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Field Day Solar Panel & Battery Demo Calculations

Learn how to calculate power requirements for radios using solar panels and batteries for a field day setting. Detailed analysis and recommendations provided.

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Field Day Solar Panel & Battery Demo Calculations

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  1. Field Day Solar Panel & Battery DemoCalculations Sam Stello KK4VR March, 2016

  2. Assumptions & Background Solar Panels and Batteries come in various sizes; for this exercise, 100 Watt solar panels and 100ah deep cycle batteries are assumed because of their availability within the club. Doubling up can be done if required to increase capacity. Kenwood TS430 power requirements can be used as an example of a typical transceiver (transistor) with 100 watt output • 12 to 16 volt dc input (13.8 nominal); 20 amp during transmit; 1.2 amp during receive (276 watts transmit; 17 watts receive) 36% efficient during transmit • TS430 external power supply requires 480 watts at full load of 20 amps, 12 volts DC; 4 amps at 120 volts AC (58% efficient at full load) • TS430 with AC Power supply combination is 21% efficient at full 100 watts output Elecraft KX3 is a QRP transceiver in common use for field day • KX3 receive power is 150 milliamps at 13.8 volts (2 watts) ; transmit power is 2 amps at 13.8 volts (27.6 watts) for 10 watt output; transmit efficiency is 36% • Elecraft KXPA100 (100 w linear) 24A peak power at 13.8v during transmit (331 watts) for an efficiency of 30%; 1mA operate power (0.14 watts) • Elecraft KX3 with KXP100 during 100 watt transmit requires 359 watts (27.8% efficient); receive is 2.14 watts

  3. Power Required for 100 Watt Tx • Using the Kenwood TS430 as a typical transceiver, we will assume: • supply power required during transmit is 20 amps at 13.8 volts (276 watts) for 100 watts RF output (36% transmit efficiency) • power required during receive is 1.2 amps at 13.8 volts (17 watts) • Assume contesting duty cycle of 50% transmission rate and a Morse Code signaling rate of 40%, then a one hour operating period requires: Tx Power Req’d = Transmitter power supply x transmit duty cycle x morse code transmit time 20 amps x 0.5 x 0.4 = 4 amp-hours (ah) per operating hour Rec Power Req’d = (Receive Power Supply x Receive Time) + (Receiver Power Supply x Transmit duty cycle x Morse code transmit off time) (1.2 amps x 0.5 duty)+ (1.2 amps x 0.5 x 0.6 receive) = 0.96 amp-hours (ah) per operating hour Transmit plus receive = 4.96ah per operating hour NOTE: for the purposes of this analysis, we will assume average power used for voice is comparable to the Morse code power usage

  4. Solar Panel Needs • The Field Day rules allow us to charge the battery(s) prior to field day using a solar panel • A 100 watt panel realistically provides 5 to 6 amps during peak sunlight (conservative estimate that depends upon weather conditions) • Average peak sunlight hours for Virginia is 4.5 hours; panels will produce lower amounts as the sunlight is reduced • 100ah battery would take approximately 2 1/2 days to charge from a dead battery condition if we only assume charging during peak daylight hours; a little over a day if the battery is already half charged

  5. Candidate Solar Panel Operating Configuration Solar Charge Controller 100 Watt solar panel 100ah deep cycle battery

  6. 100 watt Operating Station using Batteries • Assuming we operate at 100 watt RF transmit power, then we need 4.96ah per hour • Use one 100ah deep cycle batteries (approx $100 each if bought new), pre-charge it for FD with solar panels • A deep cycle battery of 100ah providing 4.96ah per hour, assuming a 10% battery reserve, would last 18 hours using our operating assumptions • SUMMARY: A 100ah battery for each radio would let us operate, if we were transmitting according to our assumptions, 18 hours with a 10% battery reserve.

