Author Topic: Off-Grid Power Systems  (Read 17121 times)

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Offline Madroaster

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Re: Off-Grid Power Systems
« Reply #25 on: October 27, 2007, 11:16:38 PM »
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The fridge is a killer, but the compressor doesn't run 1440 min (24 hrs) a day.Find the model # of your fridge or pick a fridge that seems similar.

Go to http://www.energystar.gov/index.cfm?fuseaction=refrig.display_products_html  and find that model and see what the EPA says the average Kwh use is. It's listed per year.

For example, a new efficient Kenmore is rated at 480 Kwh/year, 40 Kwh a month.
That calculates to 7 x 175 PV panels and 6 of the 6 VDC 350 amp batteries just to serve the refrigerator!!  :o
 

Wait--I'm confused.  If an appliance is rated at X kWh/year, then it can be divided by 365 for an average daily requirement.  Correct?

A Sun Frost RF16, rated at 0.48kWh/day * 365 = 175kWh/year.  Correct?

A Brand X model, rated at 335kWh/year / 365 = 0.91kWh/day.  Correct?

The way I read it, basing my entire electrical needs on a Sun Frost DC model-based system will require 86kWh/month, while basing it on a Brand X model-based system will require 112kWh/month.  

Unless I'm wrong, either Sun Frosts are prohibitively consumptive, or I misread what you said, or you have some error I don't quite understand.  But my thinking is more in line with what you wrote in this thread:

Quote
FYI, IF a person was to consider an electric, compressor driven refrigerator however, I am not convinced that the large additional cash outlay for the Sunfrost (type) is counterbalanced by the lower energy use. I ran the numbers many months ago. A less expensive, but highly rated (but not as frugal on power as the Sunfrost) refrigerator saves a bundle on the purchase. I calculated that spending a part of the difference on another good PV panel would provide the needed power difference.  :-/ :-/ :-/ :-/

Can you clarify this for me, please?

As a side note, if anyone's interested--taking the data from that website quoted above and playing with it in Excel for a while yields some pretty interesting results when you sort by different variables.  Specifically interesting is creating a ratio of annual energy use to volume (especially when you previously sort for configuration (chest freezer, fridge only, manual defrost, etc.)).  It really helps you narrow down appliance choices.  Neat stuff that we couldn't have done even 15 years ago.

Cheers,
--Derek

Offline glenn kangiser

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Re: Off-Grid Power Systems
« Reply #26 on: October 28, 2007, 03:16:49 AM »
Derek, my numbers are  175/12 =14.6 KWH per month or less than 1/2 kwh per day.

The brand x would come in at 27.9 kwh pwr month or under 1 kwh per day

This pretty well agrees with my fridge and new freezer.  The freezer comes in at less usage than advertised per the Kill-a-watt meter.  It is the most efficient Sears freezer we could find and there is a great range of difference in their range of models, some using twice as much power for the same size.  Chest freezers without a defrost cycle are most efficient.

Chest refrigerators or a chest freezer converted to a refrigerator are very efficient also but you don't see them often.  The chest keeps the cold air from falling out every time you open the door.

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Re: Off-Grid Power Systems
« Reply #27 on: October 28, 2007, 05:06:38 AM »
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chest freezer converted to a refrigerator

How would you do that?

Offline peter nap

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Re: Off-Grid Power Systems
« Reply #28 on: October 28, 2007, 05:20:44 AM »
Glen and Don.....this is straying a little further OT, but since I've been looking at usage meters, what's your opinion (Cost aside) of:

New Kill-a-Watt EZ

and the

Watts Up Pro

The Watts Up seems to have a few features that will give more detailed information over time as well as a USB port.

Any others you can think of?

Offline glenn kangiser

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Re: Off-Grid Power Systems
« Reply #29 on: October 28, 2007, 05:26:16 AM »
I read abut it somewhere.  I'm pretty sure all you would have to do is modify the thermostat or if the range on it is wide enough you may only have to set it warmer.

Here it is -- [highlight]Uses 100 watts per day[/highlight].

http://mtbest.net/chest_fridge.pdf

http://mtbest.net/part-list.pdf
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Offline peter nap

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Re: Off-Grid Power Systems
« Reply #30 on: October 28, 2007, 05:30:38 AM »

Offline MountainDon

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Re: Off-Grid Power Systems
« Reply #31 on: October 28, 2007, 09:26:41 AM »
Quote
Wait--I'm confused.
Derek, let's see what I can clarify.

