Developing countries face a multitude of challenges related to sustainable development. Many of them are run by dysfunctional central governments unable to provide their citizens with reliable access to basic services such as electricity and clean water. These difficult conditions typically drive citizens into multi-dimensional poverty and place businesses at a competitive disadvantage. The recent advancements in renewable energy technologies such as hybrid renewable energy systems (HRES) offer hope for innovative decentralized solutions that can tackle energy shortages at acceptable costs while maximizing the economic efficiency of such systems.
Off-grid HRES have emerged as a sustainable and eco-friendly solution to meet the energy needs of remote and isolated locations that are not connected to the conventional power grid.
These autonomous systems harness sunlight to generate electricity, providing a reliable and independent source of power for various applications such as rural electrification, telecommunications, agriculture, and off-grid homes and cabins.
Furthermore, off-grid solar PV systems can also be integrated with other renewable energy sources, such as small wind turbines or micro-hydro systems, to create a hybrid system. This approach enhances the overall energy generation capacity and reduces the dependence solely on solar power, ensuring a more stable and reliable power supply.
Today, most solar panels provide an energy efficiency rating between 11 and 15 percent, which is the percentage of solar energy that is being converted into useable electricity, which leaves us with the question: What happens with the remaining harnessed solar energy?
In a HRES, excess electricity or surplus power can be defined as the unused part of produced energy by the power generation components. This can happen in any energy system that supplies a specific demand. When the battery is fully charged or the generator’s minimum output exceeds the load (case showed on the graph), renewable energy resources might generate excess electricity that cannot be directed to either load demand or the batteries. Consequently, this part of electricity must be either dumped or curtailed.
The amount of produced excess power is an important factor for the voltage and frequency stability of the hybrid energy system and must be null to ensure that the system is stably operating and supplying electricity to consumers with high reliability. This parameter also affects the economic viability of the hybrid energy system. By introducing energy cost as the proportion of the total cost of the energy system to the useful power, the lower excess electricity in each specific hybrid configuration results in higher useful electricity (higher energy efficiency) and lower energy cost. In off-grid HRESs, unusable electricity will go to waste. In the power wasting process, the excess electricity is diverted to an unproductive dump load (typically a resistor bank). Using an unproductive dump load essentially wastes the excess HRES output and can be equivalent to curtailment.
Surplus electricity is not a problem in some parts of the world, such as Europe, where most regions have access to the synchronous electrical grid. But efforts to on-site consumption of electricity due to energy losses on long transmission lines, as well as to cover the mismatch between power generation and demand at severe peaks, are still an interesting issue to solve even in these countries.
However in developing countries, where most of the installed HRES are off-grid, such as in Lebanon, which had a solar PV systems peak in the last three years, the dumped energy challenges are still non tackled.
Focusing on the case of Lebanon, a country that faces a complete collapse of public services following a unique financial and economic crisis, many citizens, communities and businesses turned into installing off-grid photovoltaic (PV) electricity systems to cover their electricity needs. It is estimated that around one Gigawatt (GW) of solar rooftop PV systems have been installed over the course of the last three years. However, due to the intermittent and weather-dependent nature of the electric output generated from PV systems, and despite the usage of storage technologies in the form of batteries, off-grid systems are generating a high share of excess electricity production that goes into waste: At any point in time when the PV output exceeds the instantaneous load and the batteries are fully charged, the produced electricity goes to waste. Previous publications has shown that the share of wasted electricity from the total production can easily exceed 30% reaching 70% in PV installations designed for water pumping.
The presence of excess electricity makes up a remarkable limitation to the wider implementation of renewable capacity in off-grid hybrid systems. Surplus power induce reductions in energy efficiency, power supply reliability, total system stability, and affordability of renewable based systems. High surplus electricity can lead to energy waste, and decreasing it may impose additional costs on the HRES. Yet, previous studies have given less interest to enhancing this parameter, where the cause behind that is the main goal of prioritizing reducing energy costs and producing cleaner energy with renewable sources.
Therefore, setting strategies that aim for managing excess electricity is becoming a critical aspect of off-grid solar PV systems. There are several approaches to handling surplus energy, each with its own benefits and challenges. One common strategy is to incorporate energy storage systems such as batteries to store the excess electricity during periods of high solar production. These batteries can then be tapped into during times of low solar irradiation, like during nighttime or cloudy days, ensuring a continuous power supply to the loads.
Another approach to utilizing excess electricity is through load management and demand-side optimization. By implementing smart systems and controls, the surplus energy can be diverted to power energy-intensive tasks or appliances when available. For instance, excess electricity can be used to charge electric vehicles, run water pumps, or store hot water in thermal storage systems, effectively maximizing the use of renewable energy resources.
However, despite the potential benefits of excess electricity generation in off-grid solar PV systems, challenges exist in its management. Seasonal variations, unpredictable weather patterns, and fluctuating energy demands can complicate the task of efficiently utilizing the surplus energy. It requires careful planning, advanced monitoring, and responsive energy management systems to strike the right balance between energy production and consumption.
In conclusion, off-grid solar PV systems have proven to be a promising solution for remote areas and locations with limited access to traditional power grids. The ability of these systems to generate excess electricity provides an opportunity to improve energy self-sufficiency and resilience. With proper integration of energy storage, load management, and hybridization with other renewable sources, the excess electricity can be effectively harnessed, contributing to a cleaner, greener, and more sustainable energy future.