On the street to 100% clear electrical energy: Six potential methods to interrupt by way of the final 10%

A rising physique of analysis has demonstrated that cost-effective high-renewable energy techniques are doable, however prices enhance as techniques strategy 100% carbon-free electrical energy—what has grow to be generally known as the “last 10% problem.”

The enhance in prices is essentially pushed by a seasonal mismatch between the timing of variable renewable vitality technology and demand. Meeting peak demand is difficult and costly for all energy techniques, however addressing the seasonal mismatch challenge for high-renewable power systems might require applied sciences which have but to be deployed at a big scale. That makes their prices and necessities unclear.

To assist transfer towards potential options for this problem, a crew of National Renewable Energy Laboratory (NREL) researchers studied trade-offs of six doable know-how methods to get from 90% to 100% carbon-free electrical energy within the United States. This work is printed in a Joule article and may also help inform decision-making at present.

“None of the strategies are perfect, and a lot of uncertainty remains, but the study highlights key challenges with the last 10% and examines all the major technology options,” mentioned Trieu Mai, NREL analyst and lead writer of the examine. “More research and development will be important to move closer to a clear solution for the last 10% and progress the United States toward a decarbonized power sector.”

What we all know to date concerning the final 10% problem

NREL has been learning quite a lot of questions associated to reaching 100% renewable technology within the United States.

In a previous Joule article, NREL outlined the techno-economic challenges of reaching 100% renewables throughout all timescales. The examine explored two forms of challenges: one associated to economically sustaining a steadiness of provide and demand and one other problem associated to designing technically dependable and secure grids utilizing largely inverter-based assets like wind and solar.

In a follow-on examine, NREL used state-of-the-art modeling capabilities to grasp doable pathways and system prices of transitioning to a 100% renewable energy grid. Results, printed in another Joule article, present that prices are considerably decrease if there’s a cost-effective supply of agency capability—assets that may present vitality in periods of decrease wind and solar generation, extraordinarily excessive demand, and unplanned occasions like transmission line outages. Other assets apart from wind, solar, and diurnal storage or load flexibility may very well be vital for overcoming the previous couple of % to a 100% renewable energy grid.

In the Los Angeles 100% Renewable Energy Study (LA100), NREL used a number of fashions to look at which assets may very well be used to assist meet the final 10% and keep reliability for the town of Los Angeles. NREL additionally not too long ago accomplished a landmark examine on reaching 100% carbon-free electrical energy by 2035. The evaluation reveals there are a number of pathways to attain the objective through which the environmental and societal advantages exceed the prices.

This newest Joule article builds on the NREL high-renewable-generation energy grid research by exploring trade-offs of potential technical options that may very well be carried out for the previous couple of %.

Six methods for the final 10%

The preferrred know-how resolution for the final 10% has three major traits. First, the perfect resolution has excessive capability credit score in order that capability is out there throughout high-stress durations and might help useful resource adequacy—one of many “three Rs of power system reliability” that have to be profitable for a secure and dependable energy system. Second, the perfect resolution has comparatively low capital prices as a result of it is not going to be used usually. And third, it depends on broadly out there assets and could be deployed at scale. NREL surveyed six know-how methods which have the potential to fulfill the three major traits.

1. Variable renewable vitality, transmission, and diurnal storage

One doable technique for reaching the final 10% depends on present applied sciences which might be at the moment being deployed. This technique builds extra variable renewable vitality, transmission, and diurnal (lower than about 24-hour) storage. In this selection, variable renewable vitality and transmission capability are sized to fulfill demand throughout every day demanding durations on the grid, with storage filling hourly provide gaps and curbing extra variable renewable vitality (be taught extra about curtailment in an NREL explainer video).

This technique may very well be extra value aggressive if there’s larger long-distance transmission to maneuver high-value variable renewable vitality to demand facilities, and if wind and solar applied sciences proceed to enhance. However, this strategy may very well be harder if wind and solar land use and website constraints enhance over time—one other subject NREL has been learning, together with the current launch of a brand new complete knowledge set of native ordinances for siting wind and solar vitality tasks.

2. Other renewable vitality

Another doable technique for the final 10% makes use of geothermal, hydropower, and biomass—applied sciences that would all play vital roles in a zero-emissions energy sector. These applied sciences don’t depend on variable solar and wind assets and might doubtlessly overcome the seasonal mismatch. However, useful resource availability, particularly at places with excessive electrical energy demand, may slender their utilization to pick out areas solely. These assets even have comparatively excessive capital prices that may be economically difficult as a final 10% technique.

Biomass-based technology may very well be another choice to supply renewable electrical energy for the final 10%. This choice has comparatively low capital value, however there are uncertainties and constraints on a gentle and sustainable feedstock provide and the price of biomass conversion.

3. Nuclear and fossil with carbon seize

Nuclear and fossil gas with carbon seize and storage (CCS) are extensively cited as doubtlessly vital assets in a decarbonized electrical energy system as a result of they’re usually reliably counted on all year long. Fossil CCS vegetation haven’t but been deployed at scale, however some research discover vital deployment potential.

However, this technique comes with challenges: restricted current deployment, value uncertainties, and environmental and safety concerns—and the excessive capital value for low utilization may create financial obstacles.

4. Seasonal storage

Seasonal storage refers to utilizing electrical energy to supply a storable gas that can be utilized for technology over prolonged durations of time, even as much as whole seasons of the 12 months. Hydrogen or different hydrogen-derived fuels are at the moment probably the most promising choices for seasonal storage. Converting hydrogen to electrical energy could be achieved utilizing gas cells or combustion applied sciences, that are being transformed for hydrogen. These electrical energy technology choices fueled by hydrogen may have low capital prices sooner or later and be viable as final 10% methods. Key uncertainties with this technique embrace the supply of the gas (hydrogen) provide and supply infrastructure.

5. Carbon dioxide elimination

Carbon dioxide elimination applied sciences can offset emissions from carbon-emitting energy technology applied sciences by drawing down atmospheric carbon. This final 10% technique is exclusive as a result of it leverages different technology belongings to help useful resource adequacy on the grid.

While there’s distinctive worth with carbon dioxide elimination applied sciences, this final 10% choice has deployment challenges. Very little carbon dioxide elimination has been deployed but worldwide, and future know-how prices stay unsure.

6. Demand-side assets

Demand-side assets, additionally referred to as demand response or demand flexibility, are a singular final 10% resolution in comparison with the opposite 5 methods studied.

Demand-side assets cut back electrical energy consumption throughout instances of system stress and assist keep away from investments in new peaking capability. Through versatile scheduling or interruption of electrical energy consumption, they will additionally cut back working prices or be used for vital grid-reliability companies. Capital prices for demand-side controls and communications tools could be low, and direct working prices are modest.

However, making use of demand-side choices as a final 10% technique requires the assets to be reliably out there over prolonged multiday durations. The scale of response wanted on days of utmost occasions may exceed the demand-response potential, and adaptability from new electrified masses is unsure.

“Given current technology costs and readiness, significant emissions reductions can occur through accelerated deployment of wind, solar, diurnal storage, transmission, and other renewable energy technologies,” mentioned Paul Denholm, NREL analyst and co-author of the examine. “Other technologies could also play a big role if they become cost competitive and widely available. We will continue to study these possible solutions, but for now, the pathway to about 90% carbon-free electricity is increasingly clear. After all, getting to 100% requires first achieving 90%.”