past, present, and future Dr Jose Bilbao, Associate Lecturer SPREE - - PowerPoint PPT Presentation

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10 years of research on PVT systems at UNSW past, present, and future Dr Jose Bilbao, Associate Lecturer SPREE Systems & Policy Group UNSW Sydney 2 Acknowledgments Team leader A/Prof Alistair Sproul PhD graduates Special thanks Dr

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10 years of research on PVT systems at UNSW past, present, and future…

Dr Jose Bilbao, Associate Lecturer SPREE Systems & Policy Group – UNSW Sydney

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Acknowledgments

Team leader A/Prof Alistair Sproul PhD graduates Dr Shelley Bambrook (2012 → moved to Germany) Current PhD students Mehrdad Farshchimonfared Simao Lin Jinyi Guo Jianzhou Zhao

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Special thanks Rob Largent!!! Systems & Policy group! 464 group!

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Heat Electricity

Thermal Collector

PVT

PV +

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Affolter et al. 2006. PVT Roadmap – A European guide for the development and market introduction of PV-Thermal technology, PV Catapult Project.

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PVT-water

(covered or uncovered)

PVT-air

(covered or uncovered)

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Shockley-Queisser limit ~ 33% for single junction (32% Si)

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http://www.vicphysics.org/documents/events/stav2005/spectrum.JPG

Multijunction SQ limit ~ 49% At best ~50% of solar energy is converted to heat, not to electricity

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Efficiency (SQ) limit depends on the cell temperature

Generally, the efficiency of solar cells decrease with temperature Most of the energy is converted to heat → increases cell/module temperature So, cooling a PV module is a good idea!

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Dupré, Vaillon, Green, 2015. Physics of the temperature coefficients of solar

  • cells. Solar Energy Materials and Solar

Cells, 140, 92-100

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Obviously, PVT is a good idea, right??

1) Decrease the temperature of the cell/module by cooling it with a fluid 2) This increases the efficiency of the cell (more electricity!) 3) We can use the ‘waste’ heat for other purposes (we get heat too!) 4) Profit!*

*In theory yes, but first we need to read the fine print

By the way, PVT is not a new idea, the first publication on the subject was by Wolf in 1976 (40 years ago!).

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PVT potential

  • High energy density: PVT systems use less space to deliver the same energy

than syde-by-syde systems (PV + SHW)

  • Potential reduction of installation cost
  • High combined efficiency between 60-80%
  • Lower PBT and EPBT compared to PV
  • Generate most of the power for a normal house
  • Potential uses in commerce and industry
  • Architectural uniformity

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Bergene and Lovvik, 1995 Elswijk et al.2004,

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How much efficiency do you want?

High temperature rise results in low thermal and electrical efficiency (bad) So, it’s better to have a low temperature rise, with high thermal and electrical efficiency (good) But then, how useful is low temperature heat??

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Bambrook 2011. Thesis: Investigation of photovoltaic / thermal air systems to create a zero energy house in Sydney Efficiency Normalised temp rise

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PVT is about trade-offs (the fine print)

Heat Electricity Efficienc y Temperature rise (Exergy)

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More useful???

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PVT/water system for developing countries

A system that could provide electricity and warm water (pre-heating) for houses Criteria:

  • Low cost
  • Available materials
  • Manufactured on site
  • Reasonable performance
  • Very low budget for building the system (use existing or low cost tools/materials) ~AUD $200

Important equipment:

  • Good weather data (including sky temperature measurement - pyrgeometer)

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‘Manufacturing’ steps

Remove JB of frameless panel (stored in Bay St)

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Bond the water channels (collector) Thermocouples

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‘Manufacturing’ steps

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Collector with polycarbonate channels Install back insulation and JB

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‘Manufacturing’ steps

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Install new frame Mount the PVT collector

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‘Manufacturing’ steps

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Mount the header pipe Seal pipe and channels

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Finished System

Water tank 100L 20 W submergible pond pump Thermocouples in inlet, outlet, back of panel, flow sensor, Pyranometer, etc… Standard panel (same model) as control (12% efficiency at STC) System worked 24/7 – daily reset (heating water during the day, cooling water during the night)

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Experimental data: PVT vs PV electricity output

The PVT system

  • utperformed the PV

module, due to higher efficiency (cooling) Except on July (stagnation ‘experiment’, i.e. no flow) What to do when no more hear is needed??

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Experimental data: PVT thermal and electrical output

Big gap between thermal and electrical

  • utput

Hence, the application must match the generation profile of PVT systems PVT used only as a solar collector

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Transient model

Example of outlet temperature – model vs experiment

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Bilbao & Sproul 2015. Detailed PVT-water model for transient analysis using RC networks, Solar Energy, 115, 680-693

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Transient model

Example of thermal energy – model vs experiment

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Bilbao & Sproul 2015. Detailed PVT-water model for transient analysis using RC networks, Solar Energy, 115, 680-693

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Transient model

Example of electrical energy – model vs experiment

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Bilbao & Sproul 2015. Detailed PVT-water model for transient analysis using RC networks, Solar Energy, 115, 680-693

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Transient model vs Steady state model

  • Transient model was hard to use (Microcap)
  • Steady state model was developed in TRNSYS (Fortran)
  • Model used a single iteration plus an empirical relation (Akhtar and Mullick, 1999) to estimate

cover temperature (Type850)

  • Both models were compared against experimental data

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Bilbao & Sproul 2015. Detailed PVT-water model for transient analysis using RC networks, Solar Energy, 115, 680-693

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Importance of sky temperature

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  • 60%
  • 55%
  • 50%
  • 45%
  • 40%
  • 35%
  • 30%
  • 25%
  • 20%
  • 15%
  • 10%
  • 5%

0% 5% 15 20 25 30 35 40 45 50 55

Tin ( C)

a) UL percentage error (Wv=2m/s, Ta=20 C, N=0)

Type50-C, Ts=Ta Type50, Ts=Ta Type50-C, Ts=Ta-18 Type50, Ts=Ta-18

Bilbao & Sproul 2012. Analysis of flat plate photovoltaic-thermal (PVT) models. World Renewable Energy Forum, Denver.

