Energy Past, Present and Future: Solar Energy

By Bri Conn

The Sun’s radiation is one of Earth’s most ancient sources of energy, but a lot has changed over the past 4.5 billion years. We have found ways to exploit not only the Sun’s heat, but also the electromagnetic properties of its radiation to create electricity. The invention of solar panels has been a technological marvel, and will likely have profound impacts on the future of energy generation, but solar has not always been an effective choice for electricity generation. Join us as we explore the history of solar energy usage from a heat source in ancient Rome, to emerging technology concepts that are out of this world!

Human use of solar energy is documented as far back as 700 BCE, as historic records show that Greeks, Romans, and later Chinese civilizations used glass materials to concentrate sunlight and spark fires [1]. Romans also found another new application of solar energy: indoor heating of bathhouses. Evidence shows that they purposely constructed sunrooms with large windows facing to the south, to allow for maximum amounts of sunlight to enter and warm the water of the baths [2].

Roman Bathhouses with large windows were one of the earliest forms of using solar energy. These windows allowed maximal sunlight to enter and heat the water. Original image can be found here.

Fast forward a few millennia, and modern scientists were able to discover new ways to make use of the Sun’s naturally abundant energy. The foundation of solar cells was built upon a discovery in 1870 by French physicist Edmond Becquerel who first documented the photovoltaic effect. This is a physical and chemical phenomenon which allows some materials to generate voltage and electric current when exposed to light [1]. In the following years, other scientists discovered that semiconductor materials such as selenium exhibited this property, and began experimentation. The first solar cell was produced by Charles Fritts in 1883, made from selenium wafers that created electricity when exposed to sunlight. This solar cell had an efficiency of less than 1% [1].

Nowadays, most solar cells are made out of silicon, a semiconductor with more ideal properties for maximizing efficiency. The first silicon solar cells were developed many decades later, by Bell Labs scientists in 1954. These early cells had an efficiency of just 4%, a large step ahead of simple lab experiments, but still most of the sunlight’s energy was lost [3] [4]. Typically, many of these solar cells are connected together to create a larger device, a solar panel, that can produce a more useful amount of power.

One of Bell Labs’ first solar panels being tested in 1954. Original image can be found here.

Early uses of solar panels were quite limited, with solar energy finding a niche in powering space electronics. Even low-efficiency solar cells are practical energy generation sources for satellites, and solar arrays. Such systems have been used on NASA and Russian spacecraft since the late 1950s [3]. Otherwise, there was minimal interest in further developing solar power - why mess around with costly solar technologies when oil was cheap and plentiful?

Working Principle of a Photovoltaic Cell: particles of sunlight (photons) strike electrons in the semiconductor material, forcing them to generate an electric current that can be used to power devices. Original image can be found here.

This would probably be a good time to explain how solar panels work. A solar cell is made out of a semiconductor material, using the photovoltaic effect [6]. What happens inside the material is that a photon (particle of light) with a lot of energy hits the semiconductor and is absorbed whenever the photon ‘strikes’ an electron in the material. This interaction transfers energy from the photon to the electron, which gives the electron enough energy to start moving through the semiconductor. This movement causes a stream of electrons to flow through the semiconductor and its attached circuitry, generating electricity [6]. Of course, solar power generation also has its drawbacks. Solar panels can only produce electricity when it is sunny outside, and are most efficient when they are oriented to capture a maximum amount of sunlight. If you decide to install solar panels - don’t expect them to be working at night time, or when your tree’s shadow blocks them from the sun!

First residential solar installation and net metering project, completed by Steven Strong and Solar Design Associates in 1979. Fun fact: the solar panels were not properly mounted, and were removed after 1 year. Original image can be found here.

The story of how solar panels got their start as a residential power technology is quite interesting. Steven Strong founded Solar Design Associates, a solar energy consulting firm, after leaving the pipeline industry amidst the first US oil embargo. Strong was convinced that there were better ways to power society than fossil fuels [3] [7]. One of the first projects Strong worked on was a solar array atop a low income apartment complex in Massachusetts. The 1979 installation consisted of the more conventional solar hot water heating technology (a network of dark water pipes on the roof, which allow water to heat naturally from solar radiation as it travels through the piping) as well as some solar photovoltaics [7] [8]. This marked the first residential use of photovoltaics - they had been used on satellites and spacecraft for decades, but had not been taken seriously as a power generation option on Earth until then [3] [7].

Modern solar hot water heating system installed on a roof. Original image can be found here.

Strong decided to wire the solar panels in connection with the utility electric meter, meaning that any excess power the panels generated would feed back into the power grid, and reduce the net electricity used by the housing complex. This practice has become known as net-metering, meaning that if the apartment drew 2000 kWh of power from the grid but the solar panels produced 100 kWh of power that was fed back into the grid, they would be billed for the 1900 kWh of net power used, rather than the gross power of 2000 kWh [3] [9]. Net-metering sounds like it makes a lot of sense - you pay for what you use minus what you give back. However, it turned out to be a controversial billing practice when residential solar panel use began to boom across the United States. 

Net metering allows customers to draw power from the grid and also provide power to the grid, while being billed for their ‘net’ consumption of power over a specified time period. Original image can be found here.

Utility companies have structured their business practice around charging customers enough to cover their costs, which includes the power generation aspect, as well as installing and maintaining vast networks of poles, wires, and cable infrastructure. When a homeowner with solar panels starts to feed electricity back into the grid, they can end up making a lot of money - they don’t have any overhead costs to think of. So if and when a homeowner is able to generate their own solar power and reduce their utility bill, it means that they are no longer paying ‘their share’ of the costs for the poles, wires, and electricity meter that connect their home to the grid. This phenomenon results in all other customers having to then shoulder the fixed costs of their solar-owning neighbour, leading to higher rates for non-solar power producing individuals [3] [9]. 

