Engr 308 CPH 3 MW CO2 comparison

This page is the compilation of a rapid research project in partnership between Engr308 Technology and the Environment (taught by Lonny Grafman) and the Cal Poly Humboldt (CPH) Facilities Management during Fall 2022. The client lead on this project is Andrea Alstone, the Energy Manager of CPH Facilities Management.

The course objective of this project is to analyze the embedded CO_2e in various types of photovoltaics compared to potential CO_2e savings from current gridmix at Cal Poly Humboldt (CPH). This question is prompted by CPH's 2022 Request for Proposals for a 3MW microgrid on campus. Another student objective was to create compelling and related CO_2e comparisons for consumers.

Research[edit | edit source]

The following research compares calculates the Embedded CO_2e of various panels types based upon a recent (2021) study, the CO_2e intensity of the Cal Poly Humboldt current energy grid, the energy production potential of the 3MW array (based upon To Catch the Sun methods), and the potential CO_2e offsets of a 3MW microgrid. This culminates in comparing the potential CO_2e offsets from the proposed microgrid against the various panel types to calculate the CO_2e buyback time in months.

This research is free, open source, and adaptable at https://docs.google.com/spreadsheets/d/1WH9XovvbbvYCipAKgsEgWIDC_OD5-B5rI2btIQIv8uc/edit?usp=sharing.

Embedded CO_2e of the panels[edit | edit source]

To determine the embedded CO2e in different panel types, we relied heavily on "A comparative life cycle assessment of silicon PV modules: Impact of module design, manufacturing location and inventory"^[1] “This [2021] study closes this research gap by comparing the environmental impacts of sc-Si glass-backsheet [G-BS] and glass-glass [GG] modules produced in China, Germany and the European Union (EU), using current inventory data.”

Scaling the findings of that study with the proposed 3MW system at CPH, we found that the embedded CO_2e in the EU G-G panel was 1,389 tons, EU G-BS panel was 1,587 tons, Germany G-G panel was 1,720 tons, Germany G-BS panel was 1,918 tons, China G-G panel was 2,480 tons, and China G-BS panel was 2,679 tons as shown in Table 1.

Table 1. Embedded CO_2e for each panel type/origin and total for the proposed 3MW array

Panel type and origin	G-G EU	G-BS EU	G-G Germany	G-BS Germany	G-G China	G-BS China	units
Embedded CO2e per peak kW	420	480	520	580	750	810	kg CO2e/kWp
Embedded CO2e in proposed array	1,389	1,587	1,720	1,918	2,480	2,679	ton CO2e

The highest embedded CO_2e was in the China G-BS panel with 2,679 tons of embedded CO_2e for the 3MW array. The lowest embedded CO_2e was in the EU G-G panel with 1,3u9 tons of embedded CO_2e for the 3MW array. The system boundary for the embedded embedded CO_2e includes production, transportation of materials, and end of life, but does not include the balance of system, installation, nor operation. Therefore these embedded CO_2e are sufficient for comparing between systems (which will have similar balance of systems, installations, and operations).

Gridmix CO2e[edit | edit source]

To determine the CO_2e of CPH's current grid we used the weighted average of our current gridmix (data sourced from https://reports.aashe.org/institutions/humboldt-state-university-ca/report/2020-05-07/OP/energy/OP-6/) with the average CO_2e intensity for each fuel type (most data sourced from https://unece.org/sed/documents/2021/10/reports/life-cycle-assessment-electricity-generation-options). We found that our current grid has a CO_2e intensity of 0.343 ton CO_2e/MWh as shown in Table 2.

Table 2. CSU Power Content (gridmix) and CO2e intensities

CSU POWER CONTENT
from SENA Power Label	2018	CO2e intensity
ENERGY	POWER MIX	per fuel type
RESOURCES	(Actual)	(g CO2e/kWh)
Eligible Renewable			Source (citation)
-- Biomass & waste	3.70%	0	EIA Biomas
-- Geothermal	3.70%	2
-- Eligible hydroelectric	0.10%	13	UNECE LCA 2021
-- Solar	11.20%	28	UNECE LCA 2021
-- Wind	10.30%	21	UNECE LCA 2021
Coal	0%	1095	UNECE LCA 2021
Large Hydroelectric	16%	147	UNECE LCA 2021
Natural Gas	55%	513	UNECE LCA 2021
Nuclear	0%	6.4	UNECE LCA 2021
TOTAL	100%	311.1	g CO2e/kWh
	Total in tons per MWh	0.343	ton CO2e/MWh

