Solar Energy

Image: Unsplash. “Photo by Andreas Gücklhorn on Unsplash.” Unsplash.com, 14 June 2017, unsplash.com/photos/photo-of-three-solar-panels-7razCd-RUGs. Accessed 21 Nov. 2023.

What is Solar Energy?

Creating solar electricity is the process by which solar panels convert the sun’s radiation into usable electrical current. These panels are made of photovoltaic cells, or the small electronic devices which actually perform this conversion. Different types of solar cells have different efficiencies, or different ratios of power output for a given solar radiation input.

Why Solar?

Solar panels provide a promising solution considering the situational requirements for Puerto Rico. Solar panels are also very weather-resistant, especially if installed properly. This makes them resilient during natural disasters, which are prevalent in Puerto Rico. They can typically withstand winds of up to 140 miles per hour, which is in the range of a category four hurricane1. Panels are also tested for safety in the event of being struck by hail or a falling object and must be deemed non-hazardous given reasonable impact pressure. The type of rack a solar system is mounted onto can also impact its weather resistance; typically, steel racks and mounting brackets are recommended for areas that are at risk for high wind speeds. Having secure steel brackets and weather-rated bolt systems can greatly increase the stability of any system. Solar panels themselves are highly waterproof and are usually developed with every effort to withstand weather events. Even so, it may be beneficial to ask contractors about weather insurance or repair plans in areas where weather conditions and debris are a strong concern.

Power Considerations

The amount of power produced with solar energy is dependent on the solar panel itself. Solar energy is affected by the maximum power rating, which represents the maximum amount of power a device can hold without damaging itself, of a given solar panel and the efficiency of the panel itself.

The amount of power produced with solar energy is also dependent on the geographic characteristics of the area the solar panel is located in. This specifically is related to the average peak solar hours of the geographic location2. A peak sun hour is when the sun’s intensity reaches an average of 1,000 watts of photovoltaic power per square meter3. Specifically, the average peak solar hours are affected by the amount of sunlight that can reach the panels. The factors affecting the amount of sunlight that reaches the panels are quantified in the data table. These considerations include the cloud amount (in %)4 and tree cover of each municipality (in hectares) which both provide obstacles to the sun’s rays, the grade or slope of the city which affects the angle of sunlight contact (greater angle results in less concentration of sunlight), and all-sky insolation clearness index5. This index represents the ratio of the total solar radiation at the Earth’s surface to the insolation6, or exposure to the sun’s rays, available at the top of the atmosphere7.

Batteries for Photovoltaic Systems

As of now, about three percent of Puerto Rico’s electricity is generated from renewable sources. Three-fifths of that portion is generated from solar photovoltaics (PV)8.

Since hurricane Maria (2017) hit Puerto Rico, over 45,000 solar panels have been installed, and most of the recent installations include batteries, the majority of which are lithium-ion9.

Lithium-Ion Batteries

As of now, lithium-ion batteries holds more than 90% of the global battery market, despite not being a very affordable battery typ10.

Lithium-ion batteries have higher gravimetric energy densities (measurement of energy stored per unit mass of a substance) and higher volumetric energy densities compared to most other batteries. Lithium-ion type batteries are also lighter. These batteries also have relatively long average lifespans, capable of lasting a minimum of 3,000 discharge/charge cycles (the life cycle of a battery –the number of times it is discharged and recharged before losing performance).  Lithium-ion batteries are very efficient and would pair well with solar-powered microgrids—systems that rely on a source of energy that varies over time (eg. amount of sunlight in a given day)11.

TechnologySpecific Energy (Wh/kg)Specific Power (W/kg) Efficiency of Energy Storage (%)Service life (yrs) 
Lithium-ion batteries75-250150-31585-955-15
Lead Acid Batteries30-5075-30070-805-15
Sodium Sulfur Batteries150-240150-23080-9015
Nickel Metal Hybrid Batteries70-100200-300705-10
Figure 1- This figure looks at the technical characteristics of five commonly used batteries technologies utilized in microgrid systems. Some of these characteristics include specific power, the power-to-weight ratio that measures the performance of a power source, and  specific energy, energy per unit of mass. In all these metrics, lithium-ion batteries have the most desirable characteristics – relatively high specific energy, high specific power, high efficiency in energy storage, and the potential of many years of service11. 