A large factor of the controversy is about who owns these solar panels and takes advantage of net metering. In the 1980s and 1990s, solar panels were much more expensive than they are today, with a home installation costing $30/W, which meant that the only people who could afford solar installations were wealthy people who owned their own homes and had discretionary income to spend. The wealth redistribution that arose from net metering benefitted wealthy homeowners while disproportionately raising the utility bills of renters and lower income individuals, who were now footing more than their share of the bill for the utility’s infrastructure [3] [9]. 

Since the 1990s, solar panel research and development efforts have led to massive increases in the efficiency and cost reduction of solar panels, which has led to a dramatic increase in solar power generation worldwide. Efficiency of modern panels has grown to 20% for residential products, which means that a single panel can now produce up to 300-400 W of power - dramatically better than early panels outputting a handful of Watts to a satellite. Cost has also been a huge factor, with the cost of both solar panels and home installation dropping exponentially to an average of $2/W in 2018 (compared to the Bell Labs cell which came out to $1785 USD/W, that’s quite the bargain!) [11] [12]. This dramatic reduction in cost is partly due to optimized installation techniques including specialized brackets that reduce the length of a typical residential install from 2 days to 4 hours, as well as improvements in the process of mass-producing panels [3] [13]. It has been estimated that residential rooftop solar panels are a viable primary energy source for 10-20 million homes in the US [13] (this is bounded by homeownership, weather conditions, orientation, lack of mature trees, etc.) which, if implemented, could make a dent in electricity-related carbon emissions.

From its humble beginnings as a way to produce fire and heat bathhouses, to today’s high tech photovoltaic innovations and controversial policies, solar energy has been an important part of human civilization, and will likely only continue to increase in relevance. New applications of solar powered electricity generation are abundant, and include exciting projects such as space-based solar power (giant solar arrays in orbit to collect and transfer solar electricity to Earth!), increased large scale solar farms to help combat climate change, increasing the resiliency and energy independence of microgrids, and new material science discoveries to optimize the efficiency of solar cells [3] [13]. With all of solar’s exciting developments on the horizon, you could say we’re at the dawn of a sunny era of solar energy!

References

[1] L. Richardson, “What is the history of solar energy and when were solar panels invented?,” EnergySage, May 2018. [Online]. Available: https://news.energysage.com/the-history-and-invention-of-solar-panel-technology/. [Accessed: January 24, 2021]. 

[2] A. Denzer, “The Roman Baths and Solar Heating,” Solar House History, January 2014. [Online]. Available: http://solarhousehistory.com/blog/2014/1/19/the-roman-baths-and-solar-heating. [Accessed: January 24, 2021]. 

[3] S. Evans-Brown et al., “Episode 28: The Accidental History of Solar Power,” Outside In: A show about the natural world and how we use it, January 5, 2017. New Hampshire: New Hampshire Public Radio. [Podcast]. Available: http://outsideinradio.org/shows/ep28

[4] D. Massey, “The Solar Battery (Photovoltaics),” Bell System Memorial. [Online]. Available: https://www.beatriceco.com/bti/porticus/bell/belllabs_photovoltaics.html [Accessed: January 24, 2021]. 

[5] US Environmental Protection Agency, “Solar Energy,” A Student’s Guide to Global Climate Change, May 2017. [Online]. Available: https://archive.epa.gov/climatechange/kids/solutions/technologies/solar.html [Accessed: January 24, 2021]. 

[6] C. Deziel, “The Effect of Wavelength on Photovoltaic Cells,” Sciencing, December 2020. [Online]. Available: https://sciencing.com/effect-wavelength-photovoltaic-cells-6957.html [Accessed: January 24, 2021]. 

[7] Solar Design Associates, “History of SDA”, Solar Design Associates. [Online]. Available: https://solardesign.com/history-of-sda/ [Accessed: January 24, 2021]. 

[8] International Water Association, “Solar water heater market to reach US$4 billion by 2025,” International Water Association: The Source Magazine, July 2018. [Online]. Available: https://www.thesourcemagazine.org/solar-water-heater-market-to-reach-us4-billion-by-2025/. [Accessed: January 24, 2021]. 

[9] GW Solar Institute, “What is “net metering” and why are people arguing about it?,” George Washington University. [Online]. Available: https://solar.gwu.edu/what-%E2%80%9Cnet-metering%E2%80%9D-and-why-are-people-arguing-about-it. [Accessed: January 24, 2021]. 

[10] Newfoundland Labrador Hydro “Net Metering,” Newfoundland Labrador Hydro. [Online]. Available: https://nlhydro.com/customer-service/meter-reading/net-metering/ [Accessed: January 24, 2021]. 

[11] S. Matasci, “How solar panel cost and efficiency have changed over time,” EnergySage, January 2021. [Online]. Available: https://news.energysage.com/solar-panel-efficiency-cost-over-time/. [Accessed: January 24, 2021].

[12] A. Han, “Efficiency Of Solar PV, Then, Now And Future”, Solar Photovoltaic: Lafayette University, April 2014. [Online]. Available: https://sites.lafayette.edu/egrs352-sp14-pv/technology/history-of-pv-technology/. [Accessed: January 24, 2021]. 

[13] J. Goldstein, “Episode 616: How Solar got Cheap,” NPR Planet Money, August 14, 2019. United States: National Public Radio. [Podcast]. Available: https://www.npr.org/2019/08/14/751234092/episode-616-how-solar-got-cheap