Energy and Environment II Recommended Answers in Red

QUIZ #3

1. Several types of solar PV collectors are used. Please state the major pros and cons of each of the types listed in the table below:

TYPE	PROS	CONS
Single Crystal Silicon	More efficient than the other Si PV cells.	Costly to manufacture. Energy-intensive manufacturing. Circular – trimming wastes.
Polycrystalline Silicon	Cheaper and easier to manufacture than single crystal – casting process. Square – no trimming wastes.	Somewhat less efficient than single crystal.
Amorphous Silicon	Thin film – cheaper to manufacture than single and polycrystalline Si. Less energy-intensive manu.	Less efficient than single and polycrystalline Si. Efficiency degrades over time.
Gallium Arsenide	High efficiency. High absorptivity – thin. Band gap energy well suited to sunlight.	High cost. Arsenic is a toxic metal – disposal is an issue.
Cadmium Telluride	Thin film – cheap to manufacture. Good band gap energy. Efficiency is stable.	Not as efficient as single crystal Si. Cadmium is a toxic metal – disposal is an issue.

Note: all of the cells listed use toxic materials during manufacturing.

2. The text mentions a 100 MW solar PV system. The capital cost would be $150 million, and the cost of the electricity produced would be 5.5 ¢/kwh. Verify the numbers: do they make sense?

This system is discussed in the third paragraph of page 125 of the text. Its capital cost is very attractive, $1.5/W_p, well below current small-user retail costs of about $3 to $6 per rated (peak) watt-electric. The large scale of the system would of course permit a very attractive cost to be obtained – nonetheless, the cost quoted (by Amoco-Enron) is very attractive. Based on the $1.5/W_p figure, the rest of the costing is realistic:

$150,000,000 x 100¢/$ = 2.9¢/kwh

100MW x 1000kw/MW x 0.20 (capacity) x 8760hrs/yr x 30 yrs

This leaves margin for the cost of money, land, O&M costs (low), and profit.