Gravity and storage

My firm was contacted a bit over a year ago by a start-up firm called "Genergy, LLC" with what appears to be an innovative technology for utilizing buoyancy to generate electricity. This post is NOT about that concept. Rather, it's a side trip down a road that originated in a post by the founder of the firm and inventor of the patented technology, Mr. Kurt Grossman, in a thread in a Linkedin group he started called "Gravity Energy." The specific thread discusses pumped hydro storage.

Photo Credit: Mitsui & Co., Ltd.

Pumped hydro storage is one of a very few currently viable methods to store energy at so-called "utility scale" or "grid scale." The idea is to use energy (typically generated by intermittent sources such as wind and solar) to pump water from a lower to an upper reservoir and then to re-capture the potential energy imparted by this process by running the water back down to the lower reservoir through a hydroelectric turbine generator (diagram at left - click to enbiggen).


The technology is, in principal, capable of turning an intermittent source into one suitable for base load power. Of course, you might recognize that hydropower from dams utilizes this principle with mother nature providing the pump via the hydrologic cycle.


In the thread, I mentioned that geography places limits on the wide-scale adoption of pumped hydro storage because of the necessity for two very large reservoirs with a large elevation difference in close proximity. This is something that we don't find naturally around every corner and that, to construct, would entail an extraordinary infrastructure expenditure. Of course, given that one of my Company's main Divisions is dedicated to quality assurance and quality control of infrastructure projects, I'm not at all opposed to such an undertaking!


But I want to "bring this storage method home," so to speak. Were I to install a solar array and utilize pumped hydro in my household, what would this entail? Let me assume that I'd like to have the ability to store sufficient energy to provide electricity to my home for three days. Such a need will most likely arise in winter when I won't need air conditioning - hot summer days usually provide plenty of sunshine and the three days' worth of winter storage should also suffice for summer nights when the sun is down.


As it happens, I've calculated my home's average continuous energy use before, and it's an embarrassingly large 2.1 kilowatts. Therefore, I need to provide 2.1*24*3 or 151.2 kilowatt hours of energy in the system's water tank (that my homeowners association will never let me build no matter how the numbers come out). Energy units are energy units, so I can convert these 151.2 kilowatt hours to 5.443*10^8 or 544.3 million joules. My system is likely to run, optimistically, at about 75% efficiency, so I'll need to store 7.258*10^8 joules. As a side note, this is the total thermal energy available from burning about six gallons of gasoline. To actually use this energy and assuming a Home Depot generator runs at 25% efficiency, I'd need to have 24 gallons available. Keep this number in mind!


Now there are two ways to increase the energy stored in a pumped hydro system: increase the quantity; and increase the height to which it's pumped. A cubic meter of water is 1000 kilograms and raising this 1000 kilograms one meter will add 1000*9.8*1 or 9800 joules. Let's say instead that I could raise it 10 meters. Note that this is 33 feet so that the average height of the water in the tank is above the tops of the roofs in my neighborhood. Now I've added 9.8*10^4 joules. This means I need to raise (7.258*10^8)/(9.8*10^4) or 7406 cubic meters of water. This is just shy of two million gallons (1.96 million) so I'll go with the two million gallon tank. This is the part where I suggest recalling the 24 gallons of gasoline.

Photo credit: San Patricio Municipal Water District

As it happens, we have a swimming pool. It's likely on the small side of average at around 19,000 gallons. So the water in about 100 of those will just do the trick! To the left is a photo of such a tank. Perhaps this explains why those who go "off grid" use batteries to store energy captured by their solar arrays and wind turbines and keep fossil fuel powered generators for those times where the batteries don't suffice.


There's much more on the practicalities (or lack thereof) for utilizing pumped hydro storage on a wide scale to store energy from intermittent sources at one of my favorites sites. It's called "Do the Math" and is published by Dr. Tom Murphy, a professor of physics at UC San Diego.

Rentier Debt and the Collapse of Debt-Based Finance | The Energy Collective

A very interesting take on the economic growth/resource constraint/self-poisoning/debt nexus.

Rentier Debt and the Collapse of Debt-Based Finance | The Energy Collective:

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The money value of time

Photo Credit: The Clock Works, Unlimited

Our Company held an event at our San Diego facility last Tuesday, June 5. Quite a few people from our Long Beach headquarters traveled to the event and it's true that alcoholic beverages were served. Thus, we determined that it was in our best interest to hire a so-called "party bus" to transport our people to the event.


My first calculation involved determining how much money we'd save in fuel by avoiding individual drivers (ignoring the possibility of carpooling). It turned out that, with reasonable assumptions, we'd avoid purchasing about $300 worth of gas. The cost of the party bus exceeded this by a factor of three, so it was risk avoidance and a good time at the cost of $600, money well-spent.


On the way down to San Diego, I was talking to one of my two partners in the Company, who suggested that I evaluate my strict 55 m.p.h. self-imposed maximum speed with respect to the value of my time. Of course, I pointed out to Brian that I'd done so on several  occasions. But that was using numbers applicable to my Jeep Grand Cherokee and my Land Rover LR3. Even with those, it was clear that saving fuel by driving 55 m.p.h. was a philosophical rather than an economic decision. I suspect that with my current vehicle, a Lexus CT200h (basically a re-badged and upgraded Prius), the numbers will be worse. Let's see.


Since many of the fuel-saving techniques I used in my previous vehicles are superfluous in the Lexus (it turns the engine off at stop lights, turns it off and uses some of the gravitational potential energy in travelling down hills to charge the battery by using the transmission to turn the electric motor to a generator, etc.) I think I'll get fairly close to my fuel savings over the "typical" driver of my vehicle by simply comparing my fuel economy to the EPA ratings for the vehicle.


Inverting the average rating for the CT200h of 42 m.p.g., the EPA suggests that the typical driver uses (1/42)=0.0238 g.p.m. (gallons per mile). My economy for the duration I've had the car is  50.49 m.p.g., so I use (1/50.49)=0.0198 g.p.m. Thus, for every mile I save 0.00400 gallons, currently worth (at $4.159/gallon) $0.0167.


On the other hand, at 55 m.p.h. it takes me (1/55)=0.0182 hours to travel that mile, whereas at 70 m.p.h. it would take me 0.0143 hours. Thus, it takes me 0.00390 hours longer to drive a mile. Since I'm reluctant to provide numbers on my blog that would enable someone to calculate my salary, I'll determine what salary would equate these numbers. This is simply a matter of dividing $0.0167 by 0.00390, yielding $4.28/hour. Suffice it to say that that severely underestimates my hourly cost.


Now, it's true that there are many inaccuracies in the calculations above. For example, it really should be isolated to highway fuel economy, where the EPA thinks I'll get 40 m.p.g. and I actually get more like 55 m.p.g. Using those numbers, $7.27 would be the wage that represents the break even point. Surprisingly, my wage exceeds this number as well.


The conclusion is, of course, that now more than ever my driving to achieve maximum fuel efficiency derives much more from philosophy (and some would say eccentricity) than economy.

Obscenity: I Know It When I See It – The New Inquiry

Another in a shockingly long series of reasons to be embarrassed to be thought of as a conservative, despite the fact that the incident described herein is the very antithesis of real conservatism. And even by the incredibly low moral standards of the modern Republican Party (of which I used to be a member) this is beneath contempt.


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