600 Kw Hrs per year

[Jason]

Beautiful daughter Dereck, thanks for sharing the photo and congrats to your family.

[Jason]

(And not sure why the "Big Grin" icon is called "Becky")

Becky? You may want to check that name again

[greenHouse]

Mazel Tov on the daughter's graduation.

[Sunking]

The end of tough years of study for her and the start of some more tough years I believe!

Thanks Russ. Yeah my Daughter has already had to make some changes in plans with the Healthcare Reform Act she is not happy with.

My wife is also a doctor and she is pretty fed up with the reform too. She has now quit accepting Medicare and Medicaid patients and is now considering just leaving the profession all together.

[russ]

@ Sunking - Congratulations to your daughter, your wife and you!

The end of tough years of study for her and the start of some more tough years I believe!

[Sunking]

Julie I am tired of debating. My comments were base on 1 fridge. I do not bother anymore with all the math and showing work. For this simple stuff I do in my head and round off. A fridge that uses 800 wh/day in Indiana only needs a 1000 to 1200 watt solar panel and a 4500 wh battery capacity.

If someone wants to know the math, there are hundreds of threads where I have done it, and even a Sticky which I will gladly direct them. I am one of those people when you are hungry, I will teach you how to fish to make make it on your own, but you gotta do the work.

Anyway I am too tired right now. Spent last night out late in OKC at Daughters graduation from OU med School.

[greenHouse]

Hold the bus right there. 2 fridges? That maybe where we parted ways. I based my comments on 1 unit using 800 wh per day.

Yeah, two of them.

Now do you understand better where I'm coming from? Because you're right about the one, but not about the two.

One is fairly simple -- 0.8KWh * 1.3 (safety factor) / 0.85 (DC discharge derating) = 1.2KWh / Day. 1.2 * 2 = 2.4KWh DC. 1.2KW (panels) * 2.2 (hours) * 0.70 (DC charge derating) = 1.84KWh / day DC. Even at 2.9 hours, that's 2.4KWh DC, which is estimated demand with =zero= left for recovering from no-sun days.

Double checking the derating factors, 0.85 * 0.70 = 0.60 full-cycle efficiency. I find 60% is more accurate for systems that don't include large amounts of float time built into the design.

Back-calculating the correct array size you get 1.2KW * (2.4KWh / 1.84KWh) = 1.6KW. The added cost is (1600 - 1200) * $2.50 / watt = $1,000. That's about two extra panels. Racking is minimal, along with wiring, DC combo box, etc. A bit expensive, but that should produce a system that almost never needs a generator. Not even during a winter holiday in a below average insolation year :becky:

As an aside, my first engineering field was Marine, and "safety factor" is all over the place there. Not including a proper safety factor is not a "value" proposition -- it means the system is guaranteed to fail in below average conditions.

(And not sure why the "Big Grin" icon is called "Becky")

[Sunking]

Not to be a pain, but could you show your work on how recovery from 2 days no sun happens with that equipment -- excluding the generator. Likewise, the "on-average" isn't going to be when it matters -- the NREL minimum is 2.2 hours for Evansville, which is a deficit (1.2KW * 2.9Hrs >> 1.2KW * 2.2Hrs ...) and if you don't design in the range of possible behaviors, you've got a client who is happy half the time -- the above average half.

And while I disagree with the OP's choice of 2 8.8 CuFt freezers (

Hold the bus right there. 2 fridges? That maybe where we parted ways. I based my comments on 1 unit using 800 wh per day.

As for the rest of it yes i stand firm an 1200 watt panel in Southern Indiana is more than enough for 1 device that average 800 wh per day with ample overkill for recovery time for those heavy use days or a few cloudy days.

There are two extremes in a electrical design: Value and Mission Critical. A homeowner fridge is not mission critical unless they are diabetic or need to have refrigerated medicine, but even then there are less expensive measures to deal with those times of extended outages.

On the value side is is risk and for a PE who stamps specs and drawings is exposed to liability so we tend not to go that route.

Logically I shoot for somewhere in between. For consumer or home owner applications I am conservative and lean more toward value design with some reasonably economical overkill. So with that said I tend to go with 5 day battery reserve (2.5 days real time), and 150% more power than average daily use under shortest day or worse case conditions. In addition it is usually less expensive to add a generator rather than more batteries and solar panel wattage to cover the extreme cases where you are likely to have several cloudy days or extreme occasional uses. Smaller systems like 100 watt panel systems do not fall under those conditions.

