CONNECTING SUN

Crossed wires: Securing CSP grid connection
Bob Moser, 21 October 2010 (CSP Today)

"…[T]ransmission is one of the most important aspects to making sure a project's time line keeps on track…[C]onsultants [work] to quell transmission doubts before signing that all-important lease agreement. Is access likely with major network upgrades? Are right-of-way issues resolved? Will any transmission issues crop up later due to environmental concerns? These often hidden questions can sink a CSP project if left unexplored…

"Even with all their ducks in a row, many CSP projects may not gain grid access in the Western US because…[t]here are more than 6,000 MW of interconnection requests in the southwestern United States, but there isn't 6,000 MW of energy demand – 6,000 MW is nearly the peak load…The energy storage option is emerging as a key factor for CSP proposals…[A]dding energy storage capacity, even just a few hours, adds real value to CSP as a capacity resource…"

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"…Storing energy in liquid molten salt is currently the state of the art in low-cost energy storage…Other storage materials like ceramic chips, synthetic oils, cobblestone, gravel and materials which change phase or chemistry via temperature continue to be tested by various companies, but none have proven as cost-efficient as liquid molten salt…The biggest advantage liquid molten salt gives a CSP project today is it's unbeatable low cost, but it also has been applied in several trough and tower plants, and has gained commercial reliability and predictability…

"The knock on steam is that it requires an expensive, thick-walled pressure vessel to house it. Even then, the amount of energy that can be stored is limited because steam takes up a lot of space per BTU. Conveying heat into solids like concrete or ceramics has been tried, but while those materials are cheap, the container they sit in and the fluid to transfer the heat jacks up the overall cost…"

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"Traditional CSP plants feature trough systems without storage. Heat transfer fluid is stored in a network of pipes that snake throughout the collector field, with no storage tanks for the Therminol oil. To add energy storage to a plant like this, developers must add salt tanks, salt pumps, salt piping, tonnes of salt and oil-to-salt exchangers…With a CSP tower plant, the inherent design already has tanks, pumps, piping and salt. Adding energy storage to a CSP plant like this would only require adding more salt inventory.

"The difference in initial cost between a tower plant with and without storage is less than 5% of the capital cost…The cost to add salt inventory to a tower plant with the necessary equipment in place is about US$15 per Kwh, compared to the cost of US$100-120/Kwh in capital costs for adding new storage equipment to a CSP plant with nothing in place…[The therminol] energy loss is around 7% of all the energy stored - a huge efficiency loss over time. Studies are underway testing the heat storage capabilities of stone and oil combinations, but molten salt is an industrially proven technique, a key for investors…"