UC Davis Microgrid

Jared Balavender, DTU

Katarina Knezovic, DTU

Adrian Unkeles, UCSC

Yingying Zheng, UCD

Problem Statement

Client: UC Davis

Goal: Carbon Neutral by 2025

Main limitation

No net metering

Considerations:

Demand reductions and energy efficiency

Increased PV generation

Storage via Batteries

Demand response

Rescheduling the cooling system

Base scenario Consumption profile for 2012

Total demand: 229,443 MWh

Baseload: 165,564 MWh

72% of annual energy consumption goes to base load

0 1000 2000 3000 4000 5000 6000 7000 800015

20

25

30

35

40

45

Pow

er (M

W)

Time of year (h)

16.3 MW of PV 32,725 MWh

Equals 14.3% of current total demand

19.8% of baseload

Total UCD consumption in 2012

Assumptions

PV efficiency degradation of 0.25% per year

No possibility of net metering

2014 data equivalent to 2012 data

Campus cooling system electricity usage remains constant

Cooling system consists of 8 absorption chillers with total rated power of 12.6 MW at an average efficiency rate of 0.7 kW/ton

Electricity price is 0.07$/kWh and constant throughout project period

Baseload remains same percentage of demand

Refined Scope: Optimize use of doubling PV generation

Analyzed Cases

UC Davis doubles PV nominal capacity to 32.6 MW and

Two scenarios for the campus consumption profile:

1) no decrease – base scenario

Consumption the same throughout 10 years

2) 5% decrease in annual demand through project period

Total demand in 2025: 144,607 MWh

Baseload in 2025: 104,305 MWh

Excess PV generation

Estimated production for 32.6 MW photovoltaic array

Exceeds the demand for 1733 hours in the base scenario

0 1000 2000 3000 4000 5000 6000 7000 80000

5

10

15

20

25

30

Pow

er (M

W)

Time of year (h)

Estimated PV Power Generation

Excess PV generation

Scenario with no consumption decrease

0

200

400

600

800

1000

1200

1400

1 2 3 4 5 6 7 8 9 10

Excess PV generation (MWh/year)

Year Loss of PV generation

1 1.78%

2 1.74%

3 1.69%

4 1.65%

5 1.60%

6 1.56%

7 1.52%

8 1.48%

9 1.44%

10 1.40%

Excess PV generation

Scenario with 5% consumption decrease every year

0

2000

4000

6000

8000

10000

12000

14000

16000

1 2 3 4 5 6 7 8 9 10

Excess PV generation (MWh/year)

Year Loss of PV generation

1 1.78%

2 2.85%

3 4.21%

4 5.84%

5 7.72%

6 9.83%

7 12.12%

8 14.60%

9 17.21%

10 19.87%

Value of lost energy

Year Value of lost generation for Scenario 1 Year Value of lost generation

for Scenario 2

1 $91,362 1 $91,362 2 $88,808 2 $145,708 3 $86,306 3 $214,952 4 $83,834 4 $297,432 5 $81,409 5 $392,334 6 $79,055 6 $498,421 7 $76,763 7 $613,301 8 $74,517 8 $737,064 9 $72,324 9 $866,887 10 $70,173 10 $998,420

TOTAL $804,551 TOTAL $4,855,881

Assuming 0.07$/kWh -> even larger losses if the price increases

Potential technologies for utilizing excess energy

Two different battery technologies

simple cost-analysis conducted

case of no consumption decrease with all excess energy stored in the batteries -> not cost effective

Customer demand response

indirect strategies not cost-effective due to low electricity price

Temporary load shifting

changing the operation schedule of cooling chillers

the most feasible solution

Current cooling system

Rescheduling cooling chillers

Scenario 1

Load shifting is effective for the months of April through October.

Operation of chillers in most inefficient temperature range still leads to net cost benefits because the PV provides all the energy at that time.

Scenario 2

Load shifting is effective throughout the year, with duration and frequency peaking in the summer

12.67 MW peak excess PV in year 10

CO2 emissions

If all the excess energy was used to power the chillers during the day, significant CO2 savings would be made

No consumption change 5% decrease in consumption every year

Year Excess generation used by cooling system (MWh)

GHG Emission (Ton CO2e)

Year Excess generation used by cooling system (MWh)

GHG Emission (Ton CO2e)

1 1,305.17 404.60 1 1,305.17 404.60 2 1,268.69 393.29 2 2,081.55 645.28 3 1,232.95 382.21 3 3,070.74 951.93 4 1,197.63 371.27 4 4,249.02 1,317.20 5 1,162.99 360.53 5 5,604.77 1,737.48 6 1,129.35 350.10 6 7,120.30 2,207.29 7 1,096.62 339.95 7 8,761.45 2,716.05 8 1,064.53 330.00 8 10,529.49 3,264.14 9 1,033.19 320.29 9 12,384.10 3,839.07 10 1,002.47 310.77 10 14,263.14 4,421.57

TOTAL 3,563.01 TOTAL 21,504.61

Conclusion and recommendations Excess energy curtailment

No decrease in consumption: $804,551 lost

5% decrease in consumption: $4,855,881 lost

Batteries and customer demand response are not cost-effective for storing the excess energy

Changing the operation schedule for the chillers

Chillers rated power higher than maximum excess peak in both scenarios

Feasible to operate the chillers even with lower efficiency rates

ZNE goal unattainable unless net-metering restriction is lifted

Future works recommendations

Analyze chillers energy efficiency when shifting the operation from night to day

Reduce the base load through energy efficiency measures

Consider second-hand batteries