To ensure that solar direct drive (SDD) appliances can keep vaccines at acceptable temperatures continuously, the installed photovoltaic array often produces excess power that is not used by the primary cooling load and this excess power generally goes unutilized.
If this power is to be used, the primary SDD appliance load must be prioritized above any other load. WHO and other organizations have been working to define how this can be done safely and reliably. In support of WHO/PQS, PATH has recently posted results from lab testing of a couple of prototype devices intended to do just this. The Solar Electric Light Fund (SELF), organized and provided the prototypes and also carried out initial field tests on this energy harvesting control (EHC) technology.
You can access the report here: http://www.path.org/publications/detail.php?i=2699
Additionally, the recently posted PQS specification and verification protocol are available on the WHO website: http://apps.who.int/immunization_standards/vaccine_quality/pqs_catalogue/catdocumentation.aspx?id_cat=36
I would be interested to know - what do people think of this approach with the intent to safely access excess power through EHCs? What do you think could be the most important uses for this power in remote health settings?
Steven P. Diesburg
Product Development Engineer
PATH, Seattle, WA, USA