New and wanting to build a back up system that can expand to main source of power.

tnt4him

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Sep 4, 2021
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I want to build a a back up system for power outages but then able to expand it later to be the main source of power. I can build my own panels but need to know what is the best efficient solar cells to buy and where? (monocrystalline N type?) I would like to build 2 to 4 425 watt solar panels for a start. Is AGM batteries the way to go or others? How much of a inverter to power the whole house and still be appropriate for starting out as back up? Battery Power control unit? I live near Portland Oregon so if there is a place to buy here for Diy'ers to save on shipping that would be great! My house is 1600sf and plenty of roof facing south. Initially, I want to be able to power the fridge, pellet stove blower, wifi, tv and maybe the washer and dryer (240v) Our heating is gas. Thanks for your advice.
 

MichaelK

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You have very unrealistic expectations as to what you can accomplish. First, I'd recommend totally forgetting about making your own panels. It's a total waste of time for the amounts of power you need to produce. With 250W grid-tie panels going for 50-60$ each, there's no good reason to try to save money making your own.

I myself would never buy AGM batteries. To me, flooded lead-acid will last twice as long and cost half as much. You can also look at Li.

You really need to perform an energy audit before making any kind of decision about inverters. But, if you are running anything with an electric motor, such as refrigerators, washers, or driers, you want to select a Sine-Wave inverter.

I have a small off-grid cabin, and I typically consume only 3-4kWh of power each day, unless I'm running the air-conditioner or well-pump. For a whole-house application, I'd look at 48V systems. I myself am using a Schneider XW+6848 inverter, that I am very happy with.

I used to live in Corvallis, so I am very aquainted with Oregon weather. What are you going to do for the 9 months of the year when it's cloudy/raining? Assume you'll get 10% output from your panels in the rain. I'd say you'd need 6000-8000W of panels to produce a meaningful amount of power on a rainy December day. Right now today, I have 7,500W of panels online making power.
 

tnt4him

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Sep 4, 2021
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Thanks Michael for replying. I lot of good information that I can use. I agree now building my own panels is not cost effective. I found on craigslist locally some new commercial grade 385w bifacial panels for $65. I bought 3 to experiment with. They all have cracked glass but I found a product Qsil 216 encapsulation from T&G solar supply that repairs and seals the glass. All panels tested 45v. I'll see how it goes. But where do I find 250w $60 panels? From December to February we get a lot of rain and cloudy days here but there is lots of sunny days inbetween. I read that the bifacial panels do well in this climate, maybe 60% on a rainy day. Better than others. I have done a energy audit and I use about 20kw per day. Our average winter electric bill is about $80 per month. We are not heavy users. But our summer bill can double if we have a lot of hot days because of the central AC. I would not want to get flooded lead batteries because of the gassing. It would not be good for our living arrangement. I'm looking at the 48 volt lithium phosphate batteries for that reason. I'm leaning towards an off grid inverter because we may someday expand to that, but not now. I'm not too familiar with names of inverters but Growatt seems to stand out.
 

MichaelK

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I also found my panels locally off Craigslist. You can easily check the voltage of your panels, but a more informative number will be the amperage they put out. I would not hold my breath expecting to get 60% output on rainy day. That is most likely marketing department BS. Stick with 10% until you have a measured value. This is easy to do. Get a clamp meter like this one. Besides being able to measure both AC and DC current, it is also designed to measure "inrush" current, the monentary spike in current draw in the first few milliseconds of startup.
Compared to me, I'd say that 20kWh/day is very high, for routine living. With lights, TV, and the refrigerator running 24/7, I use around 3-4kWh per day. I only consume 20kWh on days I'm pumping water. Your first job should be focusing on cutting your consumption rather that building your system.

I've always gone with lead-acid. I consider off-gassing to be a non-issue. You really don't what your power system in the living room anyway. Have it positioned in the garage, or some small ultility room, something like an unused laundry room. Running a central air-con off-grid is going to be very, very expensive. I run just one 8000BTU wall unit.

If you want to buy a quality off-grid inverter, look at names like Magnum, Schneider, and Outback. Make sure you get an inverter with ample surge capacity for electric motors. Most AiO high-frequency inverters only surge to 200% current for 16mS or so. That most likely will NOT start a big electric motor with a high inrush value.
 

tnt4him

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Sep 4, 2021
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A correction, we use about 5kw per day. The misinformation was from PGE phone conversation. I checked my account usage graph and at the most summer months with the AC blasting we hit 12kw. We are a family of 4 with somebody home all day mostly. Thanks for the info on names of inverters. I am very interested in the Schnieder Conext SW6048 4kW 48vdc inverter/charger 120/240vac. Not sure if it has ample surge capacity or AiO high frequency. But I will ask before purchase. From what I have read about hybrid inverters I could charge my batteries (which will be two 48v 100ah LiFePO4) off the grid for ready to use in an outage. Since I live in a populated area our outages are usually just hours not days. What I am trying to figure out is if the hybrid converter can supply percentage of PV power while supplementing the balance with grid. And if needed I could have a generator assist if solar and grid fail. I found 2 48v 100ah for about $1900 which is more than the lead acid but my wife just doesnt like the gasses even if it was in the garage, which it will be.
 

MichaelK

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Do you actually mean the Conext SW 4048?
I have the 24V version of the same unit and I am very happy with it. Here are their specifications.
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Note that the 5 second surge is 41A, which at 240V is 9800W. The starting surge of my well-pump is 38A, and I've read that other people using a Conext can barely get their pumps started. That's why I have Schneider's XW+ to run my well-pump. It has a 52A starting surge. But, unless you want to run a >1hp motor, the 4048 will handle anything in the house except maybe whole-house 240VAC air conditioning.

My 4024 was purchased for my workshop to run my power tools, and it has run everything without a single hiccup. It is a transformer-based low frequency inverter. This inverter can be connected to both the grid, and a generator, though I have not focused any attention on grid connections because there is none. I have charged my batteries via the generator input (ACin#2), and it does that admirabliy.

I'm sorry, but I have to say that problems with outgassing are just anti-lead propaganda by the lithium guys to justify their grossly overpriced selections. With the slightest bit of ventilation, and it will never be noticable. My very first system had the batteries located in the living room. The only time there was any noticable outgassing was on the day I commisioned a new battery bank for the very first time. I still maintain it's a non-issue.
 
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