After learning quite a bit about how the sun’s energy is created, and how that process might be reproduced on earth, we turn now to methods of harvesting the energy from the sun. Heat energy is the easiest form to store and distribute and is useful for heating water and home. (The advantage of solar […]

The operation of this device follows the steps indicated in Figure 6.17: step 1 is absorption of a photon by a dye molecule. Typically, the dye is a metal-organic ruthenium complex with response in the wavelength range 700-900 nm, light that is not absorbed by the titania. This is the idea of dye sensitization, to […]

The “Li-drifted germanium detector” (http://en. wikipedia. org/wrki/Germanium_ detector#Germanium_detector.) is an elegant commercially available solid-state device to measure the energy of a single high-energy gamma ray photon. A pure single crystal of germanium is treated in a special way with lithium, so that the mean free paths of electrons and holes are larger than the dimensions […]

Commercial storage and transport ofhydrogen is conventionally at high pressure in steel cylinders, or aluminum-lined containers reinforced with carbon fibers, or as liquid in a cryogenic container. The network of hydrogen “filling stations” in California dispenses hydrogen at 5000 psi and at 10000psi (~330 bar to 660 bar). There are significant energy costs in pressurizing […]

The main properties of the sun as an energy source are its energy density, 1366 Wm—2 at the top of the earth’s atmosphere; the highly directional nature of its radiation, and its spectrum. For simple estimates, we will take the sun as a black body at 6000 K. Starting from the energy density of the […]

State-of-the-art performance of such a dye-sensitized cell is shown in Figure 6.18. The dye-sensitized solar cell represented in Figure 6.18, under simulated AM 1.5 G irradiation, exhibited short-circuit photocurrent 20.5 mA/cm2, open-circuit voltage 720 mV, and efficiency 10.4%. This efficiency is close to the best value ever obtained in this kind of cell. The dyes […]

Equations 2.11-2.16 and 3.15 are applicable to the electron and hole states in semiconductor “quantum dots,” which are used in biological research as color – coded fluorescent markers. Typical semiconductors for this application are CdSe and CdTe. A “hole” (missing electron) in a full-energy band behaves very much like an electron, except that it has […]

As an upper limit on hydrogen that might be needed, we can calculate the hydrogen production equivalent in energy to the U. S. electricity usage per year, which was 460 GW in 2004 [122]. The total electric energy in 2004, then, taking a year as 3.154 x 107s, was 1.45 x 1019 J. If the […]