As shown in the graph and table below, most renewable electricity is generated by hydroelectric power. Solar energy lies in third place behind wind.
Electricity generated from renewable sources. From Our world in data (2018). The ‘Others’ category includes biofuels (e.g. burning wood, animal and agricultural wastes), geothermal energy and wave/tidal power)
Despite only being in third place the growth in solar electricity has been spectacular over the last 20 years and, in addition to having an almost unlimited potential, it has a number of other advantages over other types of renewable energy, which I’ll talk about in this post.
Growth in electricity generation by renewables from 1996 to 2016
Domestic electricity meters measure consumption in kilowatt hours. One terawatt hour (TWh) is equal to one billion kilowatt hours.
Environmental impact of different types of renewables
The environmental impact of large hydroelectric installations such as the Hoover Dam is enormous. After construction, large areas become flooded – sometimes destroying biologically rich and productive land. Damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs usually involves displacing people and wildlife. Over the last 50 years, tens of millions of people have been forced to leave their homes, which have disappeared under large reservoirs.
The Hoover Dam constructed between 1931 and 1936 can generate up to 2 gigawatts (2 billion watts) of electric power
One particular risk of hydroelectric power is flooding. Over the past decades there have been many disasters where dams have failed, and people have lost their lives in the ensuing floods. The worst event occurred in 1975 in China where, according to Human Rights Watch, between 86,000 and 230,000 died as a result of a catastrophic dam failure which the Chinese government kept quiet about.
Large wind farms can look ugly and, because they are normally situated in rural locations, are perceived by many as spoiling the beauty of the natural environment. People living close to wind farms often claim that they are noisy. The noise level 300 metres away from a wind turbine is around 43 decibels, roughly the same as that in a kitchen from a typical domestic fridge.
Large wind farm in Oregon – Image from Wikimedia Commons
Opponents of wind farms often point to the increase in bird fatalities. However, this is often overstated and many other man-made activities cause a much greater number of bird deaths. For example, in the USA in 2013, wind turbines were estimated to be responsible for 100,000 to 440,000 bird deaths whereas cats were responsible for between 365 million and 1 billion and up to 80 million birds were killed by cars.
Even through the total number of bird fatalities are relatively low. Some studies have shown that wind farms affect birds of prey disproportionately. This may be because certain types of bird like vultures have blind spots in their visual field which mean they cannot see objects directly in front of them (such as wind turbines) when flying.
However, the environmental damage due to solar power is relatively limited. Although large solar farms need to cover significant amount of land, the impact can be miminised by building them in dry desert areas, which have relatively little vegetation. Smaller scale installations can be created by covering the roofs of existing buildings with solar panels, which has virtually no environmental impact.
The Topaz solar farm built in the California desert. The farm covers a total area of 19 km2 (not all of which is covered with solar panels) and generates around 1.25 TWh of electricity per annum.
Interestingly, even geothermal energy has a significant environmental impact. Fluids drawn from deep underground carry a mixture of gases, notably carbon dioxide, hydrogen sulfide (which nowadays is spelt with an ‘f’ rather than a ‘ph’ even in the UK) methane and ammonia. If released into the atmosphere these pollutants contribute to global warming and acid rain.
Availability of energy
With the sole exception of the polar regions in the winter, every location on the Earth gets some sunlight. For example, in the cloudy north west of Scotland the solar irradiance averaged out over a year is 72 Watts per square metre, about one fifth of its value in the cloudless desert areas near the equator.
In contrast, because hydroelectricity is generated by the kinetic energy of rapidly moving water, it requires both large volumes of moving water and also a height gradient so that the water moves rapidly. A country with a large flat terrain would not be able to generate much hydroelectric power.
Wind farms need to be built in places where the wind is strong and reliable. In general, a wind speed of at least 25 km/h averaged out over the year is needed to make wind farms economic. This means that wind farms are located in coastal areas, at the tops of rounded hills, open plains and gaps in mountains and increasingly (particularly in the UK) offshore
Small scale generation
A key advantage of solar power is its ability to generate electricity on pretty much any scale. A single solar panel has exactly the same efficiency as a large array of a million panels. A panel 1 metre square will generate up to 250 watts of electricity, if connected to a rechargeable battery it can provide a cheap and reliable source of electricity. This is particularly useful in the world’s poorest countries which are mostly situated at sunnier latitudes and have a more modest demand for electricity compared to richer countries. Once the initial cost of installation has been paid the running costs of a solar array are very low.
In contrast, small wind turbines are not as efficient as larger turbines and so need to be situated in an area of above average wind in order to generate reasonable amounts of power. They also require a very smooth airflow: the smaller turbines are very susceptible to turbulence – so if you live near trees, or in a built-up area, a wind turbine is unlikely to be efficient.
Small scale hydroelectric plants which generate less than 10 kw are known as pico hydro systems and although they are relatively cheap to build, need a constant supply of water running downhill and have moving parts which need to be serviced and maintained.
Providing electricity to off grid communities
A recent BBC radio programme made the point that for people living without electricity, the day ends just after sunset. Light at night needs to supplied by candles or by kerosene lamps. Candles are dim and don’t last. Kerosene is expensive and gives off toxic fumes. The programme claimed that kerosene lanterns and cooking stoves cause an estimated two million deaths every year, but did not provide any evidence for this. (see note below). There is also a fire risk. Homes made of wood or other natural materials are highly flammable, at constant risk from candle flames and kerosene spills.
Solar panels, connected to rechargeable batteries, change almost every aspect of this rural domestic existence. electricity on tap at home for lighting and cooking means that children, and adults are not only healthier, because they’re not exposed to toxic fumes but can study at night, improving their education and therefore their futures. It also enables them to easily charge mobile phone batteries and so become part of the global community.
In my next post I’ll talk about the costs of solar energy and how it is becoming cheaper and cheaper over time.
- Hazards of cooking with kerosene
According to Lam et al (2013), combined studies that evaluated kerosene cooking provided some limited evidence that the fumes may impair lung function, promote asthma, and increase infectious illness and cataract risks. However, the paper goes on to say that studies are few, study designs and quality are varied, and results are inconsistent, limiting any conclusions that can be drawn.
There are two different ways of generating electricity from sunlight.
- One way is to concentrate the Sun’s energy using mirrors onto a small area and use the heat generated to produce steam to turn a turbine which generates electricity. This is known as Concentrated Solar Power (CSP)
- The other way is use arrays of photovoltaic cells (more commonly known as solar panels) to generate electricity directly from sunlight. Around 98% of solar electricity is generated this way and throughout this post when I refer to solar energy or solar electricity I mean electricity generated this way
Our world in data (2018) Global renewable energy consumption over the long-run, Available at: https://ourworldindata.org/renewable-energy (Accessed: 15 April 2019).
Science Direct (2014) The UK solar energy resource and the impact of climate change, Available at: https://www.sciencedirect.com/science/article/pii/S0960148114002857(Accessed: 15 April 2019).
Lam N. L., Smith K. R., Gauthier A, Bates N M (2013) Kerosene: a review of household uses and their hazards in low and middle income countries, Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3664014/ (Accessed: 15 April 2019).