How the Electrical Grid and Renewable Energy Works

The electricity you use in your house came from a ray of sunshine, a gust of wind, or a conventional power plant less than a second ago. This is because electricity travels near the speed of light and the electrical grid must balance the supply and demand of electricity instantaneously. There is no way to have “surplus electricity” on the grid unless you store it, or else it must be used immediately. There are people who work for Independent System Operators (ISO’s) and Regional Transmission Operators (RTO’s) to forecast electricity needs and balance this delicate market so that the supply and demand of electricity always match.

However, renewable energy is intermittent by nature, which makes this intricate supply and demand market challenging to keep in balance:

  • Solar panels only work during the daytime, when the sun is shining
  • Wind energy is unpredictable
  • Hydroelectric power is seasonal

Depending on the time of the day, season, and weather variations, electricity generation sources might change. Below is a snapshot of all electricity generated (split by source) in the U.S. for a week in early December 2021:

There is also variation in electricity need by region of the U.S. and by season of the year:

Source: U.S. Energy Information Administration, U.S. Hourly Electric Grid Monitor

We know we must supply our electrical grid with 100% renewable energy, but since renewable energy supply doesn’t match our electricity demand, polluting power plants are dispatched because they can be turned on and off as needed to fill in the demand gaps.

Managing a grid in this way without storage becomes challenging, even at renewable penetration rates as low as 15-20%. Even then, significant amounts of solar and wind are curtailed, because the grid can’t respond fast enough or effectively to their unexpected swings in power production, and there isn’t enough storage to absorb the periodic excesses of electricity supply. It would be far more challenging, or impossible, to manage a 100% renewable grid without significant amounts of electricity storage that can time-shift supply of electricity.

Because our current grids lack the storage infrastructure to make full use of renewable energy, even at 20% renewable energy supply, we have seen solar and wind energy curtailed: This means that there isn’t anyone to use the power that is generated so the power providers turn off the solar panels or wind turbines because they are generating too much energy at that point in time. We can’t turn on and off 75% of the traditional power plants in the U.S. because they take more than one hour to start up after they have been shut down--some power plants, such as those powered by coal and nuclear fuel, actually require more than half a day to reach full operations so these “baseload” sources of energy are not changed on a daily basis. Lastly, the traditional power plants we can dispatch in less than an hour are called peaking power plants, but they tend to be the most pollutive.

Solar in the California ISO (CAISO)

California generates 15% of its electricity supply from solar energy and 7% from wind energy (in total, 33% of California’s renewable energy came from renewable sources in 2020).

Source: CAISO Managing Oversupply

In the last few years, during the spring, California has curtailed (or turned off) upwards of 300,000 MWh of electricity each month--this is completely clean renewable energy that could power 300,000 homes, and it simply cannot be used due to the lack of storage. In other words, a city like Oakland, CA could have 100% clean, renewable energy powering the homes of all of their residents each spring, if we only are able to store this energy.

Specifically, in the middle part of the day when solar energy peaks but demand and usage doesn’t, we need to store that excess energy which is generated from rooftops and solar farms in California, and release it back to the grid at the end of the day and in the morning before the sun comes out. TerraStor does exactly this - with zero emissions and cost-competitively.

TerraStor shifts excess solar energy from the midday to the evening

Wind in the Texas ISO (ERCOT)

The Texas ERCOT market generates 24% of its electricity from wind power, its second largest source of energy (natural gas is the biggest source at 42%.) It currently curtails about 4% of the wind energy and that percentage will likely increase as more wind and solar energy is added onto the grid.

Source: LCG Consulting ERCOT 2021 Outlook Report

It is typically windier in the mornings and in the evenings, so TerraStor enables wind energy development by storing the excess renewable energy generated for diurnal usage or to support seasonal variation in wind.

TerraStor shifts wind generation

Hydropower in the Northwest (RTO West)

Hydropower is the second largest source of renewable energy in the U.S. (7.3%). Like wind and solar power, hydropower generation fluctuates, but unlike wind and solar its fluctuations tend to be seasonal rather than diurnal. For instance, in the U.S., hydropower generation tends to be the greatest during the spring, when snowpack is melting off the mountains, causing rivers and reservoirs to swell. Unfortunately, the spring is often when power demand in the U.S. is the least, since weather is temperate, calling for neither heaters nor air conditioners.

Source: Electric Power Monthly,

To deal with this mismatch in supply and demand, extremely long duration grid-scale energy storage over the course of weeks and months is needed. Most technologies, including batteries, cannot store energy effectively over such a long period of time, but TerraStor’s technology, which uses compressed air energy storage, can do this with little to no capacity degradation or self-discharge.

TerraStor shifts hydroelectric generation

By making renewable energy more reliable and dispatchable, the cost of electricity for end consumers will drop because less of it will be wasted and we won’t need polluting and expensive peaker plants.

In the U.S. we only have 25 GW of storage, but we will need 680 GW of storage to enable a mostly renewable energy electrical grid. Globally, 174 GW exists, and needs to increase a whopping 400X to enable the renewable energy transition.

However, grid-scale storage is hard to build--we will have to figure out the right site that has the transmission lines to carry the energy from the generating source to the storage site, store the energy efficiently, and then send the electricity back out to those who need it at the right time. Storing a power plant’s worth of power for a duration of even several hours, let alone days or weeks, is an incredible feat in itself. This is exactly the challenge that we are ready to tackle, and our expertise in power markets, energy storage systems, and geologic reservoir engineering puts us in the best position to solve this problem at scale. Please visit our technology page for more information on how compressed air energy storage works.