When oversized is really the right size


From pv magazine USA

Researchers recently published a paper in which they seek to understand how far we can go with wind and solar.

The research analyzes 39 years of hourly wind and solar generation data across 42 countries. An evaluation of “perfect” transmission without energy storage finds that the most reliable renewable electricity systems are wind-heavy and satisfy countries’ electricity demand in 72% to 91% of hours (or in 83% to 94% of hours by adding 12 hours of storage).

The research found, however, that even in systems which meet more than 90% of demand, “hundreds of hours of unmet demand” may occur each year.

The research quantified the power, energy, and utilization rates of additional energy storage and demand management, (curtailment), as well as the benefits of regional aggregation. The models evaluated three levels of excess generation and storage (none, three hours, and 12 hours).

Notably, the researchers concluded that wind and solar generation resources that were sized at 1.5 times along with three hours of energy storage would meet all but 200 hours of demand scattered throughout any given year.

Prior research by Calderia suggested that the United States could reach a dependable power grid made up of 80% wind and solar power with approximately 12 hours of energy storage. This 80% model would require no additional power grid transmission resources.

The models found that countries with larger land areas can (obviously) build wind+solar power grid systems with greater reliability. For systems without integrated energy storage, the ability to meet energy demand increased by 7.2% for every factor of 10 increase in land area.

When three or even 12 hours of energy storage are added, patterns begin to emerge.

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The top left of the above chart shows a standard volume of generation with no energy storage. It shows a clear linear increase in reliability associated with the country’s area. But, in cases where three or 12 hours of energy storage are added, generating capacity increases by 50%, and reliability increases dramatically.

In fact, when looking at the lower right box with 12 hours of batteries and 1.5x standard generation, the ability of wind and solar to meet electricity demand brings all of the nations analyzed in the study above 97%; several countries were modeled as meeting 100% of demand.

The research suggested a trade-off point exists for excess generation and energy storage as a 10% increase in excess annual generation is equivalent to 3.9 hours of storage.

The paper showed that even with energy storage, gaps in the schedule of heavy wind plus solar systems still find periods where dispatchable resources will be needed. And though it is easy to suggest fossil-based facilities as a solution to these down times, it will become economically challenging to do so, as the mined volume of those fuel sources – coal and gas – declines.

Additionally, technologies like hydrogen, vehicle batteries, nuclear, and hydro will be needed to fill in the weak spots. If we do figure out how to limit our political squabbling and build intra- and international transmission, we will achieve maximum renewable energy resource utilization.

If we do find that “oversizing” wind and solar deployment beyond currently defined standard system sizing is in fact the best way to size things, then the word “oversize” is a misnomer.

When these projects are generating electricity in amounts greater than the power grid’s demand, entrepreneurial spirits and asset owners no doubt will seek ways to make better use of these resources.

Generally, it would not make sense to place expensive hardware — such as hydrogen electrolyzers or bitcoin mining rigs — at renewable generation project sites to run “only” when the sites are overproducing.

It would make sense, however, to place energy-hungry industries near renewable generation, with the intention to run on both grid power and on summertime peak generation power which otherwise would have been curtailed. In this way, we can bring down average electricity prices for these facilities, and create a valuable resource out of necessary, seasonal excess.

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