Difference between PVT models calculating heat loss coefficient (UL) when sky temperature is considered Sky temperature is particularly important in PVT collectors, due to the high emissivity of its surfaces

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Domestic Hot Water (DHW) system optimization

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DHW system in Sydney - Covered vs uncovered

Uncovered Covered

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Series or parallel (thermal) configuration does matter, but effect is small Covered system provide a higher combined output (but electricity output is greatly reduced) PVT works, but it really depends on the application!

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Sky cooling (measured data)

  • 5

5 10 15 20 25 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Sydney Temperature (°C) Tamb Avg_day (°C) Tsky Avg_day (°C) Tamb Avg_night (°C) Tsky Avg_night (°C) 27

  • 545
  • 809
  • 862
  • 1126
  • 1045
  • 1085
  • 1200
  • 1000
  • 800
  • 600
  • 400
  • 200

Jan Feb Mar Apr May Jun Average daily Night Radiative Cooling (Wh/m2)

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Radiative vs Convective losses

Simulated data from the tuned model Goal was to determined how much cooling was due to radiative losses and convective losses

200 400 600 800 1,000 1,200 1,400 1,600

Total cooling during night periods (W)

a)

Qconv Qrad Qbe 28

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Night sky cooling simulation results

Assumptions

  • TMY2 weather files for all locations.
  • PVT modules at 10 degrees tilt.
  • Effects of surroundings were excluded

(rooftop installation ensures good sky view factor).

  • Constant flow rate of 0.02 kg/s.m2
  • Singapore (Af), Tucson (BSh), Sydney

(Cfa), and Hamburg (Dfb).

200 400 600 800 1000 1200 1400 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average Nightly Radiative Cooling Wh/m2 SYDNEY SINGAPORE TUCSON HAMBURG

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Night sky cooling simulation conclusions

  • Uncovered PVT systems can be used for

night radiative cooling.

  • Night radiative cooling potential from 400

Wh/m2 to 900 Wh/m2 per night.

  • It is possible to provide cooling through the

whole year.

  • The percentage of radiative and convective

cooling depends on many variables (+10% to 20% can be obtained from convective cooling).

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200 400 600 800 1000 1200 Sydney Sydney (30 deg Tilt) Singapore Tucson Hamburg Average Nightly Radiative Cooling Wh/m2 Convective Radiative

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Updated PV/T hot water setup

PVT collectors donated by Solimpeks

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New PVT/air roof

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Desiccant solar PVT cooling system

PVT roof will provide heating during winter Cooling in summer via desiccant and IEC

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Ground coupled PV/T desiccant air cooling cycle

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Guo, Bilbao, Sproul. Ground Coupled Photovoltaic Thermal (PV/T) Driven Desiccant Air Cooling. 2014 Asia-Pacific Solar Research Conference

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PVT seems like a very good idea

  • High energy density per area
  • High Thermal + PV efficiencies (potentially)
  • Co-generation and even tri-generation possibilities

But…

  • Complex (plumber + electrician + 2x standards)
  • Needs to be tailored for each application – ‘right’ application
  • Not great penetration or market (first panel in 70s)
  • Hence, currently PTV systems are expensive and rare

Yet, BIPVT and high efficiency cells might change this

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Cell efficiency vs Temperature coefficient

Panasonic Champion SHJ cell

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Bilbao, Dupre, Johnson. On the effects of high efficiency solar cells and their temperature coefficients on PVT systems. PVSEC-25, Busan, November 2015

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Three cell ‘efficiency’ candidates

Cell Efficiency (%) Module (% / Wp) Temperature Coefficient (Pmpp %/K) Medium 20% 17.6% / 290W

  • 0.38%

High 30% 26.4% / 435W

  • 0.22%

Higher 40% 35.2% / 580W

  • 0.05%

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Electrical efficiency increases with cell efficiency Thermal efficiency decreases But, total efficiency increases (slightly)

25 35 45 55 65 75 85

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Simulation example – DWH in Sydney (1yr data)

Similar trend between cover and uncovered systems (compared with previous results) Amount of thermal energy

  • utput could be ‘tuned’

depending on the application

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Simulation example – DWH in Sydney (1yr data)

PV performance does not ‘suffer’ as much, because of low temperature coefficients

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PVT future summary

  • Increase in cell efficiency results in lower temperature coefficients (Pmpp)
  • Hence, there is less efficiency gains by cooling PV modules
  • However, this also means less penalty by running the modules ‘warmer’
  • Balance between ratio of electrical and thermal output (e.g. better for DHW) → better suited to

meet load profiles

  • Low cost of PV could open the door for using PVT modules in higher temp systems like

BIPVT

  • IEA SHC is working on defining a new PVT task https://www.iea-shc.org/event?EventID=1554

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Q&A Thank You!

Dr Jose Bilbao – Systems & Energy Policy Group, SPREE j.bilbao@unsw.edu.au

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