Calc's seem reasonable?

Re: Calc's seem reasonable?

Cutting and Pasting Columns sometimes looks better if you use "Go Advanced" and the "#" button.

It pasts {code} and {/code} (using [] instead of {}) -- This will better keep the Tabs and Spaces.

Here is an example of QUOTE tags (note, I pasted output to NOTEPAD and copied back to get rid of the formatting:

Month Solar Radiation
(kWh/m 2/day) AC Energy
(kWh) Energy Value
($)
1 3.62 329 41.12
2 4.59 378 47.25
3 5.22 479 59.88
4 6.11 535 66.88
5 6.36 575 71.88
6 6.47 565 70.62
7 7.01 629 78.62
8 6.67 596 74.50
9 6.62 568 71.00
10 5.41 485 60.62
11 3.87 338 42.25
12 3.35 306 38.25
Year 5.45 5784 723.00

vs CODE tags:

Month    Solar Radiation
(kWh/m 2/day)    AC Energy
(kWh)    Energy Value
($)
1      3.62          329        41.12   
2      4.59          378        47.25   
3      5.22          479        59.88   
4      6.11          535        66.88   
5      6.36          575        71.88   
6      6.47          565        70.62   
7      7.01          629        78.62   
8      6.67          596        74.50   
9      6.62          568        71.00   
10      5.41          485        60.62   
11      3.87          338        42.25   
12      3.35          306        38.25   
Year      5.45          5784        723.00    

And here is a paste with formatting directly into the edit window (with WYSIWYG turned on--The A/A button in upper left of edit menus):




Month
Solar Radiation
(kWh/m²/day)
AC Energy
(kWh)
Energy Value
($)


1
3.62
329
41.12


2
4.59
378
47.25


3
5.22
479
59.88


4
6.11
535
66.88


5
6.36
575
71.88



6
6.47
565
70.62


7
7.01
629
78.62


8
6.67
596
74.50


9
6.62
568
71.00


10
5.41
485
60.62


11
3.87
338
42.25


12
3.35
306
38.25


Year
5.45
5784
723.00




You sometimes have to play around to make it work...

Anyway, your image post did work.

3.5 kWH per day is a good sized load... And would be fairly expensive to run off of solar 100% of the time--Although, during summer does make it a bit more doable.

-Bill

Re: Calc's seem reasonable?

Anyway, using Winnipeg Mn. Canada in PV Watts with fixed array set to -15 degrees from latitidue or ~35 degrees from horizontal (summer setting):

Month      Solar Radiation (kWh/m2/day)
1      3.01     
2      4.07     
3      5.27     
4      5.74     
5      6.32     
6      6.35     
7      6.43     
8      6.05     
9      4.62     
10      3.58     
11      2.42     
12      2.57     
Year      4.71      

Pick May through September wiht 4.62 hours minimum sun (run generator some more during last month):

Battery sizing for 1-3 days of storage (pick 2 days as optimum) and 50% maximum discharge (for longer battery life):

• 3,483 WH per day * 1/0.85 inverter efficiency * 2 days storage * 1/0.50 max discharge * 1/24 volt bank = 683 AH battery bank @ 24 volts

To charge such a battery, we recommend from 5% to 13% rate of charge from solar:

• 683 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,286 Watt array minimum
• 683 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,572 Watt array nominal
• 683 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,344 Watt array "cost effective maximum"

And, assuming a minimum (long term average) of 4.62 hours of sun per day:

• 3,483 WH per day * 1/0.52 overall system efficiency * 1/4.62 hours of noontime sun per day = 1,450 Watt array minimum

So, the recommended array for a "nominal 2 day battery with 50% max discharge" and an array that would carry you from February through September would be around ~1,450 to 3,344 Watt array--With ~2,572 being a really nice "nominal array" that would give you:

• 2,572 Watt array * 0.52 system efficiency * 3.58 Hours of sun in October = 4,788 WH of sun per day

So, that would still exceed your minimum daily estimated power requirement.

I am still not sure if you calculated the numbers exactly correct... I will have to take a closer look--But a 3.3 kWH per day system is a pretty nice amount of power for a "near normal" off grid home, running efficiently.

If you were going "bare bones", you could look at 1,000 WH (1 kWH) per day, and see what you would dump.

Now--For off grid systems that are used less than ~9 months a year, a smaller off grid system with "generator support" may be a possible option.

Poster ChrisOlson (and others) has some good advice here for "swimspam" :

Choosing a good generator
genset alternator failure (and if your generator is not generating AC? What to look for/do--Thread started by "Unicornio" from Spain)
Demonstration of Generator Support (A couple inverters that will share AC loads with the generator--smaller generator with large load support)

End result--you get what you pay for.

Basically, use the battery+inverter for nights and daytime "minimal" loads. And use the generator when more power is needed (cooking, evenings at home with everything turned on).

With Generator Support, you can use a smaller generator too--The Off Grid inverter (with generator support feature) will let you use a relatively small genset and supply surge power as needed.

Larger generators are more fuel efficient (kWH per gallon of fuel), but if all you need is ~1,000 watts or less of continuous power (running lights, TVs, computers, fans, etc.) on average--A smaller genset can save you fuel costs overall.

I.e., Running a 1,600 watt Honda eu2000i at 400-1,000 watts for something like 9+ hours ot 5+ hours per gallon--Vs running an 8 kWH diesel set at 1,000 watts at closer to 1/2 gph (plus seriously under loading the generator which can create its own problems) or using even more fuel with a gasoline genset running at light loads.

-Bill

Re: Calc's seem reasonable?

Refrigerators are a wild card... You can get some that are down on the 1.2-1.8 kWH per day average range (hot weather more, cold weather less).

If you can use a chest freezer setup as a refrigerator, you can get down towards ~0.250 kWH per day... Of course, most spouses do not accept moving baskets around for refrigerator use.

If you are there near full time--Then an electric fridge is probably going to be a good solution (with larger PV system). If not, then a propane fridge may be the better way to go (at least until you move their full time).

For most systems, it the smaller loads that run 24x7 that really drive up overall power consumption (fridge, freezer, computer running 24*7, DVR's, Sat Receivers, etc.). Turns out that running a 1,500 watt microwave 20 minutes per day is not nearly as costly.

Power usage is a highly personal set of choices--Just trying to make sure you have the right information for you to make your decisions--not trying to force you down any particular road.

-Bill