600 Kw Hrs per year

[kbhale]

I'm going to be buying two 8.8 cubic foot chest freezers for my retirement home in southern Indiana. Plan to put a thermostat on one and use it as a frig. I want to run both off solar and have enough batteries back up for 48 hours. Energy star rating is 294 Kw Hrs per year for each.

Just looking for some ideas, what I would need to supply the 600 Kw Hrs per year.

[Sunking]

I'm going to be buying two 8.8 cubic foot chest freezers for my retirement home in southern Indiana. Plan to put a thermostat on one and use it as a frig. I want to run both off solar and have enough batteries back up for 48 hours. Energy star rating is 294 Kw Hrs per year for each.

OK first you do not have enough battery capacity, you need a minimum of 5 days. At 48 hours you will be discharging the batteries too deeply each day (50 %) and shorten the battery life to a year or two instead of 5 to 7 years discharging 20% per day.

As for panel wattage goes 600 Kwh / 365 days = 1.65 Kwh day. So the panels will need to generate a minimum of 3.2 Kwh per day. So with Indiana 2.6 Sun Hour day you will need a panel wattage of 3200 wh / 2.6 h = 1230 watts using a PWM controller, or 950 watts using a MPPT controller.

Battery capacity = 1625 wh x 5 days = 8125 wh. To find the battery amp hour capacity divide 8125 by the battery voltage. So if using 12 volts 8125 wh / 12 volts = 677 Amp Hours.

[kbhale]

Thanks. It's good to know it's do able.

[greenHouse]

OK first you do not have enough battery capacity, you need a minimum of 5 days. At 48 hours you will be discharging the batteries too deeply each day (50 %) and shorten the battery life to a year or two instead of 5 to 7 years discharging 20% per day.

That's only true if he's cycling the batteries to 50% DOD each and every day.

You also didn't include recovery time in your array size calculation, which means the batteries run down and stay run down.

[Sunking]

Why would anyone design to 50% DOD each day? The design I mentioned is 20% per day. My calculations are spot on based on the info provided. 1230 watts is more than enough to recover from a cloudy day or two.

[greenHouse]

Why would anyone design to 50% DOD each day? The design I mentioned is 20% per day. My calculations are spot on based on the info provided. 1230 watts is more than enough to recover from a cloudy day or two.

I don't know. Why did you when you told him not to use that for a backup calculation?

As for recovery, 2.6 sun hours into 1230 watts isn't enough to recover, not that you bothered to specify the number of days to recover. Hint: how many days before he can have two more days of no sun?

[Sunking]

The fridge uses 294 Kwh per year. That works out to 294 Kwh / 365 days = .805 Kwh per day. A 1230 wat solar panel in Indiana on Xmass day will produce 1230 watts x 2.6 hours = 3198 Kwh at the terminal. At the output of a PWM charger roughly 2 Kwh per day. That is more than enough for any recovery factor. Care to guess what happens in Spring, Summer, and Fall?

Julie I suggest you get a Solar Design guide written by Dr John Wiles of NMSU. FWIW John wrote NEC 690, and developed the solar design standards for Sandia National Labs. That is where I learned working with him on the NEC code making panel.

[greenHouse]

The fridge uses 294 Kwh per year. That works out to 294 Kwh / 365 days = .805 Kwh per day. A 1230 wat solar panel in Indiana on Xmass day will produce 1230 watts x 2.6 hours = 3198 Kwh at the terminal. At the output of a PWM charger roughly 2 Kwh per day. That is more than enough for any recovery factor. Care to guess what happens in Spring, Summer, and Fall?

I don't have to guess because I also know that it isn't "2.6 hours" like magic. That is the average amount of sun (it actually isn't since you don't know =where= in Southern Indiana -- some parts have even less than that), including periods of poor weather. Since the actual above-the-horizon times cosine-effect time is much greater than 2.6 hours, there have to be days with little or no sun -- that's called "Statistics". And you've not bothered to calculate how many days to recovery. For that matter, the 294 KWh per year isn't a magical number either. It's the ideal value, which doesn't include not-so-ideal behavior.

Julie I suggest you get a Solar Design guide written by Dr John Wiles of NMSU. FWIW John wrote NEC 690, and developed the solar design standards for Sandia National Labs. That is where I learned working with him on the NEC code making panel.