  7. 100 watt Operating Station using Battery and a Solar Panel • Assuming we operate at 100 watt RF transmit power, then we need a 4.96ah per hour power supply • If we pair a solar panel with a 100ah battery, assuming 5 hours of peak sunlight per 24 hours, then: • A 100w solar panel can provide 5 amps for 5 hours during field day, or 25ah in 24 hours • The 100w solar panel and 100ah battery combination can provide 115ah with 10% battery reserve • A deep cycle battery of 100ah with a 100w solar panel providing 4.96ah per hour, assuming a 10% battery reserve, would last 23.2 hours • SUMMARY: For a radio operating with 100 watts transmitting power, a 100ah deep cycle battery with a 100w solar panel at each station would last almost the entire field day (23 hours of operating time) with a 10% battery reserve.

  8. 50 watt Operating Station using one Battery • Assume contesting duty cycle of 50% transmission rate and a Morse Code signaling rate of 40%, then a one hour operating period requires: Tx Power Req’d = Transmitter power supply x transmit duty cycle x morse code transmit time (0.5 x 20 amps)* x 0.5 x 0.4 = 2 amp-hours (ah) per hour Rec Power Req’d = (Receive Power Supply x Receive Time) + (Receiver Power Supply x Transmit duty cycle x Morse code transmit off time) (1.2 amps x 0.5 duty)+ (1.2 amps x 0.5 x 0.6 receive) = 0.96 amp-hours (ah) per hour receiving Transmit plus receive = 2.96ah per operating hour • A deep cycle battery of 100ah providing 2.96ah per hour, assuming a 10% battery reserve, would last 30.4 hours (field day is 24 hrs!) • A deep cycle battery of 100ah providing 2.96ah per hour each for TWO RADIOS, assuming a 10% battery reserve, would last 15.2 hours • SUMMARY: A 100ah battery would last the entire field day; or alternately, if we shared one battery for every two stations, we could operate 15 hours (according to our assumptions) *Assumes linear scaling of power, that is, if we reduce transmit power by half then power supply requirement is halved; this should be a good approximation

  9. Two 50 watt Radios sharing one Battery and one Solar Panel • Assume contesting duty cycle of 50% transmission rate and a Morse Code signaling rate of 40%, then a one hour operating period requires 2.96ah per operating hour, as derived previously • If we pair a solar panel with a 100ah battery, assuming only 5 hours of peak sunlight per 24 hours, then: • A 100 w solar panel can provide 5 amps for 5 hours during field day, or 25ah over 24 hours • The 100 w solar panel and 100ah battery combination can provide 115ah with 10% battery reserve • This provides 19.4 hours of operating time • SUMMARY: One 100ah deep cycle battery with one 100 w solar panels (one set for every two stations) would last almost the entire field day (19 hours) if we were transmitting according to our assumptions

  10. Equipment Needed for Six Operating Stations

  11. Equipment Needed for Four Operating Stations

  12. Recommendations (1) • For our club, there is little likelihood that we would operate at the assumed rates during field day • Most of our stations are not on the air (transmitting) more than a few hours over the field day period • We probably average less than 10 hours operating per station • We have never operated more than six stations and usually only use four • We typically do not transmit more than 50 watts due to concerns over RF interference • When we are operating, we do not typically transmit 50% of the time • We are not dedicated contesters so we tend to listen more than we transmit • The history of Field Day for this club leads me to think that any of battery-only or battery-solar panel options will meet our club needs for a field day trial run

  13. Recommendations (2) • I think we could find enough equipment for a six station, 3 battery (100ah) & 3 solar panel system demo at field day. We should operate at RF power of 50 watts, which gives us almost full time operating. • I will provide two 100 Watt solar panels and will have two 100ah RV batteries for field day. Jack has a 40 Watt solar panel and may have some batteries. • We can prepare additional batteries and a backup generator in case something doesn’t work or we get surprised. A generator may be required anyway if a club member wants to use a tube based transceiver, which would require 115 volt AC power to operate. • We should use power monitoring instrumentation to gather power usage data. • We can also provide dedicated batteries for some stations, if 100W operation is needed by someone. We can scale-up the batteries to 150ah or double–up the batteries (100ah wired parallel) for 100% operating times at high power with additional operating time margins, if we think that is needed.

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