Evaluation of Usage vs PV vs Battery needed

westbranch

Evaluation of Usage vs Battery vs PV for DECEMBER power use for our in-progress Off-Grid 1200 sq. ft. lake home.

Assumptions: It’s dark till 08:30 and it is dark after 15:30. There is no appreciable change until mid Feruary; 2 retired Adults, one web based consultant.

I have worked to be realistic in estimation of hours of all usage in December. Appliance Watts consumed are nameplate ratings so may be a bit lower in reality. K-a-Watt measurements used if available.

I have used LED’s where possible, otherwise CFLs: 25w and 15w. I oversized the wattage for CFLs where we are uncertain as to amount of needed light, I also may have over planned for more fixtures as well. I am pretty sure we can downsize on some but will not know till next winter for sure. After the fridge (22%), our highest daily use is (lots of) lights followed by computer/ entertainment related. Old TV to get replaced later by efficient LED, etc.

So the Numbers:

Usage: 7150 Wh per day (I know, it’s a bit high but I overestimated lights in winter, the man cave is dark)
7AM to 11 11 – 3PM 3-7PM 7 – 11PM overnight
17% 17% 30% 27% 10%

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Battery: Absolyte GX2000 AGM @ 2000Ah(8Hr) = ~ 2250Ah (20Hr)
Using 2250 Ah rate 50% = 1125Ah
50% DoD @ 24V = 27,000 Wh
7150 Ah x 3days = 21,450 Wh or 41% DoD…. Seems good so far…

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PV: 24 x 130W = 3120W x .75 (winter derate) = 2340W ({6x4} 48 V array)
2340W x 3 hr = 7020 Wh… 120 W under charged

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Charger: Meanwell 1000 - 24V, 34.7A (1000W)
Generator: Honda Eu3000is (2800 W continuous)

Comments re what I may have missed???

I will attach graphs of use per day when I get it figured out....:grr:grr

solarvic

Re: Evaluation of Usage vs PV vs Battery needed

Actually some of the old tv,s are preety efficient. I have a Toshiba 36 inch crt color that only uses 90 watts. :Dsolarvic

BB.

Re: Evaluation of Usage vs PV vs Battery needed

Can you vent cold air to the fridge in winter to reduce power usage?

A laptop vs desktop/entertainment system can really save energy...

In the end, the Kill-a-Watt meter will tell you a lot. It sounds like a fair amount of power usage unless there is heating/cooking use of electricity.

-Bill

westbranch

Re: Evaluation of Usage vs PV vs Battery needed

Attachment not found.

Not much chance of getting cold air in, its a new build and quite! well insulated but I have considered moving it to the pantry area as it will be cooler there.

A couple of big killers are the sat modems both TV and internet, Sat will be on all day as will at least one of the computers. One LT and 1 base model for now. Biggest though is lights as there are several on at the same time in different parts of the house.

attached is my Workbook that is all based on the "Use by Hrs" page. its all itemized.... phew!

HTH

stephendv

Re: Evaluation of Usage vs PV vs Battery needed

Nice and detailed!
You might also want to add the inverter's standing losses as another 24 hour load. And another 5% of total for inverter losses.

Given the price of PV, if I were you I'd shovel some more onto the pile.

rabbit_39

Re: Evaluation of Usage vs PV vs Battery needed

The fridge isn't really 66Watts x 24 hours is it? I mean if it is rated for 66Watts and plugged in for 24 hours, it may only be using 66 watts 12-18 hours of the day rather than all 24. That's my guess anyway. Unless the fridge is opened and closed all the time.

niel

Re: Evaluation of Usage vs PV vs Battery needed

in looking over the list there are some obvious things to me that can be cut back on. for instance the 2 hall lights can be shaved back to 2 9w cfls and it would probably work well enough for you at that wattage. another big area are the printers. i doubt you are printing that much so unplug it or put it on another switched power strip for convenience. try going with a car stereo and headphones at times as this can cut so much wasted power, but 12vdc will be needed for it.

of course i don't believe you will have all of that on as indicated and you can use that as a safety margin. i did notice how you list the refrigerator as running at 66w. is it really 66w running or did you average it for the hour just like mine actually draws close to 140w running, but at 50% duty cycle?

never mind as i missed your post addressing it. boy am i slow to type or what?

westbranch

Re: Evaluation of Usage vs PV vs Battery needed

Guys, here is the updated /reworked version. touched up graphs and added a data page, locked some of the entire pages where they are 'a product' of another page. Overall looking more balanced.

Neil, dropped some time on printers, just have to 'program' the brain to remember...

Stephendv, thanks added the inverter losses in the comparison at the end, assumed 24 hr for standby loads too. may be less but trying to do a worst case scenario.

S-Vic, ''envy"...... checked our CRTs and the 20 yr old Sanyo pulled about 95W, but our 29" Sony is a real hog at ~120W + parasitic...

Additional Comments??