WetEV
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Re: Economics of Renewable Power, simplified.

Fri May 19, 2017 11:04 am

RegGuheert wrote:... and can achieve a 70% round-trip efficiency[/url]. That's the kind of performance we need to achieve to make long-term storage a viable possibility.


I disagree.

Long term storage is more driven by cost than efficiency. The opposite of short term storage.

Let me try out an example to illustrate:

$0.10 primary generation from solar cells. 10% ROI + expenses.
Li-ion batteries, $100 per kWh, 90% round trip efficient.
Flow battery, $1 per kWh, 25% efficient.

Cost for a short term storage: assumed to be once per day.

Battery total cost = energy cost + capital cost = 0.10/0.9 + 100*.1/365 = $0.14/kWh
Flow total cost = energy cost + capital cost = 0.10/0.25 + 1*.1/365 = $0.40/kWh

Cost for long term storage: assumed to be once per year.

Battery total cost = energy cost + capital cost = 0.10/0.9 + 100*.1/1 = $10.11/kWh
Flow total cost = energy cost + capital cost = 0.10/0.25 + 1*.1/1 = $0.50/kWh

To build a system with a minimum cost, some fraction of the storage should be low cost (and perhaps low efficiency) and some should be high efficiency and higher cost. Lowest cost will come with some amount of excess generation, enough short term storage to cover daily to a week or so, and some lower efficiency longer term storage.

This is the point to something like hydrogen fuel cells, which is a type of flow battery. Flow batteries are generally not potentially useful for cars, as the potential low cost technologies have low specific energy densities (kWh/mass).
WetEV
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RegGuheert
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Re: Economics of Renewable Power, simplified.

Fri May 19, 2017 6:02 pm

WetEV wrote:
RegGuheert wrote:... and can achieve a 70% round-trip efficiency[/url]. That's the kind of performance we need to achieve to make long-term storage a viable possibility.
I disagree.

Long term storage is more driven by cost than efficiency. The opposite of short term storage.
Actually, both long-term and short-term storage are driven by cost. (That's why there is virtually no installed storage beyond pumped hydro.) They have different cost drivers, but efficiency is a key driver for both of them.
WetEV wrote:Let me try out an example to illustrate:

$0.10 primary generation from solar cells. 10% ROI + expenses.
Your example fails here. You assumed that the per-kWh cost of generation is the same for every bit of generation which is added. In fact, the per-kWh cost of generation goes up as more is added, since additional generation results in lower-and-lower additional kWh of generation. In the extreme case, once you have enough generation, additional generation has an infinite per-kWh cost since it provides no additional generation. (It may have other value, however, such as redundancy or margin.)

But we CAN readily calculate the relative costs of the low- and high-efficiency long-term storage options since the author of the article I linked provided details of how those two options impact the overall performance of the system. Here are the numbers:

RM = Renewable Methane
RMG = Renewable Mixed Gas

Code: Select all

Component                 No Tier 2      RM       RM Cost      RMG         RMG Cost
-----------------------------------------------------------------------------------
Tier 2 efficiency                        34%                   70%           
Wind                        75 GW       75 GW       $0        72 GW         -$6B
Solar PV                    80 GW       80 GW       $0        75 GW         -$5B
Tier 1 storage             300 GWh     300 GW       $0       200 GWh       -$10B
Tier 1 inverters            60 GW       60 GW       $0        60 GW          $0
Electrolyzers                           40 GW      $20B       30 GW         $15B
Gas turbine generation                  40 GW(Exist)$0
Fuel cells                                                    40 GW        $280B
Tier 2 Storage                      14,000 GWh      $1B   18,000 GWh        $18B
====================================================================================
Total Costs:                                       $21B                    $304B

Cost assumptions:
Wind: $1/W
Solar PV: $2/W
Tier 1 storage: $100/kWh
Electrolyzer: $500/kW
Gas turbine: $3000/kW (But it is already exists!)
SO Fuel cell: $7000/kW
Tier 2 Storage (Natural Gas): Guess: Low since it can be stored in the existing pipelines and storage facilities.
Tier 2 Storage (CO2): Guess: $1/GWh

So this result agrees with your conclusion in that the lower-efficiency solution is cheaper. But the ONLY reason for that is that the natural gas generators already exist as does some of the natural gas storage. I used TODAY'S costs for solid oxide fuel cells. If in 2030, the solid-oxide fuel cells are the same cost or cheaper than natural gas turbines, then the result goes the other way by a long shot for systems that do not already have the gas turbines.

Let's see what the author comes up with regarding the 2030 cost model for these scenarios.
RegGuheert
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RegGuheert
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Re: Economics of Renewable Power, simplified.

Sat Aug 19, 2017 10:33 am

RegGuheert wrote:Let's see what the author comes up with regarding the 2030 cost model for these scenarios.
O.K. Here is the author's follow-up post regarding the overall cost to move Texas to renewables by 2030.

Here is his list of projected per kW costs for equipment:

Image

Here is what I had projected:

RegGuheert wrote:Cost assumptions:
Wind: $1/W
Solar PV: $2/W
Tier 1 storage: $100/kWh
Electrolyzer: $500/kW
Gas turbine: $3000/kW (But it is already exists!)
SO Fuel cell: $7000/kW
Tier 2 Storage (Natural Gas): Guess: Low since it can be stored in the existing pipelines and storage facilities.
Tier 2 Storage (CO2): Guess: $1/GWh
So here is where we differed:

- My wind costs matched his high-end wind costs.
- My PV costs were about 3X his PV costs.
- My battery costs were about 2X his battery costs.
- My electrolyzer costs matched his low-end costs.
- My gas storage costs were about 4X his low-end costs.

Anyway, the author did not price the fuel-cell option. Here is what he came up with for system costs using natural gas generators:

Image

The bottom line is that he projects wholesale costs to be between 6.1 c/kWh and 9.2 c/kWh in by the year 2030. If his numbers are in the ballpark, it seems possible that Texas could pull this off. They certainly have a much better chance than Germany of being able to do this.
RegGuheert
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Reddy
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Re: Economics of Renewable Power, simplified.

Tue Aug 22, 2017 2:23 pm

Certainly TX has more solar, and probably more wind, than Germany. If only they would connect more to the US grid and send the excess to adjacent states.
Reddy
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