As many of you attending Maker Faire might recall, I mentioned the "March 27" date, where the ISO (Independent System Operator) asked solar facilities to "turn off".

Reproduced here, is an excerpt from that April 11, 2016 NPR article Stephanie Joyce and Lauren Sommer:
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Solar energy records are falling left and right in California these days, as the state steams ahead
toward its ambitious renewable energy goals.  But the success of solar has brought about a hidden downside: on some perfectly sunny days, solar farms are being told to turn off.  That’s because in the spring and fall, when Californians aren’t using much air conditioning and demand for electricity is low, the surge of midday solar power is more than the state can use.  It’s becoming a growing concern for those running the grid at the California Independent System Operator. At their Folsom headquarters, a team continually manages the power supply for most of the state, keeping the lights on for some 30 million people.  “It’s constantly solving a constant problem, meaning you’re always trying to balance,” says Nancy Traweek, who directs system operations for the grid.

Ups and Downs of Renewables
On March 27, a sunny day, some solar farms had to shut down because there was more power on
the grid than Californians were using. In the past, balancing California’s electric was fairly straightforward. The power supply was constant, coming from natural gas and nuclear power plants that put out a steady stream of electricity.

But the growth of solar and wind power has thrown a wild card in the mix. The sun and wind are
much less predictable.  “All of a sudden you have a major cloud that comes over a solar field,” Traweek says, and that causes the solar power to drop off.

“That [power] needs to come from somewhere else immediately,” she says.

So grid operators have to keep the natural gas plants running in the background. If they’re turned
off, many take four to eight hours start up again.California’s highest demand for electricity also happens right as the sun goes down, when Californians come home from work and lights turn on. Grid operators need natural gas power plants at the ready to meet that peak and to fill the gap that’s left by solar power.

But add up all those energy sources – solar, wind, natural gas, as well as hydropower, nuclear and
others – and on some days, they’re making more electricity than California needs

“When it gets really bad, now we really got to start cutting as much as we possibly can,” Traweek
says. “If that’s not done, then you could have a blackout.”

So, grid operators have to tell solar farms to shut off.

“That’s zero-carbon, clean energy,” says Keith Casey, a vice president at the California Independent
System Operator. “It would just be a travesty to curtail large amounts of it.”

Casey says the problem will only get worse as more solar and wind connect to the grid. California
plans to hit 50 percent renewable energy by 2030.

Joining Grids Across the West
California’s grid operator is developing a solution, one that is garnering controversy across state
lines.  Right now, California’s grid runs mostly on its own, like an island. But there are power lines reaching across the West.

“You’re operating your little piece of the system,” Casey says, “but if you can operate it as an
integrated whole, you can just operate the system more efficiently.”

So, Casey is proposing California join up with its neighbors. Instead of having lots of electric grids
across the West, each doing their own thing, there would be a larger regional grid, sharing power
across state lines.

When California has too much solar power, neighboring states would buy it, preventing California
from having to switch off the solar farms.

“It’s a win-win,” Casey says. “We really think we need to seize the most efficient opportunities that
are out there for integrating renewables.”

I want to post the graphic that I showed at Maker Faire, that explains my working concept.
On the right-hand part of the picture, the image shows a full reservoir below the two blue parallel containment walls (heheh...sounds 'nuclear'!)  with the leaf spring stack (yellow) arranged in a circular form.  These springs are sheets of fiberglass.  I am thinking, that perhaps steel (being so cheap with a worldwide glut) might be a significant add-in as a leaf spring.

As the hydraulic fluid (red) is pumped into the bladder (not visible, too thin for this drawing) by a hydraulic pump (powered by electricity from renewable sources) the bladder assumes the least possible geometric shape, which is a circle, and pushes the containment walls into a circle.  Because the containment walls are attached at their uppermost end to the leaf spring stack, the deformation of the containment walls into a circle draws down the leaf spring stack into a flat oval (left image).  Energy is stored in the deformed spring stack, rather than by any elastomeric substance (e.g. rubber) or compressing a gas (which is typically the case in most hydraulic accumulators).

