Experiment Design of a Photovoltaic/Thermal Hybrid System Maria Browne Department of Civil, Structural and Environmental Engineering, Trinity College Dublin Dr. Sarah McCormack You Supervisors’ Names Here Prof. Brian Norton 15th February 2013 Maria Browne Trinity College Dublin Today my talk will be on the design and installation of a PV/thermal hybrid system My supervisors are Dr. Sarah McCormack and Prof. Brian Norton

Effect of Temperature on Photovoltaics Photovoltaic (PV) cells produce thermal energy (85%) along with electrical energy (15%) when exposed to sunlight Temperature effects are more pronounced in silicon solar cells, excess of heat causes the PV cell to become less efficient (a reduction of 0.5%/K) Research suggests in organic and some plastic solar cells an increase in temperature increases their performance Give a bit of background 15% efficient that means that 15% of the solar energy is converted in to electrical and the remainder into heat, that’s a lot of heat remaining in the panel thereby increasing its temperature Effects of increased temperature of a PV panel, Important to try regulate the temperature because silicon, both poly and mono make up over 90% of solar panels sold globally Research suggests organic and some plastic cells solar cells an increase in temperature increases their performance

Phase Change Materials Phase Change Materials (PCM) can be used for thermal control in building integrated photovoltaic, thereby maintaining efficiency PCM can absorb large amounts of heat without changing temperature-latent heat Various types of PCM; organic (fatty acids, paraffin wax), inorganic (salt) and eutectic (mixture of compounds) The type of PCM applied to a system depends on the following properties; -phase change temperature (ºC) -enthalpy of phase change (J) -heat capacity (J/Kg) -thermal conductivity (W/m K) Use PCM to regulate temperature, thereby maintaining efficiency Go into PCM in a little bit of detail Latent heat, can absorb large amounts of heat without changing temperature Mainly use liquid to solid phase change as gas can be difficult to contain Types of PCM available Importance of the their thermal properties, Melting temperature, must be in the range to enable charging and discharging Enthalpy to ensure high rate of absorption of heat when changing phase, larger amounts of heat stored the more heat available for use Heat capacity, changing temperature during sensible heating again more stored energy available for other applications Thermal conductivity must be high so that the heat transfer from the panel through the PCM and into the water is efficient

Use of Phase Change Materials for Thermal Control in Building Integrated Photovoltaics Previous research includes regulating the temperature of PV cells by integrating PCM to maintain PV efficiency (Hasan, 2010) I am concentrating on thermal energy stored in the PCM and using it for a suitable application e.g. water heating, space heating Designed and currently installing a PV/thermal hybrid system on the roof of Kevin Street, DIT Electrical energy is generated by the PV, thermal energy is transferred from the PV to PCM and this thermal energy will then be used to heat water Explain the way in which the experiment works, the reference and the PV/PCM system, then the thermosyphons and the water tank, the transfer of heat, from the PV to the PCM to the water, measuring the temperature using thermocouples, initially was a BIPV system, now a hybrid unit, passive thermal control unit, regulating temperature of PV but also heating water,

Use of Phase Change Materials for Thermal Control in Building Integrated Photovoltaics How thermosyphon was inserted into the container The black pieces are to ensure the copper piping remains in place Thermosyphon constructed in copper piping Then can be seen in the semi-complete container and the way in which it was fixed in place Finally, the completed sealed container is attached to the solar panel There are six holes on the back of the container, thermocouples will be placed here will go into more detail later Thermosyphon, through which the water will flow Thermosyphon inserted in the semi-complete container Completed container attached to the solar panel

Use of Phase Change Materials for Thermal Control in Building Integrated Photovoltaics Phase Change material which will be used is a eutectic, comprising of fatty acids, capric (75%) and palmitic (25%) Shown to be thermally stable Below is a table showing the properties Capric/Palmitic Acid Properties   Melting point 22.4 ºC Heat of Fusion 195 kJ/kg Thermal Conductivity 0.139 W/ mºC (liquid) 0.143 W/ mºC (solid) Specific Heat Capacity 2.4 KJ/kgK (liquid) 2.2 KJ/kgK (solid) Density 0.79 kg/m³ (liquid) 0.87 kg/m³ (solid) Go through all the positives of the capric/palmitic fatty acid properties Why better than RT20 just say? Shown to be thermally stable following various thermal cycles Corrosion, not a huge issue, unlike that of other PCMs such as salt hydrates Initially, salt hydrate was chosen found to be very corrosive

What values are being analysed in the system? The transfer of heat across the system will be measured using a series of K-type thermocouples Twisted K-type thermocouples will be used back and front of the PV in the water cylinder ambient temperatures Stainless steel sheath thermocouples will be used to measure the temperature of the water flow in the pipes The temperature of the PCM inside the container A thermal paste has been applied to the back of the PV and the container to enhance thermal contact What are we going to measure? The heat transfer across the system using thermocouples, see from the front of the PV through to the back The front and back use twisted K-type thermocouples, all of which have been calibrated The middle of the PCM uses stainless steel sheath thermocouples I mentioned earlier the holes in the back of the container, they are for the compression glands as shown in the image onscreen, a thermocouple will then be inserted through the gland To maximise the heat transfer from the PV to the container, thermal conductive paste has been applied between both surfaces

What values are being analysed in the system? The following are measured in the electrical system PV voltage PV current Battery voltage Battery current Other values being measured are Rate of flow Solar radiation Spectral radiation As for the electrical aspect of the system, the current and voltages for the PV and battery in each system will be measured As in the diagram you can see the electronic board, Take the first system for example, PV will be connected to the fuse, then shunt, through the switch and then on to the charge controller The shunt is used to measure the current Potential dividers which are not on the board have been attached to bring the voltage of the devices down to ensure no damage to the dataloggers What does the charge controller do?? Allocate the power from the PV to the batteries or to the load The battery will connect through the fuse, to the shunt, switch and then onto charge controller The resistors are there to ensure that the power generated by the PV will be used when the battery is fully charged

Use of Phase Change Materials for Thermal Control in Building Integrated Photovoltaics Predicted Results Regulate the temperature of the system An increase in the temperature of the water in the system Maintained efficiency of the thermal controlled system Assess the value of heat loss to the surroundings Suggest ways to optimise the system Go through expected results

Image of the complete thermal/hybrid system Completed system Hope to start testing this summer

Thank you for your attention. Any questions? Thank you and any questions??