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Off-Grid Cabin in Thompson, PA and Geneva, AL

By Ryan Purnell

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Electric Load and Weather Patterns

Thompson, PA

Geneva, AL

As for the electrical loads for each location, I chose to do a mid-rise apartment in each location so that I would have an accurate residential load profile for both locations. I then scaled down the electrical load to the average daily electrical load for a house in each location, which for Thompson was 29 kWh per day and 40 kWh per day for Geneva. This checks out with the Dmaps for both locations, as it is evident that the increased summer load in Geneva should increase the average daily consumption.

In terms of the weather patterns, Thompson does not perform as well as Geneva, mainly due to increased participation and colder temperatures. Thompson is in the Snowbelt, and sees greater rain and snowfall than the average for the United States, as well as a greater number of days with precipitation and a decreased amount of sunny days, which will definitely reduce the output of any solar installations. Additionally, the average low is much lower than the average for the U.S., which adds heating concerns over the winter, however the average high is considerably less than the U.S. average, meaning that it takes less energy to keep it cool during the Summer.

Geneva experiences an even greater rainfall average than Thompson, however it has less rainy days and considerably more sunny days than the U.S. average as well as no snowfall, all of which are beneficial for PV production. Additionally, the average summer high is greater than the U.S. average, meaning that there will be an increased load to keep it cool over the summer, however the Winter low is also greater than the U.S. average, so there will be less energy needed to keep it warm over the Winter.

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Design Constraints and Goals

Diesel Generator with CHP
Lithium Ion Batteries
Renewable fraction of 50% or higher
CO2 emissions reduced by at least 35% with respect to base case
Resilience- At least 1 day of autonomy
Economics
Sustainability/Emissions

For my design, I chose to use a diesel generator since diesel would be more viable for a remote off-grid location than natural gas. Also, I chose lithium ion batteries over lead acid due to the increased efficiency and lifespan provided by them.

As for my goals, I wanted to provide a renewable energy fraction of greater than 50% as well as a reduction in CO2 emissions by at least 35% with respect to the base case, which sort of go hand in hand. Prioritizing both of these constraints means that a majority of the energy will come from renewable sources, which will greatly reduce fuel consumption and emissions, however it will come with a substantially greater initial cost.

Finally, and perhaps most importantly, I chose to prioritize a compromise between economics and resilience, as increased resilience always comes with an increased cost. Eventually I settled on wanting at least 24 hours of autonomy, allowing me to have a substantial amount of breathing room without skyrocketing the price of the design too much. Essentially, 1 day of autonomy will enable me to weather out cloudy days without relying too heavily on the generator, give ample time to get more fuel if I run out and provide a safety net in case anything goes wrong with the generator overnight or during a cloudy day.

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Base and Final Architectures for Thompson

PV (kW)	Generator (kW)	LI ASM (kWh)	Converter (kW)	NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
0	3	0	0	72481	0.48	5491	1500	0	3872	10138

PV (kW)	Generator (kW)	LI ASM (kWh)	Converter (kW)	NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
9	3	40	3	83320	0.559	2354	52,883	51.2	1164	3061

Chosen architecture is less economical than the base case
IRR is 3.4% and simple payback is 13 years
CO2 emissions reduced by 69.8%
Price of resilience and sustainability is $10,839

Chosen Architecture

Base Architecture

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Thompson Discounted Cash Flow

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Base and Final Architectures for Geneva

PV (kW)	Generator (kW)	LI ASM (kWh)	Converter (kW)	NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
0	4	0	0	96967	0.496	7,316	2000	0	5187	13580

PV (kW)	Generator (kW)	LI ASM (kWh)	Converter (kW)	NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
12	4	56	4	99352	0.508	2319	69,379	72.5	768	2018

Chosen architecture is less economical than the base case
IRR is 5.4% and simple payback is 11 years
CO2 emissions reduced by 85.1%
Price of resilience and sustainability is $2,385

Chosen Architecture

Base Architecture

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Geneva Discounted Cash Flow

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Electricity Generation Breakdown

Thompson Geneva

Generator peaks in the Winter for Thompson due to reduced solar output
Generator peaks in the Summer for Geneva due to increased cooling demand
Generator produces more electricity in Thompson than Geneva due to reduced solar production

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Multi-Year Analysis

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Compare Load Growth of 0% vs 2% For Thompson

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
83320	0.559	2354	52,883	51.2	1164	3061

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
93729	.525	3160	52883	41	1911	5015

2% Load Growth

0% Load Growth

Chosen configuration was able to meet the increasing load
Largely met by the generator
Increased fuel consumption and emissions

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Compare Load Growth of 0% vs 2% For Geneva

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
99352	0.508	2319	69,379	72.5	768	2018

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
111629	0.474	3268	69,379	57.8	1715	4495

2% Load Growth

0% Load Growth

Chosen configuration was able to meet the increasing load
Largely met by the generator
Increased fuel consumption and emissions

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2% Increase in the Price of Electricity from the Utility

Not applicable because I did an off-grid design

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0.5% Decrease on Annual PV Production For Thompson

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
83320	0.559	2354	52,883	51.2	1164	3061

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
84914	0.571	2478	52883	47.5	1283	3372

0.5% Decrease

0% Decrease

Results:

