RegGuheert
Well-known member
Utility-scale solar or rooftop?SageBrush said:
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ABG: U.S. carbon emissions spike in 2018 after years of falling
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^^ Utility. After all, we *were* talking about land use requirements.
Rooftops are not included in land use area.
Starting from (as shown earlier) annual consumption
2.5 PWh for electric,
2.0 PWh for transport
We need 4.5 PWh to replace current fossils for those purposes
If half is rooftop then 2.25 PWh will be land use by large scale utility solar* that enjoys a 25% CF = ~ 2.5 kWh annual production per STC watt.
==> 0.9 TW
*That presumes all the electricity replacement is solar. This is obviously (and practically) a quite pessimistic starting point since wind is a major contributor with close to 50% higher CF. Moreover, a large fraction of the wind will be off-shore if sanity prevails. And just for completeness' sake, I'll mention that close to 20% of oil is spent in processing. Between large scale on-shore wind and PV we can look forward to an average utility CF of 30 - 35%. That works out to a mid-range of about 3 kWh annualy per rated watt.
Recalculated:
2.5 PWh for electric
1.6 PWh for transport
4.1 PWh combined.
Half rooftop, so 2.05 PWh utility
20% off-shore wind so 1.6 PWh on-shore
==> 0.55 TW utility on-shore.
Congrats; you are off by a factor of 15x.
Rooftops are not included in land use area.
Starting from (as shown earlier) annual consumption
2.5 PWh for electric,
2.0 PWh for transport
We need 4.5 PWh to replace current fossils for those purposes
If half is rooftop then 2.25 PWh will be land use by large scale utility solar* that enjoys a 25% CF = ~ 2.5 kWh annual production per STC watt.
==> 0.9 TW
*That presumes all the electricity replacement is solar. This is obviously (and practically) a quite pessimistic starting point since wind is a major contributor with close to 50% higher CF. Moreover, a large fraction of the wind will be off-shore if sanity prevails. And just for completeness' sake, I'll mention that close to 20% of oil is spent in processing. Between large scale on-shore wind and PV we can look forward to an average utility CF of 30 - 35%. That works out to a mid-range of about 3 kWh annualy per rated watt.
Recalculated:
2.5 PWh for electric
1.6 PWh for transport
4.1 PWh combined.
Half rooftop, so 2.05 PWh utility
20% off-shore wind so 1.6 PWh on-shore
==> 0.55 TW utility on-shore.
Congrats; you are off by a factor of 15x.
iPlug
Well-known member
We researched going with a ground source heat pump before we instead replaced our old AC unit and gas furnace in the spring of 2018.
We are on 1/3 acre and in a 2,550 sq ft house. Like most new and existing homes, we could only do vertical wells which are the priciest. It would have cost at least $20k more to do that instead of going with the most efficient air sourced heat pump. These are costs that one could never recoup from saving on electricity costs.
Could see the cost of the heat pump equipment decreasing a decent amount if manufactured at a larger scale, but not sure the install/drilling costs could be cut enough.
We are on 1/3 acre and in a 2,550 sq ft house. Like most new and existing homes, we could only do vertical wells which are the priciest. It would have cost at least $20k more to do that instead of going with the most efficient air sourced heat pump. These are costs that one could never recoup from saving on electricity costs.
Could see the cost of the heat pump equipment decreasing a decent amount if manufactured at a larger scale, but not sure the install/drilling costs could be cut enough.
We don't have gas lines (and my housemate is terrified of gas anyway) so for us the backup fuel is home heating oil. I hate that stuff. This gives me more of an incentive to spend more, even though I can't hope to do more than break even in the long term at current prices. With such a high switchover temperature for air source (25F, right?) we'd still be using fuel oil at least a third to half the time in Winter. That doesn't appeal to me at all.
GRA
Well-known member
Rooftop PV (and solar water heating) are great, and achieve the highest power densities for any VRE, but it's nowhere near enough to run our economy. Smil includes all of that in his calcs, and the total roof space, never mind the realistically usable roof space, is a small fraction of the area needed.LeftieBiker said:
GRA
Well-known member
As I've urged people to do before, I suggest you and others read the book for yourself so we're all working from the same set of numbers, as Smil cites all his sources, shows where they agree or differ, and shows all his calcs including what assumptions he's making (and he's often erring on the side of assuming considerable improvements in the tech), as well as efficiency and conservation. Again, it'sSageBrush said:
https://www.amazon.com/Energy-Transitions-Global-National-Perspectives/dp/144085324X
I'd also recommend his
https://www.amazon.com/Power-Density-Understanding-Energy-Sources/dp/0262529734
although much of the information in that is repeated in "Energy Transitions". For those who don't have access to a good inter-library loan program and/or who don't want to buy the book, another good and more accessible source for the numbers, although now getting a bit outdated (2009), is David Mackay's "Sustainable Energy: Without the Hot Air", available online here: https://www.withouthotair.com/
Household use is a small fraction of the energy used to keep our society going. BTW, Smil shows the actual capacity factors and efficiency of specific utility-scale PV plants in service in various countries (often very recent installations, as the book was published in 2016).
