“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

## Saturday, August 10, 2019

### Solar energy is GREAT but...

 Image credit: 4Patriots, LLC
As is pretty clear from previous posts (and despite my current vehicle, airplane, and travel itinerary), I'm a very big fan of renewable energy. And thus, also a fan of solar power. But sometimes solar isn't appropriate for a particular application. To the left is a collage from 4Patriots, LLC, let's see if this device is in the "inappropriate" category.

This is a charger for such electronics as cell phones, tablets, etc. Is this an appropriate application? Lithium ion battery in the device is specified on the advertising web site as storing 8,000 mAh (milliamp hours) or 8 amp hours. The solar array is specified as delivering 1.5 watts.

Let's first see if the 1.5 watts is reasonable. To do so, we'll need to estimate the size. Using the measuring tool in Tracker Video Analysis and Modeling Tool, I estimate that there is an area of about 0.0068 m^2 of solar cells. This is actually generous as I've used to whole area of the face of the charger with the cells. And, during bright sunlight at my location if I hold the device facing the sun I can count on about 350 w/m^2 over the course of a day of actual insolation. Let's give the solar cells an estimated efficiency of 18% (again, generous) and figure the charging can take place at the rate of 350*.18*0.0068=0.42 watts. Well, if we use a full 1000 watts/m^2, we get 1.22 watts. I'd say that the 1.5 specification is an exaggeration at best.

Well, let's go with the 1.2 as a compromise between the 1.5 watts claimed and the 0.42 watts by my best estimate. And let's think about an iPhone 8, standard model. Such a phone has a battery capacity of 1.821 amp hours at 3.7 volts. This means it will deliver 1.821 amps at 3.7 volts for 1 hour, or 3,600 seconds. Since volts * amps is watts, we have 6.7377 watts. Since joules of energy are the same as watt seconds, we can use 3,600 seconds * 6.7377 watts to determine that the iPhone 8 battery stores 24,256 joules. Charging at 1.2 watts, or 1.22 joules/second, we find that it will take 24,256 joules/1.2 watts = 20,213 seconds or 5.6 hours to go from complete discharge to full charge.

Of course, if you're in the middle of nowhere with no other way to charge your phone and you're completely discharged, you won't need to wait for 100% charge to use your phone. Below is a graph of time needed as a percentage of charge from complete discharge. You can click on it to enlarge. Keep in mind that this is specific to the iPhone 8, other phones with different (and typically larger) batteries will be different. The new Samsung Galaxy Note 10+, for example, will carry a 4,300 mAh battery pack, well over twice as large as that in the iPhone 8, and the Apple iPhone XS Max sports a 3,174 mAh battery pack. And, of course, charging is a non-linear process so don't use this as a "to the minute" guide. It's more of a very best case scenario.

Still, this is actually a lot better than I'd anticipated when I started. It would take about an hour to go from complete discharge to 20%, certainly enough to make a few calls or send some texts. Of course it assumes perfect efficiency in the charger circuit but the efficiency is likely to be fairly high. Even if we use the low end estimate for the area of the solar array, the device will still give usable energy in a not too extreme amount of time, though if we use the more conservative estimates for insolation and charging on a state of the art, top of the line phone, we'd be looking at something more like 7 hours to go from complete discharge to 20%. Nevertheless, unlike the two previously published posts I linked above, this seems to be a good use of a small solar panel.

## Tuesday, August 06, 2019

### Energy Vault Revisited

 Image credit: Energy Vault
Two posts back I discussed Energy Vault, a "Swiss-U.S." company whose concept for energy storage is based on the use of tower cranes to  stack concrete blocks. The blocks would be raised with electric motors to store gravitational potential energy when energy is either plentiful or cheap  and lowered, turning generators, when energy is expensive (arbitrage) or unavailable from renewable sources.

I subscribe to a YouTube channel from a British chemist, Dr. Philip Mason, who calls himself
 Image credit: drunken-peasants-podcast.wikia.com
"Thunderf00t" and, when he's not criticizing modern feminism or proselytizing for atheism, he "debunks" various concepts. Among several others have been Hyperloop (the linked video is one of several he's done on this topic), Solar Roadways (again, one of many videos he's done on this topic and a topic I've covered), and the Water Seer. His videos tend to be long, repetitive, and repetitive (see what I did there?) but, typically, are convincing.

