The paper examines the economic impact of space weather by drawing on hourly data from the PJM power grid over the period 1 June 2000 through 31 December 2001. The PJM grid is one of the largest power pools in North America. As of 31 December 2001, its service area had a population of approximately 22 million and included all or part of Pennsylvania, New Jersey, Maryland, Delaware, Virginia, and the District of Columbia. Market prices are determined for every hour of the day. As of June 2000, there are actually two markets for energy: a real-time market in which market participants can buy and sell electricity in real time and a day ahead market that allows participants to enter into transactions one day ahead of time. The existence of these two markets allows us to disentangle the effect of space weather conditions from other factors (such as fuel prices and expected demand) that affect the baseline price (as established in the day ahead market) for wholesale electricity. Several econometric analyses are conducted. The first examines the contribution of space weather to transmission congestion within the power grid. Building on the first analysis, the second analysis constructs an econometric model that examines the impact of space weather on the real-time market. Factors considered in the model include the outcome in the day ahead market, the level of generation utilization, unexpected demand, generation outages, unexpected transmission outages that are believed to be terrestrial in origin, and space weather. The results indicate the presence of space weather effects on the real-time price even after controlling for the other factors. A third model examines whether these space weather impacts affect subsequent prices in the far larger day ahead market.