Solar Lighting Design Guide ¨C Determine Power Assembly

Part 5 of the solar lighting design guide is about determining the power assembly. Now that you know what area of coverage you are requiring by determining the lumen requirements for the project, as well as the required operation profile, it is time to determine what size solar power assembly will be required. This is determined by a simple calculation after some additional information is gathered.

Solar Power Assembly Sizing
Step 1 – Take the wattage of the fixture and divide by 12 to determine the amps required to operate the fixture for 1 hour. You divide by 12 as solar power systems are typically 12 VDC; however, some are 24 VDC, but this formula will still work out correctly in the end.

Step 2 – Multiplying the fixture amps by the number of hours of operation per night will provide you with the total required power consumption per night. If dusk to dawn is required, knowing the time on the longest night of the year is how this is determined. Florida has approximately 13.25 hour nights in the winter where New York has 14.5 hour nights. Split time or after dusk for x number of hours can also be used to determine. When dealing with motion, how many hours will it operate on average is what is calculated.

Step 3 ¨C Multiply the total amps required by the total number of fixtures that need to be powered by a single solar power assembly. If 1 fixture is all that is going on the power system, then you can skip this step. However, there are some applications, like with signs, bollards or landscape lighting, where multiple fixtures are all used on a single solar power assembly.

Step 4 ¨C add 20%. The reason for this is to include a little bit of overage to ensure that the system will operate as promised for years to come. As solar ages, the power produces slowly degrades. After 25 years or so, the power is down around 20% from its original production performance.

Step 5 ¨C Divide by the total number of sun hours available in your location in the winter. This can be found online and by looking at the local NSOL guides. Remember to look at winter availability and not a yearly average as the system will not operate the same during different times of the year unless sized for worst case.

Step 6 ¨C Determine how large a power assembly is required. Each power assembly provides a different amp current and the system needs to provide over what is required. For example, our SEPA100 provides 5.46 +/- Amps per hour, up to 11 or so amps in New York or 24 or so amps in Florida for a single day in the winter.

Battery Assembly Sizing
Step 7 ¨C Determine the battery assembly size by multiplying the number of amps required per night by the number of days backup you require. The minimum autonomy we provide is 5 in most applications; however, the further north the more this increases due to depth of discharge changes with batteries in colder weather.

Understanding all these factors can make or break a system and why ¡°off-the-shelf¡± systems are not used when a reliable system design is required. Each system should be designed for the specific project requirements and understanding all the steps above will allow for reliable system design that will operate for 25+ years.