[Jason]

nice! yall are awesome

[Sunking]

Well maybe one of these days you'll put your photo as your avatar so we can see what a real deal smart ass looks like :P

What pix? This one? :becky:

[greenHouse]

Well maybe one of these days you'll put your photo as your avatar so we can see what a real deal smart ass looks like :P

I put mine in so y'all can see what a pain in the @ss looks like

[greenHouse]

Yes I know that, and we are talking about winter. I am not so sure you Xmas day argument is valid with a 8 cubic feet fridge, but is irrelevant IMO. With a 1200 watt panel on average in December generates about 3 Kwh, with 2 Kwh usable which allows for decent recovery times. But again is still irrelevant because one piece of equipment every off-gridder should have is a generator to make up and recover when you have a few cloudy days or extreme uses.

Not to be a pain, but could you show your work on how recovery from 2 days no sun happens with that equipment -- excluding the generator. Likewise, the "on-average" isn't going to be when it matters -- the NREL minimum is 2.2 hours for Evansville, which is a deficit (1.2KW * 2.9Hrs >> 1.2KW * 2.2Hrs ...) and if you don't design in the range of possible behaviors, you've got a client who is happy half the time -- the above average half.

And while I disagree with the OP's choice of 2 8.8 CuFt freezers (at almost 600KWh total, compared to 445KWh for my 25CuFt all-in-one), I'm unclear about how that choice makes it so people go in and out of a fridge more (or less) on holidays than otherwise? It's just what people "do" when they are at home (or a friend's) and enjoying themselves. Even the ISOs know it and put that into their day-ahead forecasts.

[Sunking]

But also, you can't take 294KWh / year and divide by 365 because that isn't how refrigerators work -- and if you've studied appliance loads, you'd know that. A fridge will use more per day in the summer (on average) than the winter. More on a weekend than a week day (on average).

Yes I know that, and we are talking about winter. I am not so sure you Xmas day argument is valid with a 8 cubic feet fridge, but is irrelevant IMO. With a 1200 watt panel on average in December generates about 3 Kwh, with 2 Kwh usable which allows for decent recovery times and twice what the fridge uses normally. But again is still irrelevant IMO because one piece of equipment every off-gridder should have is a generator to make up and recover when you have a few cloudy days or extreme uses.

[Jason]

Jason,

No, I'm going to point out that the mods allowed him to insult me for days on end for no good reason. I've yet to see him called to task for the =dozens= of insults he offered up the last time I was here.

Julie, I'm not taking sides here and sorry if it seems that way. Dereck and I generally communicate via email or private messages. I made it clear to him about the insults when it first started. In fact, he almost took a long break from the forum because of this whole ordeal, so I wrote several messages to try and talk him out of doing that. I've emailed you a couple of times (not regarding this), but just general, friendly emails and didn't get any response, so I wrote you here where I know you'd see it.

The whole point of the post is just to say there are better ways to get your point across without unleashing insults or attacks. You guys are even when it comes to them, and I just wanted to bring it to your attention. It's not something I like to do, especially cause I love having you both here, but just something that has to be said. I get complaints for the bashing, then I push the message forward. Not only that, but I put lots of time and money into this forum, and don't like seeing anything less than quality, educational information.

And I don't follow him around. I received an e-mail saying there was an update to a thread I'd posted in. I checked the "new" posts and found that Dereck was making unsupported pronouncements in a number of threads.

Again I'm not taken sides, it's an observation I've made. I'd say the bigger half of your posts are quoted replies from Sunking, so that's why it appears that way. That may not be your intention, which you said, so I apologize for that.

As I said to Dereck, it may be better to NOT post than to post incorrect information simply because it's free advice. Properly sizing an off-grid system isn't all that hard. Not asking the OP for the needed information, then guessing at a solution is just laziness and doesn't advance the understanding of the art.

I wouldn't consider his posts necessarily wrong, but just more conservative than your POV maybe? I completely understand where your coming from, I'm down for debates, and love reading them, but when the insults start, that's when I have to step in, otherwise when do they end? From what I can tell, you guys would go back and forth all week.

BOTH of you can defend your POV without insults. I've been around forums enough to notice the trend of people getting really cocky behind the keyboard and saying stuff they wouldn't say to people in their face. The rules of courtesy and respect are thrown out the window. If a couple people get away with it, before you know it, more people are being rude, insulting and just plain out not caring. This forum is still in it's infancy, and I'd prefer it to be a place of education rather than drama corner in the solar industry.

I resemble that remark. :becky: But in all honesty I do it on purpose, not to insult, but to get the OP attention or a wake up call.

Well maybe one of these days you'll put your photo as your avatar so we can see what a real deal smart ass looks like :P

[Sunking]

Sure he may not have the right answer everytime and can sometimes be a smart ass,

I resemble that remark. :becky: But in all honesty I do it on purpose, not to insult, but to get the OP attention or a wake up call.