Modeled and Measured Operating Temperatures of Floating PV Modules: A Comparison

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The performance and amphibious operation potential of a new floating photovoltaic technology

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The galvanostatic intermittent titration technique for silicon-based li-ion battery anodes : theory and experimental validation

Lithium ion batteries (LIBs) are the battery of choice for a number of applications, and the LIB market is growing rapidly. Good kinetic abilities is important for many applications, such as electric vehicles, grid storage and portable electronics. The galvanostatic intermittent titration technique (GITT), is a method used to determine the diffusion constant of Li in electrode materials. Three experimental parameters, pulse time, current rate and relaxation time, need to be chosen for GITT experiments. In this study, the influence of these parameters on the calculated diffusion coefficients are explored. The effect of these parameters were studied in a main experiment where a series of GITT charge/discharge cycles were conducted with the pulse length being doubled in each iteration. The experiment was run with three current rates, C/10, C/5 and C/2, on different batteries. The cells used in the experiment were half cells with silicon thin films as working electrodes. The thin films had a thickness of 60 nm and 80 nm. A total of 18 cells where used, 9 with each thin film thickness. A secondary experiment was performed on two of the cells, one of each thickness, to test the influence of a longer relaxation time. The data resulting from the GITT experiments was analysed using the programming language Python. The diffusion coefficients determined by GITT experiments were found to vary significantly with choice of parameter values. The largest change in results was observed in the second experiment with longer relaxation time. A sufficiently long relaxation time was therefore deemed important to achieve good results with GITT. The validity of two simplifications made during in the derivation of the GITT method were tested for different pulse lengths. The pulse lengths where these simplifications are valid depend on the current rate utilized. A lower current rate allows for longer pulse times. For the cells used in this thesis a pulse length between 8 - 64 s at a current rate of C/10 were deemed a good choice, as the simplifications are valid in this range and too much noise at low pulse lengths is avoided.Litium-ion-batterier er det foretrukne batteriet for en rekke anvendelser, og markedet for litium-ion-batterier er stadig i vekst. Gode kinetiske egenskaper er viktig for mange anvendelser, slik som elektriske kjøretøy, lagring i kraftnett og bærbar elektronikk. Galvanostatisk intermitterende titrering (GITT) er en teknikk som brukes til å beregne diffusjonskonstanter for litium i elektrodematerialer. Tre eksperimentparametre, pulstid, pausetid og strømrate, må bestemmes for å gjennomføre et GITT eksperiment. I denne oppgaven undersøkes innflytelsen av disse parameterne på de beregnede diffusjonskoeffisientene. Innflytelsen av eksperimentparameterne ble studert i et hovedeksperiment hvor en serie GITT opp-/utladninssykler ble gjennomført, med en pulstid som ble doblet hver iterasjon. Eksperimentet ble gjennomført med tre strømrater, C/10, C/5 og C/2, på forskjellige batterier. Cellene brukt i eksperimentet var halvceller med tynnfilmer av silisium som arbeidselektrode. Tynnfilmene hadde tykkelsene 60 nm og 80 nm. Totalt ble 18 celler brukt, 9 av hver tykkelse. Et tilleggseksperiment ble gjennomført på to av cellene, en av hver tykkelse, for å teste innflytelsen av en lengre pausetid. Dataene fra GITT eksperimentene ble analysert ved hjelp av programmeringsspråket Python. Diffusjonskoeffisientene beregnet gjennom GITT eksperimentene varierte signifikant med valg av parameterverdier. Den største endringen i resultat ble sett i det andre eksperimentet med lenger pausetid. En tilstrekkelig lang pausetid ble derfor ansett som viktig for å oppnå gode resultater ved bruk av GITT. Gyldigheten til to forenklinger som ble gjort under utledningen av GITT ble også undersøkt for ulike pulstider. Forenklingene er gyldige for ulike pulstider avhengig av strømraten som blir brukt. Ved en lavere strømrate kan lengre pulstider benyttes. For cellene som ble brukt i denne oppgaven ble en pulstid på 8 - 64 s ansett som et godt valg, ettersom forenklingene er gyldige i dette området og for mye støy ved lave pulstider unngås.submittedVersionM-M

The galvanostatic intermittent titration technique for silicon-based li-ion battery anodes : theory and experimental validation

Lithium ion batteries (LIBs) are the battery of choice for a number of applications, and the LIB market is growing rapidly. Good kinetic abilities is important for many applications, such as electric vehicles, grid storage and portable electronics. The galvanostatic intermittent titration technique (GITT), is a method used to determine the diffusion constant of Li in electrode materials. Three experimental parameters, pulse time, current rate and relaxation time, need to be chosen for GITT experiments. In this study, the influence of these parameters on the calculated diffusion coefficients are explored. The effect of these parameters were studied in a main experiment where a series of GITT charge/discharge cycles were conducted with the pulse length being doubled in each iteration. The experiment was run with three current rates, C/10, C/5 and C/2, on different batteries. The cells used in the experiment were half cells with silicon thin films as working electrodes. The thin films had a thickness of 60 nm and 80 nm. A total of 18 cells where used, 9 with each thin film thickness. A secondary experiment was performed on two of the cells, one of each thickness, to test the influence of a longer relaxation time. The data resulting from the GITT experiments was analysed using the programming language Python. The diffusion coefficients determined by GITT experiments were found to vary significantly with choice of parameter values. The largest change in results was observed in the second experiment with longer relaxation time. A sufficiently long relaxation time was therefore deemed important to achieve good results with GITT. The validity of two simplifications made during in the derivation of the GITT method were tested for different pulse lengths. The pulse lengths where these simplifications are valid depend on the current rate utilized. A lower current rate allows for longer pulse times. For the cells used in this thesis a pulse length between 8 - 64 s at a current rate of C/10 were deemed a good choice, as the simplifications are valid in this range and too much noise at low pulse lengths is avoided

CFD modelling to derive U-values for floating PV technologies with large water footprint

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