I'm looking for feedback on proposed battery and panel sizing at a radio site, if anyone is interested. It has both microwave (48V continuous loads) and VHF (12V intermittent loads). I'm curious how my math is with these calculations, and whether or not I am able to design a good system, or if I still need some training. I talked about this site in another thread, but thought it might make a good stand-alone thread.
Insolation data seems to average 3 to 3.5 kWh/m^2/day at this site, with about 50 degree panel orientation, so I went with 3.
There are two DC systems, one 48V and one 12V. No load inverters are used, all loads are DC. The site currently has solar and batteries, but the batteries will need to be replaced soon and I don't think we sized the solar array adequately when we originally installed it about 12 years ago. It has depended quite a bit on the backup generator.
48V loads: 20A * 24hr = 480 Ah/day, * 48V = 23,040 Wh/day.
48V Battery size: 115,200 Wh based on 2.5 days til 50% discharge. That's 2,400 Ah.
Array size for 48V: 23,040 Wh * 2 (on/off controller) / 3 kWh/m^2/day winter insolation = 15,360 watt 48V array.
12V loads: Ten stations, 20A transmit, 0.5A receive/standby, 10% TX duty cycle, = 588 Ah/day, * 12V = 7,056 Wh/day.
12V battery size: 35,280 Wh (2.5 day to 50% DoD) /12V = 2,940 Ah.
12V Solar array size: 7,056 * 2 (on/off controller) / 3 kW/m^2/day = 4,704 watt 12V array.
There is a 15 kW propane generator on site for additional charging with two 500 gallon tanks. It monitors the battery voltages and starts at whatever we set it to. I'm wondering if it should be set to a voltage that approximates 50% DoD, or something else.
It's a snow site that is difficult to get to, it takes about a day to plan and a half day to get there. Maybe that makes a difference in the amount of autonomy that is needed. It's an important site for highway patrol, etc., especially in the winter.
If anyone would like to confirm or correct my thinking, that would be great.
Steve
Insolation data seems to average 3 to 3.5 kWh/m^2/day at this site, with about 50 degree panel orientation, so I went with 3.
There are two DC systems, one 48V and one 12V. No load inverters are used, all loads are DC. The site currently has solar and batteries, but the batteries will need to be replaced soon and I don't think we sized the solar array adequately when we originally installed it about 12 years ago. It has depended quite a bit on the backup generator.
48V loads: 20A * 24hr = 480 Ah/day, * 48V = 23,040 Wh/day.
48V Battery size: 115,200 Wh based on 2.5 days til 50% discharge. That's 2,400 Ah.
Array size for 48V: 23,040 Wh * 2 (on/off controller) / 3 kWh/m^2/day winter insolation = 15,360 watt 48V array.
12V loads: Ten stations, 20A transmit, 0.5A receive/standby, 10% TX duty cycle, = 588 Ah/day, * 12V = 7,056 Wh/day.
12V battery size: 35,280 Wh (2.5 day to 50% DoD) /12V = 2,940 Ah.
12V Solar array size: 7,056 * 2 (on/off controller) / 3 kW/m^2/day = 4,704 watt 12V array.
There is a 15 kW propane generator on site for additional charging with two 500 gallon tanks. It monitors the battery voltages and starts at whatever we set it to. I'm wondering if it should be set to a voltage that approximates 50% DoD, or something else.
It's a snow site that is difficult to get to, it takes about a day to plan and a half day to get there. Maybe that makes a difference in the amount of autonomy that is needed. It's an important site for highway patrol, etc., especially in the winter.
If anyone would like to confirm or correct my thinking, that would be great.
Steve
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