A solar power forecasting system can provide forecasts of solar power output by photovoltaic plants over multiple time frames. A first time frame may be several hours from the time of the forecast, which can allow utility personnel sufficient time to make decisions to counteract a forecasted shortfall in solar power output. For example, the utility personnel can decide to increase power production and/or to purchase additional power to make up for any forecasted shortfall in solar power output. A second time frame can be several minutes from the time of the forecast, which can allow for operations to mitigate effects of a forecasted shortfall in solar power output. Such mitigation operations can include directing an energy management system to shed noncritical loads and/or ramping down the power produced by the photovoltaic plants at a rate that is acceptable to the utility to which the photovoltaic plants provide power.