Solar Power Generated thermal Energy - How to Maximize Its Performance and Life Expectancy

Transcription

1 IBM Research Zurich Science & Technology Concentrated Photovoltaic Thermal Multigeneration: Ecological and Economical Benefits Brian R. Burg, Angelos Selviaridis, Stephan Paredes, and Bruno Michel*, Advanced Micro Integration Project, Advanced Micro Integration

2 Agenda Problem: Large energy, water and cooling demands Inefficient current systems Need for sustainable and efficient energy and water in sunny regions Energy Efficient provider of both electricity and heat Water Efficient heat driven desalination/purification Cooling Efficient heat driven cooler Best Solution: Match energy provider with thermal user Thermal storage to enable energy on demand HCPVT technology: Best solar to electrical, water, and cooling efficiencies Basic questions: Energy payback time and life cycle analysis Countermeasures against global warming: Climate engineering Overall payback time including albedo changes and white roofs Urban heat islands Energy demand of cities as function of temperature Economic mechanisms in solar industry - reasons and countermeasures Summary and Conclusions 2

3 The Fresh Water Solar Dilemma Freshwater stress in 2025 Freshwater stress and solar abundance coincide Half of world population with fresh water scarcity Water scarcity threatens food security 50% water consumption increase by 2025 Solution: leverage dilemma! - use the SUN Membrane distillation with CPVT waste heat UNEP/GRID-Arendal, 'Freshwater Stress 1995 and 2025', UNEP/GRID-Arendal Maps and Graphics Library,

4 Large Energy Demand in Sunny Regions Peak with sorption cooling Peak with compr. cooling Off Peak Base Load Off Peak Tripled global cooling demand ( ) predicted by International Energy Agency (IEA) Driven by growth markets in hot regions Vapor-compression cooling strains power grid Solution: Solar thermal cooling with afternoon peak output when demand is highest HCPVT with heat driven sorption chillers provides cooling without loss of electrical output Smallest solar fields maximized yield No water consumption: Dry cooling, no cleaning Data Center or HCPVT 4

5 Concentrated Photovoltaic Thermal Systems PV chip with intermediate substrate PV chip direct attach Single Cell Module (SCM) PV chip direct attach Multi Cell Module (MCM) 2000suns ~ 10 KW test vehicle Large Multi Cell Receiver (MCR) 6 5x5 cm² receivers TIM 1 PV Cell heat sink TIM 1 PV Cell Manifold Si cooler chip assembly 1 st level manifold TIM 2 5

6 Value Proposition Concentrated Photovoltaic Thermal Radiation input 850 W/m 2 Loss in optics 20% Overall System Yield 80% Core technology: Multi cell package with 10x lower thermal resistance for 5000 suns and >25 years lifetime Doubled system output 6 Electrical system yield 25% 210 W/m 2 using triple junction chip Long-term improvement to 35% Thermal system yield: 55% 460 W/m 2 converted to: Cooling yield of 2.8 kwh/(m 2 day) with a COP of 0.6 Desalination yield of l/(m 2 day) with GOR of 7

7 Advantages of HCPVT System Higher concentration factor Air cooling looses 50ºC in package and wastes heat 10x reduced package thermal resistance allows 90ºC fluid removes heat from 100ºC cells for >2000 suns Heating / Hot water 4.6 kwh/(m 2 day) COP = 1 Yield 55% Higher electrical efficiency PV, CPV, and CSP have overall system yield <25% 350ºC solar thermal systems dissipate 75% waste heat High concentration allows triple junction PV with >30% yield Desalinated water, heating, and cooling from waste heat HCPVT makes heat re-usable without degrading PV efficiency System output 80% Electrical power, desalinated water and cooling at lower cost Superior HCPVT system performance >50% heat available on top of the electrical yield OR Cooling 2.8 kwh/(m 2 day) COP 0.6 HCPVT Irradiance 850 W/m 2 or 8.8 kwh/(m 2 day) OR Desalination 30-40l/(m 2 day) GOR 7 AND Electrical Power 2.2 kwh/(m 2 day) yield 25% NASA SSE Release 6.0 Data set 22-year Monthly & Annual Average ( ). Map by DRL (2008) 7