Case Study

Martin Garcîa Middle School (MGMS), a school in Toa Baja (a municipality on the northern coast of Puerto Rico) collaborated with Blue Planet Energy, an energy storage company, to implement a PV-system with a subtype of lithium-ion batteries: a lithium iron phosphate battery12.

Lithium iron phosphate (LFP) batteries do not rely on rare minerals (such as neodymium and dysprosium which are critical elements used in many modern technologies and are very difficult to extract from the Earth’s crust), and remain stable under extreme climate conditions –such as Puerto Rico’s typical hot climate– thus LFP batteries can maintain a long lifecycle with little to no maintenance requirements13. 

With such a battery in place, MGMS was able to act as the community’s shelter for electricity during extreme weather periods. With clean energy backed up by a battery with a total capacity of 112 kWh, MGMS had kitchens available for use year-round to serve food for lower-income families. Students at the school were no longer missing out on class time due to the frequent outages in the region, which average around 30 outages per year12.

References
  1. “Can Solar Panels Withstand Hail and Hurricanes?” EnergySage, 8 June 2017, www.energysage.com/solar/solar-panels-hail-hurricanes/. Accessed 29 Nov. 2023. 
  2.  “How to Calculate Solar Panel Output? (+ Kwh Calculator).” The Green Watt, 21 Feb. 2023, http://thegreenwatt.com/how-to-calculate-solar-panel-output/. Accessed 28 Nov. 2023.
  3.  Kielar, Hanna. “Guide to Peak Sun Hours.” GreenLancer, GreenLancer, 29 Mar. 2023, www.greenlancer.com/post/peak-sun-hours. Accessed 28 Nov. 2023.
  4.  “2022 Deforestation Statistics for Puerto Rico.” Deforestation Statistics for Puerto Rico, Mongabay, https://rainforests.mongabay.com/deforestation/archive/Puerto_Rico.htm. Accessed 28 Nov. 2023.
  5.  “Power.” Prediction of Worldwide Energy Resource (POWER) | Data Access Viewer Enhanced, NASA, https://power.larc.nasa.gov/beta/data-access-viewer/. Accessed 28 Nov. 2023.
  6.  “Insolation.” Insolation – an Overview | ScienceDirect Topics, https://www.sciencedirect.com/topics/earth-and-planetary-sciences/insolation. Accessed 28 Nov. 2023. 
  7.  “Center for Satellite Applications and Research – NOAA / NESDIS / Star.” NOAA / NESDIS / STAR Website, www.star.nesdis.noaa.gov/smcd/emb/radiation/solar_resource_definitions.php. Accessed 28 Nov. 2023. 
  8.  “Puerto Rico Profile.” Eia.gov, 2022, www.eia.gov/state/print.php?sid=RQ#:~:text=For%20fiscal%20year%202022%20(July%202021%E2%80%94June%202022)%20about,and%20landfill%20gas%2Dfueled%20facilities. Accessed 28 Nov. 2023.
  9. “Microgrids in Puerto Rico Keep Rural Communities Connected | Article | EESI.” Eesi.org, 2023, www.eesi.org/articles/view/microgrids-in-puerto-rico-keep-rural-communities-connected. Accessed 21 Nov. 2023.
  10. “Fact Sheet | Energy Storage (2019) | White Papers | EESI.” Eesi.org, 2019, www.eesi.org/papers/view/energy-storage-2019#:~:text=Lithium%2Dion%20batteries%20are%20by,energy%20density%20and%20are%20lightweight. Accessed 21 Nov. 2023.
  11.  Zarate-Perez, Eliseo, et al. “Battery Energy Storage Performance in Microgrids: A Scientific Mapping Perspective.” Energy Reports, vol. 8, 1 Nov. 2022, pp. 259–268, www.sciencedirect.com/science/article/pii/S2352484722012598#b35, https://doi.org/10.1016/j.egyr.2022.06.116. Accessed 28 Nov. 2023.
  12.  “Blue Planet Energy Creates Resilience Hubs at Puerto Rican Schools.” SolRenew, solrenew.com/blue-planet-energy-battery-storage/. Accessed 21 Nov. 2023. 
  13.  Critical Minerals – Topics – IEA. “Critical Minerals – Topics – IEA.” IEA, 2023, www.iea.org/topics/critical-minerals. Accessed 21 Nov. 2023.