Help a newb assembling a system

[Spelunking]

Hi all,

I am assembling a solar system and I would needs some help accessing if what I want to di is viable or if I will ending up burning down the house or frying some components.

First I would rate my overall knowledge from 1 to 10 as a solid 3 (maybe 4 if I take my vitamins) so I probably know just enough to not hurt myself but probably ruin some expensive equipment if not guided.

The objective:

This is meant as a backup for now, meant to power lights (not the entire house), a fridge, a chest freezer an oven and some other odd appliances (think toaster, coffee machine, charge cell phones, etc.). But I want to be able to upgrade and add more off-grid capability.

If I go by my power bill I consume on average 17kWh per day, but this comes with a caveat, much of that power is used for heating water, pure waste and appliances that are constantly on just consuming and that will be left out of the system entirely, and 2 pumps (I have a well, that I *think* is 100 ft, roughly 30 meters, deep that fills a ground level cistern from where another pump draws water to serve the house and garden, keep in mind the last pump turns on every time the pressure gets lower than 1.5 bar, so quite often), those pumps are power hogs and I will address them in the future, but for now they are tied to a diesel generator. I think that if I cut enough "fat" I can lower it to 10 kWh.

So onto the system itself:

I am thinking of using a Growatt SPF 5000 ES powered by 6 or 7 500w panels in series and use 2 pylontech US 3000C 48v batteries in paralel as a power bank.

The panel's specs will be provided below as the batteries and the MPPT/Inverter are very common and a known variable

Should the battery cable that connects to the growatt be 2 or 4 gauge?

I am not connecting this to the grid, so I am thinking about connecting the growatt to it's own panel where the appliances will be connected to, through a power outlet. So should the breakers be of what amperage, (20, 15, 40?), and how thick should the gauge of the wire be? I am thinking 12 but that is just a guess.

I am in southern Europe, so I get a lot of sun (annoyingly so), and the power being 230v 50hz that would mean I won't need any transformers right? In theory I could just plug an appliance into the growatt and expect it to power up, correct?

For now this is all I can think of, sorry for the infodump but this is so you have as much info as possible, so you know as much as possible and are not frustrated.

Below, you will find a diagram of what I intend to do and specs for the solar panels.

Thank you in advance for your help

 

[Spelunking]

So, what do you think, is this a good idea? A bad one? A really bad one? Anything you would do differently?

 

[MichaelK]

Most likely 7 panels might not work, because it is a prime number. First, can you post the specifications of your particular Growatt? What is the maximal Voc for panel input? Seven of those panels in series would be putting out 362Voc, and that's at room temperature. At freezing they would pass 405Voc. What are your winter lows like? Keep in mind that solar voltage goes up as the temperature goes down. The specifications of the unit will decide.

I'd guestimate that you can get by with about 4-5kWh of power per day, if you try to be really conservative. That means though no electric oven, and only using the toaster in daylight hours. I'd suggest getting a propane-powered camping stove, and linking that to a 5gal barbeque tank. At my place I make my toast on the stove with a teflon pan. It works. An electric oven? I'd forget it! Toaster oven, maybe, but only in the daylight.

Even in December, when you are likely to get only 2sunhours per day, you should be able to generate 6kWh per day in clear weather.

 

[Spelunking]

Most likely 7 panels might not work, because it is a prime number. First, can you post the specifications of your particular Growatt? What is the maximal Voc for panel input? Seven of those panels in series would be putting out 362Voc, and that's at room temperature. At freezing they would pass 405Voc. What are your winter lows like? Keep in mind that solar voltage goes up as the temperature goes down. The specifications of the unit will decide.

I'd guestimate that you can get by with about 4-5kWh of power per day, if you try to be really conservative. That means though no electric oven, and only using the toaster in daylight hours. I'd suggest getting a propane-powered camping stove, and linking that to a 5gal barbeque tank. At my place I make my toast on the stove with a teflon pan. It works. An electric oven? I'd forget it! Toaster oven, maybe, but only in the daylight.

Even in December, when you are likely to get only 2sunhours per day, you should be able to generate 6kWh per day in clear weather.

As I live in southern Europe winter here will go maybe to -5 Celsius, about 41 Fahrenheit, and those -5 would be a real oddity and expected to last just a couple of days. It is not uncommon for me to get 10 hours of sun even in winter. I get sun from 7 AM to 7 PM in summer and at least 5 hours of sun in winter

This model of Growatt is rated for 450VOC maximum input so I would be well below. I did not know prime numbers would be involved.

If my electric oven is 2500 watts and I am producing 3000 Watts should not be able to run it if the sun is out?

