Development potential of local rooftop solar photovoltaic systems and solar DC power supply & energy efficient glazing technologies

Prof. Lu Lin, Vivien (吕琳）

Department of BSEThe Hong Kong Polytechnic University

Building Layout:Building orientation and external obstructions

Building Geometry: structural ratios and external shadings

Thermal Physics:Envelope physical properties

Infiltration:Air-tightness criteria

Building Passive architectural design classification

1. Development of local rooftop PV systems — Feed-in tariff policy

https://www.hkelectric.com/en/customer-services/smart-power-services/feed-in-tariff-scheme

1. Development of local rooftop PV systems — PV-suitable rooftop area

Solar-Architectural Rules of thumb, used to estimate the PV-suitable rooftop area with the buildings’ ground floor area.

The procedure to estimate the potential PV-suitable rooftop area.

Development potential of rooftop solar PV systems

1. 利用遙測影像技術計算出可安裝的屋頂面積（考慮了太陽輻射

的遮擋，屋頂暖通設備，電梯，平台等建築因素）。

2. 根據可用屋頂面積，組件安裝要求（包括最佳安裝角度和間

距），計算太陽能光伏板的安裝容量。

3. 根據可用屋頂上的光伏太陽能估算，來模擬計算全年的發電量.

1. Through combining airborne LiDAR data and spatially analysis, the total rooftop area which is available for installing PV systems was estimated.

Development potential of rooftop solar PV systems2. A methodology of determining

the PV-suitable rooftop area using Geographical Information System (GIS) was presented. The extraction of PV-suitable rooftop area was based on the building footprint. Five important criteria, viz. ground features, rooftop barriers, shadow, slope and the minimum permission area, were used to filter the area that is unsuitable for installing PV systems during the area extraction process. The total PV-suitable rooftop area was estimated to be 39.2 km2

3. The maximum usable rooftop area for solar panels is 39 km2. The maximum rooftop installation capacity is 4.67 ×106 kWp. The maximum power generation from rooftop PV systems is 4.67 ×106 kWh which is 10.7% of the total electricity use in Hong Kong.

可用安裝屋頂面積最高約為最大可安裝光伏系統容量為4.67×106 kWp (港燈南丫島發電廠現時總發電容量為3.76 ×106kW)。 可安裝的光伏系統每年最多可發電 4.67 ×106 kWh(度)，可用

來提供香港全年總用電量的 10.7%*。

Rooftop potential & power generation estimation

* 如果基於更為嚴格的可用面積篩選條件和不同安裝角度，數據可能不同。

2. Solar DC power supply systemThe War of the Currents

Electrification of the Country occurred in late 1800s Battle of alternating current (AC) versus direct current (DC) won by Tesla• 1893 Chicago World Fair• AC was better for long-distance transmission• Received backing by Westinghouse• Power electronics did not exist Thomas Edison’s initial power systems were DC microgrids• Over 50 DC microgrids had been installed by 1886• Systems were installed in the US, Russia, Chile and Australia

The Inefficiency of AC Buildings

Source: http://www.techadvantage.org/wp-content/uploads/2018/03/BO1D-63851-Andrew-Yip.pdf

Traditional AC architecture is a system architecture that requires independent building systems that need separate wiring or wireless controls for data using a multitude of power conversion devices and switches. (Complex, inefficient, unreliable)DC architecture is a system architecture that integrates building systems using existing wires for power and data with a single point for bi-directional power conversion without the need for switches. (Single pipeline for power and data)

AC Building VS DC Building

Energy landscape is quickly leaning towards DC… 80% of residential and commercial loads are DC 20% of electric production is used by lightingTechnology Development Policy DevelopmentMore native DC building equipment Climate change goalsMore DC based distributed generation Renewable generationDeclining cost of on-site storage Energy storageAdvances in power electronics Zero-net energy (ZNE) buildingsEvolving DC power standards Electric vehiclesBetter power quality Disaster resiliency

HeaterPump

Glass 玻璃

3. Energy efficient glazing technologies

Nowadays, glazing materials have been widelyused to replace conventional building envelopesfor the purpose of aesthetic and lightning inmodern buildings.目前，因為美觀與照明需求，玻璃幕墻在建築

中大量應用。

For the purpose of daylighting照明In order for aesthetic美學需求

If not being cleaned very frequently, theglass accumulates dust and influence itsaesthetic. 玻璃如果不經常清洗非常容易

積灰，從而嚴重影響美觀。

Summer(夏季) Winter(冬季)The thermal model of house in summer and winter

冬季和夏季室內外熱平衡圖

The large area glazing materials on roofs and curtain walls will lead to the dramatic increase of electricity consumption of air-conditioning system, resulting in high energy use.玻璃幕墻使得大量陽光進入建築，

提高了空調的能耗。

Heat gain through the glass windows is over 10 times higher than the external walls.在香港通过窗体的单位面积的得热量是墙体的10倍以上。

If not being cleaned very frequently, theglass accumulates dust and influence itsaesthetic. 玻璃如果不經常清洗非常容易

積灰，從而嚴重影響美觀。

The large area glazing materials on roofs and curtain walls will lead to the dramatic increase of electricity consumption of air-conditioning system, resulting in high energy use.玻璃幕墻使得大量陽光進入建築，

提高了空調的能耗。

Heat gain through the glass windows is over 10 times higher than the external walls.在香港通过窗体的单位面积的得热量是墙体的10倍以上。

