There is a strong connection between renewable energy and energy storage. Energy storage can be used to balance supply with demand in a number of ways:

• Dispatch generating plant to maximise income
• Dispatch generating plant to provide a predictable output
• Reduce the need to reinforce grid connections
• Control frequency and voltage on isolated systems
• Provide back up or reserve power in the event of grid interruption

This is a widely debated topic with many factors to be considered.  We think that the network issues are more likely to be significant in the near term than simply shifting energy from one time of day to another. Storage is not essential - but it can be helpful.  It is not correct to say that renewable energy cannot be stored (see link).  The technology exists and it can be done!

A useful unbiased introduction to how renewable energy might influence the operation of a power grid can be found on the National Grid website - look for their 2020 consultation. 

There are some worthwhile reports:

The UKERC report on intermittent renewable energy. Intermittency can be managed,
but there will be additional costs. We would like to see this report expanded to look
at how cost effective storage would be in managing the large scale integration of
renewable energy.
www.ukerc.ac.uk/ResearchProgrammes/TechnologyandPolicyAssessment/
TPAProjectIntermittency.aspx

The California Energy Commission; report on Improving the value
of wind energy generation through back up generation and
energy storage.
www.energy.ca.gov/pier/final_project _reports/ CEC-500-2005-183.html

European Wind Energy Association: Large scale integration of wind energy in the European power supply: analysis, issues and recommendations (December 2005). This report does need to be read quite carefully. The report suggests there are no issues with windpower integration at the moment, but in the future there will be, hence the references to electrical energy storage
www.ewea.org/fileadmin/ewea_documents/documents/publications/grid/
051215_Grid_report.pdf