8 HCPVT Technology Low Cost Photovoltaic Thermal Concentrator from innovative materials (KTI Project) Size: 10kW electrical and 25 kw 90ºC Yields: 25% electrical, 55% thermal, and 80% total Cost: LCOE 0.07 $/KWh, <250 $/m 2 aperture area Timing: Commercial system in 2016 Microchannel cooled multichip receiver with 10x lower thermal resistance Key Aspects: Concrete tracking and supporting structure, inflatable mirrors with 10x lower cost than steel/glass technologies Combination with adsorption cooling and membrane distillation desalination W. Escher, S. Paredes, S. Zimmermann, C. L. Ong, P. Ruch, and B. Michel, Thermal management and overall performance of a high concentration PV, Proc. CPV-8 (2012). B. R. Burg, S. Paredes, T. Tick, W. Escher, and B. Michel, Receiver integrated cooling of highconcentrating photovoltaic thermal systems for efficient heat recovery, under review (2014). 8

9 Basic Questions Why are we promoting solar technologies? As a sustainable energy source Is sunlight a free resource? YES Is solar energy free? NO there are costs and emissions 1. There is CAPEX and OPEX of the solar power station 2. Solar installations contain gray energy 3. Black surfaces trigger radiative forces 4. Urban heat islands triggered by solar installations increase cooling demand Which is the best solar technology? The one with the highest overall efficiency and lowest radiative forcing. 9

10 Technologies Compared A) Coal/peat power plant 958 g CO 2 /kwh Efficiency 45% Lowest fuel cost, largest emission Emissions associated with technologies TABLE 2. Fossil fuel world average CO 2 emissions. 11 Fossil Fuel CO 2 emissions Oil 796 g CO 2 / kwh Coal/Peat 958 g CO 2 / kwh Gas 451 g CO 2 / kwh B) Oil fired power plant 796 g CO 2 /kwh Efficiency 42% Medium fuel cost, medium emissions A) Multi-crystalline Silicon panels Efficiency 13.2% B) Mono-crystalline Silicon panels Efficiency 14% C) CdTe Thin film solar technology Efficiency 8% C) Gas fired CHP plant 451 g CO 2 /kwh Efficiency > 65% D) Concentrated photovoltaic technology Highest fuel cost, lowest emission Efficiency 27% Fuel associated cost and emissions enforce efficiencies > 40% Economy favors multi crystalline Si and thin film solar with efficiencies of 8-14% Do solar systems have no CO 2 emissions? Do solar systems have no fuel associated cost? 10

11 Energy Payback due to Embodied Energy Sum of all the energy required to produce any goods for an entire product life-cycle (Life cycle Assessment, LCA). Includes raw material extraction, transport, manufacture, assembly, installation, disassembly, deconstruction and/or decomposition as well as human and secondary resources. Energy payback time increases for higher latitude locations due to lower energy production (3x longer in Germany than in the Mediterranean) Hours of solar energy per day 1600 kwh/m 2 /day = 4h (pale red) NREL, DOE Office of Energy Efficiency and Renewable Energy, January 2004, PV FAQs Conclusion: Deploy solar panels in the desert to maximize benefit? 11

12 Albedo Reflection coefficient, from Latin albedo "whiteness" or albus "white," is the diffuse surface reflectivity or the ratio of reflected to incident radiation from zero for no reflection of a black to 1 or 100% for reflection of a white surface. The Earth planetary albedo, is 30-35% because of cloud cover, but varies because of different geological features. The term was introduced by J.H. Lambert in aspx&documentid=315&menugroup=climatechange Solar collectors are black surfaces with an albedo ~0.05 irrespective of their efficiency High Albedo Low Albedo 12

13 Energetic Balance and Radiative Forcing per m 2 ~5% 81% ~5% 81.8% ~5% 87% ~5% 68% Crystalline Silicon Multi cryst. Silicon Thin film Solar Concentrated PV 14% 13.2% 8% 27% Lower efficiency larger area Radiative forcing: Each m 2 of surface with 0.01 lower albedo causes 3x10-15 K to climate warming or corresponds to emission of 7kg of carbon dioxide (Akbari 2012). More efficient technologies need smaller surface for a given electrical output HCPVT provides less radiative forcing 18% instead of 68-87% Yellow: incident and reflected solar radiation. Red radiative forcing ~5% 18% Concentrated PVT 27% 50% 13

14 Overall Payback Time of PV Including Albedo Changes Desert Case (α=0.4) 0.01 albedo change 7 kg CO 2 emissions / m albedo change 245 kg CO 2 emissions / m 2 Sensitive to placement (background albedo) Sensitive to insolation 8 Payback time depends on comparative fossil energy source Years 6 4 Inclusion of albedo change favors efficient solar technologies over less efficient ones Changed sequence of technologies Payback time is relatively short with respect to life expectancy of 30 years 2 0 Multi-Si Mono-Si CdTe (Thin film) HCPVT Multi-Si Mono-Si CdTe (Thin film) HCPVT Multi-Si Mono-Si Oil Coal/Peat Gas Grey energy Desert albedo change from 0.4 to 0.05 CdTe (Thin film) HCPVT 14