Thanks for the answer mate, I can tell you it already helped, below you can find the inverter's specs

 

[45North]

The sun is still low in Europe in winter. Even Lyon France is only at 45 deg north.

 

[Spelunking]

The sun is still low in Europe in winter. Even Lyon France is only at 45 deg north.

I see, I am a bit lower than that tough, think southern Spain. But I do see your point. Any way to mitigate this apart from adjusting the tilt angle? What difference would it be if the angle is correct solar power wise? Is the light "weaker"? Or is it a matter of panel alignment?

 

[MichaelK]

I see, I am a bit lower than that tough, think southern Spain. But I do see your point. Any way to mitigate this apart from adjusting the tilt angle? What difference would it be if the angle is correct solar power wise? Is the light "weaker"? Or is it a matter of panel alignment?

The adverse tilt is the same reason that the plant Earth has seasons. At an acute angle, the same amount of sunlight is spread across a larger area, hence the decrease in solar radiation per square meter.

BTW, 10 hours of sunlight is NOT the same as 10 sunhours. A sunhour is a shorthand number to serve as a multiplier to determine what your panels will produce per day. Not knowing your location, I'd guess you have just 3 sunhours per day in December.

The prime number simply means that you can't divide the total panels into parallel strings. 4, 6, 8, or 9 panels could be divided into 2, 3, or even 4 parallel strings. Seven though can not. The good news though is that my concern was irrelevent, because your inverter has a 450V limit, and your winter lows will never boost the voltage up to that.

I myself use rotating mounts that are adjustable for both azimuth, and declination, so I can always optimize my insolation. I find that rotating my panels East in the morning can about double my solar output around 8am. Though I may adjust my panel azimuth every few hours, I only adjust my declination every few months.

 

[Spelunking]

The adverse tilt is the same reason that the plant Earth has seasons. At an acute angle, the same amount of sunlight is spread across a larger area, hence the decrease in solar radiation per square meter.

BTW, 10 hours of sunlight is NOT the same as 10 sunhours. A sunhour is a shorthand number to serve as a multiplier to determine what your panels will produce per day. Not knowing your location, I'd guess you have just 3 sunhours per day in December.

The prime number simply means that you can't divide the total panels into parallel strings. 4, 6, 8, or 9 panels could be divided into 2, 3, or even 4 parallel strings. Seven though can not. The good news though is that my concern was irrelevent, because your inverter has a 450V limit, and your winter lows will never boost the voltage up to that.

I myself use rotating mounts that are adjustable for both azimuth, and declination, so I can always optimize my insolation. I find that rotating my panels East in the morning can about double my solar output around 8am. Though I may adjust my panel azimuth every few hours, I only adjust my declination every few months.

I did not know about that, my goober mind went like "light is light, so mo light mo better is is all the same". I will look into it so I can optimize as much as possible. Is there a website where I can push in my exact location and get a sunhour average?

I will probably go with 6 panels then, I think with 8 I go over the 450V limit, or I will be too close to it for comfort.

So in theory if I get 3 sunhours in December I would be getting about 3 kWh so 9 total that would cover the batteries (about 7kWh) and little else (I know the advertised wattage will be different that reality, this is just so I can wrap my head around it)

If I really need more I can always get another growatt, as they can function in tandem, and add more panels.

If it was you, would you invest in another inverter/solar panels or more batteries? To me it seems that if I don't get the wattage above a certain level in winter, it would be pointless to have more batteries as they will not get enough juice to be charged

 

[MichaelK]

If it was you, would you invest in another inverter/solar panels or more batteries? To me it seems that if I don't get the wattage above a certain level in winter, it would be pointless to have more batteries as they will not get enough juice to be charged

Both actually. The inverter specs help a lot. You can expand up to 6000W, with 100A of battery charging. Your batteries though a rather on the small size, and I personally have a far larger battery bank. It looks like one of these batteries is optimized for 37A of charging, so two would be 74A. To get 74A with your panels you'd need 74A X 50Vcharging X 1.175 fudgefactor = 4350W of panels. At 500W that's 8 panels. Since 8 would push you over the 450V limit below freezing, I'd wire them as 4S2P.

In regards to your oven, yes, sure, running it when there's enough watts coming in is just fine. Just not at 8pm.

 

[WYtreasure]

I did not know about that, my goober mind went like "light is light, so mo light mo better is is all the same". I will look into it so I can optimize as much as possible. Is there a website where I can push in my exact location and get a sunhour average?

Welcome to the party Spelunking.

