Building New 24 All In One System, Help with Everything

[HomesteadDad]

I would like to build an off grid system that I could run a couple freezers and a refrigerator off of, and use as a backup power system if the grid went down for any length. I am looking at buying from signature solar and starting with the growatt 3000 all in one
https://www.signaturesolar.us/produ...id-inverter-by-growatt?variant=39494574899405

I'd also buy from signature solar this battery
https://www.signaturesolar.us/products/24v-200ah-lifepower4-battery-by-eg4?variant=39792056959181

I was looking at used solar panels like these.

USA MADE $39 PANELS! 180W 24pc Pallet - UL Listed Solar American Made USED | eBay

Find many great new & used options and get the best deals for USA MADE $39 PANELS! 180W 24pc Pallet - UL Listed Solar American Made USED at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Lot of 20 Used 240W 60 Cell Polycrystalline Solar Panels Vinyl Cracking Silver | eBay

Find many great new & used options and get the best deals for Lot of 20 Used 240W 60 Cell Polycrystalline Solar Panels Vinyl Cracking Silver at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I wouldn't use all those panels, as I have some friends who are interested in some panels as well.

One of my questions is what would be the best amount of panels to connect to this system and in what configuration? I live in Michigan, which from what I can find averages 4.1 peak hours of solar per day. I have grid power now, so I'd like to run that as a transfer source. For running my ac loads(fridge, freezer, anything else) I'd like to run the power to a subpanel. Would I need to run busbars, shunts, fuses, etc?

Thank you for any help.

 

[DThames]

You might consider panels from Santan Solar's web page. Your second listing is one of theirs. I have purchased both new and used panels from them and have been well taken care of by Santan.

I am working on a standby power system myself. You asked about how many panels. If you look in the Growatt manual for the 24v, you will see max PV is stated at 2000w. So an array somewhat larger will serve you by adding a bit more when the sun is not right overhead. Also, if you order panels in by truck freight and you can afford it, get extra panels. What if you were without power for weeks and had to live off of it? You might need to use a reasonable amount of power in the day and also be charging the battery. So a second charger and more panels are something to consider, depending on how serious you are.

I have 2, 3000w 24v Growatts and right now I have 1500w and 1200w arrays on them respectively. I am working to put up 6 or 8 more 300w panels and feed an EPever Tracer charger with that third array. All go to the same battery bank. I want to be able to run 3000w or so during the day and be charging at the same time.

 

[DThames]

Looking at Santan's current offering, you might want to get the Snail Trail panels over the Cracked Vinyl ones. While even higher in price, this one looks fair for a used panel. One thing to consider is mounting cost. It costs about same to mount a 250w panel as a 400w panel. Fewer mounts, let cost and work. edit...and this panel.

 

[DThames]

can't get the link to work with Edit. This one.

 

[HomesteadDad]

You might consider panels from Santan Solar's web page. Your second listing is one of theirs. I have purchased both new and used panels from them and have been well taken care of by Santan.

I am working on a standby power system myself. You asked about how many panels. If you look in the Growatt manual for the 24v, you will see max PV is stated at 2000w. So an array somewhat larger will serve you by adding a bit more when the sun is not right overhead. Also, if you order panels in by truck freight and you can afford it, get extra panels. What if you were without power for weeks and had to live off of it? You might need to use a reasonable amount of power in the day and also be charging the battery. So a second charger and more panels are something to consider, depending on how serious you are.

I have 2, 3000w 24v Growatts and right now I have 1500w and 1200w arrays on them respectively. I am working to put up 6 or 8 more 300w panels and feed an EPever Tracer charger with that third array. All go to the same battery bank. I want to be able to run 3000w or so during the day and be charging at the same time.

I was thinking about starting by buying 8 panels, so just less than 2000 watts. Maybe only connect 4 to start, or probably all in the right configuration? I like the idea of the growatt as I could add another later and stack them. I want to start relatively small and prove the concept to my wife of saving money.

 

[HomesteadDad]

can't get the link to work with Edit. This one.

