Neal Mann Nuclear


2022-01-28 10:32:35 .... Copyright 2021 Neal Mann.... Reviewer: Mihai (Mike) G. Pop, Dr. Eng.

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Electricity Generation

    The reactor is intended to be included in a complex with the reactor and heat exchangers, air-Brayton cycle turbine generators with a power capacity about 2.5 times that of the reactor, and a salt (NaCl) thermal storage reservoir with a capacity of at least 8 hours of reactor output. The turbine generators could also have the capacity to burn natural gas or hydrogen or liquid fuel to provide extra power when the salt thermal reservoir is too cool to meet an elevated power demand. The salt thermal storage isolates the reactor power output from the sometimes erratically varying net electricity demand. The reactor can run at full power almost all of the time, the reactor power should only be decreased when the electricity demand is low and the thermal storage is fully charged.

    When electricity demand (and the price) is low, the excess energy from the reactor is used to heat the salt rather than generate electrical power. When demand is higher than the reactor capacity (and the price is also high), heat from the salt is added to the heat from the reactor to generate extra electrical power. With a design having several air-Brayton cycle turbine generators per reactor, the last one can be used (for example) only an hour or so most days, but it will be when the price is the highest so it will still generate more revenue than its cost. In addition, if there is a sufficient stock of liquid fuel, in a crisis situation the complex can generate peaking power at up to the full capacity of the turbine generators for a week or more.

    On most days the daily variations in power demand combined with the variations in production by wind and solar mean that some hours will have low demand and few generators operating, other hours will have many if not all generators running. On most days some generators will be turn off sometime and some generators will be started. By always starting the generator that has been idle the longest the workload is shared equally among the generators and all the generators are known to work. Even if the generators are not all used at the same time for weeks or even months, they are all used enough that in a crisis the full peaking power will actually be available.

    Wholesale electricity prices are set with power auctions which match power offered at various prices by power producers with bids by users to buy power at various prices. When the matchup of offers and bids is settled, a fair market price is reached and all offers to sell below the fair market price become accepted contracts at the fair market price and all bids to buy above the fair market price become contracts at the fair market price. (bids and offers exactly at the fair market price have their quantities pro rated.) This method encourages all traditional power producers to offer all of their production capacity at their marginal cost of production, knowing that if the fair market price is below their marginal cost they won't be stuck with a money losing contract and if the fair market price is above their marginal cost they will be paid the fair market price and make a nice profit or at least pay some of their fixed costs.

    Wind and solar producers have essentially no marginal cost of production, so they offer their entire capacity at zero so they will get the contracts. As long as the total active wind and solar capacity is less than the demand the fair market price will be set by the cheapest other power producers. When wind and solar production exceeds the demand, the fair market price falls to $zero (price collapse). At first this only occurs for a few hours on sunny summer days. As more solar capacity is added this expands to several hours on most summer days and a few hours on sunny spring and fall days. Eventually, no new solar capacity will be built because there is no return on investment if the price is zero. Wind capacity may still be built because a wind producer can make money even if it only sells power an average of 20 hours a day when solar is not producing. Eventually, there may be enough wind capacity that just the wind capacity is greater than the demand sometimes and the price collapse occurs more hours on more days and investors stop building wind capacity.

    The ability to store energy (batteries, water in a reservoir behind a hydroelectric dam, or heat storage in a nuclear reactor complex) changes the picture. An entity with storage doesn't just bid or offer at a price which assures the most contracts at a price which doesn't lose money, the entity offers or bids (or both) many batches at different prices in order to manage the storage capacity to sell small amounts of power at low prices and lots of power at high prices, or buy lots at low prices and little at high prices. If there is significant storage capacity. it smooths out price fluctuations and stabilizes the grid for everyone.

    When producers fail to meet their contracts or users have higher demand than their contracts they are required to buy power on the spot market. Sellers on the spot market include buyers who have less actual demand than their contracts or producers who have extra production capacity instantly available. Prices on the spot market tend to fluctuate quite wildly and in a crisis situation (Texas in February 2021) can skyrocket by orders of magnitude. The existence of extra storage capacity can greatly reduce the fluctuations of spot market prices.

    For a nuclear plant with thermal energy storage, the ability to generate extra energy from a stock of liquid fuel and the ability to reduce the power of the nuclear reactor when the heat storage is full have the same effect as a bigger storage capacity, but at a cost. When the liquid fuel is consumed it adds a direct cash cost. When the nuclear power is reduced, the opportunity to sell the power is lost, increasing the capital cost share of all the power which is produced. Adding actual storage capacity has a cost, it is not used all the time so it increases the cost of all the energy that is stored. The right amount of storage capacity is not obvious. The storage capacity chosen affects the total capital cost, the price margins, and the grid stability.

page last modified 10/11/2021