632. Dam Gravity

M. Rehemtulla for QUOI Media Group

Tuesday morning. When I wrote these posts about two weeks ago, I mentioned PG&E. Guess what? They just announced that tomorrow my county is slated for a possible shutoff of power because of projected high winds. Even if that doesn’t happen, a regular power outage is likely. While you are reading this, there is a good chance I will be reading a book by sunlight through the window, because I won’t have any electricity to power my computer. I would find that ironically amusing, except my stove and refrigerator also won’t be working. At this moment I might be eating cold beans out of a can.

Additional, 6 hours later, it is now almost certain that we will be blacked out, and that it might well last up to five days. Posts come to you from WordPress, not directly from my computer, and I have a month of posts in the can so, see you later. Now back to what I already wrote.


This is a continuation of last post. What does a kid with a toboggan have to do with solar energy storage, you ask? You’ll find out by the end of the post.

If you have any science background at all, please forgive the next few paragraphs as I set things up for something you may not know.

A battery does not hold electricity like a can holds Coke. The electrons which are present inside the battery do not go into your device. They travel from the (-) pole to the (+) pole, and essentially the same electrons are there in a discharged battery as are in a charged one.

It is the flow itself which powers your device. The flow is caused by chemicals inside the battery changing from a high energy configuration to a low energy one. This is true of the lithium ion battery that just burned up your hoover board, and equally true of the car battery in your great-grandad’s 1950 Nash Rambler. Such batteries are recharged by running electricity back through them to return the low energy chemicals to a higher energy state.

In other words, batteries don’t store electricity, they store energy. Chemical energy, and there are many other ways to store energy besides batteries. Let’s look at one.


Last post I invited you to take a trip with me from the California foothills toward the coast. Now we have dropped down out of the brown hills, have crossed the hot, flat, agriculturally green Central Valley, and suddenly our car turns its nose upward because we have reached the Coast Range which stands between us and the ocean. We are on Highway 152 and to our left is the imposing dam of San Luis Reservoir.

Everyone knows the story of rainfall on mountains. California lives on it. Sunlight on the Pacific raises moisture which gets an uplift first by the low Coast Range and then by the High Sierra. The west side of the Coast range and the western Sierra foothills get winter rain in moderate quantities, and west side of the high Sierras gets a big dump of snow which melts in spring to fill reservoirs all over the western foothills, providing irrigation and electricity to California.

The eastern side of the Coast Range and of the Sierras get squat.

Where San Luis Reservoir is located, there isn’t enough local rain or snow to fill it. Water is brought to it by a system of canals, accumulated in the forebay and pumped up into the reservoir.

Sounds goofy, right? The dam exists to harvest in spring and store for summer, water that has already passed thorough the other reservoirs and would otherwise go to the ocean. Of course it’s controversial; everything related to water in California is controversial.

So what does this have to do with solar cells on the roof? San Luis Reservoir not only stores water, it is essentially a giant storage battery for electricity.

When the water arrives at the forebay, it is pumped, by electricity, up about 320 feet into the reservoir. When it exits the dam to be used, it passes through a hydroelectric generator, recouping much of the energy originally used to lift it. It isn’t 100% efficient system, but nothing is.

Batteries store energy by chemical change. There are innumerable other ways to store energy, many of them new, complicated, expensive, and with unknown dangers. Carrying a load uphill to store gravitational energy, and getting that energy back when the load comes down is old, simple, and well known. Kids have been doing it with toboggans ever since there have been snow, toboggans, and kids. (See, I told you I’d explain that photo.)

In California, people have been doing the same thing for a hundred years or more in tankhouses, water tanks attached to houses which allow gravity flow so you don’t need to turn the well pump on every time you open a faucet. The one shown here even used wind power to get the water out of the well and up into the tank.

This was done for the sake of the water, but it could as easily be done for the sake of storing energy. With twin tanks, one high and one low, there would be no reason to “use up” the water. It could even be structured in tandem with the house’s normal water usage.

I submit that a good engineer could turn this into a cheap, simple, and easy way to harvest solar power all day and use it all night, without frightening Mother Nature. You would simply use excess solar electricity to pump water upward all day, and drain it back through a turbine and generator that night.

How much water, how high would we have to pump it, how much would the raised tank cost? Would it be practical? Would it make money for the ones who provide the system? Who knows; that’s for some young engineer is search of a project to determine. Will it be you?

Since I didn’t invent this technique, I can’t ask for royalties once you perfect it. I will, however, expect a finder’s fee.

And if any of you out there know of someone who is already doing this, I would love to take my tongue out of my cheek and hear about it.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s