Tolba93
New Member
I am building a solar off grid system that has 24/7 constant load (230 W total). I actually have space constraints so i tried to reduce the size of the PV array as follows: (days of autonomy is 2).
To explain what i am trying to do, i am trying to size the PV array so that it can charge the battery bank to full in two clear-sky days instead of one clear-sky day if for example i start with a depleted battery which might happen if i get two cloudy days. Given the fact that i sized my batteries for 2 days of autonomy. so i did the following:
- I sized the batteries as follows: 230W x 24 h = 5.52 kWh, Then multiplied by 2 days of autonomy and divided by DOD (0.8 for LiFePO4) so i got 13.8 kWh and after selecting the batteries i ended up with: Battery Bank Capacity = 15.36 kWh
- I calculated the PV system size by dividing the battery capacity by PSH and then divided by system losses. That will be 15.36/5/0.648=4.74 kWp.
Lets call this "PV full" = 4.74 kWp
- I calculated the required PV system to run the load by dividing only my daily required energy by PSH and then by system losses. That is 5.52 /5/0.648 = 2.13 kWp
Lets call this "PV load" = 2.13 kWp
- I tried to calculate the PV array size that will produce the energy that actually goes for charging the battery only and not for the load by doing: PV full - PV load = 4.74-2.13 = 2.61 kWp
Let's call this "PV charge full"=2.61 kWp
(I assume that "PV charge full" here is the PV array that will produce the amount of energy that can charge the battery to full in one day with clear sky if i start with a depleted battery)
- I divided "PV charge full" by 2 which will make my battery charge to full in two days with clear sky instead of one. That is 2.61/2= 1.305 kWp
Lets call this "PV charge half"= 1.305 kWp
- Finally i added "PV charge half" + "PV charge load" = 1.305 + 2.13 = 3.435 kWp.
So my final PV system size is 3.435 kWp which will run the load 24/7 year-round and in case the battery got depleted after two days of clouds, the battery will recharge to full in two clear days instead of one, which allowed me to reduce the PV array size.
Is that correct?
Please help by giving your feedback. Thank you.
To explain what i am trying to do, i am trying to size the PV array so that it can charge the battery bank to full in two clear-sky days instead of one clear-sky day if for example i start with a depleted battery which might happen if i get two cloudy days. Given the fact that i sized my batteries for 2 days of autonomy. so i did the following:
- I sized the batteries as follows: 230W x 24 h = 5.52 kWh, Then multiplied by 2 days of autonomy and divided by DOD (0.8 for LiFePO4) so i got 13.8 kWh and after selecting the batteries i ended up with: Battery Bank Capacity = 15.36 kWh
- I calculated the PV system size by dividing the battery capacity by PSH and then divided by system losses. That will be 15.36/5/0.648=4.74 kWp.
Lets call this "PV full" = 4.74 kWp
- I calculated the required PV system to run the load by dividing only my daily required energy by PSH and then by system losses. That is 5.52 /5/0.648 = 2.13 kWp
Lets call this "PV load" = 2.13 kWp
- I tried to calculate the PV array size that will produce the energy that actually goes for charging the battery only and not for the load by doing: PV full - PV load = 4.74-2.13 = 2.61 kWp
Let's call this "PV charge full"=2.61 kWp
(I assume that "PV charge full" here is the PV array that will produce the amount of energy that can charge the battery to full in one day with clear sky if i start with a depleted battery)
- I divided "PV charge full" by 2 which will make my battery charge to full in two days with clear sky instead of one. That is 2.61/2= 1.305 kWp
Lets call this "PV charge half"= 1.305 kWp
- Finally i added "PV charge half" + "PV charge load" = 1.305 + 2.13 = 3.435 kWp.
So my final PV system size is 3.435 kWp which will run the load 24/7 year-round and in case the battery got depleted after two days of clouds, the battery will recharge to full in two clear days instead of one, which allowed me to reduce the PV array size.
Is that correct?
Please help by giving your feedback. Thank you.
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