Integration costs
Costs to integrate wind and solar have been estimated in a few studies, but depend largely on local weather conditions. However, these studies are mainly conducted for several wind farms over a large spatial scale. There are fewer figures for the cost to integrate solar PV to the grid in the US. Xcel Colorado estimates that the solar PV integration costs are USD 3.51 to 7.41 per MWh for 800 MW of solar capacity in a 6,922 MW peaking system with gas prices of USD 7.83 to 11.83 per mmBtu.
Balancing supply and demand
A large number of interconnected, intermittent generation sources operating over a large spatial scale may effectively smooth out the variability between individual generation sources. However, variation will in output will still occur in the short and longer term.
Coupling intermittent renewable sources to a number of electricity production and storage sources could be used to meet the energy demand of a given facility or community, known as a hybrid power system. The power sources used depend on the local geographical and temporal constraints, and can be used to meet demand from remote applications such as communication stations, military installations and rural villages. Full renewable power hybrid systems are in operation and have been mainly applied to remote hybrid systems in China. One of the most cost effective hybrid systems for a microgrid, a small-scale grid, is a photovoltaic array and a micro hydro turbine.
Therefore, more or less electricity is generated than meets demand. Excess electricity can be exported, dumped, stored as another form of energy and/or other electricity sources feeding into the grid can be modified accordingly. An electricity deficit can be met by electricity imports, ramping up or turning on of other electricity generating sources (backup power) and using stored energy. Another option is to use demand management to balance supply and demand imbalances.
Storage is one of the more expensive options to balance supply and demand, but it is increasingly attractive to meet high renewable energy penetration targets. However, the situation outlined in Figure 4 is based on conjecture.