Decreased PV production
Increased costs
Increased fuel consumption
Increased emissions

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0.5% Decrease on Annual PV Production For Geneva

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
99352	0.508	2319	69,379	72.5	768	2018

NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)	Ren. Frac. (%)	Fuel (L/yr)	CO2 (kg/yr)
101271	0.519	2467	69,379	68.2	921	2417

0.5% Decrease

0% Decrease

Results:

Decreased PV production
Increased costs
Increased fuel consumption
Increased emissions

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Sensitivity Analysis

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Nominal Discount Rate

Discount Rate	NPC ($)	COE ($)	Operating Cost ($/yr)
5%	94625	0.46	2381.44
8%	83320	0.56	2354.44
10%	77939	0.63	2315.83
15%	69178	0.83	2185.67

Discount Rate	NPC ($)	COE ($)	Operating Cost ($/yr)
5%	110578	0.41	2350.45
8%	99352	0.51	2318.56
10%	93937	0.58	2269.83
15%	85050	0.76	2102.06

Geneva

Thompson

Used to find real discount rate, which is used to convert from one-time costs to annual costs and accounts for inflation
Higher discount rates were able to greatly reduce the cost of both designs
A 10% discount rate makes the Geneva MG design more economical than the base case, 15% for the Thompson MG
Shows the effectiveness of increased funding and tax credits

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Battery Cost Multiplier (applied to all 3 cost types)

BES Cost Multiplier	NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)
0.5	65845	0.43	1902.44	41251.58
1.0	83320	0.56	2354.44	52883.16
1.5	100795	0.69	2806.43	64514.74
2.0	118270	0.81	3258.43	76146.31

BES Cost Multiplier	NPC ($)	COE ($)	Operating Cost ($/yr)	Initial Capital ($)
0.5	75067	0.38	1675.23	53410.84
1.0	99352	0.51	2318.56	69379.27
1.5	123638	0.64	2961.89	85347.69
2.0	147923	0.77	3605.23	101316.1

Geneva

Thompson

Battery cost did not alter the MG configuration or battery size in any way because only one simulation was ran
More expensive batteries decreases the cost effectiveness of both designs
Cheaper batteries makes MGs that use them more feasible

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Battery Degradation %

Degrade %	NPC ($)	COE ($)	Operating Cost ($/yr)	Fuel (L/yr)
30%	83320	0.56	2354.44	1164
50%	75308	0.50	1734.65	1164
70%	73716	0.49	1611.48	1164

Degrade %	NPC ($)	COE ($)	Operating Cost ($/yr)	Fuel (L/yr)
30%	99352	0.51	2318.56	768.3395
50%	88353	0.45	1467.68	768.3395
70%	86167	0.44	1298.59	768.3395

Geneva

Thompson

Reduces the NPC of the batteries, which is a large portion of the total NPC
Allowing for degradation beyond 30% before replacement considerably reduces the NPC of both designs
Interesting that the fuel consumption does not increase, even though I thought the generator would need to pick up the slack of the degraded batteries

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Diesel Price ($/L)

Diesel Price ($/L)	NPC ($)	COE ($)	Operating Cost ($/yr)	Base Case NPC
1.0	83320	0.56	2354.44	72841
1.5	90846	0.59	2936.61	97506
2.0	98372	0.62	3518.78	122531
2.5	105898	0.65	4100.96	147556

Diesel Price ($/L)	NPC ($)	COE ($)	Operating Cost ($/yr)	Base Case NPC
1.0	110578	0.41	2350.45	96967
1.5	99352	0.51	2318.56	130497
2.0	93937	0.58	2269.83	164027
2.5	85050	0.76	2102.06	197557

Geneva

Thompson

Fossil fuels may not always be the cheapest available fuel, seen in rising gas prices today
Increased fuel costs make the MG designs less cost effective, but increase the costs of the base case even more
Increased fossil fuel costs make microgrids are more economical compared to conventional means

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Results Recap

Thompson

Geneva

The chosen constraints result in feasible MG designs in both locations, but not the most cost effective options
Requiring 1 day of autonomy is the largest contributor to the increased NPC of the chosen constraints

PV (kW)	Generator (kW)	LI ASM (kWh)	Converter (kW)	NPC ($)	Initial Capital ($)	Ren. Frac. (%)	CO2 (kg/yr)
9	3	40	3	83320	52,883	51.2	3061

PV (kW)	Generator (kW)	LI ASM (kWh)	Converter (kW)	NPC ($)	Initial Capital ($)	Ren. Frac. (%)	CO2 (kg/yr)
12	4	56	4	99352	69,379	72.5	2018

Constraints

Diesel Generator with CHP
Lithium Ion Batteries
Renewable fraction of 50% or higher
CO2 emissions reduced by 35% or higher
Resilience- 1 DOA
Economics
Sustainability/Emissions

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Conclusions

Different climates result in different requirements for MG designs
You have to pay for increased resiliency and sustainability in a MG design
Cheapest configuration is not always the best configuration, it depends heavily on the requirements of the system
Factors like battery and solar degradation, as well as potential load growth should be accounted for in MG calculations

Economic feasibility of microgrids improved by:

Better discount rates and/or tax credits
Cheaper battery technology
Allowing for increased battery degradation before replacement
Increased fossil fuel costs