Calculating your Required Photo Voltaic Capacity


This page continues on from our Getting Started electrical load summary and the Calculate Battery page example.  In spite of the fact that we configured battery capacity to 98.4 AHr we need to look back a bit within the battery calculation to the point where daily requirement with reserve was calculated at 41 AHr. This is because the Photo Voltaic panels need to recoup the electricity lost in previous days while maintaining power required for today .  The remainder of the battery calculation was to optimize and make cost effective the battery array.

Solar Voltaic (PV) panels are rated in Watts.  Lets first normalize and state the battery charge requirement in Watts.  41 AHr @12V calculates to 492 Watt Hours @ 12V. (41 X 12V =  192 Watt Hours)

Hours of Effective Sunlight

Let's assume this is a summer application and your area receives an average of 5 hours of effective* sunlight per day.  This calculates to a requirement of 94.5 Watts required from the PV array (492 Watt Hours 5 hours of average effective sunlight).

This works if you're using your cottage for two or two and a half days per week because the system will recuperate itself in the four and a half days you're away.  If you are at the cabin all week and want those expensive batteries charged up as soon as possible but don't want the generator clattering away to catch up there's another factor to consider...

Recuperation Days

Recuperation Days are a factor used to describe catch-up.  If you've had two days of inclement weather, weather where your PV panel has contributed next to nothing but your electrical loads continued then the configuration for the weekender-only won't work for you because your solar panels will only keep your batteries at the low level but will not catch up.  If you chose a recuperation factor of two days you would need 141.7 Watts of PV panel.  Then your solar panels will catch up the electrical shortfall within two days.  The math behind this factor is as follows. ((94.5 Watt requirement  2 recuperation days) + 94.5 Watt requirement = 141.8 Watts)

Saving you from Battery Math

We have developed a MS EXCEL spreadsheet tuned for the Canadian environment to assist our Canadian clients with these calculations.  Contact us by email and we'll help you with your calculations.

It is our sincere hope that our long-winded explanation has helped you understand and demystified system configuration!  Configuration is half the equation, the other half is comprised of using the appropriate technology and properly installing it.  You're half way there!