Hi there,

I've just joined this forum and wanted your kind opinion on a query which I had whilst using HOMER pro.

Q. How to validate HOMER's calculation?

Given: residential load = 11.26 kwh/day, peak = 2.09 kw, Lowest Irradiation = 5.3 kwh/m2/day

ANS:

HOMER's result: (All calculation done using 'HOMER optimizer' option)

PV array: capacity = 5.37, mean output = .999 kw, array efficiency = 18.6%, energy out = 23.9 kwh/day

Battery: capacity = 2585.4 AH, energy out =6.10 kwh/day, energy in = 7.60 kwh/day, round trip efficiency = 80%

Converter capacity: capacity = 2.74 kw, energy out = 11.24 kwh/day, energy in = 11.84 kwh/day, efficiency = 95%

My Result:

PV array capacity = user needs / (min. av. Irradiation x system efficiency)

Assuming system efficiency = 60%, array capacity = 11.26 / (5.3 x 0.6) = 3.5409 kw

Battery capacity = 11.26 kwh / 12 v = 938.3 AH

Assuming 70% losses, 80% Depth of Discharge (given) and 1.65 days of autonomy (given) Battery capacity = 938.3 x 1.65 / (.70x.80) = 2,764.6339 AH

Converter capacity:

Ideal PV array to Inverter ratio is 1.2-1.3.

Therefore, inverter capacity = 3.54 / 1.25 = 2.832 KW

QUERIES:

1. Why is the PV array capacity oversized?

2. How is the Battery size determined? (formula)

3. How is the Converter size determined? (formula)

4. Below is the Single Line Diagram of the system components with their input and output energy.

- Where does the input of 11.84 kwh/day to Inverter come from?
- where does the input of 7.6 kwh/day to Battery come from?
- Where does the output of 23.9 kwh/day from PV go to?

HOMER FILE and Single Line Diagram of System Components available here

https://drive.google.com/open?id=0B5K0ZuCr-AK_WUNGVGx6cExJaDA

Your comments are welcome.