Featured The Dirty Truth About Combustion Engine Vehicles

Wind is actually pretty great on Hawaii because of the trade winds.

 

It's Hawaii, real estate is not cheap.

I figure they have both, but how affordable is it to overbuild them? Is the cost, money and space, better than some hydrogen for longer term energy storage? Battery costs start adding up when building storage for days to weeks. Hydrogen may have a smaller footprint, depending on storage method, and it could be put to use beyond grid storage. Offsetting natural gas use was mentioned, as well as making methanol or other fuels. Which more than likely will end up going into a ship there than some land vehicle.

This probably one of the few cases where hydrogen actually works out.

 

And what's the dirty truth about this thread???

First, it cherry picks it's car models and then it does the same with assumptions. For instance the top BEV is one specific model and year of TESLA. If you average ALL the BEVs it's quite likely to find that the best PHEV is cleaner than the average BEV. The Prius Prime already matches the top BEV for energy per mile, within a single percent.

Like all discussions, you can't really make a statement that BEVs are cleaner than Hybrids simply because both categories are very broad and the points of comparison are different depending on a variety of variables.

Dan

 

First, most of this thread has been discussing solar power and grid storage. Second, the main comparison is EV vs non-plug-in. Third, when it comes to EVs, Tesla has name recognition, and is the biggest seller of EVs in the US and some other markets. Their biggest seller is also one of there most efficient models. It sells more in a month here then many inefficient EVs sell in a year. Tesla not being brought up by someone in these threads wouldn't be normal.

@austingreen made two posts in this thread comparing a Tesla model to a comparable Toyota one. They were in response to the claimed efficiency of hybrids without plugs. His main conclusion, "Of course you can pick less efficient bevs or less efficient hybrids, but the hybrid does reduce ghg significantly versus the non hybrid models, but a phev or bev will reduce it more, especially in the future." These were the only posts in the thread to bring up specific car models.

In post #8, I brought up the UCS's Cleaner Cars Cradle to Grave study. The MPG of equivalent CO2 emissions figure they use in the grid map is based on an average plug in. That is BEV and PHEV that were available for sale at time of compilation, including the electricity guzzling ones. The best EV one uses the Ioniq Electric, Model 3, and Prius Prime.

Again, the main topic isn't which EV is better, but that plug ins are better than cars that don't have a plug. As for the OP video, it was made as a counter to the anti-plug-in argument that EVs aren't clean because electricity generation isn't clean. It makes this point with the, likely correct, assumption that the ones making the argument haven't considered how much energy goes into making gasoline.

 

I just found out a fact that puts "massive storage" into context.

How much storage would have been required to avoid the Texas blackouts last month? Answer: 1,560GWh. That's the entire output of at least 10 fully-built-out giga-factories for a year. Just for Texas. Just for one 4-day event.

I think people generally don't have a clue just how much energy storage we need (and currently use) to handle multi-day events and seasonal energy storage. Take a look at this:



That's normal US natural gas seasonal storage. The amounts between the peaks and the troughs are absolutely enormous. For simplicity, let's call it around 2000 on the chart. That's 2000 BILLION cubic feet. That's over 600,000 GWh. To put that in perspective, the Nevada Gigafactory is probably producing on the order of 25-50GWh of batteries a year. Another way to look at it is this. If all 300 million cars in the US were EVs and all had 100kWh batteries, those cars would store 30,000 GWh - about 5% of the current seasonal storage usage.

 

Grid storage isn't limited to batteries.

It's intended use isn't as emergency back up. In that case, there are other steps to take first. How much power generation would Texas have lost if they taken the recommended winterization steps?

 

None. But as variable generation replaces thermal generation, this issue will change from handling events to handling normal day to day and year to year operations. And batteries are unlikely to ever be able to handle the need. This is the exact reason I think hydrogen is a viable vehicle fuel. I know this isn't intuitive but these issues are completely related. Hydrogen can be stored underground much the way natural gas is now, and in huge quantities. I don't recommend returning the energy to the grid except in rare circumstances (and I have a plan for how to do that too) but rather as an alternative to curtailment caused by overbuilding relative to the capacity of the grid.

