Euijin Hwang

Monitoring the battery status for photovoltaic systems

Photovoltaic power systems in Korea have been installed in remote islands where it is difficult to connect the utilities. Lead/acid batteries are used as an energy storage device for the stand-alone photovoltaic system. Hence, monitoring the battery status of photovoltaic systems is quite important to extend the total system service life. To monitor the state-of-charge of batteries, we adopted a current interrupt technique to measure the internal resistance of the battery. The internal resistance increases at the end of charge/discharge steps and also with cycles. The specific gravity of the electrolyte was measured in relation to the state-of-charge. A home-made optical hydrometer was utilized for automatic monitoring of the specific gravity. It is shown that the specific gravity and stratification increase with cycle number. One of the photovoltaic systems in a remote island, Ho-do, which has 90 kW peak power was checked for actual operational conditions such as solar generation, load, and battery status.

Final report for CCQM-K17: pH determination on a phthalate buffer by Harned cell measurements

The second key comparison for the quantity pH, CCQM-K17, was carried out to assess the degree of equivalence of the national primary measurement procedures used to determine the pH of primary standard buffer solutions. The CCQM-K17 comparison allows estimations of the capability of ten national metrology institutes (NMIs) to determine the pH of a phthalate buffer of unknown concentration at different temperatures. The key comparison was co-ordinated by the CCQM Working Group on Electrochemical Analysis and piloted by the Physikalisch-Technische Bundesanstalt (PTB) with assistance from the National Institute of Standards and Technology (NIST) and the Slovak Institute of Metrology (SMU). The measurement results of the NMIs agreed not at the same level as for the first key comparison on pH CCQM-K9. The results obtained by seven of the eleven participants agree very well within the uncertainty stated by the participants. Four participants obtained results somewhat lower. The two groups of results are most obviously evident at a measurement temperature of 37xa0°C. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).

CCQM-K34 Final Report: Assay of potassium hydrogen phthalate

The key comparison CCQM-K34 was organized jointly by the inorganic and electrochemistry working groups of the CCQM as a follow-up to the pilot study CCQM-P36 to test the abilities of the metrology institutes to measure the amount content of acid in solid weak acids. The Slovak Institute of Metrology acted as the coordinating laboratory, and seven NMIs expressed interest in participation. All participants used constant current coulometry at different levels of sophistication. In general very good agreement of the results was observed; some possible problems were highlighted. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM.

Final report of CCQM-K96.1 `Determination of amount content of dichromate'

The CCQM-K96.1 key comparison was a subsequent bilateral comparison to the CCQM-K96 Determination of amount content of dichromate. The comparisons were organized jointly by the inorganic analysis and electrochemical analysis working groups of the CCQM to test the abilities of the metrology institutes to measure the content amount of dichromate. The NIM China has obtained unsatisfactory results from the CCQM-K96. The NIM requested a bilateral comparison to demonstrate its capability after improvement. The KRISS acted as the coordinating laboratory and served as a link to the reference value of CCQM-K96. Both participants used high-accuracy constant current coulometry. A good agreement of the results was observed. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).