-1.000 -.500 .000 .500 1.000Building Orientation

External Obstruction AngleExternal Wall Thermal Resistance

External Wall Specific HeatWindow SHGC

Window U valueWGR

Overhang Projection RatioInfiltration Air Mass Flowrate…

SRRC

1

2

3

45

Different building design factors on building energy use 影响能耗的建筑设计参数

Window

Window/wall ratio

Different types of window glasses 不同的窗体玻璃

Clear glass Low-E glass Tinted glass

• Cheap，便宜

• Poor thermal performance，隔熱性能差

（Cite: https://www.getninjas.com.br）

（Cite: http://www.acuffglass.com/）• Expensive，昂貴

• good insulating properties，隔熱性能好

• 缺點：由於膜層強度較差，一般都製成中空玻璃使用而不單獨使用

• Decoration，裝飾

• Poor insulating properties，隔熱性能差

Other new glazing technologies 其它玻璃

Solar PV glazing 光伏窗

Vacuum glazing真空玻璃

Heat insulation coating 隔热涂层

中空玻璃是由兩層或多層平板玻璃構成，四周用高高氣密性粘劑密封，中間充入乾燥惰性氣體，有效的降低玻璃的傳熱係數。缺點：中空玻璃提高最大的是其導熱性能，而不是其隔熱性能。

中空玻璃

Key properties of glazing windowsU-value: How well the thermal insulating performance of a window.

Solar heat gain coefficient (SHGC): The heat gain due to the incident solar radiation.

Visible light transmittance (VLT)

1

11/ / 1/n

o i i ii

Uh l k h

SHGC N First part: transmitted solar radiation determined by the solar transmittance of the window. Second part: inward flowing heat gain due to the absorbed solar radiation of the window.

1sol sol sol 1vis vis vis Transmittance + reflection + absorptance =1

Solar radiation is radiant energy from the sun, which provides light and heat for the Earth. Of the light that reaches Earth’s surface, infrared radiation (wavelengths from 700 nm to over 1 mm) makes up 49.9% and visible light (wavelengths from 380nm to 760nm) provides 42.3%. Ultraviolet radiation (100 ~ 400 nm) makes up just over 8% of the total solar radiation.太陽輻射來自於太陽，在地球表面的太陽輻射中紅外光（700 nm~1 mm以上）占總能量的49.9%，可見光（380~760 nm）占42.3%，紫外線（100~400 nm）占8%。

The near infrared ray (NIR) whose wavelength ranges from 760nm to 2600nm

近紅外光（760~2600 nm）

Solar radiation spectrum (Cite: http://geologycafe.com/)

1. Transparent: most visible lightcan transmit the glass. Introduction of daylighting is little influenced.透明性：大部分可見光可透過，

不影響照明

2. Heat blocking: most IR ray and UV light are blocked.隔熱：隔絕大部分紅外及紫外線

3. Self-cleaning: super-hydrophilicself-cleaning property (TiO2)自清潔：具有超親水自清潔性能

自清潔透明隔熱玻璃塗料 Our functional coating

Super-hydrophobic self-cleaning technology超疏水自清潔技術

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3 1, 2: 塗覆在砂岩表面Coated on sand stone surface3: 塗覆在木板表面Coated on wood surface

Average nano-particle size is only 5 nm平均納米粒子粒徑 5 nm.After the coating process, the transparency is onlydecreased by 0.23%經過塗蓋程序後，透過率損失小於 0.23%

6065707580859095

300 400 500 600 700 800 900 1000 1100 1200wavelength

Transparency

Super-hydrophilic self-cleaning coating Advantage 優點: Maintain high transparency 保持良好高透過率

22http://news.tvb.com/programmes/innovationgps/595d06126db28c19648b4567 (12’35”)

PolyU Invention 理大研發

Conventional self cleaning agent 傳統自動清潔漿料

Cost 成本 每平米少於HKD12/m2< HKD12/m2

每平米少約 HKD80 - 160/m2~ HKD80 - 160/m2

Life Span 壽命 20 years 年 20 years 年Fabrication method制作方法

工廠端(絲網印刷) / 已製成的貨品(噴塗)Factory side，screen-printing atclient side

只能工廠端生產Can be only produced infactory sideProduction process 生產流程

簡單 Simple 複雜 Complicated Applications 應用 Photovoltaic power generation,glass, aluminum, stainless steel

太陽能光伏板、玻璃、鋁、不鏽鋼

glass, aluminum, stainlesssteel玻璃、鋁、不鏽鋼

PolyU Invention vs Conventional self cleaning coating理大研發 vs 傳統自動清潔塗層

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Awards and Local Media Report

2017 Hong Kong Green Innovations Awards 香港绿色创新大奖

TechConnect 2017 Global Innovation Award, Multi-functional transparentnano-coating for glass, TechConnect World Innovation Conference & Expo,U.S.A., 14-17 May 2017 美国2017年全球创新大奖

Gold Medal “High dispersed transparent heat insulation paints for glass”, 68thInternational Invention Exhibition in Nuremberg, Germany, October 2016

Awards 奖项

http://news.tvb.com/programmes/innovationgps/595d06126db28c19648b4567 (12’35”)

Conclusion and my future planSolar DC power supply is a promising technology to achieve zero-net energy (ZNE) buildings in near future. Development of thermal smart glazing

for Hong Kong (ECF) Development of solar-driven seawater

desalination and DC power supply system for household fresh water supply and power supply for isolated islands in Hong Kong (ITF-ITSP Tier 3)

Thank you!