Small Scale Offgrid Solar PV: Installation Manual
Appendix 2: Optimal Tilt Angle for a solar panel in Guatemala.
The optimal tilt angle for maximum solar gain is a function of latitude but also the use and
efficiency of the solar system during the year. A panel with a steeper tilt be exposed to more
solar irradiation in winter months when the sun is lower; although the average solar irradiation
/ m²/day would be higher if the tilt were the same as latitude. Latitude in Guatemala is 14º
(37' 15" N.)
A solar pumping system, for example, would require a tilt angle for maximum solar gain during
summer months; to cope with the heaviest demand for pumping. Optimal tilt for summer months
= (angle of latitude – 20º) 5º
For year round electrical load, an offgrid solar system should be installed in a way that captures
maximum solar irradiation during winter; the months when it‟s most difficult to keep the battery
charged. In Ecuador and other tropical countries with consistent solar irradiation through the
year, the tilt angle can be the same as latitude. However, in temperate zones of Guatemala the
optimal tilt = (angle of latitude + 20º) 35º.
Optimal tilt angle for maximum total generation during the whole year is the same as
latitude 15 º. For example a grid connected solar energy installation.
Appendix 3: Installations with more than one battery
Small installations with just one solar panel normally need just one battery. Nevertheless for
100 – 235W installations it‟s possible that two batteries will be needed to achieve the required
voltage and capacity. Sometimes just one battery at the necessary voltage and capacity will be
more expensive than combining two weaker batteries. The voltage of a group of batteries =
(number of batteries connected together in series) x voltage of one battery. The capacity of
the group = (number of batteries connected together in parallel) x capacity of one battery.
Never mix different types of battery.
This table recommends the battery configuration for different solar panels between 100W and
235W. With no consumption profile for design, optimal capacity is based on the panel‟s daily
generation in Guatemala (assuming 4.5 Peak Sun Hours); with 2 autonomy days and 50% Depth of
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