143 Photovoltaics

Photovoltaic (PV) cells directly convert sufficiently energetic photons in sunlight to electricity. Because sunlight is a diffuse resource, large array areas are needed to produce significant power. However, offsetting this is the zero cost of the fuel itself. Today, there is a PV market worldwide of the order of 100 MW per year. Figure 1.10 shows a typical flat plate PV panel.

Prices for PV arrays have dropped by at least two orders of magnitude in the past three decades but still appear to be too high for many applications in the U.S., where the present utility grid offers an alternative. However, in mountainous areas where the grid does not exist or in developing countries where electricity infrastructure investments may never be made, PVs can produce power more cheaply than the common ICE alternative.

Attractive features of PV systems include emission-free operation, no fossil fuel consumption, low-temperature thermal cogeneration (using building

FIGURE 1.9

10-kW microturbine (courtesy of U.S. Department of Energy, Pacific Northwest National Laboratory).

FIGURE 1.9

10-kW microturbine (courtesy of U.S. Department of Energy, Pacific Northwest National Laboratory).

FIGURE 1.10

Solar PV panel (courtesy of NREL).

FIGURE 1.10

Solar PV panel (courtesy of NREL).

integrated modules) possible for space heating, excellent modularity (nearly any building related load can be matched well by multiple units), maintenance negligible, except where batteries are involved, and excellent part load efficiency.

The key barriers to PV usage include: (1) the price of delivered power exceeds other DG resources; subsidies exist in some states that make PV-pro-duced power competitive, and (2) temporal match of power produced to load is imperfect; batteries or other systems are often needed.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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