Suggestion on this setup for a complete beginner.

Re: Suggestion on this setup for a complete beginner.

Welcome to the forum Hochin!

More or less, the chances that you will be happy with one each of the above--Is not very high.

The right way to start is to use a Kill-a-Watt type meter (for AC) or A DC Amp*Hour/Watt*Hour meter and measure your loads.

Once we know the loads and better understand your needs, we can start some calculations.

However, I can give you some round numbers that will be a good start. A 1 kWatt*Hour per day system will usually power a laptop, printer, cell phone/networking, some lights (or 1,000 Watt*Hours -- Or around 100 Amp*Hours @ 12 volts DC).

If it is only 8 hours on a laptop and charging your cells phone, you might do OK with 500 WH per day. I will do a 1,000 WH per system calculation, but you can basically divide everything by 1/2 for a 500 WH per day system.

First, the battery bank. Assume you will be using an AC inverter (300 Watt MorningStar TSW 12 VDC inverter is a very sweet unit). Assuming 2 days of "no sun" storage and 50% maximum discharge (longer battery life):

• 1,000 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 392 AH @ 12 volt battery bank

The above battery bank is roughly 4x 6 volt @ 200 AH "golf cart" batteries. If you are only using power during sunny days, and don't need more than 1 day of backup, you could use a smaller battery bank.

To size the solar array, we have two calculations to make. One based on charging the battery bank with 5% to 13% rate of charge... And the second based on power used and how much sun you have.

First, charging rate...5% rate of charge is good for weekends and seasonal usage. 10%-13%+ is good for full time off grid usage:

• 392 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 369 Watt minimum array
• 392 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 738 Watt nominal array
• 392 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 960 Watt "cost effective" maximum array

Next, sizing based on the available sun... Using PV Watts for a fixed array, tilted to 22 degrees from horizontal for Lihue Hawaii:




Month
Solar Radiation
(kWh/m²/day)


1
4.79


2
5.17


3
5.08


4
5.48


5
5.31


6
5.65


7
5.48


8
5.76


9
5.91


10
5.40


11
4.44


12
4.43


Year
5.24



Use 4.43 hours of sun minimum:

• 1,000 WH per day * 1/0.52 end to end system eff * 1/4.43 hours of sun per day = 434 Watt array minimum based on load...

So, depending on size of the battery bank and the actual amount of power per day you want (knowing that you should not plan on using 100% of the predicted solar power per day, but something like 65 to 75% per day--And good days you can use more).

For a 1,000 WH per day 120 VAC system, with 2 days of storage--A 434 Watt to 738 Watt solar array is certainly justifiable.

If you have multiple days of bad weather--Then you should also have a small genset.

Anyway... A starting point for discussion.

-Bill