Biosolarni krov — 12 mjeseci podataka iz Rovinja Bio-solar roof — 12 months of data from Rovinj
Biosolarni krov kombinira zeleni krov (vegetacija) i solarne panele na istoj krovnoj površini. Ideja nije nova — u Njemačkoj i Švicarskoj instaliraju se od ranih 2010-ih — ali u Hrvatskoj smo postavili prvi mjereni pilot projekt u studenom 2024. na hotelu u Rovinju. Nakon 12 mjeseci imamo podatke.
Opis pilot projekta
Hotel (100 soba, ukupna površina ravnog krova 1.400 m²) podijeljen je na tri zone. Zona A (520 m²): klasični solarni paneli na standardnim balastiranim nosačima. Zona B (480 m²): biosolarni krov — sedum pokrivač između nizova panela. Zona C (400 m²): referentni ravni krov bez ikakvih nadogradnji.
Na Zoni B postavljeno je 48 bifacialnih panela Jinko Tiger Neo (440 Wp) na nosačima podignutima 35 cm iznad sedum sloja. Sedum mješavina: Sedum album, Sedum reflexum, Sedum spurium, Allium schoenoprasum (luk vlasac za privlačenje oprašivača). Supstrat debljine 8 cm.
Instrumentacija: temperaturni senzori na stražnjoj strani 8 panela po zoni, solarni senzori (pyranometer), mjerači vlažnosti supstrata, CO2 senzor, kamera za praćenje biodiverziteta.
Temperatura panela: ključni nalaz
Temperatura panela kritično utječe na njihov prinos — svaki stupanj Celzijusa iznad 25°C smanjuje učinkovitost kristalnog silicija za 0,36-0,4% (koeficijent temperature, specifičan za model panela). U ljetnim uvjetima, paneli na standardnoj betonskoj podlozi (Zona A) dosezali su temperature i do 74°C, dok su paneli na biosolarnom krovu (Zona B) bili u prosjeku 4,8°C hladniji kroz cijelu godinu (6,2°C hladniji u srpnju i kolovozu).
Razlog: sedum isparava vlagu (evapotranspiracija) i time hladi okolni zrak, a vegetacijski sloj sprječava zagrijavanje podloge. Efekt je najizraženiji u ljetnim poslijepodnevima — upravo kada je solarna produkcija inače najniža zbog pregrijavanja.
„4,8°C prosječne razlike u temperaturi panela — to se na godišnjoj razini pretvori u +3,2% prinosa. Nije dramatično, ali je mjerljivo i konzistentno."
Energetski prinos: +3,2% godišnje
Ukupni godišnji prinos Zone B (biosolarni) bio je 68.240 kWh, a Zone A (standardni) 66.100 kWh pri jednakim instaliranim kapacitetima (48 panela iste specifikacije). Razlika od +3,24% direktno je pripisiva nižoj radnoj temperaturi panela. U apsolutnim iznosima, to je ~2.140 kWh više godišnje za isti investicijski trošak u panele.
Biodiverzitet i mikroklima
Kamera za praćenje biodiverziteta zabilježila je 14 vrsta oprašivača na sedum krovu u periodu travanj-rujan, uključujući 3 vrste divljih pčela lokalnog značaja (Osmia cornuta, Halictus rubicundus, Andrena flavipes). Temperatura unutar hotela (mjerena na potkrovnom podu) bila je prosječno 1,4°C niža ljeti u sobama ispod Zone B nego ispod Zone A — potvrda termoregulacijske uloge zelenog sloja.
Vlažnost supstrata ostala je iznad 20% čak i u srpnju i kolovozu bez navodnjavanja — sedum album je iznimno otporan na sušu i ne zahtijeva dodatno navodnjavanje u istarskom mikroklimatu.
Ekonomika: isplati li se nadoplata?
Biosolarni krov skuplje je rješenje od standardnog: zeleni krov (supstrat + vegetacija + hidroizolacijska zaštitna ploča) dodaje oko 45-65 €/m² na ukupan trošak. Za Zonu B (480 m²) to je dodatnih ~25.000-30.000 € u usporedbi s golosolarnom instalacijom.