But first a question: You used a figure of "A Sun Frost RF16, rated at 0.48kWh/day * 365 = 175kWh/year." I do see that number on the Sunfrost website. But the EPA figure for that model is 254 Kwh/year. Since all the figures on the EPA comparison chart have been arrived at by the same EPA testing method, and not what the manufacturer reported, I would only compare numbers from that EPA worksheet.

There is a Sunfrost, model RF12, that carries an EPA rating of 171 Kwh/year, but it's smaller.

I picked a Kenmore model at random for the example calculation of 480 Kwh/year. Some of the models on the EPA sheet may not be currently available except from old inventory. So today I went to the Sears website and used their selection eliminator. I came up with some available Kenmore fridges to compare.  One is their model# 6787. It uses 407 Kwh/year (EPA). Part of the problem with comparing this Kenmore to the Sunfrost of the size. Kenmore just doesn't have a model that's really comparable to the SF R-16. The Kenmore is bigger.  :-/

Searching some more, a more comparably sized Frigidaire, FRT17HB3C, has an EPA rating of 391 Kwh/year. Not much better than the larger Kenmore. Therefore I believe it's safe to say that it would not be difficult to find a "normal" Energy Star fridge that uses about 400 Kwh/year.

400 Kwh is 146 Kwh more than 254 Kwh; 57% more than 254. So the Sunfrost appears to the Energy Star King (out of available ready to use new refrigerators) , but at a price of around $2600 - 2800 + freight

Now, back to my statement "480 Kwh/year, 40 Kwh a month. That calculates to 7 x 175 PV panels and 6 of the 6 VDC 350 amp batteries just to serve the refrigerator!!" That was calculated on tjm73's solar deficient location. The tables indicate Rochester, NY has a minimum winter solar sun-hours of 1.58. For comparison my NM location has a minimum winter solar sun-hours of 6.01. That's 3.8 times as much usable solar sunshine, or 3.8 times fewer PV panels required. Geographic location makes a big difference in calculating solar PV power generation expense.

Re-running the Rochester figures at 400 Kwh, instead of 480 reduces the # of 175 watt panels to 6, instead of 7.

Running the numbers for my NM location on the 400 Kwh fridge gives the result of 2 panels required. Lucky me. My location is what I based my statement: "....however, I am not convinced that the large additional cash outlay for the Sunfrost (type) is counterbalanced by the lower energy use.", on. I should have emphasized that my opinion was based on a location with similar solar exposure. That was deficient on my part and I'm sorry for that.

At this point I have to consider whether or not the expensive Sun frost ( $2600+) is the correct choice, or the relatively cheap (<$500) Frigidaire plus 175 watt 2 panels, $1600 (+ batteries ?). Or maybe the Servel propane at is the best choice, best compromise at around $1300 shipped to my home city.  :-/ :-/ :-/  (Compromise because propane is a fossil fuel you buy from somebody else. And no, I don't want to get into methane production, or whatever.  ;D

I hope I made some sense.





« Last Edit: October 28, 2007, 11:50:02 AM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: Off-Grid Power Systems
« Reply #32 on: October 28, 2007, 12:02:08 PM »
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.....New Kill-a-Watt EZ   and the    Watts Up Pro
I had a quick look. The Kill-a-Watt EZ is much like the older one I have, but without the cost calculator. Since I've never bothered calculating the actual cost from the power company, that doesn't really interest me if I have to pay more than $5 for the feature. [I never looked at the price diff between old and EZ]

The Watts Up Pro offers more ability, especially if you spring for the optional computer interface/software. But once again, for my purposes all I wanted to do was obtain some real world power use figures. If I make changes and reduce actual power paid for my meter and power bill tells me what's really important. But that's just me. [Watts Up Pro is tempting, but I have enough things to occupy my time.   ;D]
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline peter nap

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Re: Off-Grid Power Systems
« Reply #33 on: October 28, 2007, 12:21:41 PM »
The biggest thing I liked about the watts up, is the ability to chart usage over time. I worked for this states  utility commission for a number of years and monthly charting saved the day for a lot of customers having a spat with Virginia power.
Of course, in those days, we used meters wit real paper charts in it.

I can't resist telling this story.

I had one fellow who had the nerve to claim Vepco was overcharging him. I went out and tested his meter and it was 99.99999. He still wasn't happy. I looked at his bills and they looked way too low for what he was using. All the seals were good on the meter so I put a graph meter in the line.