 

Batteries aren't the only option for grid storage. The geological formations that work for natural gas and hydrogen storage could also work for compressed air. We may have an excessive amount of sites for pumped water, and there are other methods of using gravity for energy storage. Other e-fuels are an option.

 

Remember, air compression is a very inefficient way of storing energy.

 

So is hydrogen. A simple compressed air energy storage(CAES) system is around as efficient as hydrogen; @ 35%. This is a diabatic system that just lets the heat of compression go to waste, and the air may need reheating to get the most work out of it.

Adiabatic systems that capture the compression heat, and reuse it to reheat the air when generating are 70%, and could co higher. These have a higher upfront cost for that heat storage subsystem. Both ways will have a longer lifespan than a battery.

I didn't see CAES as a major part of grid storage, but it is an alternative method available. The question of where are all these batteries come from is a valid one. My point is that we aren't limited to batteries.

 

CAES is only really viable if you combine it with natural gas.

Hydrogen is much more efficient than CAES because YOU DON'T RETURN THE ENERGY TO THE GRID! You can't use CAES as a vehicle fuel.

 

Hydrogen will not be used for grid storage by and large until electrolyzer/fuel cells efficiencies improve. There may be very specific use cases where energy storage with hydrogen makes sense. It makes more sense to use that hydrogen for anything other than electricity production to store back into the grid... like filling up a vehicle.

Having said that, electrolyzer efficiency has reached 90% in industrial scales, and an Israeli company has invented a different technology to boost that up to 95%. So I wouldn't discount the possibility either.

 

Since the theoretical limit is 84%, I'd like to know how they did their math.

 

When the grid is mostly variable production, how then will hydrogen help electric production match up with demand if it isn't being put back into the grid? Using renewable electric during periods of excess production to make something isn't grid storage, it's a co-product to renewable electric.

As I said, compressed air is just one example of grid storage besides batteries. There are others. So available grid storage solutions aren't limited by our battery production.

 

Where did you get that figure?

90% efficiency: Haldor Topsoe to build large-scale SOEC electrolyzer manufacturing facility to meet customer needs for green hydrogen - Green Car Congress
95% efficiency: Breakthrough technology could produce green hydrogen at $1/kg

 

LHV = 33.3kWh/kg
HHV = 39.4kWh/kg

The best you can do it put in the HHV and get out the LHV: 33.3/39.4 = 84.5%.

They must be ignoring the loss I just mentioned. Some people do that. I consider it dishonest.

 

That's right - it's co-production, but it's *controllable*, which converts variability into controllability.

The best on-grid storage is no on-grid storage. Dispatchable load is better.

 

Can you explain LHV and HHV in the context of hydrogen production? I don't understand. I think it's reasonable to assume most other people also don't know what you were referring to.

 

Lower Heating Value/Higher Heating Value

To convert water into hydrogen, you essentially have to add energy equivalent to converting water to steam (the phase change from liquid to gas) plus obviously breaking the H2-O chemical bonds. When you put the hydrogen through a fuel cell you don't get that energy back (the phase change energy), so that's usually deducted in the efficiency of the electrolyzer.

Another way to look at it is, if you have an electrolyzer with no losses, it will take 39.4kWh to generate a kg of hydrogen. If you then put that hydrogen through a fuel cell with no losses, it'll produce 33.3kWh of electricity and water vapor. When that water vapor condenses it releases that difference as heat, which you can't use to re-create electricity.

 

Electrolysis cannot occur without first vaporizing the water?

That doesn't make sense to me. Efficiency of the fuel cell determines how much energy is wasted. Waste energy at the fuel cell is heat. That heat results in the production of water vapour instead of water. Why should that have anything to do with how efficient the electrolyzer was?

Edit: Hydrogen doesn't go through the phase change. It's the water that does. Did you mean to talk about the energy loss due to phase change of water molecules?