Dropping names doesn't work with me. Knowing what you're guessing (badly) about would be what you'd need to do. Showing your work would be another solution.

"Indiana" is a state, it is not a specific location where all of the effects of weather can be used to calculate the correct insolation. And if you =had= read the NREL charts (instead of guessing ...), you'd know that "average" insolation is a range between minimums and maximums. Which you also didn't show.

If you =had= worked with Wiley, I suspect you'd have known that the difference from one end of Indiana, or even one side of a hill, to the next can be significant. =Weather= is the primary cause of differences in insolation since change in latitude isn't great enough. And =weather= changes greatly depending on location. Which you don't know.

(Also, the word is "watt" not "wat")

[Sunking]

I don't have to guess because I also know that it isn't "2.6 hours" like magic.

That is where you are wrong. I was not guessing, I quoted from NREL Evansville Indiana for the month of December. That is as far south as you can get in Indiana. So 1230 watts is more than adequate.

But to your point, there has to be some educated guesses as the OP does not supply enough information. I only get dead accurate when provided the information or paid to do it. Forums are free advice,

[greenHouse]

That is where you are wrong. I was not guessing, I quoted from NREL Evansville Indiana for the month of December. That is as far south as you can get in Indiana. So 1230 watts is more than adequate.

But to your point, there has to be some educated guesses as the OP does not supply enough information. I only get dead accurate when provided the information or paid to do it. Forums are free advice,

"South" doesn't matter -- "weather" matters. The difference, for example, between East Chicago and Bloomington, which is barely any difference in latitude in the grand scheme of things, is significant because of Lake Effect weather. The differences between Houston, Austin, Waco and Dallas -- not a lot of difference in latitude -- are all dominated by =weather= patterns. Even where I live, the difference between downtown Austin and where I live (almost to Round Rock, for anyone with a map) is about 5% to my favor.

As for only giving accurate information when being paid, perhaps you should stop posting? I'd rather not post than intentionally post wrong information, which is what you're doing here. Generally speaking, intentionally posting wrong information doesn't lead to being paid to give correct information ...

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). More on a holiday than a work day (on average). So while you're just plain wrong ("guessing" is a better term, but "guessing" is also "wrong") about Xmas (one 's' in the standard abbreviation) insolation, you're even more wrong because a typical Xmas day, spent with family and friends and lots of food, is going to be an above average fridge day, and four days past the solstice, pretty low on the sun-hours. Like the way my 445KWh / year fridge managed to use 2.2KWh one day last month and my solar harvest is going to hell in a hand basket.

[Jason]

While you may find it entertaining to find threads Sunking makes post in, challenge everything he is saying, and make childish insults, the majority doesn't.

Sunking is here EVERY DAY helping people with their questions. Sure he may not have the right answer everytime and can sometimes be a smart ass, but he puts forth the effort and time and is a tremendous help. His number of helpful posts greatly outweighs the few bad days. Having said that, Julie you have been helpful too and it doesn't go unnoticed but I've noticed this trend of you following Sunkings posts and creating a huge non-sense argument in people's threads. The OP of these threads doesn't like it and will move on.

Sure you know your stuff, but coming here for the sole purpose of finding posts Sunking makes to argue his statements aren't appreciated. Your not on the attack at WS all the time, so I'd appreciate the same respect here.

I'm sure your response would be he's giving inaccurate information and your correcting him to make sure visitors are getting (what you see) as truth, but do you think the average visitor is going to know which person is 100% right? of course not. That's why you guys are throwing out all these credentials and experiences to persuade the average visitor your argument weighs more. People come here to learn, and when they have to sift through the bs to find the answer, most likely they will leave. The majority of the people here are older, wise, professionals and not into reading the mental sparring.

If your going to help people and give advice (minus the insults), great...the community appreciates it. But adding in all the unnecessary stuff, for example correcting Sunkings spelling, is ridiculous. He mis-types watts one time and you point it out? Come on guys, your 3 hours away from each other, go grab a couple drinks and work it out.

[Mike90250]

Moderator Disclaimer

Without a paid consult, members here can only guide you on the right direction. The more info you provide (panel specs, your location, roof angle and orientation) the better we can estimate your situation.

As you can see, MANY factors can influence what can and cannot be done. One is how fat your checkbook is, and how thin it will be after you install solar and batteries.

[greenHouse]

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.

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.

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.

[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.

[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