I was thinking a pallet of panels to get the best price.

 

[DThames]

I was thinking about starting by buying 8 panels, so just less than 2000 watts. Maybe only connect 4 to start, or probably all in the right configuration? I like the idea of the growatt as I could add another later and stack them. I want to start relatively small and prove the concept to my wife of saving money.

Saving money....not very likely unless you are paying a lot for Kwh.
I would argue you to not buy less then 3000w of panels. Also, have a plan on how you want to connect them before you setting on count. For example, a 60 cell panel will have a Voc of about 38-40v. The Growatt can take 150v input, as I recall. So you can only put 3, 40v panels in series. You can do 3 in series, times 2 or 3 in parallel. 9x300w would give you 2700w max and allow something close to the 2000w max for a larger part of the day. If you you did only 6x300w, you would never hit 2000w and would only hit 1800w on freakish minutes. So if 60cell, you would want something you could divide by 3 evenly. Different math for 72cell, so plan it out first.

 

[HomesteadDad]

Saving money....not very likely unless you are paying a lot for Kwh.
I would argue you to not buy less then 3000w of panels. Also, have a plan on how you want to connect them before you setting on count. For example, a 60 cell panel will have a Voc of about 38-40v. The Growatt can take 150v input, as I recall. So you can only put 3, 40v panels in series. You can do 3 in series, times 2 or 3 in parallel. 9x300w would give you 2700w max and allow something close to the 2000w max for a larger part of the day. If you you did only 6x300w, you would never hit 2000w and would only hit 1800w on freakish minutes. So if 60cell, you would want something you could divide by 3 evenly. Different math for 72cell, so plan it out first.

So you're saying to overpanel the system because the likelihood of hitting peak numbers is extremely low?

 

[HomesteadDad]

Saving money....not very likely unless you are paying a lot for Kwh.

On my most recent power bill I was charged $233..35 for 1237 kwh of power. I believe that comes out to $.18/kwh of power.

 

[DThames]

So you're saying to overpanel the system because the likelihood of hitting peak numbers is extremely low?

Yes. A charger that will output X amps, will only output X amps, if it can get the power from the panels. If more power is available, no problem.

Not to scale but something like this with the blue line being the max power the charger will pull from the array. The curve below is actual production from 25 Oct...as far as the shape of the power over the daylight hours.

 

[HomesteadDad]

Yes. A charger that will output X amps, will only output X amps, if it can get the power from the panels. If more power is available, no problem.

Not to scale but something like this with the blue line being the max power the charger will pull from the array. The curve below is actual production from 25 Oct...as far as the shape of the power over the daylight hours.

View attachment 70672

That is great, for some reason I thought if there was too much power going in from panels it would fry the all in one. That is really good to know. Thank you.

 

[DThames]

That is great, for some reason I thought if there was too much power going in from panels it would fry the all in one. That is really good to know. Thank you.

A PWM type charger that is poorly designed ($12 model) may not have proper current limit. The panels are a power source. The battery (for a PWM charger) is the load. The PWM tries to modulate/adjust the load to properly charge the battery. But if of a poor design, it may not current limit, so the battery looks more like a short circuit than a proper load. Yes, that could be an issue.

Modern MPPT chargers, load the panels to their max power point, constantly adjusting the load to get the most out of the panels. But at the same time, they are providing power from a DC to DC conversion to charge the battery. These systems are micro-processor controlled. Any respectable design will have a current limit and will just go to that limit and sit there.

Many have issues understanding this but think about your house with a 200amp service coming in that can deliver WAY more than 200amps. You turn on a 100w light. How many amps does it draw, 200 amps, 300 amps and trip your main breaker? No, it draws less than an amp because it is fixed load. Chargers are a dynamic load but should not exceed their rating. it is their job to do that.

Also, my Growatt has a setting so that I can limit the amps to the battery if I want to. So you can dial it back if you have reason. But on less than ideal sun angles or less then a perfect blue clear sky, over paneling a system will get you more KWH per day.