Nº 9 2011 > Climate change
Environmental benefits of a universal mobile charger
How much energy should mobile-phone chargers really consume?
Raffaele Bolla and Roberto Bruschi, University of Genoa and CNIT, Italy
Gianluca Griffa and Flavio Cucchietti, Telecom Italia
Nearly two billion new mobile phones are sold worldwide every year, and most of them are bought to replace obsolete models. If the old phone chargers are not compatible with the new devices, then they are thrown away too, even if still operational. With more than a billion devices becoming e‑waste each year and a huge quantity of potentially unnecessary new chargers being produced, the environmental implications are enormous.
This article looks at the outcome of a study on mechanical, electrical and life-cycle assessment characteristics of a wide range of mobile-phone chargers and highlights similarities, differences and improvement opportunities.
A sample of more than 50 chargers from official brands and compatible part suppliers was used in the study. The chargers were selected to represent the most recent and widespread models on offer from mobile-phone brands, plus some older models to gauge historical trends.
The weight of the charger is likely to be the parameter most closely correlated with the environmental impact of the charger. Figure 1 shows the weight of the chargers with and without the cord versus the output power rating of the chargers. It should also be noted that the weight of a charger can represent as much as 30–40 per cent of the total amount of material used in constructing a mobile phone plus charger, with 60–70 per cent of the material being used for the phone.
The results presented in Figure 1 show that there is limited correlation between the weight of the chargers and their rated output power. This suggests that the mass of electronic and plastic parts of the charger do not change markedly with respect to the output power. From Figure 1, it can also be seen that the weights of chargers with the same output power ratings are widely scattered. Because weight is directly linked to environmental impact, it would be advisable to urge manufacturers to optimize their products, aligning them with the best (lightest) in the corresponding category. Overall, the lightest chargers tended to be those with medium to high output power.
No-load power consumption
Chargers are often left connected to mains without any load, either because the handset has been removed or because the battery is fully charged. It is therefore important to minimize energy consumption during this no-load period. Figure 2 highlights the limited correlation between the no-load energy consumption parameter and the rated power. It seems reasonable to conclude that no-load efficiency is largely independent of output power, but generally depends on charger design.
Figure 3 illustrates the energy-efficiency characteristic of the sample chargers. Despite the similarity in the shapes of the curves, it can be seen that the values of maximum energy efficiency vary, and the chargers take different times to achieve these values. This leads to the conclusion that energy efficiency depends on the quality and design of the charger, rather than on the rated power. Further, different examples of the same equipment may show significantly different behaviour, as highlighted in Figure 4. Probably, the chargers produced by different manufacturers have different circuitry.
Figure 5 shows the output voltage of the chargers versus the output current. Surprisingly, some chargers provide output voltages up to twice their declared values, never actually providing 5 V. Three of the chargers even exceeded the maximum voltage allowed for the USB. Not only is this confusing for users, but it could also damage the products for which the chargers are used. Thus, another point for manufacturers to consider is the alignment between declared rating and real output current.
Towards a standard charger
Figure 6 illustrates the ratio between the number of models of chargers with USB ports and the total number of models produced by different manufacturers. Three vendors state that all their chargers are USB-compatible, and all vendors offer at least one USB-compatible charger.
Life-cycle assessment of chargers
Based on the results of a life-cycle assessment of sample chargers, the environmental performance of different chargers was compared from two perspectives: energy consumption in the use-phase; and the environmental impact of the materials used to build the chargers. The life-cycle assessment methodology is based on the ISO 14040 and 14044 standards.
First, four chargers were analysed to highlight the following environmental indicators related only to the manufacturing phase:
- gross energy requirements for a single product (total energy consumed during the overall manufacturing process);
- global warming potential (total emission of all greenhouse gases, reported in terms of kg CO2 equivalent);
- acidification potential (acidification caused by gases released to the atmosphere).
The results of this analysis are shown in Figure 7. There seems to be no direct relationship between environmental impact and maximum output current. Most of the environmental impact appears to derive from the electronic components of the device (more than 70 per cent), as compared with the plastic and metal components of the casing.
A second life-cycle analysis was performed on nine mobile-phone chargers to quantify their efficiency and their related environmental impact over a two-year period assuming two types of use:
- load (charger properly charging the mobile phone): 400 cycles (2 hours per cycle);
- no load (charger left plugged in to electricity distribution system but not being used to charge a mobile phone): 8 hours per day.
Figure 8 shows that the environmental impact of the load period is typically higher than that of the no-load period; the opposite was true of just one charger. Surprisingly, the most powerful charger had the lowest no-load power consumption.
Our analyses indicate that there is huge potential for improvement in regard to the environmental impact of chargers. A universal charger for mobile phones is not only needed, but is also feasible. We conclude that such a universal charger should:
- provide an acceptable level of output current (say 750 mA or, even better, 1000 mA);
- be small and light;
- offer the greatest energy efficiency (close to 0 Watt when not charging);
- be USB-compatible;
- respect eco-design criteria so as to minimize environmental impact;
- be sold with a reminder to customers to unplug the charger when not in use.
All these requirements are expressed in the second version of ITU–T Recommendation L.1000, issued in May 2011. This standard is already starting to be implemented in new and current products, such as the iPhone Micro USB Adapter and the AT&T Zero Charger.