David Lingfors

Net load variability in Nordic countries with a highly or fully renewable power system

Increasing the share of intermittent renewable energy (IRE) resources such as solar, wind, wave and tidal energy in a power system poses a challenge in terms of increased net load variability. Full ...

Illumination performance and energy saving of a solar fiber optic lighting system.

The illumination performance and energy savings of a solar fiber optic lighting system have been verified in a study hall--corridor interior. The system provides intensive white light with a high luminous flux of 4500 lm under 130000 lx direct sun radiation at a 10 m fiber distance from the sun-tracking light collector. The color temperature that describes the light color perceived is 5800 ± 300 K, i.e. close to the direct sunlight outside, and the color rendering index (86), that describes how well colors are rendered under the light source, is higher for the solar lights than for the supplementary fluorescent lights (77). Thus this high quality solar lighting improves the visibility of all kinds of objects compared to the fluorescent lights. Annual lighting energy savings of 19% in Uppsala, Sweden and 46% in southern Europe were estimated for a study hall interior, as well as 27% and 55% respectively in an interior illuminated 16 h per day all days of a year.

Benefits of glass fibers in solar fiber optic lighting systems.

The transmission properties and coupling of solar light have been studied for glass core multimode fibers in order to verify their benefits for a solar fiber optic lighting system. The light transportation distance can be extended from 20 m with plastic fibers to over 100 m with the kind of glass fibers studied here. A high luminous flux, full visible spectrum, as well as an outstanding color rendering index (98) and correlated color temperature similar to the direct sun light outside have been obtained. Thus the outstanding quality of solar light transmitted through these fibers would improve the visibility of all kinds of objects compared to fluorescent and other artificial lighting. Annual relative lighting energy savings of 36% in Uppsala, Sweden, and 76% in Dubai were estimated in an office environment. The absolute savings can be doubled by using glass optical fibers, and are estimated to be in the order of 550 kWh/year in Sweden and 1160 kWh/year in Dubai for one system of only 0.159 m(2) total light collecting area. The savings are dependent on the fiber length, the daily usage time of the interior, the type of artificial lighting substituted, the system light output flux, and the available time of sunny weather at the geographic location.

Dual-domain visual exploration of urban solar potential

Traditional methods for estimating the solar energy potential in buildings determine energy yields on an annual base and make use of highly aggregated geo-spatial data. This work proposes a method for detailed assessment of the potential solar energy yield in the temporal and spatial domain. Solar irradiance is evaluated using numerical methods based on hourly variation of solar irradiance and on actual building geometry. Results of our initial studies allow exploration of the variation patterns in solar yield depending on local and time-varying factors, which cannot be seen in coarse level solar planning tools. This helps identifying surfaces with good solar yield that are deemed unfavorable according to traditional planning practices.