Geothermal Energy to Balance the Grid
Our previous post discussed the need for a constant, reliable, and renewable energy source. This transformative source will help balance the intermittent renewable energy of wind and solar, that increasingly dominates the production of current electricity needs.
In contrast to inconsistent renewable energy sources, geothermal energy provides baseload generation of electricity, capable of supplying dependable power to meet demand. Geothermal holds an estimated availability factor of 92%, which is higher than any other form of power generation. In addition, geothermal energy is immune to the effects of climate change. It has the capacity to provide the energy balancing demanded by existing power grids. Unfortunately, because geothermal energy provides baseload electric power, utility companies will not contract for geothermal just to balance the electric grid. This is because when geothermal and the intermittent renewables are all running at the same time, the utilities will be paying for power that they don’t need. Also, the current levels of geothermal energy generation is small compared to wind and solar energy.
At the same time, we need to replace fossil fuels that are used for transportation and related purposes. As mentioned before, hydrogen is a promising replacement option. The problem with hydrogen as a solution to global warming is that over 90% of the hydrogen used today is produced by steam reformation of methane or other methods using fossil fuels, all of which actually produce additional greenhouse gases. This problem is avoided by generating electricity from renewable resources to produce hydrogen by electrolysis, which will use electricity to split molecules of water and make clean hydrogen. Unfortunately, current methods of electrolysis are inefficient, and therefore too expensive to compete with fossil fuels. This leaves us with two challenges: a need for a constant, renewable energy as well as increasing the generation of low cost clean hydrogen.
The cornerstone for the solution to both of these problems is very high-temperature geothermal energy. Producing electricity from high-temperature geothermal resources, both from existing reservoirs such as the Salton Sea and from new high-temperature reservoirs, and combining electricity generation with hydrogen production by electrolysis, could provide the additional renewable energy needed to accelerate transition and replacement of transportation and heating fossil fuels. Moreover, a recent study forecast energy costs for the periods from 2015 to 2020 and from 2035 to 2040. This study projected geothermal energy will have a lower levelized cost of electricity than any other form of generation for both periods. Geothermal will thus be less expensive than fossil fuels and other forms of renewable energy. Geothermal will solve both the need for balancing as well as providing a lower cost fuel for clean transportation and heating purposes. Geothermal becomes a win-win for both sides of the energy coin. Cost, efficiency, and practicality becomes the driving force for change.
The desired balance on the electric grid utilizes load following power plants, which adjusts its power output as demand for electricity fluctuates throughout the day. Load following could, under appropriate conditions, be achieved more economically and effectively than with batteries. This is possible by using geothermal resources to generate electricity, both for sale and for electrolysis to produce hydrogen as a non-polluting transportation fuel, as well as to preheat the feedwater for such electrolysis. As both power generation and electrolysis of water are more efficient at high temperature conditions, the best environment to test this concept is in very high temperature, preferably supercritical, geothermal reservoirs. The Iceland Deep Drilling Project (IDDP) aims to investigate such supercritical geothermal conditions.
In 2009, Phase 1 of the IDDP created the hottest geothermal well in the world (450oC) but it was too shallow to reach supercritical pressures. Phase 2, beginning in 2016, will drill to greater depth to reach the appropriate pressure and temperature conditions. In California, the Salton Sea and the Geysers geothermal fields both offer high temperatures at drillable depths. In fact, in some parts of the Salton Sea geothermal field temperatures exceeding the critical temperature are likely at a depth of approximately 3.5 kilometers. This creates the possibility of large-scale production of clean hydrogen to alleviate serious greenhouse gas levels and air pollution produced by combustion of fossil fuels in Southern California.
The greatest potential world-wide for such systems is along oceanic spreading centers, where seafloor mountain ranges and trenches are formed through volcanic activity. This seafloor spreading produces supercritical geothermal resources for 65,000 kilometers around the world. These high temperature geothermal wells could produce at a constant flow rate. This results in generating electricity for the grid when needed for balancing. Furthermore, this would also generate electricity and heating feedwater to supercritical temperatures for electrolysis to produce hydrogen as a fuel for transportation and oxygen for industrial purposes. Electrolysis can be ramped down in seconds. Load balancing power can thus be provided to the grid immediately. This option and process is more efficient than natural gas-fired generation.
Geothermal power plants operate at a constant rate, so the electrolysis is constant thus justifying the higher capital investment needed for the most efficient electrolytic cells. If the technical issues are solved economically, we can use the least-expensive electricity to produce the least-expensive hydrogen. In contrast, current proposals for electrolysis using renewable energy would occasionally use excess power from intermittent resources that have a higher electricity cost than geothermal. Since these resources only run occasionally, they will support only less-efficient electrolytic cells producing more-expensive hydrogen. The higher capital costs of highly efficient electrolysis, and the volume of hydrogen that will be needed to replace carbon-based transportation and heating fuels, will require baseload geothermal energy, not intermittent renewables.
The use of geothermal energy will not only increase the contribution of geothermal to the overall portfolio of renewable resources, it will also, by providing the capacity to balance the grid, avoid the decrease in capacity and energy values of wind and solar power. This in turn allows renewables to expand more rapidly. Because hydrogen will go into the kind of inventories that the economy has always used for transportation and heating fuels, hydrogen is a form of storage that does not impose an additional expense or burden on the economy, like batteries will.
With a foundation of baseload, high-enthalpy geothermal energy and supercritical electrolysis, all renewable resources can work together to advance, and replace fossil fuels in transportation as well as in electricity. This replacement combines of the best of both speed and efficiency.