Page 73 - Alternative Energy Systems in Building Design

SOLAR POWER SYSTEM COMPONENTS 49

Figure 3.14 External view of inverter electronics. Photo courtesy of Solectria
Renewables.

Institute of Electrical and Electronics Engineers The Institute of Electrical
and Electronics Engineers (IEEE) provides suggestions for customers and utilities alike
regarding the control of harmonic power and voltage flicker, which occur frequently on
utility buses, in its IEEE 929 guideline (not a standard), Recommended Practice for
Utility Interface of Photovoltaic (PV) Systems. Excessive harmonic power flow and
power fluctuation from utility buses can damage a customer’s equipment. Therefore, a
number of states, including California, Delaware, New York, and Ohio, specifically
require that inverters be designed to operate under abnormal utility power conditions.

Power-limit conditions The maximum size of a PV power cogeneration system
is subject to limitations imposed by various states. Essentially, most utilities are con-
cerned about large sources of private grid-connected power generation because most
distribution systems are designed for unidirectional power flow. The addition of a large
power cogeneration system, on the other hand, creates bidirectional current flow
conditions on the grid, which in some instances can diminish utility network reliability.
However, it is well known that, in practice, small amounts of cogenerated power do
not usually create a grid disturbance significant enough to be a cause for concern. To
regulate the maximum size of a cogeneration system, a number of states have set
various limits and caps for systems that generate in excess of 100 kW of power.