Your numbers are much too high currently, although they may be accurate in the future in a few places. For example, the typical utility-scale PV is about 10% efficient, because they use cheaper Cd-Te or similar modules rather than crystalline silicon, let alone multi-junction silicon; land is cheaper than modules for them. Smil assumes efficiency improvements to 15 or 20% for his calcs, i.e. that prices for more efficient module types will come down. And PV has the highest power density of all RE. As to capacity factor, the only place utility PV achieves 25% is in the Arizona desert and a few similar sites around the world, with most coming in around 15-20% IIRR, and more than a few in the 10% range (northern areas with lots of clouds, like Germany). Tracking might boost the 25% sites to 30%, at higher cost of course.
So again, rather than trying to do the calcs all over again, why not let someone else do it for all of us and then we can argue over that.
Let's put a number on that, using an updated analysisGRA said:
https://www.nrel.gov/docs/fy16osti/65298.pdf
1.5 TWh a year
And by the way, the authors baseline assumptions were 16% panel efficiency and 14% losses to the inverter. A 2019 recalculation would increase the result by close to 50% and "we ain't done yet."
RegGuheert
Well-known member
Nonsense. The electricity needs to be replaced both *when* and *where* it is being consumed. You CANNOT replace 4.5 PWh of dispatchable generation with 4.5 PWh of renewable generation which is not dispatchable. You CANNOT use optimistic capacity factors to represent how much electricity is available.SageBrush said:
Somebody sold ridiculous numbers like you are bandying about to the German government and they are now experimenting on their citizens. The results are very clear: Germany is not cutting emissions, but they have among the highest electricity costs in the world. Why? Because wind power is NOT dispatchable. You have to wonder what a country running on 100% renewable energy is supposed to do during the 5% of the time when the wind generators are producing about 5% of their nameplate capacity:
GRA
Well-known member
So, you're saying that because the numbers don't agree with your pre-existing conclusions, then they must be wrong.SageBrush said:
RegGuheert
Well-known member
Solar water heating is actually not so great in cold weather like they have in wintertime in upstate New York. The efficiency drops dramatically and the reliability is quite poor (everywhere). After quite a bit of research, we determined that a heat-pump water heater and a few more net-metered PV modules was a much better and cheaper solution for our application.GRA said:
GRA
Well-known member
Uh huh, using trackers in the best areas of the U.S. Of course, that doesn't change the fact that there's all the existing PV at lower levels of CF, which will be around for decades to come. Now, to expand they have to build the transmission lines to move the power where it will be used.SageBrush said:
Well, if your attitude is that any numbers which disagree with your existing conclusions can't be right, then there really isn't anything to talk about. I'm at least willing to read new info and change my conclusions when it's justified.
RegGuheert
Well-known member
That is my conclusion because I have actually looked at the problem.SageBrush said:
Don't forget fairy dust.SageBrush said:
RegGuheert
Well-known member
Thanks! Using Amazon's "Look Inside" feature, I like what I have read so far. I think this bit of text from the introduction is pertinent here:GRA said:
...and this...Vaclav Smil in Energy Transitions said:
Vaclav Smil in Energy Transitions said:
The power companies are not going away.
Before I bought my leaf I may have been able to afford to go off grid.
With an EV and plug in hybrid, I don't think I can afford it. Mainly the battery.
If those utility solar panels are running an average of around 26% of name plate then the vast majority of them are fixed, or are on broken trackers.
The IEA says that the US has 60 billion watts of PV installed as of 3rd Q of 2018.
2018 started with 55 billion wattts, so average that to 57 billion watts for all of 2018?
That 57ish billion watts made 1.2% of all the power generated in the US.
Just work forwards or backwards as need from those numbers, assuming the added panels are installed in similar conditions and setups as existing capacity.
Before I bought my leaf I may have been able to afford to go off grid.
With an EV and plug in hybrid, I don't think I can afford it. Mainly the battery.
If those utility solar panels are running an average of around 26% of name plate then the vast majority of them are fixed, or are on broken trackers.
The IEA says that the US has 60 billion watts of PV installed as of 3rd Q of 2018.
2018 started with 55 billion wattts, so average that to 57 billion watts for all of 2018?
That 57ish billion watts made 1.2% of all the power generated in the US.
Just work forwards or backwards as need from those numbers, assuming the added panels are installed in similar conditions and setups as existing capacity.