Most recently, Thunderf00t targeted Energy Vault, concluding that it's a scam meant only to collect investor money. I'll summarize his points as I understand them and then state my reaction. Per Thunderf00t:
• No working installation yet exists, the pilot project (video here) shown in various places does not come close to demonstrating the viability of such a system and, other than that pilot, there's nothing but CGI animation.
• Such a scheme will not be effective in windy areas due to inability to control the precise placement of the concrete blocks and the inherent problems with cranes in wind.
• The cost would be excessive in comparison with alternative gravitational storage systems (specifically, pumped hydro storage).
• The system could not have the lifespan claimed due to its environmental exposure, intrinsic wear, fatigue, etc., especially in areas where sun and wind for renewable energy generation are plentiful, such as deserts.
• The configuration envisioned by Energy Vault is not optimized to maximize the storage of potential energy because of the way the blocks are stacked.
It takes Thunderf00t 24 minutes to make these points. He repeatedly contrasts the Energy Vault system with pumped hydro storage systems in terms of both cost and of capacity. He glibly glosses over the fact that the geographic/geological situation that is optimal for such a system severely limits feasible locations. And, it should be noted, I agree completely that pumped hydro storage is a superb option where geography and environmental considerations permit. Unfortunately, there are not a lot of such locations.

Another point misunderstood by Thunderf00t is the of the claimed ability of the Energy Vault system to quickly "ramp up," in 2.9 seconds to full power according to Energy Vault. Thunderf00t posited that utilities aren't in need of such a quick ramp up, but this isn't correct. Utilities utilize a variety of systems to provide reliable power, from frequency response, to spinning reserve, to peaking, to base load in order of increasing ramp up times from less than a second through several hours. Thunder00t seems to be thinking only of peaking or base load. For application to supplying energy from solar or wind plants when "the sun doesn't shine and the wind doesn't blow" this analysis would be correct but this is undoubtedly not the only potential application envisioned by Energy Vault.

In any case, addressing the points above:
• It's clearly true that no working demonstration at scale yet exists. However, the technology of lifting concrete with tower cranes is quite standard. I could go out to one of my company's projects tomorrow and watch such a thing happen. As mentioned in my earlier post (and as Thunderf00t mentioned repeatedly), the IP claimed by Energy vault isn't tower cranes or concrete, it's the software that controls the crane movements so as to maximize storage and production and precisely place the blocks even during windy conditions. The fact is that every innovation starts out as an idea with no working model at scale. Time (and investment) will tell if the concept is viable.
• Thunderf00t only addresses the proposed use of the system for storage of wind generated electricity, presumably because that's what's shown in the renderings on Energy Vault's web site. Of course, the system would be equally suitable (if it works at all) for solar sites. But, as mentioned above, Energy Vault claims that their control software will enable the system to operate in windy conditions. Many tower cranes have a maximum wind speed limit of 20 meters/second or 44.7 m.p.h. Thunderf00t has pulled up a web site that appears to refer to a specific crane model that limits wind speed to 10 meters/second (he converts this to 30 m.p.h. though it's actually about 22 m.p.h.) but, even in the page he shows, it's stated that "typical values vary from 9 to 20 m/s." I'll concede that I'd need to see the control system operating in a 20 m/s wind though.
• In his cost estimate, Thunderf00t states that "a tonne (here I assume he means a metric ton, 1000 kg. or 2,205 pounds) of concrete costs about $100." I don't know what it costs in Great Britain or the Czech Republic (where I believe he's working) but in the U.S. a pretty basic concrete mix costs around$100/yd^3 and that cubic yard weighs about 4,050 pounds or 1.84 tonnes. So Thunderf00t's tonne of concrete costs about $54. Later in the video, he does come down to a number near this. As I mentioned, he compares the cost to pumped hydro, but the locations shown in the renderings have no suitable geography. Given the need for storage, if pumped hydro were suitable everywhere, we'd see more of it. Thunderf00t mentions that the vast majority of energy storage IS pumped hydro but that's because there's so little storage! • With respect to duration, I concede that I also see serious problems. Energy Vault mentions a 30 year lifetime but does not mention maintenance! As Thunderf00t states, tower cranes consist of a massive collection of moving parts, many of which will be under significant stress and subject to cyclic loading. It's a recipe for all manner of mechanical failure. • As to optimizing stacking, it's very clear that it would be better to have all the blocks be able to go from ground to top and back to ground as Thunderf00t helpfully demonstrates with children's blocks on a table but the logistics of the system won't allow that. The question isn't whether some other configuration would be better but rather what is the best configuration that can be achieved. When all is said and done (and, as the wag said, when all is said and done, much more is said than done), there are many reasons to question the feasibility of such a system and, before I'd invest my money in the venture, I'd need more than is shown on the web site. But Cemex Ventures has invested in Energy Vault. Cemex Ventures is the venture arm of Cemex, a large producer of cement, concrete and other building materials. The size of the investment is not stated. I've covered a number of non-electrochemical (that is, other than batteries) storage companies and modalities in this blog, some seemingly credible and some seemingly ridiculous. This one seems to be somewhere in the middle. I'm not as certain as Thunderf00t and his commenters that it's a scam but I'm not ready to sink my nest egg into it! Update: Energy Vault has received a$110 million investment from the SoftBank Vision Fund. Of course, the Vision Fund has been in the news a LOT lately and not in a good way, having had to bail out We Work and losing money from the IPO of Uber.