Question 9.16: Battery Storage Calculation in a Cold Climate. Suppose that ......

Battery Storage Calculation in a Cold Climate. Suppose that batteries located at a remote telecommunications site may drop to −20ºC. If they must provide 2 days of storage for a load that needs 500 Ah/day at 12 V, how many amp-hours of storage should be specified for the battery bank?

Step-by-Step
The 'Blue Check Mark' means that this solution was answered by an expert.

From Fig. 9.39, to avoid freezing, the maximum depth of discharge at −20ºC is about 60%. For 2 days of storage, with a discharge of no more than 60%, the batteries need to store

$\text{Battery storage} \ = \ \frac{500 \ {Ah}/{day} \ \times \ 2 \ {days}}{0.60} \ = \ 1667 \ Ah$

Since the rated capacity of batteries is likely to be specified at an assumed temperature of 25ºC at a C/20 rate, we need to adjust the battery capacity to account for our different temperature and discharge period. From Fig. 9.42, the actual capacity of batteries at −20ºC discharged over a 48-h period is about 80% of their rated capacity. This means that we need to specify batteries with rated capacity

$\text{Battery storage} \ \left(\text{25ºC, 10-hour rate}\right) \ = \ \frac{1667 \ Ah}{0.8} \ = \ 2083 \ Ah$

Question: 9.22

Sizing an Array for a 150-ft Well in Santa Maria, California. Suppose that the goal is to pump at least 1200 gallons per day from the 150-ft well described in Example 9.21 using the Jacuzzi SJ1C11 pump. Size the PV array based on Siemens SR100 modules with rated current 5.9 A, mounted at an L + 15º ...

From the solar radiation tables given in Appendix ...
Question: 9.21

Total Dynamic Head for a Well. What pumping head would be required to deliver 4 gpm from a depth of 150 ft. The well is 80 ft from the storage tank, and the delivery pipe rises another 10 ft. The piping is 3/4-in. diameter plastic, and there are three 90º elbows, one swing-type check valve, and one ...

The total length of pipe is 150 + 80 + 10 = 240 ft...
Question: 9.20

PVs for the Cabin in Salt Lake City. The cabin from Example 9.18 needs 3000 Wh/day of ac delivered from an 85%-efficient inverter. For a 24-V system voltage, a 90% Coulomb efficiency, and 10% de-rating (de-rating factor = 0.90), size a PV array using Kyocera KC120 modules. ...

From Table 9.3, the Kyocera KC120 is a 120-W modul...
Question: 9.18

Battery Sizing for an Off-Grid Cabin. A cabin near Salt Lake City, Utah, has an ac demand of 3000 Wh/day in the winter months. A decision has been made to size the batteries such that a 95% system availability will be provided, and a back-up generator will be kept in reserve to cover the other 5%. ...

With an 85% efficient inverter, the dc load is [la...
Question: 9.15

Accounting for Inverter Losses. Suppose that a dc refrigerator that uses 800 Wh/day is being considered instead of the 1140 Wh/d ac one given in Example 9.14. Estimate the dc load that the batteries must provide if an 85% efficient inverter is used (a) with all loads running on ac and (b) with ...

a. With all 3109 Wh/day running on an 85% efficien...
Question: 9.14

A Modest Household Demand. Estimate the monthly energy demand for a cabin with all ac appliances, consisting of a 19-cu. ft refrigerator, six 30-W compact fluorescents (CFLs) used 5 h/day, a 19-in. TV turned on 3 h/day and connected to a satellite, a cordless phone, a 1000-W microwave used 6 ...

Using data from Table 9.10, we can put together th...
Question: 9.19

Impact of a Blocking Diode to Control Nighttime Battery Leakage. A PV module is made up of 36 cells, each having a reverse saturation current I0 of 1 × 10^−10 A and a parallel resistance of 8 Ω. The PVs provide the equivalent of 5 A for 6 h each day. The module is connected without a blocking diode ...

The voltage across each PV cell will be about 12.5...
Question: 9.17