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SPECIAL REPORT: ECOBUILD 2011


he sun is our planet’s largest source of energy. Reserves of nuclear and fossil fuels are limited, and bio-energy requires enormous amounts of land already used to produce food. An alternative is needed to fulfill the world’s energy needs, about 450 EJ (quintillion Joules)1


T


per year at the present rate. WHY PHOTOVOLTAICS?


Concentrating solar installations are cheaper and more efficient than PV panels, but require direct sunlight and lots of unused land, such as deserts, and massive investment in infrastructure to transport electricity to where it is needed, plus they are strategically very risky. In the UK land is at a premium and the light is diffuse due to clouds and humidity; photovoltaic panels are capable of capturing this diffuse light and producing energy even on cloudy days. By distributing generation in the areas that consume electricity one can use the existing grid without major modifications. The Microgeneration strategy is a major incentive for solar energy deployment in the UK.


UK ENERGY


The UK is a densely populated country with notoriously variable weather. Hardly any of the land is available for massive solar farms. The UK consumes 380 TWh of electricity per year2


, mostly generated


from fossil fuels. Solar energy yields from PV panels in the UK average 750 kWh per kWp installed3


(1 kWp = ~7m2 of PV


panel); assuming a 30° roof inclination and 65% of surface available for PV panels, the average yearly energy yield of residential land in the UK is 80 kWh/m2


.


The total land area occupied by buildings in England is 2400 square kilometres4


, of


which over 60% is residential; UK total building area can be estimated at 2850 square kilometres (England is 84% of the UK population5


), thus BIPV roofs could


produce 228 TWh per year, or 60% of the electricity needs. The rest could be provided by 1240 square kilometres of ground mounted PV panels using 1% of the 115,000 square kilometres in England marked as “Green space”. This UK BIPV scenario involves


1) BP Statistical Review 2008 – total yearly world energy demand is 10,878 Mtoe = 457 EJ 2) http://erih.com.tr/


Alt2Devam.aspx?I=4&dil=2&K=8&B=2 3) Derived from JRC’s PV Estimation Utility for London


6| SUSTAINABLE FM | FEBRUARY 2011


BIPV: WHY IT MAKES SENSE IN THE UK Mike Tommasi, System Photonics S.p.A.


installing 500 GWp of PV panels over say 25 years. Assuming that the price will average 1.5€/Wp, the total investment needed is 26 billion GBP per year. At current 0.11 GBP/kWh electricity rate, the yearly revenue from 380 TWh would be 42 billion GBP, leaving room for storage systems.


STORAGE


Storage is needed due to the fact that we need more energy in winter, while PV panels produce the most energy in the summer. The UK’s DECC reports6


UK


electricity usage at around 24 TWh in the summer months rising to a peak of 32 TWh in January. Comparing this demand to the monthly supply curve obtained on the JRC’s PV Estimation tool7


, it is


estimated that 24% of the total yearly energy production needs to be stored in order to satisfy winter needs, i.e.: 90 TWh for the UK.


Distributed battery storage would be prohibitively priced – at 0.33€/Wh for Lithium batteries, we are talking about several trillion pounds… But the UK has about 22 TWh of hydroelectric8


same electrical performance as normal PV panels while remaining affordable, plus they must: • look good and integrate well with architecture;


• be conceived as a building material • be designed to be installed like roof tiles, by a roofer, on traditional wooden roof structures;


• withstand heavy wind and snow loads, and the weight of a technician walking on them;


• meet roof tile standards as well as PV panel standards;


• keep the roof waterproof even in severe weather and hailstones;


• be constructed with materials that are recyclable with low energy inputs;


• frameless construction in order not to trap dirt and water.


Normal PV panels do not meet any of the above criteria and they use materials that require high energy inputs for recycling, such as Tedlar plastic and EVA encapsulants.


A certain number of BIPV specialists generating


capacity, a small figure compared to other similar sized EU countries, and there are plans to quadruple this; hydro could be used to provide storage, by operating the turbines in reverse, pumping water back up to the top reservoir.


WHY BIPV? We have shown that PV panels on UK roofs have the potential of producing 60% of UK electricity needs. Roof photovoltaics reduce the impact of renewable energy sources on the countryside and on agriculture, but they must integrate harmoniously into British traditional architecture, or they will never be accepted. Non-integrated above roof solutions are an unsightly blight on the beautiful UK countryside and towns, they also seriously impact property values. True BIPV products need to be designed from the outset to function simultaneously as a roof covering and as a PV generator, with no compromises on aesthetics or on efficiency, offering the


4) According to the Generalized Land Use Database Statistics for England http://www.communities.gov.uk/publications/ planningandbuilding/generalisedlanduse 5) http://www.woodlands-junior.kent.sch.uk/ customs/questions/population.html


(Solarcentury, Atlantis, Saint Gobain Solar, Dow, Monier Redland) have emerged on the solar scene with products that meet some or all of the above criteria. SYSTEM Photonics meets all the above criteria with BIPV roof tiles featuring an innovative glass-on-ceramic construction, with Bosch monocrystalline cells embedded in a toughtime-proven ionomer encapsulant by Dupont.


CONCLUSION


Densely populated countries with weather like the UK are ideal candidates for solar energy. BIPV tiles capture direct and diffuse light even on cloudy days. There is enough roof surface area available in the UK to provide 60% of the national electricity needs. Coupled with hydroelectric generation and storage and some ground based generators, true BIPV could provide 100% of electrical needs reliably throughout the year, with minimal impact on architecture, landscape and infrastructure.


www.system-photonics.com


6) http://www.decc.gov.uk/en/content/cms/ statistics/source/electricity/electricity.aspx 7) http://re.jrc.ec.europa.eu/pvgis/ apps3/pvest.php


8) BP Statistical Review 2008 – UK hydro 1.9 Mtoe = 22TWh per year


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