Energy production and potential avoided CO_2e[edit | edit source]

To determine the potential offset CO_2e from the grid, we determined the average monthly energy production of the 3MW grid and applied the CO_2e intensity of our current grid. Monthly insolation data is from NREL, a conservative 90% was chosen for the balance of system (BOS) efficiency, and average shading of 2% was applied based upon meetings with the client. Table 3 shows the monthly values of energy production and CO2e avoided in tons. The total yearly production was estimated to be over 4,000 MWh and the total yearly CO_2e avoided was over 1400 tons.

Table 3. Monthly energy production and potential offset from the proposed 3MW microgrid at Cal Poly Humboldt

Month	Insolation (hr/day)	Month Length (days/month)	Energy (MWh)	Monthly CO2e avoided (ton CO2e/month)
January	2.893	31	237.3	81.4
February	3.309	28	245.2	84.1
March	3.876	31	317.9	109.0
April	4.664	30	370.2	126.9
May	5.248	31	430.5	147.6
June	6.084	30	482.9	165.6
July	5.212	31	427.5	146.6
August	4.672	31	383.2	131.4
September	5.14	30	408.0	139.9
October	4.249	31	348.5	119.5
November	3.185	30	252.8	86.7
December	2.664	31	218.5	74.9
		Total	4122.7	1413.6

CO_2e Buyback Time[edit | edit source]

These data were combined to determine how long it would take to buy back the CO2e embedded in various photovoltaic types compared to the current CPH grid. Figure 1 displays these data combined in one image.

This study of Glass-Back sheet (G-BS) and Glass-Glass (G-G) modules from EU, China, and Germany compared two metrics: carbon dioxide emissions and time. It was concluded that the embedded CO_2e in the EU G-G panel was 1,389 tons and the buyback period was 11.5 months. The embedded CO_2e in the EU G-BS panel was 1,587 tons and the buyback period was 14 months. The embedded CO_2e in the Germany G-G panel was 1,720 tons and the buyback period was 15.5 months. The embedded CO_2e in the Germany G-BS panel was 1,918 tons and the buyback period was 16.5 months. The embedded CO_2ein the China G-G panel was 2,480 tons and the buyback period was 20.5 months. The embedded CO_2e in the China G-BS panel was 2,679 tons and the buyback period was 22 months.

Table 4. CO_2e buyback time for each panel type/origin

Panel type and origin	G-G EU	G-BS EU	G-G Germany	G-BS Germany	G-G China	G-BS China	units
Embedded CO2e in proposed array	1,389	1,587	1,720	1,918	2,480	2,679	ton CO2e
CO2e buyback time compared to grid	11.5	14	15.5	16.5	20.5	22	months

The calculations and assumptions used to calculate these results can be seen in further detail in this spreadsheet - https://docs.google.com/spreadsheets/d/1WH9XovvbbvYCipAKgsEgWIDC_OD5-B5rI2btIQIv8uc/edit?usp=sharing.

This spreadsheet is site-specific but may be used by others interested in performing similar analysis. The user inputs are highlighted in yellow with calculations in white. Similar grid matrix data and panel power information is needed to apply the spreadsheet to different campuses.

Presentation[edit | edit source]

The following slides are from our final presentation to the client: https://docs.google.com/presentation/d/11gYHjBrmQFkhDH26e5PBzdSP02SDJQbHkzOqKovidGo/edit?usp=sharing

Caveats[edit | edit source]

This was a rapid analysis from a general education course. We suggest you use make a copy of the spreadsheet^[2] and evaluate it yourself. Below are some aspects to keep in mind:

• We relied on one study for the embedded CO2e in panel types.
• We did not include most embedded CO2e components that are site specific and the same (e.g., getting the panels to Humboldt, site installation, etc.).
• We did not include the Time-Of-Use variability CO2e in our gridmix, which will be quite impactful when using batteries to load shift.
• This did not look at opportunity costs, future value of money, or anything besides a simple carbon dioxide buyback time.

Compelling Comparisons[edit | edit source]

Multiple compelling CO2 comparisons were created by students to appeal to consumers. The following are some examples from students in Engr308 Technology and the Environment during Fall 2022.