Renewable Energy Sources
As mentioned before, energy sources powered by the sun, wind, water and earth’s heat are considered renewable because they are not depleted as we utilize them allowing for a sustainable future. We use fossil fuels and other non-renewable energy sources at a rate in which their reserves cannot be replenished faster than we attain them.
Some renewable energy sources are intermittent. Since the sun doesn’t shine at night and the wind doesn’t blow all day we cannot produce energy 24/7. This means that the capacity installed (kilowatts) must be multiplied by the hours and a capacity factor in order to determine generation (kWh).
Yearly Generation = Installed Capacity (kW) * 8,760 hours/year * Capacity Factor (%)
In the Virgin Islands the capacity factor for solar photovoltaic resources has not yet been measured but is estimated at 16%, based on data from South Florida. The capacity factor for wind in the Virgin Islands ranges between 23-39% for both onshore and offshore installations.
Although capacity factor is a percentage it should not be confused with the efficiency. Efficiency is the actual electricity produced divided by the total primary energy. For PV solar panels efficiency ranges from 15-22% and for wind turbines from 35-45%.
This right bar on this graph shows examples of common renewable energy sources used in the USA. The largest sources are hydroelectric and biomass. However wind, solar and geothermal are continuing to increase as technology continues to improve.
Solar Energy in the VI
In the Virgin Islands we are known for our warm sunny days all year long. Solar PV uses light (photons) to move electrons and create an electrical current.
Fortunately, the cost of solar panels has been exponentially decreasing over the past few years as technology and production continue to improve. In fact, renewable energy sources are comparable if not better than traditional fossil fuels.
So if solar is cheaper than fossil fuels, why aren’t we installing more capacity? The issue is that as we install more intermittent solar it cannot be easily balanced by the local grid. Therefore, a high penetration of solar resources requires energy storage to sustain the community during the night-time hours or cloudy days.
Wind Energy
The equation for the power produced by a wind turbine is a function of the swept area of the blades and the cube of wind speed, which is proportional to the height. This is why current trends in wind turbine design is towards becoming bigger and higher.
The maximum theoretical efficiency is 59% also known as the Betz limit (see graph below). This is because wind turbines slow incoming wind and capture its energy. If the turbine captured all the energy, no wind would pass through the blades causing the turbine to stop moving. Considering current turbines have efficiencies ranging from 35-45% this is quite impressive (remember a car engine only has an efficiency of 13%).
Energy Storage
In a traditional centralized electricity grid system, energy production is being constantly adjusted to exactly match the consumer’s electricity demand, the load. This is because storing electricity has proved quite a challenge. However, with the rise in popularity of intermittent distributed renewable energy generation, energy storage has become an important topic.
While there are a range of potential energy storage technologies, the Virgin Islands has mainly considered batteries such as Lead-acid, Lithium-ion, Nickel metal hydride and flow batteries.
Other possible forms of storage could include small-scale pumped hydro or thermal storage.
The End of Oil?
When people say peak oil what do they mean? Peak oil refers to the moment when oil production is highest and will shortly after begin a sharp decline due to lack of resources. Some say we only have 50 years left until this occurs while others predict that end of oil will never come. Before we address these discrepancies let’s learn some terminology on resources, reserves, production and end of oil.
Resources are the total fossil fuels present in the earth, both known and unknown. This number is in decline because we consume resources at a rate faster than they can be regenerated.
Reserves are the fossil fuels that are currently economically extractable. Over the years this number is actually increasing as technological advances and economic growth allow us to mine fossil fuels from unconventional sources such as shale oil and deep sea beds.
Even through worldwide our consumption of oil is increasing the amount of reserves has actually grown over the past 20 years due to technological advancements. This graphic is from BP Statistical Review of World Energy 2019
The Reserves to Production (R/P) ratio gives an estimate of the years of the resource left if all conditions remain the same as today. Since the total reserves are continuing to increase, even as production increases the R/P ratio is not changing over time, keeping the end of oil forever on the horizon.
Each year BP puts out a Statistical Review on World Energy. In 2019, the R/P ratio for oil was 50 years, but in 2009 it was even less, 42 years. This shows how technological advances are pushing back the “end of oil”.
In terms of combating climate change by reducing emissions of greenhouse gases from fossil fuels we cannot depend on resource depletion or the economic market to fix our problems. We must invest in research and development of more affordable clean and renewable energy and enact policy and systemic change to the energy market as we know it today.
Energy and Climate Change
Anthropogenic climate change (global warming) is caused by the enhanced greenhouse effect due to the emission of gases, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), etc. whose molecules trap heat within the atmosphere.
The majority of these emissions are due to the burning of fossil fuels for electricity generation, heating, industry and transportation. An additional 10% of U.S. emissions are due to livestock, soils, and rice farming from the agriculture sector.
Data from EPA Inventory of Greenhouse Gases