The residual demand, which is defined as electricity demand minus power supply from variational generators, is getting important to be considered as installations of variational generators to power grid systems are increasing. Because variational power generations and electricity demand fluctuate due to variations in weather, the residual demand is supposed to be influenced by weather variations. However, understanding of the variability of the residual demand is not deepened adequately. Therefore, we investigated variability of the residual demand to deepen understanding of the mechanism for how meteorological variability of photovoltaic (PV) power generating systems affects the variability of the residual demand. Because there is not enough long observation data to analyze the variability of residual demand and power supply from PV systems, numerical simulations were performed using numerical models of electricity demands and PV systems. Local and seasonal characteristics of variations in the residual demand are generated by variations in the electricity demand and power supply from PV systems and the correlation between the electricity demand and power supply from PV systems. It was an interesting finding that installation of PV systems causes reduction of variability of the residual demand depending on some situations of areas and seasons.

In the previous paper, author has proposed an equivalent circuit between PV module/string and the ground which consists of one resistance and multiple RC-components, and it was also described that at least two of them had higher attenuation frequency than 1Hz. In this paper, some new results obtained from further experiments and discussion are shown as follows: four RC-components which had high attenuation frequency were found, i.e. ≈50kHz, ≈10³Hz, ≈10²Hz, ≈10¹Hz, respectively. Under rain condition, on the other hand, their attenuation frequencies and resistances decreased and their capacitance increased very much. These four RC-components affect risk of electrical shock. A preliminary-stage discussion on the electrical shock, which was based on the estimates of the RC-components obtained under both no-rain and rain conditions, pointed out that the risk of electrical shock drastically increase under rain condition.

Solar power generation, which converts solar energy into electricity, began to be developed in earnest after the oil crisis of 1973, and it has now become an important energy source that can solve the energy and global environmental problems. The authors have been involved in the development and promotion of such solar power generation for 50 years, and in 1992 installed the first solar power generation system with reverse power flow for an individual residence in Japan. This report describes the process of installing this system through many difficulties, and the results of longterm performance for 30 years after its installation. The average annual degradation rate of power output during the first 20 years of installation was 0.44%/year, which was good, but output clearly began to decline after 23 years, and the average annual degradation rate from 23 to 30 years was 5.96%. The degradation of polycrystalline Si solar cells was mainly due to an increase in series resistance.