heat pump with SPF 3.5 draws ~17,100 kWh electricity and delivers 60,000 kWh heat, of which a defined renewable share is credited. A 20 kWp PV array at 1,100 kWh/kWp yields ~22,000 kWh/yr - compare that to total demand, not to peak load.
Rule of thumb
Efficiency first: every kWh of demand avoided is cheaper than a kWh of new renewable supply.