Solar photovoltaic panels of a floating test array on a reservoir in Singapore (Source: The Straits Times)
Singapore recently announced plans to test the feasibility of using floating solar photovoltaic farm on water as a means to increase the capture of renewable energy for its electricity grid (The Straits Times, http://www.straitstimes.com/singapore/worlds-largest-floating-solar-photovoltaic-cell-test-bed-launched-in-singapore; Today, http://www.channelnewsasia.com/news/singapore/tengeh-reservoir-to-host-world-s-largest-solar-panel-testbed/3232878.html). In its testing phase, the programme seeks to evaluate the efficacy of different solar photovoltaic solutions for efficiency in capturing solar energy when placed as a farm floating on water in a drinking water reservoir.
While the programme marks an attempt in creative use of limited space in the land scarce island to increase provision of renewable energy into the overall energy mix, placement of solar photovoltaic panels as an array in a drinking water reservoir raises serious concerns on possible pollution of the water source from human activities at maintaining the panels as well as leaching of pollutants such as polymer additives and heavy metals from paints on the solar array into the water.
Although drinking water treatment plants should be able to remove the pollutants introduced by the floating solar photovoltaics, cost of treating the raw water would inevitably increase with no guarantee that process stability of treatment plant would not be affected. Additionally, as the amount of pollutants leaching from the solar photovoltaic panels varies, efficiency at removing pollutants during the drinking water treatment process would also fluctuate; thereby, adding risk to the safety of the potable water produced. Deploying the floating solar panel array near the coastal sea may be an alternative. However, the additional cost needed to engineer structures capable of withstanding waves and wind need to be considered.
Having a large floating solar photovoltaic array for harnessing energy from sunlight is one example of a centralized approach to feeding in renewable energy into the electricity grid. However, the alternative approach of distributed generation and local consumption may be more appealing to a high population density city with many high rise housing apartment blocks such as Singapore.
Specifically, small solar photovoltaics array could be installed on the rooftops of many public housing blocks in Singapore with a storage battery for modulating the flow of electricity generated to the end users in the same housing block. Thus, locally generated electricity is consumed at the same locale; thereby, reducing energy loss due to conversion and transmissions inefficiency (such as the case of feeding in electricity from a centralised production facility to the national power grid), as well as allowing electricity generated in the day to be available for peak load in the night. Hence, distributed generation, while more expensive compared to centralized generation of solar energy in terms of capital cost and difficulty of installation (i.e., batteries and weight considerations for rooftops), offers more flexibility in feeding in renewable energy into the grid. Any shortfall in capacity from the distributed generation within the block can be easily augmented with grid power that also connects through the batteries. In essence, the concept is similar to using a smartphone on battery power: once the batteries start to run low, the smartphone can be charged while continuing to be used.
Current grid level energy storage solutions should be able to provide for the energy needs of a single housing apartment block, while continuous innovation in enhancing safety and power density should enable batteries to serve as the central modulator for connecting renewable power to the conventional electricity grid and help modulate fluctuations in current and voltage. Hence, in a land constrained city, distributed generation of solar energy may be the more viable path forward for increasing the proportion of renewable energy in the city’s energy mix given the difficulty of feeding in renewable energy (without a storage mechanism to solve the intermittency problem) into a centralized power grid.