Power quality and modern energy for all

Fig. 1 shows the study locations, marked as small circles and squares, with the lines representing the centralized grid. Our interviews with ZECO customers suggested that temporal and spatial voltage differences characterized electricity access on the local distribution system. For instance, “Electricity is variable - it cuts out, then comes back. This can be like four times [in a day].” Others agreed that “electricity goes up and down [without warning]” (Materials and Methods). A refrigerator salesman explained spatial variation, saying that, “if you are far away from the transformer, then the electricity the household gets is less stable than if you were closer to the transformer.”

Voltage monitoring measurements across the island (Fig. 1) revealed localized voltage fluctuations as well as regional disparities, with some houses experiencing levels well below the island’s nominal voltage of 220 V. Fig. 2 shows voltage profiles for 2 households connected to the same distribution feeder, with one transformer. The household toward the end of the feeder (farther from the transformer) experienced lower average voltage and significantly worse fluctuations, dropping as low as 155 V (30% below nominal). In such an environment, customer loads and electrical equipment are not expected to operate reliably or as designed (26).

For a more granular view, we instrumented households in 2 sites (A and B) with low-cost voltage sensors (Fig. 3). The sites had similar socioeconomic status but were located on distinct parts of Unguja’s grid; results from 2 different feeders are more robust than those from a single feeder (SI Appendix). We collected voltage data between December 2016 and June 2017. Each sensor is represented by a letter in Fig. 3, with sensor a closest to the transformer. Figs. 4 and 5 show the voltage drops across the sensors for each site, with the y axis showing per unit (PU) voltage (voltage measured divided by nominal voltage [220 V]). The shaded region indicates ±10% of nominal voltage (1.1 to 0.9 in PU). Although voltage profiles at each sensor varied from week to week, there is a general dropping trend with distance from the transformer. However, voltage does not drop monotonically down the feeder; the time of day clearly matters (Fig. 2). Furthermore, in site B, sensor e captured mean and maximum voltages higher than at sensors c and d (Fig. 5).

These voltage fluctuations are outside of the range of acceptability by any standard we are aware of. However, as low voltages affect end-use devices differently, these measurements alone are insufficient to understand the effect that constrained grids have on customers. For example, one interviewee said that his voltage always dropped when his neighbor used his welders, while others did not recall any voltage variability. To explore these effects further we conducted detailed household surveys on customer experiences and perceptions.

Surveys from 151 households revealed an array of damaged electrical appliances, from fridges to light bulbs, across all socioeconomic strata. Pooled results from sites A and B revealed similar losses of appliances. Thirty-eight households identified appliances in their home that were not working. Five of these households had multiple broken appliances, such as fluorescent lights, fans, radios, televisions, electric cookers, refrigerators, and irons. One interviewee reported that his fridge had broken after a power surge. Another agreed, noting that after a power outage, he came home to a broken television and fridge. Asked about the lifespan of light bulbs, one participant replied, “usually they last about three months. Electricity goes up and down, up and down… so they never last [as advertised].” Many interviewees echoed this observation. An electric appliance shopkeeper noted that when customers purchased a fridge without a voltage stabilizer, they often returned to the store, fridge broken. Even low-end fridge stabilizers on the island cost 20 USD, or up to 40% of the 2013 monthly income. Another participant explained, however, that a voltage stabilizer was not a guarantee against material loss: “I was using a stabilizer. There was a short in the stabilizer so the current went straight through. I lost everything.”

We cannot establish causality between poor power quality and the damage to these respondents’ appliances; appliances break for many reasons other than voltage fluctuations. But our voltage measurements revealed periods in which voltage was well below the standard of 10% of nominal (27), which can, and does, lead to damaged appliances (20, 21, 28).