15 Countermeasures to Global Warming and Radiative Forcing Climate engineering / geoengineering, is the intervention in the Earth s climatic system to reduce global warming. 1) Carbon dioxide removal from the atmosphere. 2) Solar radiation management offsets greenhouse gases by causing the Earth to absorb less solar radiation. Geoengineering is a third risky option for tackling global warming, alongside mitigation and adaptation. Tree planting and cool roofs underway. Ocean fertilization and sulfur aerosols tested. Radiative forcing for 2005, relative to the pre-industrial era (1750). Solar irradiance is 5% of contribution of greenhouse gasses (carbon dioxide, methane and nitrous oxide). IPCC, Summary for Policymakers, Human and Natural Drivers of Climate Change, 2007.? Active Solar Passive Solar / White Roofs 15

16 Are Active or Passive Solar Technologies better Countermeasures to Global Warming?? White roof reduce urban temperatures White roofs even beat green roofs in this effect An inconvenient truth in large low latitude cities 16

17 Overall Payback Time of PV Including Albedo Changes and White Roof Effect White Roof Case (α=0.8) 0.75 albedo change 525 kg CO 2 emissions / m 2 Inclusion of albedo change favors efficient solar technologies over less efficient ones Changed sequence of technologies Payback time is relatively long with respect to life expectancy of 30 years in particular for thin film technologies Years Multi-Si Mono-Si CdTe (Thin film) HCPVT Multi-Si Mono-Si CdTe (Thin film) HCPVT Multi-Si Mono-Si Oil Coal/Peat Gas CdTe (Thin film) HCPVT Grey energy White roof albedo chg. from 0.8 to

18 Urban Heat Islands Reducing Urban Heat Islands: Compendium of Strategies, Heat Island Reduction Strategies The annual mean air temperature of a 1 million+ city is 1-3ºC warmer than its surroundings max. differences are 12ºC. Surface temperature difference are >25ºC. Surface energy budgets of urban areas and rural surroundings differ because of differences in land cover, surface characteristics, and level of human activity. Such differences affect the generation and transfer of heat, which lead to different surface and air temperatures. 18

19 Energy Demand of Cities in Sunny Regions Increases with Temperature Slope shows ~8% / K Heat island is 2ºC (due to albedo Δ-0.1) Text uses 3% / K White roof countermeasure (albedo Δ +0.5) Cooling effect up to 10ºC Solar: Installation (albedo Δ-0.25) Warming effect 2.5 * 2 = 5ºC Net difference up to 15ºC Peak demand increase exceeding >100% In New Orleans, electrical load increases once temperatures exceed 25ºC 2x at 38ºC. Increased energy demand for cooling on hot, summer weekday afternoons, when offices and homes are running cooling systems. Adding a solar collector on white roofs triggers an 8x larger heat island effect but provides electrical energy. Cooling per multi (2-3) storey house 25 kw / 100m 2 = 0.25 kw/m 2 is fully needed 100% duty cycle for ΔT> 15ºC. Cooling demand persists over night but solar input is only available for 25% of the time. With COP of 4 for compression cooling this needs a 25% efficient PV system. Only HCPVT systems can be deployed because radiative forcing is 4x lower. (Graph from 19

20 CPVT Driven District Cooling: Economic Value of Heat 1. Cooling loop for CPVT receiver on tracker level 2. Fluid loop for collection of thermal energy on power plant level connected to storage 3. Fluid loop for transfer of thermal energy between storage and thermal user 4. Fluid loop to transfer chilled water or fresh water to consumer No heat island effect DNI > 2000 kwh/(m²year) results in better health of inhabitants and much lower Moderate heat island effect cooling energy demand over CPVT power station White roofs no active solar! 1 25km 4 50km consumer 2 Thermal storage Heat exchanger 3 Thermal user Cooling Thermal user Desalination Other needs Heat and electricity demand is correlated with temperature Delivery of cooling reduces power line congestion Place HCPVT station were heating requirements are high and heat losses are low 10MW CPVT power plant Thermal user at/off CPVT plant V. Garcia, S. Paredes, C. L. Ong, P. Ruch, and B. Michel, Exergoeconomic analysis of high concentration photovoltaic thermal co-generation system for space cooling, Renewable and Sustainable Energy Reviews 34, 8-19 (2014). 20