A month later, he was still bitching so I told the company to swap his meter. He went ballistic over that. The next month, his bill nearly doubled so I checked the graph...same usage. I had the Power Company pull the meter apart and found he had wired a photoresistor in line with the potential coil. When the sun went down, it quit recording.

Why he complained....I haven't a clue :o But having that chart as a reference was a lot of help.


Offline MountainDon

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Re: Off-Grid Power Systems
« Reply #34 on: October 28, 2007, 12:24:24 PM »
As for converting a chest freezer into a chest refrigerator, the successful tinkering would bring personal satisfaction.  :) But I don't like chest fridges or freezers.  :(

We have a small chest freezer and a small upright, and there is no doubt the chest is more efficient than the upright, mainly (only?) because the cold air doesn't spill out when you open the door. But I always seem to be rummaging more in the chest type than I do in the upright. When possible most frozen goods are in the upright with the chest reserved for overflow of things like a dead elk/deer/cow. If you don't open the door a lot I don't think the upright is much worse than the chest.  :-/

I might rethink my home side by side fridge/freezer if I was solar generating all my power and storing the power in enough batteries to run everything when the sun doesn't shine.

So I'm kind of here and there on this power question. At home one set of criteria [for grid intertie] and in the mountains [off grid] another.

« Last Edit: October 28, 2007, 01:23:04 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: Off-Grid Power Systems
« Reply #35 on: October 28, 2007, 12:45:04 PM »
Of course for the die-hard tinkerer one could always build their own ammonia absorption refrigerator and/or freezer.  ::) ;D

http://www.nh3tech.org/abs.html

Like Allie Fox (Harrison Ford) in Paul Theroux's book, made in to a movie  "The Mosquito Coast".

http://www.amazon.com/Mosquito-Coast-Paul-Theroux/dp/0618658963/ref=pd_bbs_sr_2/105-7550156-2238024?ie=UTF8&s=books&qid=1193607783&sr=8-2

http://en.wikipedia.org/wiki/The_Mosquito_Coast

http://www.peterweircave.com/mosquito/
« Last Edit: October 28, 2007, 12:46:27 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: Off-Grid Power Systems
« Reply #36 on: October 28, 2007, 02:04:12 PM »
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I can't resist telling this story.
Love that story, Peter. Makes you wonder.... must have forgotten he tampered with the meter. I'd think that swapping the meter would be one of the first things if a customer complained enough.

I heard of a case, or cases, back home where several neighbors on one street got caught stealing power from the power company. Back then the city owned hydro company did a lot of flat rate water heater hookups. You paid by the size and number of electric heater elements in the tank. People swapping their smaller elements or adding a second was commonplace, but those folks were usually caught more readily. I think there was a tank size factor as well. But there was no controller that limited the amount of power that could be used. That was strictly limited by cable and fuse size. The water heaters were all situated in the basement and wired with BX armored cable. So the one neighbor replaced the cable with heavier and jumped up the fuses too. Then he used that power for some special outlets he used for electric room heaters. He did several neighbors too. They got caught when one of the neighbors got caught when he complained about blowing fuses frequently.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline glenn kangiser

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Re: Off-Grid Power Systems
« Reply #37 on: October 28, 2007, 02:24:26 PM »
Don't forget about our member, Gary's website-- lots of free stuff there.  http://www.builditsolar.com/

Gary has a link to the Solar Ice project from Home Power. I thinke I have a copy of the PDF somewhere.  It used to be free but is now a $5 archive item from HP.



You could build one from the information in this PDF.
« Last Edit: October 28, 2007, 02:25:06 PM by glenn-k »
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Offline glenn kangiser

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Re: Off-Grid Power Systems
« Reply #38 on: October 28, 2007, 02:33:47 PM »
Matter of fact I do -

"Always work from the general to the specific." J. Raabe

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Offline Sassy

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Re: Off-Grid Power Systems
« Reply #39 on: October 28, 2007, 05:51:52 PM »
After we started spending most of our time in the underground cabin, I kept expecting the power bills to decrease  at our house in the valley - they just kept going higher.  I called the power company to inquire - they asked me to go out & read what the meter #'s were.  I read them back - they kept telling me I needed another # - I said "no, there are only 4 #'s!"  Anyway, come to find out, they had been reading the meter wrong - it was an old meter - after that the bills were about a 1/3 of what they had been.  The month I called, the bill was around $275-300 - the next month, $80 & they've been low ever since.  Never could get them to refund all the over-charges  >:(
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Offline glenn kangiser