Respondents were asked whether they recalled any voltage-related problems in the past month. Reported voltage-related problems included everyday inconveniences such as dimming lights to the point that it was difficult to see, fans growing softer and “weaker,” insufficient power for large appliances, and sudden voltage spikes that damaged appliances. Households were also asked to identify the 3 most severe problems associated with their electricity connection; the menu of response choices included voltage problems, billing, maintenance, utility problems, and several others (details in SI Appendix). We assigned a PU voltage to each survey response based on the mean PU voltage of the sensor closest to the respondent’s household (see Figs. 4 and 5 and SI Appendix for further details). Fig. 6 shows responses, pooled for both sites, to the 2 questions based on their given PU voltage. While we found no clear pattern associated with experiences of voltage-related trouble in general (Fig. 6, Left), we found a positive trend between households’ perceptions of voltage as a top problem and power quality (Fig. 6, Right). Specifically, for those that identified voltage fluctuations as a top concern, our measurements indeed corroborated their low power quality.

The appliances people owned also correlated with their perceptions of voltage quality. Those who owned only low-tier appliances (e.g., lights, televisions, or irons), which are common and less sensitive to voltage fluctuations, tended to raise fewer concerns about voltage than those who owned top-tier appliances such as fridges, freezers, or blenders. Fig. 7 shows that 8 of 52 (15%) participants who owned only low-tier appliances considered voltage-related problems a top concern, compared with 44 of 99 (44%) with top-tier appliances.

This study provides household-level insights into the nature of electricity access in constrained systems, using Unguja, Tanzania, as an illustrative case. We found that the quality of electricity varied significantly for households connected to these grids. We captured extreme voltage fluctuations during certain hours, showing that, in these capacity-constrained conditions, when and how others on the same distribution line consume matter greatly for an individual household. Without boosters and voltage regulators, which utilities often do not provide, and without in-home ways to mitigate voltage drops, which low-income communities cannot afford, households farther down the feeder experienced worse voltage fluctuations than those near the transformer. Although some drops and fluctuations in voltage occur in all systems, the drastic voltage fluctuations across both sample sites indicate pervasive inconveniences and the risk of costly damages, undermining the promise of both adequacy and equity that universal connectivity is supposed to promote.

Our voltage measurements and household surveys show that having an electricity connection (i.e., access) is not at all the same as having a reliable or adequate electricity service (16). While rarely analyzed in the electricity and development literature, our work shows the many ways in which power quality and unreliability matter to low-income communities. The quality of electricity services shapes households’ ability to use their “access.” In Unguja, households reported lights that were too dim to be useful, larger appliances that could not be operated, and fridges that could not reliably store food. Low or extreme voltage can mean needing to replace appliances more frequently or purchase voltage stabilizers, resulting in higher costs for an already cash-constrained population. It can mean not being able to rely on appliances that have been purchased; even with a fridge a household may need to shop and cook daily, or even with an electric cooker the biomass stove cannot be retired. While those respondents who considered voltage quality a top problem tended to have top-tier appliances, even those with more common electrical appliances were impacted by poor power quality. Households from all socioeconomic strata indicated that they would consider paying more for better quality service.

Unguja is only one of many communities where resource-constrained utilities strive to provide electricity to cash-poor consumers. In Kenya, for example, an increase in the number of household connections “has been matched by an equally sharp decrease in average residential consumption” (ref. 15, p. 8). Our findings suggest that inadequate power quality on the supply side limits consumption by damaging appliances or discouraging consumers from buying others that they may wish to use. In turn, low consumption contributes to low cost recovery, potentially constraining the utility’s capacity to invest in infrastructure, such as line voltage regulators or distributed energy sources sited close to the customers (29) that could deliver better power quality. This negative feedback between utility revenue and consumer demand highlights the consequences of the financial pressure that utilities and consumers face as grid systems spread (30).

Our findings reveal that power quality (or a lack thereof), measured here as voltage magnitude and variability, is an essential factor in determining the benefits that electrification can deliver. On the Unguja grid, the ability to benefit from the basic accoutrements of modern life—exactly what universal access to modern energy services aspires to provide—is not guaranteed. In the quest to attain modern energy for all, therefore, energy and development scholars must take seriously what constrained grids are actually able to offer SSA communities. While these systems undoubtedly offer increasing opportunities, they do so at present in ways that are neither adequate nor equitable.