solar power calculations required.

[Qaisar Azeemi]

HI,

i want to run 100W load with solar Energy for 24 hours. sunlight here is available for 8hrs only. now how much watt solar panel that i should use and how much Capacity (AH) pb batteries are required for that purpose. can solar panel charge the batteries in day light when no sunlight is available? kindly give me formulaic calculations. and also give me the formulas used.

thanking you in anticipation.

Best Regards

 

[ccurtis]

The total energy required to power the load per day is 100 Watts times 24 Hours, or 2400 Watt-hours. Since the batteries can only be charged during sunlight, the solar panel must provide enough energy to run the load and charge the batteries during that 8 hour period, in other words, to provide the total daily energy during one 8-hour period. 2400 Watt-hours divided by 8 hours is 300 Watts. Therefore, the solar panel must provide 300 Watts -- excluding battery inefficiency, battery charge/discharge rate, and other losses and issues, of course.

The batteries must provide 100 Watts, or, assuming 120V, 100/120=.8 Amps. For 16 hours (number of discharge hours), that is .8 * 16 = 12.8 Ahrs -- also assuming linear discharge, independent of discharge rate.

Those are ideal minimum requirements. Of course, this is not the ideal world. You don't discharge a battery to zero energy just before the sun comes up, so you pick batteries that have considerably greater capacity than 12.8 Ahrs. You also don't pick a solar panel that has just enough output to charge the batteries to minimum charge and power the load before the sun goes down, so you pick one having considerably greater output.

The batteries must also be capable of being charged to capacity faster (8 Hrs) than that same capacity is diminished (16 Hrs) using twice the charging current that it is discharged at. I don't know if that is possible.

 

[BioniC187]

The rate at which a battery discharges and charges are very different. All rechargable batteries take longer on the charge cycle, so charging for 8 hours then use for 16 isn't gonna happen. It is limited by the characteristics of the battery itself, only being able to accept a certain current rate, going beyond this could damage the battery, result in harm to the user. What is it that you are trying to do?

 

[nsaspook]

There are FLA battery types that can be charged at the C/4 or faster rates with a normal discharge profile being C/8 (C is the Ah capacity of the battery/hours of charge cycle). The charge efficiency at those rates will be lower but still at about 80% during most of the high current (bulk) cycle.
https://www.electro-tech-online.com/custompdfs/2012/06/Charging_and_Discharging_BU-RS-614.pdf
https://www.electro-tech-online.com/custompdfs/2012/06/S-600.pdf

In practical terms you would need Solar Power at least 3 to 4 times the power used when the losses from wiring, power conversion and storage (double the load requirement to keep discharge at 50%) are accounted for.

 

[crutschow]

The rate at which a battery discharges and charges are very different. All rechargable batteries take longer on the charge cycle, so charging for 8 hours then use for 16 isn't gonna happen.

Don't know why you say that. There is no limitation as to how slow you can discharge a battery. The only limitation is that you shouldn't discharge it at a rate faster than its ratings.

 

[BioniC187]

I meant for an application such as this, but yes, no limitation on discharge, to be technical

 

[crutschow]

I meant for an application such as this, but yes, no limitation on discharge, to be technical

Well, this is a technical forum.

But why is his application any different? He wants to charge for 8 hours and discharge for 16 hours. Nothing wrong with that.

I believe you are thinking about maximum rates. The maximum battery charge rate is generally less than the maximum discharge rate.

 

[awt]

Hello Azeemi,
there are some informations you need to provide to solve this once.
1, at what voltage do you want to run your 100W load? Let me assume 12V, your energy consumption for 24hrs is (100 * 24 = 2400WH). Now divide this by the voltage (i.e, 2400/12 = 200AH). Also note that you can not completely discharge the battery, so you need to include the discharge capacity of the battery in your calculation. Some literature say deep cycle battery can be discharged up to 80% its capacity- find out for your battery type. Let's assume deep cycle, the battery that you will need is (200*100/80 = 250AH)
2, What is the solar insolation of your area? This already includes hours for sun in its computation. Find out for your area, you can get it on internet. You need to know the efficiency of the whole system: estimate losses associated with various component to calculate the efficiency. Apply this formula to get your PV rating (2400/(insolation*efficiency)).
Best of luck.