Large scale photovoltaic array deployment for lacustrine and marine environments: A critical review. ENGR 6116 E – Seminar Series Kim Trapani Research Supervisor: Prof. Dean Millar
Introduction Advances in renewable energy have resulted in large scale offshore deployment of renewable technologies, exploiting wind, tidal and wave energy. Water covers almost 71% of the earth’s surface; hence a great proportion of the solar resource is not exploitable using traditional onshore photovoltaic (PV) arrays and configurations.
Offshore PVs An offshore PV array would consist of floating PV panels. In large scale application this could consist of a number of standard size devices or of a scaled up version. Far Niente, California
Current Offshore Technologies WIND TIDAL WAVE North Hoyle, 60MW La Rance, 240MW Aguçadoura, 2.25MW Oahu, 40kW Thanet, 300MW Strangford Lough, 1.2MW
Strangford Lough, 1.2MW North Hoyle, 60MW Far Niente, 110kW Aguçadoura, 2.25MW La Rance, 240MW Thanet, 300MW Oahu, 40kW
Wind Resource Where the power extracted is: P = ½ρAv3 Example of a typical wind rose and power output from a wind farm On average a typical wind turbine site is intermittent, that is at 0m/s for 3-4% of the time.
Horns Rev, Denmark 80 x V80 Turbine spacing is 7D x 7D
Wind Technology • Advantages: • Developed technology • Low physical footprint • Disadvantages: • Wake effects • Visual impacts • Cut in/Cut out speed Typical spacing for offshore wind farms: >7D Horns Rev, Denmark GLOBAL INSTALLED CAPACITY – 2056MW
Tidal Barrage (Boyle, 2004) • Advantages: • Developed technology • Predictable and controlled power output • Disadvantages: • Major environmental impacts • Requires large catchment area • Visual impacts TIDAL BARRAGE
Marine Current Turbines (MCTs) Typical spacing MCTs is 5 – 8D Retrieved from http://green-tide.org/technology/ MCTs • Advantages: • Predictable • Minimal impacts • Disadvantages: • Subject to wake effects • Minor visual impacts
Attenuating WECs • Advantages: • Sector leader (has sold 4 units!) • Disadvantages: • Device complexity • Need for maintenance • Scales only with more devices Attenuator – the energy absorber is of comparable magnitude to the wavelength of incident waves and aligned parallel to the wave propagation direction. ATTENUATING WECs Utilisation of biodegradable hydraulic and transformer fluids.
Point Absorber WECs • Advantages: • Higher density installed capacity • Disadvantages: • Submerged components Point absorber – the energy absorber is very small with respect to the wavelength of incident waves. POINT ABSORBER WECs Retrieved from www.oceanpowertechnologies.com Spacing requirements for OPTs Powerbuoys is 5D* * According to proposal from Coos Bay Wave Park
Terminating Absorber WECs • Advantages: • High absorption efficiency • Disadvantages: • Requires large catchment area • Arms fall off! • Moorings Terminator – the energy absorber is of comparable magnitude to the wavelength of incident waves and aligned perpendicular to the wave propagation direction. TERMINATING ABSORBER WECs Retrieved from http://www.wavedragon.net
Yield Production kWh/kW
Economics Data compiled from case studies and EWEA, 2009
Albedo Effect The increase in diffuse lighting from the water surface, could be as much as 60% higher depending on the angle of incidence. Similar increases in diffused lighting could be expected from surfaces with snow/ice.
PV Technologies: Review • There are two main PV technology types in the market: • Crystalline solar cells • Amorphous solar cells Crystalline Cells Amorphous Cells η = 9 – 11% Mono-Crystalline Cells η = 14 – 15% ~ 0.140 kWp/m2 ~ CAN $ 2.50/Wp Poly-Crystalline Cells η = 13 – 14% ~ 0.140 kWp/m2 ~ CAN $ 2.00/Wp ~ 0.080 kWp/m2 ~CAN $ 1.00/Wp
Waste Heat in PVs When PV panels are exposed to direct sunlight only a fraction of the rays is converted into electricity, the rest is converted into waste heat – this is what determines the efficiency of a PV panel. PV panels only converts light of a certain wavelength according to the panel’s band gap. It though still absorbs most of the solar spectrum (apart from that which is reflected at the PV surface), and what is not converted into electricity is given out as waste heat.