To release energy stored in the spring stack deformation, hydraulic fluid is released from the bladder, and is directed through a hydraulic motor/440v AC generator combination, and back into the no-pressure reservoir.

Brief Info as Distributed at 2016 Maker Faire

Ultra-Linear Hydraulic Accumulator

What is a “Hydraulic Accumulator”? Hydraulic accumulators have been in use in systems utilizing hydraulic oil to power equipment for well over one hundred years. It is basically a reservoir of pressurized oil, integrated into a hydraulic pump and hydraulic motor system to perform heavy-duty work (think backhoe, and other earth-moving equipment, as well as oil drilling/oil platform equipment). The accumulator acts to smooth the oil pressure in the hydraulic system.

There are several methods used to pressurize the oil in a hydraulic accumulator. Most typically, compressed nitrogen gas is used. Note that springs are used, but all these methods (save the weight loaded reservoir) have a problem: power decreases rapidly, if more than 20% of the oil stored is used.

Here is a link to a file published by hydraulics specialist company Hydac description of high-pressure accumulators that use a bladder:

http://www.hydac.com.au/MessageForceWebsite/Sites/279/Files/E.3.203.3.03.12.pdf

This gives you some insight into what an "accumulator".  Here are two pictures of a large array of accumulators, as well as smaller, varied accumulators:

 

What do you mean by “Ultra-Linear?” Most hydraulic accumulators are small in size. My proposed device would be approximately five feet high, three feet wide, and stretch in a line (not particularly straight, not particularly level) for a half-mile, or more.

Why not use “pumped hydro” reservoirs to store renewable energy? Unfortunately, constructing two large reservoirs to contain the vast amounts of water needed to make an economic system of energy storage, is constrained by geography and geology. Useful sites for pumped storage are almost never near urban centers demanding significant amounts of power. This hydraulic system could be located in straight line locations, such as along metropolitan freeway land.

Why have no hydraulic accumulators heretofore been used to store energy from wind, solar, tidal, and other renewables? Note the drawing above. Most accumulators use compressed gas, and the problem with compressed gas is that it heats up, and energy is lost as the heat dissipates. There are very few places where compressed gas is used to store megawatts of electricity. You have to use springs, or a heavy weight, to avoid Carnot Efficiency losses. Even then, a large volume of oil is required, and converting that oil under pressure to electricity has been not very efficient up to now.

What has changed? Are there more efficient hydraulic motors now?

Enter Artemis Intelligent Power (http://www.artemisip.com/) By using computer controls, Artemis has achieved 90%+ "Overall Efficiency" (blue line) in converting pressurized oil to rotating power.

Using a rotating generator offers the best quality power for a wider set of businesses and homes.

Where are the springs in your system? I am using fiberglass springs, which outperform steel springs over time. The latest Chevrolet Corvettes use a front fiberglass leaf spring in place of steel, as it gives better performance (millions of cycles before replacement) and weight savings.

Why use leaf springs? The sheets of fiberglass, configured as multiple sheets, give a more constant spring rate if designed correctly. The fiberglass sheet also functions as an enclosure, protecting against weather, as well as performing to store energy.

What about individual battery power in homes? (e.g., Tesla Home Battery) It should prove 25% cheaper to use this “Ultra-Linear” grid-scale system, powering four to five hundred homes for eight hours, than installing individual battery systems in every individual household. The Independent System Operator that distributes utility electricity throughout California could better utilize solar power plants and wind turbine farms if larger entities were consistently available to absorb excessive renewables generation.

System Build Comparison Building lithium batteries requires specialized employees, and high engineering costs, as does the construction of Pumped Hydro facilities. The Ultra-Linear Hydraulic Accumulator could be produced anywhere with limited training, and shipped to urban as well as remote locations (think Western Alaskan villages) where local residents could be trained to both build the system as well as maintain its operation.