Building Research Establishment 20 th June 2007 Integrating a large solar array to enhance the performance of a low energy building. - A Case Study Keith Tovey ( 杜伟贤 ) M.A., PhD, CEng, MICE, CEnv HSBC Director of Low Carbon Innovation: and Charlotte Turner: School of Environmental Sciences CRed Why go Solar PV?

Original buildings Teaching wall Library Student residences

Nelson Court Constable Terrace

Low Energy Educational Buildings Elizabeth Fry Building ZICER Nursing and Midwifery School Medical School Medical School Phase 2

The ZICER Building The Solar Arrays Performance of PV Issues of Shadowing Electrical Integration Economic Issues Life Cycle Issues Integrating a large solar array to enhance the performance of a low energy building.

ZICER Building Heating Energy consumption as new in 2003 was reduced by further 50% by careful record keeping, management techniques and an adaptive approach to control. Incorporates 34 kW of Solar Panels on top floor Low Energy Building of the Year Award 2005 awarded by the Carbon Trust.

Two large open plan offices: Note: extensive use of computers

Top floor is an exhibition area – also to promote PV Windows are semi transparent Mono-crystalline PV on roof ~ 17 kW in 10 arrays Poly- crystalline on façade ~ 6/7 kW in 3 arrays ZICER Building

ZICER Building PV performance Façade (kWh)Roof (kWh)Total (kWh)

Performance of PV cells on ZICER

Load factors Façade: 2% in winter ~8% in summer Roof 2% in winter 15% in summer Output per unit area Little difference between orientations in winter months Performance of PV cells on ZICER

All arrays of cells on roof have similar performance respond to actual solar radiation The three arrays on the façade respond differently Performance of PV cells on ZICER

Orientation relative to True North

Arrangement of Cells on Facade Individual cells are connected horizontally As shadow covers one column all cells are inactive If individual cells are connected vertically, only those cells actually in shadow are affected.

Performance of PV cells on ZICER

(A) Actual ZICER costs – no grant (B) Actual ZICER costs – with grant of £ (C) Avoided costs (ZICER) – no grant (D) Avoided costs (ZICER) with grant of £ (E) Average EU costs in 2006 (F) as E with 50% capital grant Performance of PV cells on ZICER Cost of Generated Electricity

Actual Situation excluding Grant Actual Situation with Grant Discount rate 3%5%7%3%5%7% Unit energy cost per kWh (£) Avoided cost exc. the Grant Avoided Costs with Grant Discount rate 3%5%7%3%5%7% Unit energy cost per kWh (£) Grant was ~ £ out of a total of ~ £ Performance of PV cells on ZICER Cost of Generated Electricity

Peak Cell efficiency is ~ 9.5%. Average efficiency over year is 7.5% Mono-crystalline Cell Efficiency Poly-crystalline Cell Efficiency Efficiency of PV Cells Peak Cell efficiency is ~ 14% and close to standard test bed efficiency. Most projections of performance use this efficiency Average efficiency over year is 11.1% Inverter Efficiencies reduce overall system efficiencies to 10.1% and 6.73% respectively

Comparison of other PV Systems Location Monitoring Period System Efficiency (%) Source Northumberland Building, University of Northumbria Pearsall Solar Office Doxford International, Sunderland, UK Mar 1998-May Jones Jubilee Campus, Nottingham University, Nottingham, UK Sept 2000-Aug Riffat and Gan Eco Energy House, Nottingham University, Nottingham, UK Sept 2000-May Omer et al. Gaia Energy Centre, Delabole, Cornwall, UK Jan 2003-June DTI PV Domestic Installations, UK (Average of six systems) 12 – 25 months 8.2 (range ) Pearsall and Hynes ECOS Millennium Environmental Centre, Ballymena, Northern Ireland Dec 2000-Dec Smyth and Mondol

Performance of Photo Voltaic Array Inverters are only 91% efficient Most use is for computers DC power packs are inefficient typically less than 60% efficient Need an integrated approach

Life Cycle Issues Embodied Energy in PV Cells (most arising from Electricity use in manufacture) Array supports and system connections285 On site Installation energy131.4 Transportation Spain > Germany > UK vehicle-kilometres Total MWh/kWp Mono- crystalline (kWh/kWp) Poly- crystalline (kWh/kWp) Energy Yield Ratios Mono-crystalline Cells As add on features Integrated into design Life Time of cells (years)

Conclusions Economics of PV was only viable on ZICER because of Grant Shading has some effect on façade, but improvements could be made by different method of wiring cells Overall Load Factor is 7.6% with 8.3% on roof and 4.7% on façade. In summer Load Factor can reach 15%. 9% of electricity is lost in inverters, and a further 50 – 60% is lost in IT equipment. Need to consider an integrated approach – possibly with DC networks in similar buildings. Important to use actual rather than test bed efficiencies in design appraisal Energy Yield Ratios are lower than many other forms of generation. Long transportation distances associated with PVs do not necessarily lead to a low embodied carbon requirement. Keith Tovey ( 杜伟贤 ) M.A., PhD, CEng, MICE, CEnv HSBC Director of Low Carbon Innovation: and Charlotte Turner: School of Environmental Sciences CRed

Building Research Establishment 20 th June 2007 Integrating a large solar array to enhance the performance of a low energy building. - A Case Study Keith Tovey ( 杜伟贤 ) M.A., PhD, CEng, MICE, CEnv HSBC Director of Low Carbon Innovation: and Charlotte Turner: School of Environmental Sciences CRed Why go Solar PV?