A problem is the current grid system is based on traditional fossil fuel plants generating electricity to meet electricity demand. Demands for power vary greatly during the day and night, and they vary considerably from season to season. Three main demands have been recognised: base load demand, peak load demand and intermittent load demand. Base load refers to continuous demand, 24 hours a day. Peak load refers to time when demand is greatest, typically when people are starting their day and travelling to work and systems are starting up, and then in reverse when people stop work and commercial consumption shuts down. Finally intermittent load refers to demand filling the gap in supply between base- and peak-load power. Fossil fuel plants can meet all of these three demands, but intermittent renewable energy sources such as wind and solar cannot any of the demands alone because they are intermittent and dependent upon the weather conditions. Therefore electricity produced by wind and solar must be carefully balanced with coal, gas, oil and nuclear plants. In order prevent excess electricity being fed into the grid at peak hours of wind and sunlight, and ensuring enough electricity is produced to meet demand. As the grid system can only cope with supply meeting electricity demand.
This balancing of the grid is only going to become more challenging due to government policies for increasingly higher percentages grid-connected renewable energy capacity. As intermittent renewable energy sources e.g. wind and solar are the most mature renewable energy technologies, policies have mainly focussed on these technologies. Gas and coal-fired power plants are one good way of balancing wind and solar power sources, but the building of plants is out of favour due to current climate change policies. Another alternative is to store excess electricity generated from intermittent renewable resources and release it during periods when demand for electricity outstrips supply. To date the grid system has very limited storage capacity, and energy storage is still very expensive. Therefore there is a need for utilities to monitor and better match supply and demand using automation, perhaps including more voltage control via substation automation. Studies in Denmark, Spain and Germany indicate that renewable energy can only account for 5% to 10% of grid-connected renewable energy capacity. Thus, the current grid system needs upgrading to integrate renewable energy capacities of 20% by 2020.
