The Irreversible Momentum of Clean Energy?

by Emil Morhardt

Barack Obama has been busy during his last days in office writing well-documented policy articles for major publications. Barely a week before turning over the Presidential reigns to Donald Trump he has commented in some detail in Science about how, in his view, the clean energy horse has left the barn and is unlikely to be stopped even by it’s most fervent detractors (Obama, 2017). He cites four reasons for believing this. The first is that as the US economy has grown, emissions have fallen; since 2008, the amount of energy consumed per dollar of GDP has fallen by 11%, the amount of CO2 emitted per unit of energy has fallen by 8%, and the CO2 emitted per dollar of GDP has fallen by 18%. Furthermore, worldwide the amount of energy-related CO2 emissions in 2016 were essentially the same as 2014, despite economic growth. He also points out that carbon pollution is increasingly expensive. Given the rhetoric of the incoming administration, though, this reasoning alone doesn’t appear to assure continuing in the same direction. Continue reading

Micro-Hydroelectricity in Building Water-Supply Pipes

by Emil Morhardt

Seems like it’s getting to the point that no possible source of power should go unharvested. This paper envisions the water tanks at the top of apartment complexes in Taiwan as mini-pumped storage projects: by installing miniature turbines in the water supply pipes feeding the building from these tanks, electricity can be generated whenever the occupants use any water. The pipes are 4–6 inches in diameter, and a single turbine can generate about 3 Watts under the expected water flows. The experimental turbine blades were printed on a 3-D printer until the engineers got the result they wanted; a set of three airfoil blades that didn’t alter the flow rate of the water. (I’m not quite sure how this could be…if the blades extract energy it seems to me that the only place it could have come from is by diminishing the flow rate. Perhaps someone could explain this in a comment.) In any event, extracting this amount of energy apparently didn’t interfere with the functioning of the water supply system. The authors figure that they could get enough electricity out of a building’s water supply lines to run a few light fixtures. They didn’t explore it much, but the drains are another obvious source of potential energy. This all seems good.

Chang, C.-Y., Huang, S.-R., Ma, Y.-H., Hsu, Y.-S., Liu, Y.-H., 2014. The Feasibility of Applying Micro-hydroelectric Power Technology in Building Water Supply Pipes.


Evaluating Taiwan’s Solar Energy Potential

Taiwan is an island country off the coast of mainland China that uses fossil fuels to supply 90% of its energy needs.  Taiwan has no domestic fuel production and demand for energy is expected to increase by 37.4% between 2005 and 2025.  As such, it is important for the country to find alternative sources of energy.  Solar power is one option that has become increasingly attractive with the rapid improvement in that field of technology.  Two types of solar technology are mainly discussed in Yue and Huang’s (2011) paper: photovoltaics and solar water heating.  The researchers study the potential of these technologies in Taiwan, taking into consideration factors such as the area available for developing solar technologies, local laws and regulations, and the cost of implementing these technologies.  The study concludes that only 0.02% of Taiwan’s solar energy potential was realized in 2009.  Adopting PV and solar thermal technologies have the potential to reduce carbon emissions by 20.9 and 2.1 million tons each year, respectively.  However, due to high population density and tall buildings, the amount of area that can be covered with solar energy harnessing technology is small compared to the number of households it must support.  As such, solar technologies will have an important, but limited effect on Taiwan’s energy sources.—Alan Hu

CD Yue, GR, Huang. 2011. An evaluation of domestic solar energy potential in Taiwan incorporating land use analysis. Energy Policy 39, 7988–8002.

            Yue and Huang at the University of Kang Ning use a mathematical expression to calculate the annual heat output of solar water heaters by multiplying the total collector area, the annual solar radiation, and average heat efficiency of the solar collector system.  The average electricity output from PV systems can be modeled with another equation that multiplies the total photovoltaic module areas, the annual solar radiation, the module efficiency, and the aggregative coefficient.
            The researchers use the city of Tainan as a case study to apply the models described above.  Yue and Huang consider Tainan’s city laws concerning protruding structures on rooftops and geologic information on the region to estimate the energy potential.  The study determines that solar water heaters can provide 369.1 GWh per year and 628.5 GWh per year through PV systems.  Analysis of buildings depending on height allowed researchers to determine that PV systems and solar water heaters can respectively provide 22% and 44% of energy demand for electricity and hot water for a 12 story building.  In contrast, PV systems and solar water heaters can provide 109% and 217%, respecitvely, of energy demand for electricity and hot water for a 4 story building.
            Yue and Huang apply the same analysis to Taiwan as a whole to determine the potential of solar energy.  PV systems are determined to be able to provide 16.3% of electricity demand whereas solar water heating systems can account for 127.5% of energy demand from heating water.  In 2009, PV systems only provided 0.02% of electricity and solar water heating systems only provided 11.6% of hot water.  As such, both technologies have plenty of room to grow.
            An economic analysis is provided to determine the economic feasibility of the technologies.  Solar water heaters have a lifetime of 20 years and PV systems have an operating lifetime of 25 years.  Using market information and a discounted cash flow, Huang and Yue determined that solar water heaters would recoup their cost in 4 years while the costs of a PV system would not ever be recouped under the current tax regime.
            Widespread adoption of solar energy technologies could have a large impact on Taiwan’s energy policy.  For example, the country would be less prone to natural disasters that disrupt energy distribution infrastructure such as the 1999 Chi-chi earthquake which halted the supply of solar energy from south Taiwan to north Taiwan.  Also, peak load energy consumption occurs over summer in Taiwan due to intense use of air conditioning, which is increasing.  This summer load peak corresponds nicely with the increase in solar energy output over summer due to increased solar irradiance. 
            The study concludes that current exploitation of solar energy potential in Taiwan is far below the maximum potential.  Energy policy needs to be modified to make PV systems economically feasible, as currently, the benefits of the systems do not recoup their costs, but energy autonomy based purely on solar energy is improbable due to high population density and the prevalence of high-rise buildings.  Nevertheless, adoption of solar energies could reduce up to 9% of the country’s carbon emissions.  Yue and Huang recommend further study using land use analysis and believe that despite the many limitations, solar energy can have a sizeable impact on the energy landscape of Taiwan.