Solar Intermittency: How Big is the Problem?

Intermittency is one of the major criticisms of solar — the majority of the energy is delivered when the sun is shining brightly, but virtually none is created at night or in substantial cloud cover.

How do solar developers view this issue — does it pose a huge stumbling block to current projects, or is it something that has been effectively managed? I spoke with two gentlemen, Martin Hermann, CEO of 8minutenergy Renewables and Paul Copleman, communications manager at Iberdrola Renewables, to find out more. 

Are there specific technologies used to deal with intermittency? Surprisingly, neither developer implements storage technologies on-site because there is no need to do so.

In fact, it seems that solar technology has already occupied a niche where it can thrive without a storage solution. 

Copleman explains, “[the] integration of significant amounts of intermittent generation is entirely feasible with the existing grid,” due to the “ability of the grid to respond to changes in generation levels in real time using the existing generation and transmission system.” Thus, on the supply side, the technology is feasible, and solar can fit into a niche market. “Solar PV’s production curve is aligned with the peak demand during the day and therefore helps to shave the peaks within a utility’s generation profile,” said Hermann.

In fact, even without storage technology, the PV intermittency seems to be effectively managed at current project scales. Mr. Copleman stresses the distinction between intermittency and predictability: “It’s important to understand that while solar is intermittent, it does not have a random generation pattern. Solar resource is very predictable, which makes grid integration less of an issue. Additionally, forecasting solar resource on a day-ahead and hour-ahead basis has a high accuracy factor.”

Besides having a predictable generation pattern, other measures are being used to tackle the problem. For example, Iberdrola is “evaluating its wind projects for where a co-located and co-interconnected solar project would increase capacity factor as well as decrease sub-hourly intermittency.” Also, project screening avoids locations where intermittency becomes a substantial issue for the system. 

While both gentlemen state that intermittent power is not a short-term problem, they agree that it would become an issue in the longer term. This would happen when solar finally moves from its current niche as a supplemental resource and transitions to become a firm, baseload resource. “Locating 1,000 MW of PV on one transmission line will clearly be more difficult to integrate than 1,000 MW of PV spread across multiple distribution and transmission lines and across a broader geographical area,” said Copleman.

Current researchers and developers of storage solutions should pay attention to two different milestones that would be game-changers in the way solar energy is utilized today. The first milestone, at three to five hours of storage, “will allow a precise overlap between the PV production curve and the demand peak of a particular utility,” said Hermann. “The second milestone, at 20 hours of storage, will enable PV to work as a base load resource.”  

Both solutions must be cost-effective though, as they will compete directly with traditional base load resources like LNG and coal. Once these milestones are reached, solar energy is set to transform the world in a much greater way.

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Siah Hong Tan is a research specialist in Singapore. He is currently performing research on material systems that might be able to convert sunlight directly into fuels like hydrogen or methanol, thus addressing the issue of enabling long term, large-scale storage of solar energy. In his free time, Siah writes articles for RenewableEnergyWorld. He hopes to better understand the social, economic, technological and business implications of a renewable energy-powered future. Siah graduated from the Johns Hopkins University with a BS in Chemical and Biomolecular Engineering in 2011.

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