Uz +3,24% godišnjeg prinosa (vrijednost ~380 €/god pri cijenama struje 2025.) i uštedu na hlađenju hotela (procijenjeno ~1.200 €/god manje za klimatizaciju potkrovnog kata), povrat nadoknade je između 14 i 18 godina. Nije spektakularno — ali uz benefite biodiverziteta, produžen vijek hidroizolacije i ESG izvještavanje, hotelska uprava smatra investiciju opravdanom.
A bio-solar roof combines a green roof (vegetation) and solar panels on the same roof surface. The concept is not new — they've been installed in Germany and Switzerland since the early 2010s — but we set up the first monitored pilot project in Croatia in November 2024 on a hotel in Rovinj. After 12 months, we have data.
Pilot project description
The hotel (100 rooms, total flat roof area 1,400 m²) was divided into three zones. Zone A (520 m²): classic solar panels on standard ballasted mounts. Zone B (480 m²): bio-solar roof — sedum cover between panel rows. Zone C (400 m²): reference flat roof with no additions.
Zone B was fitted with 48 bifacial Jinko Tiger Neo panels (440 Wp) on mounts raised 35 cm above the sedum layer. Sedum mix: Sedum album, Sedum reflexum, Sedum spurium, Allium schoenoprasum (chives to attract pollinators). Substrate depth 8 cm.
Instrumentation: temperature sensors on the back of 8 panels per zone, solar sensors (pyranometer), substrate moisture sensors, CO2 sensor, biodiversity monitoring camera.
Panel temperature: the key finding
Panel temperature critically affects yield — every degree Celsius above 25°C reduces crystalline silicon efficiency by 0.36-0.4% (temperature coefficient, panel-model specific). In summer conditions, panels on standard concrete substrate (Zone A) reached temperatures of up to 74°C, while panels on the bio-solar roof (Zone B) were on average 4.8°C cooler throughout the year (6.2°C cooler in July and August).
Reason: sedum evaporates moisture (evapotranspiration) and thereby cools the surrounding air, while the vegetation layer prevents substrate heating. The effect is most pronounced on summer afternoons — precisely when solar production is otherwise lowest due to overheating.
"4.8°C average difference in panel temperature — this translates on an annual basis to +3.2% yield. Not dramatic, but measurable and consistent."
Energy yield: +3.2% annually
Total annual yield of Zone B (bio-solar) was 68,240 kWh, and Zone A (standard) 66,100 kWh with identical installed capacity (48 panels of the same specification). The difference of +3.24% is directly attributable to lower panel operating temperature. In absolute terms, that's ~2,140 kWh more annually for the same investment in panels.
Biodiversity and microclimate
The biodiversity monitoring camera recorded 14 pollinator species on the sedum roof between April and September, including 3 species of locally significant wild bees (Osmia cornuta, Halictus rubicundus, Andrena flavipes). The temperature inside the hotel (measured on the top floor) was on average 1.4°C lower in summer in rooms below Zone B than below Zone A — confirming the thermoregulatory role of the green layer.
Substrate moisture remained above 20% even in July and August without irrigation — Sedum album is exceptionally drought-resistant and requires no additional watering in the Istrian microclimate.
Economics: does the premium pay off?
Bio-solar roofs are a more expensive solution than standard: the green roof (substrate + vegetation + protective waterproofing board) adds around €45-65/m² to the total cost. For Zone B (480 m²) that's an additional ~€25,000-30,000 compared to a bare solar installation.
With +3.24% annual yield gain (worth ~€380/year at 2025 electricity prices) and savings on hotel cooling (estimated ~€1,200/year less for top floor air conditioning), the payback on the premium is between 14 and 18 years. Not spectacular — but with biodiversity benefits, extended waterproofing membrane lifespan, and ESG reporting value, the hotel management considers the investment justified.