Effect of Efficiency with Heat “Temperature coefficients provide the rate of change (derivative) with respect to temperature of different photovoltaic performance parameters” (King, Kratochvil, & Boyson, 1997) STC - Standard Temperature and Conditions: Temp. = 25°C Irradiance = 1000W/m2 Air Reference Mass = 1.5 Temperature coefficient is -0.4342%/K for tested PV panel at STC. ↓ η ∝ ↑heat
Heat Transfer In ground mounted PV arrays this heat would have to be extracted through radiation, convection and conduction using air as the medium. Radiation: P = eσA(T4 – Tc4) P – net radiated power e – emissivity σ– Stefan’s constant A – radiating area T – temp. of radiator Tc – temp. of medium Convection: ∆Q = hA∆T ∆Q – heat transfer h – convective heat transfer coefficient A – surface area ∆T – temperature gradient Conduction: ∆Q = -kA∆T/l ∆Q – heat transfer k – thermal conductivity A – surface area ∆T – temperature gradient l – length
Heat Transfer In ground mounted PV arrays this heat would have to be extracted through radiation, convection and conduction using air as the medium. Radiation: P = eσA(T4 – Tc4) P – net radiated power e – emissivity σ– Stefan’s constant A – radiating area T – temp. of radiator Tc – temp. of medium Convection: ∆Q = hA∆T ∆Q – heat transfer h – convective heat transfer coefficient A – surface area ∆T – temperature gradient Conduction: ∆Q = -kA∆T/l ∆Q – heat transfer k – thermal conductivity A – surface area ∆T – temperature gradient l – length Hence the heat extracted depends on the temperature and thermal conductivity of the medium. Since h is a factor of k
↑ Efficiency with ↓ Temp. Hence at lower air to water temperatures the efficiency of the PV panels would be higher – thus giving a higher power output. Thus at -55°C the efficiency of the PV panel would be ~ 19% compared to the 14% at STC
Thermal Conductivities (Water vs. Air) (Hukseflux, 2010) The change of fluid medium from air to water would imply a significantly higher thermal conductivity. Hence the fraction of heat extracted through conduction would be higher, since the heat extracted is directly proportional to the thermal conductivity. This will though require testing in order to determine the increase in efficiency of the PV due to the enhanced heat conduction medium. ↑ η ∝ ↑heat extracted ∝ k ∆Q = -kA∆T/l
PV Reliability With moored devices the scenario is slightly different since the reliability of the whole structure relies on the device maintaining its moored position. • PV has no moving part • Minimal maintenance (other than maintaining surfaces clean) • Conventional technologies rely on mechanical movement WECs have a mooring failure rate of 0.555/annum*. *Thies, Flinn, & Smith, 2009 ↑PV Reliability implies ↓Lower Failure Rate Self Cleaning Surface
Land Competition ↑Population ∝ ↑Agricultural land requirement United Nations, 2004 IIASA Data 2000
Floating PV Devices: Review Far Niente, CALIFORNIA Solarolo, ITALY (TTi, 2008) (Faenza-Lugo, 2009) • First floating PV array installation. • Tilted at the optimal solar gain angle. • Floating on pontoons. • Gaps between panel arrays for cleaning access and avoiding panels shading. • Laid almost horizontal over a support structure. • Fixed structure. • 7-8% output reduction due to being horizontal. • Cleaning access available.
Design Concepts • Modular unit • Central buoy – for dry cable coupling • Electrodes/heating elements • Flexible to deform according to oncoming waves • Transparent to minimise blocking of sunlight with the water column • Scalable device • Central buoy – heating PCM • Slightly raised for a gradient • Articulating according to oncoming waves
Design Criteria • Self-cleaning • Anti-fouling protection • Modular or scalable for large scale application • PVs cooled to allow enhanced yields • Heating element incorporation to ensure maximal availability in lacustrine environments (freezing and snowed waters) • Easily deployed • Materials with least environmental impacts or which mitigate the impacts • Modules connection according to required voltage output • Electrical safe connections, and availability for eventual access to electrical systems during operation phase • Mooring configuration which allows the higher installation packing
Device Loadings The design should account for the loading forces, depending on the site’s environment, to ensure that the device remains in place during its operational periods and also that it produces the optimal power output.
POTENTIAL IMPACTS • Environmental Impacts: • Sunlight blocking of the water column • Reduction of oxygen levels • Electro magnetic fields from the cables • Social Impacts: • Fishing and leisure exclusion zone • Collision risk
Simulation Stage Simulation work is required to estimate the yield which could be expected from a floating PV device, since the tilt at which the rays would be incident to are continuously changing according to the movement of the device. Time dependent numerical modelling for the device at the simulated orientation Time dependent wave simulation modelling of the device Net yield estimation for particular device
Wave Simulation Modelling Both SWAN and OrcaFlex are capable of producing a time dependent motion study, based upon a specified wave model. Retrieved from www.orcina.com SWAN is a geometrical model based which defines the wave spectrum according to the characteristics of the region’s bathymetry. OrcaFlex is a dynamic analysis simulation software which allows evaluation of entire offshore systems.
Irradiance Numerical Modelling R is the ratio between the horizontal and the tilted plane for the various irradiance factors (i.e. direct, diffused and reflected) Hence by applying the inclination factor derived from the wave simulation, the yield will be estimated.
Testing and Large Scale Application A small scale model will be deployed, to investigate the performance of the offshore device and conclude discrepancies with the estimated yield. PERFORMANCE Actual power output Estimated power output COMPARISON Tested estimation for large scale offshore PV installations
Conclusion Photovoltaic devices floating on the water is a relatively new concept, which needs to be developed further if it is to be considered as another renewable offshore technology. Compared to other offshore technologies, offshore PVs have the potential to be cost competitive – with predictable power outputs. When considering large scale ground mounted structures it has the potential to be more efficient and could essentially produce a better yield per m2.
Research Partners 1. Mining Innovation, Rehabilitation and Applied Research Corporation (MIRARCO), Sudbury, Northern Ontario, Canada (Lead Partner). Key contact: Prof. Dean Millar. 2. Laurentian University, Sudbury, Northern Ontario, Canada. Cooperative Freshwater Ecology Unit/Department of Biology. Collaborating contact: Prof. Charles Ramcharan. 3. CANMET Energy Technology Centre, Varennes, Québec, Canada. Collaborating contact: Dr. Sophie Pelland. 4. Loughborough University, Leicestershire, UK. Applied Photovoltaics Research Group. Collaborating contact: Prof. Ralph Gottschlag, Head of Group. 5. University of Exeter, Cornwall Campus, UK. Peninsula Research Institute for Marine Renewable Energy (PRIMaRE). Collaborating contact: Dr. Lars Johanning, Head of PRIMaRE.
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