  The intermittent nature of the renewable energies increases the operation
costs of conventional generators. As the share of energy supplied by renewable
sources increases, these costs also increase. In this paper, we quantify these
costs by developing a market clearing price of energy in the presence of
renewable energy and congestion constraints. We consider an electricity market
where generators propose their asking price per unit of energy to an
independent system operator (ISO). The ISO solve an optimization problem to
dispatch energy from each generator to minimize the total cost of energy
purchased on behalf of the consumers.
  To ensure that the generators are able to meet the load within a desired
confidence level, we incorporate the notion of load variance using the
Conditional Value-at-Risk (CVAR) measure in an electricity market and we derive
the amount of committed power and market clearing price of energy as a function
of CVAR. It is shown that a higher penetration of renewable energies may
increase the committed power, market clearing price of energy and consumer cost
of energy due to renewable generation uncertainties. We also obtain an
upper-bound on the amount that congestion constraints can affect the committed
power. We present descriptive simulations to illustrate the impact of renewable
energy penetration and reliability levels on committed power by the
non-renewable generators, difference between the dispatched and committed
power, market price of energy and profit of renewable and non-renewable
generators.
