System sizing checkup

Re: System sizing checkup

New_Climber wrote: »

I have a garage/shop/barn that currently doesn't have any electric wired to it. I have been using a 100ft ext cord to get some power for lights.

Honestly, I would dig a trench and bury some 3 conductor+ground 10 AWG or 8 AWG direct burial cable (I think code is 18" deep minimum) and bring 120/240 VAC to the shop.

Then look at solar for the education/backup power...

I am wanting to install a small solar system to be used for all my overhead lighting. My load I currently foresee is 10 - 13w CF over head lights of which I see using for about 5hrs per day, for half the week.

So, is my calculation correct that I will need 650w of capacity (13w*10ea*5hr)?

• 650 Watt*Hours per day.

Then for battery capacity: 32XHS-12v has 105ah at 5-hr rating....This battery gives me 1260watts total over 5hrs? (am I reading the battery information correctly)?

Nominally, recommend 1-3 days of "no sun" plus 50% maximum discharge for long life. For 2 days of power:
650 WH * 1/12 volt battery bank * 2 days no sun * 1/0.50 max discharge = 217 AH per day

You can go with 105 AH @ 12 volts, but you will only have one day of "no sun" carry through. And a bit shorter battery life--But it is certainly a valid configuration.

As for panels, I already have 2-Grape solar 185w, 36wmpp....So to make a rough estimate of how much power these can produce I just took total rated power and halved it...so I can make about 185w/hr. I live in the pacific northwest so using peak sun of 3.5hrs per day, I can produce about 640w per day.

2*185 watts * 0.52 system eff * 3.6 hours of sun per day = 692 WH per day of 120 VAC power (approximately)

Note that you should never plan on using 100% of your power every day--But if you go in the shop every other day, you will be OK.

Questions:

Are my calculation remotely correct? Also, I am not sure if I have enough power production to recharge my batteries, especially in the winter when I get the least amount of sun?

If you are on the cost, the amount of sun can be terrible. Using PV Watts fixed array tilted to latitude for Quillayute WA:

Month    Solar Radiation
(kWh/m 2/day)
1      1.51     
2      2.21     
3      3.12     
4      4.04     
5      4.73     
6      4.74     
7      4.91     
8      4.57     
9      4.37     
10      3.31     
11      1.87     
12      1.85     
Year      3.44

So, yes, during winter you may need a lot more panel or use a lot less power. That Marine layer is a killer.

I know I also will need an inverter and charge controller, but I just want to see if I was on the right path to start with?

The Rogue 30 amp MPPT controller would be a great fit.

The MorningStar 300 watt 12 volt TSW inverter is the best small / 12 volt inverter out there right now.

-Bill

Re: System sizing checkup

New_Climber wrote: »

Basically, I am using this solar system more as an education lesson then to get power to the shop. The battery I quoted, I already have for a travel trailer, and I have the panels, so I am somewhat half way there with equipment.

As for your correction as quoted, you highlighted HOURS per day. With my plan, I would use 13w*10ea=130w per hour the lights are on. If I use them 5hr per day, isn't it a total of 650watts per day? Or are you correcting my mis-use of terminology?? Meaning 650watts total per days, should be stated as 650watt hours (wh) per day? As I have learned, using the correct terminology makes getting help so much easier.

The confusing part is the Watts per Hour... Watts is already a Rate (like Miles per hour). There is not a Watts per Hour (--actually there is, it is the equivalent to acceleration or ft/sec²).

Multiply Watts * Hours gives you Watt*Hour which is equivalent to MPH * Hour = Miles driven.

I understand the desire to learn more about solar by starting with a small system... Your system will work fine (within its limitations).

-Bill

PS: Watts are already Joules Per Second (J/S)... And somebody decided to call the "derived unit" a "Watt".

Sort of like naming Miles per Hour a "Bill". And Bill*Hours would be miles driven.