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Re: Off-Grid Power Systems
« Reply #40 on: October 28, 2007, 06:42:59 PM »
We suspect that they had been adding a zero at the end or somehow making up the 5th number that the new meters have.  I think our meter was from 1952.
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Offline tjm73

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Re: Off-Grid Power Systems
« Reply #41 on: October 29, 2007, 05:26:21 PM »
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After we started spending most of our time in the underground cabin, I kept expecting the power bills to decrease  at our house in the valley - they just kept going higher.  I called the power company to inquire - they asked me to go out & read what the meter #'s were.  I read them back - they kept telling me I needed another # - I said "no, there are only 4 #'s!"  Anyway, come to find out, they had been reading the meter wrong - it was an old meter - after that the bills were about a 1/3 of what they had been.  The month I called, the bill was around $275-300 - the next month, $80 & they've been low ever since.  Never could get them to refund all the over-charges  >:(

I woudl think documented overcharges could be used to force at least a credit applied to future bills.

Offline Madroaster

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Re: Off-Grid Power Systems
« Reply #42 on: October 29, 2007, 05:50:39 PM »
Quote
Quote
Wait--I'm confused.
Derek, let's see what I can clarify.

But first a question: You used a figure of "A Sun Frost RF16, rated at 0.48kWh/day * 365 = 175kWh/year." I do see that number on the Sunfrost website. But the EPA figure for that model is 254 Kwh/year. Since all the figures on the EPA comparison chart have been arrived at by the same EPA testing method, and not what the manufacturer reported, I would only compare numbers from that EPA worksheet.

Agreed.  My bad.

Quote
There is a Sunfrost, model RF12, that carries an EPA rating of 171 Kwh/year, but it's smaller.

I picked a Kenmore model at random for the example calculation of 480 Kwh/year. Some of the models on the EPA sheet may not be currently available except from old inventory. So today I went to the Sears website and used their selection eliminator. I came up with some available Kenmore fridges to compare.  One is their model# 6787. It uses 407 Kwh/year (EPA). Part of the problem with comparing this Kenmore to the Sunfrost of the size. Kenmore just doesn't have a model that's really comparable to the SF R-16. The Kenmore is bigger.  :-/

Danby makes a manual defrost 17CuFt fridge (no freezer), D1707W which is pretty close to the R16.  It uses 335kWh/year according to the EPA.  That's a good approximation.

Quote
Searching some more, a more comparably sized Frigidaire, FRT17HB3C, has an EPA rating of 391 Kwh/year. Not much better than the larger Kenmore. Therefore I believe it's safe to say that it would not be difficult to find a "normal" Energy Star fridge that uses about 400 Kwh/year.

400 Kwh is 146 Kwh more than 254 Kwh; 57% more than 254. So the Sunfrost appears to the Energy Star King (out of available ready to use new refrigerators) , but at a price of around $2600 - 2800 + freight

Now, back to my statement "480 Kwh/year, 40 Kwh a month. That calculates to 7 x 175 PV panels and 6 of the 6 VDC 350 amp batteries just to serve the refrigerator!!" That was calculated on tjm73's solar deficient location. The tables indicate Rochester, NY has a minimum winter solar sun-hours of 1.58. For comparison my NM location has a minimum winter solar sun-hours of 6.01. That's 3.8 times as much usable solar sunshine, or 3.8 times fewer PV panels required. Geographic location makes a big difference in calculating solar PV power generation expense.

Ahah.  I didn't realize you were referring to his specific location.  That does make a big difference.

Thanks for the clarification.  It makes perfect sense now.  I'm in the same boat you are...which appliances to use with which power system.  Sometimes my head hurts.  Hopefully my wallet won't.

Offline MountainDon

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Re: Off-Grid Power Systems
« Reply #43 on: October 29, 2007, 05:56:41 PM »
Quote
Danby makes a manual defrost 17CuFt fridge (no freezer),
Yes, the freezerless fridges do use less. But I want and use a freezer. Been used to having one for so long it's a must. But if you don't need a freezer that could be an excellent choice. I beieve sunfrost makes some fridge only too. But still pricey.

I believe one of the things tat makes the RF-16 so good is it has a compressor for the fridge and one for the freezer.

A normal fridge actually only cools the freezer. There's a bleed of cold air (for lack of knowing the proper term) from the freezer to fridge.
« Last Edit: October 29, 2007, 06:00:12 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

 

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