21 Conclusion and Summary Support for efficiency in solar industry was not strong enough Because solar energy was considered a free resource For free resources there is no pressure to use them efficiently Oil, coal, gas are no free resources therefore power stations are very efficient With radiative forcing by solar panels solar energy looses its status as a free resource Triggers a new roadmap to efficient systems Geoengineering proposes white roofs to prevent or even revert heat islands Solar deployments collide with this approach Solar installations increase demand for cooling in sunny cities which eliminates their benefit Building integrated solar installations in urban areas in the sun belt are the wrong approach The best technology choice are highly efficient solar power stations outside of cities that provide district cooling so that no heat is pumped into the air anymore in cities Dark surfaces minimized to reach a maximum of electrical and cooling output HCPVT with district cooling minimizes the amount of heat dissipated 21

22 Thank You! Contacts: Dr. Bruno Michel IBM Zurich Research Laboratory Acknowledgements This research was supported by the Commission for Technology and Innovation (CTI), Switzerland (KTI PFIW-IW). The authors thank Gianluca Ambrosetti, Airlight Energy, for helpful discussions. 22

23 Introduction to Concentrated Photovoltaics Electricity from photovoltaics (PV) Rapid PV industry growing fast price reductions Low yield because of focus on collector material cost Concentrated photovoltaics (CPV) Higher-efficiency (30%) reduces $/W for concentration higher than 400X Less than half the module area and better match to load profiles CPV discards 70% of the collected energy as heat Concentrating solar power (CSP) Troughs with 70% recovery and 42% efficient steam engine (<30% efficient) Thermal storage possible (hot water/molten salt) Efficiencies of current CSP and PV systems are smaller than 30%, consume water HCPVT is the solution for cogeneration Eliminate disadvantages of CSP, PV, and CPV to allow system efficiencies >35% High electrical efficiency AND medium grade heat recovery Key: IBM Research Zurich world leading low thermal resistance package Low cost thermal storage 23

24 Concentrator Photovoltaic (CPV) Concept Principle: Concentrator optics to focus sunlight on small, efficient solar cell. Advantage: Expensive cell area reduced by concentration ratio lower LCOE LCOE = levelized cost of energy Reaches grid parity first. Disadvantage: Active cooling to leverage potential at high concentrations. Incoming Sun Light (1 Sun ~1000W/m²) Source: Fraunhofer ISE Concentrating optics (e.g. Fresnel lens) focal length Concentrated beam (>300 suns) Peak production maintained during >8h High efficiency multi-junction solar cell Heat spreader 24

25 Economic Mechanisms in Solar Deployments Complex high-performance vs. less complex low-performance technology. 0.7 Lower LCOE of the simpler technology (green) favors scale-up which reduces 0.4 cost and LCOE faster than the complex 0.3 technology (blue) The situation reverts when the simple 0 technology stagnates (blue line, diamonds). Years The continued improvement of the higher performance technology (cyan) reduces LCOE below the level of the simple technology after 14 years (cross over, blue and green). 1 Peak deployment of the low efficiency 0.9 technology in year 11 and a dip in the overall deployment in year 14 due to 0.6 the lagging development of the high- 0.5 performance technology (yellow, grey) Faster deployment when the high per- 0.2 formance technology is subsidized to compensate for this economical flaw (LCOE acc). Years Eff. LT Eff. HT CAPEX LT CAPEX HT LCOE LT LCOE HT LT Deploy HT Deploy Eff. LT Eff. HT LCOE LT LCOE HT LCOE HT Sum 25

26 High Concentration Photovoltaic Thermal System using Low-Cost Innovative Materials Efficient, cost-competitive HCPVT system converts 80% radiation and provides electricity at $/KWh Levelized Cost of Energy (LCOE) Solar-electrical conversion efficiency >25%, with <250 $/m 2 cost per aperture area (<1$/Wp), and >50% heat recovery Novel materials exploited for mass-production of low-cost concentrator and high performance receiver 2000x concentration onto microchannel-cooled dense receiver array of ~40% efficient 3J PV chips at safe temperatures 3x lower cost by concrete trackers and pneumatic optics Business model with tracker and mirror fabrication in deployment regions (~98% mass and ~50% value) and delivery of high-tech receiver and concrete molding tools Stand-alone units to supply electricity, water, and cooling Protective PTFE foil for desert operation with minimal cleaning large area high performance receiver 3J PV cell low cost large dish-like concentrator (joint development with partner) 26