Think of a solar panel like you would a magnifying glass, assuming you've played with one, the only time you get the tiny white dot is when the alignment is perfect. That's the moment (hour or two) when your panels will put out their maximum power. Before and after that "moment" they put out somewhat.

Play with this sun toy and see if it helps.
www.suncalc.org/#/39.3182,-1.0907,2/2021.12.21/10:33/1/3

My signature has a couple links which may be helpful.

 

[Spelunking]

To get 74A with your panels you'd need 74A X 50Vcharging X 1.175 fudgefactor = 4350W of panels.
In regards to your oven, yes, sure, running it when there's enough watts coming in is just fine. Just not at 8pm.

Could you please go a bit more in depth about how important is amperage vs wattage or voltage? Or if you know a video I can watch on it, could you please send it my way? Is amperage more important than kWh or are they just different things?

So I should first optimize battery and solar panels and only then look at another inverter, makes sense.

Another question, my batteries have a capacity of around 7 kWh. So if the array is producing 4kWh, shouldn't the batteries be charged in about 2 hours?

Think of a solar panel like you would a magnifying glass, assuming you've played with one, the only time you get the tiny white dot is when the alignment is perfect. That's the moment (hour or two) when your panels will put out their maximum power. Before and after that "moment" they put out somewhat.

Play with this sun toy and see if it helps.
www.suncalc.org/#/39.3182,-1.0907,2/2021.12.21/10:33/1/3

My signature has a couple links which may be helpful.

Those Links helped a lot especially the sizing tool, it helps keep everything within limits

Thanks a million guys

 

[MichaelK]

Could you please go a bit more in depth about how important is amperage vs wattage or voltage? Or if you know a video I can watch on it, could you please send it my way? Is amperage more important than kWh or are they just different things?

So I should first optimize battery and solar panels and only then look at another inverter, makes sense.

Another question, my batteries have a capacity of around 7 kWh. So if the array is producing 4kWh, shouldn't the batteries be charged in about 2 hours?

As a general rule of thumb, you want to reduce amperage to the lowest level practical, and increase the voltage to the maximal level possible. Hence, 24V and 48V systems instead of 12V. Amp generate heat, and lots of amps flowing through thin wire produces lots of heat.

In terms of storage though, we are not talking amps here, we are talking amphours. Because the voltage is fixed at either 12V, or 24V, or 48V, you increase capacity by increasing the amphours available.

If you think the Growatt is going to work for you, I don't see the need to look elsewhere.

Although your batteries have 7kWh of storage, you are making the assumption that it's going to get charged back up the next day. That is a mistake. For a real off-grid system, you need to start thinking in terms of day of autonomy. That is, how many days the system can operate with NO solar. What happens if a winter storm blows in and the sky is dark for 3 days? Production will be zero when the panels are covered with snow.
When your system shuts down do you just sit there in the dark and wait for the weather to clear. Do you let all the food in your freezer start to thaw and spoil? The concept of days of autonomy is for when things don't go as planned.

For my own system, I can go 4 days before my batteries reach 50%. I haven't run my generator in two years now. I just have to start it every several months or so, so the piston does not rust in the cylinder again.

 

[Spelunking]

Thank you for the answer, I will look into it, I will go forward with your recommendations. For now I can only afford 6 pannels but will upgrade to 8 with the recommended config (4s2p).

Just 2 more questions,

1) since I have to start with these 6 should I just wire them 6s or should I do 3s2p? I can not go lower than 150v or the inverter might not work, so my guess is that 3s2p would be a bad idea.

2) wire gauge. From the battery to the inverter I need to use 4 AWG as per the manufacturer's recommendations, but what wire gauge should go from the inverter to the sub panel, and from the sub panel to the outlets? Are the gauges the same for both? Can I use 10 AWG for everything or is it too little (or too much)? Should I go with a thinner gauge for the appliance outlets, say 14 gauge and use the 10 for the inverter to panel connection?

 

[WYtreasure]

Spelunking, if you're down to just 2 questions you're doing great.

Oversized wires are a bit difficult to work with. You should only have to do it once though. Undersized wires are counterproductive and can even be dangerous.
I don't think 4 awg is large enough for the battery to the inverter. Figure out how many amps the wire needs to carry before you decide. I could be missing something though.

 

[Spelunking]

Spelunking, if you're down to just 2 questions you're doing great.

Oversized wires are a bit difficult to work with. You should only have to do it once though. Undersized wires are counterproductive and can even be dangerous.
I don't think 4 awg is large enough for the battery to the inverter. Figure out how many amps the wire needs to carry before you decide. I could be missing something though.

Well for now I have 2 questions, but I don't even know what I don't know, after these two questions I am sure I will be left with two more, but I don't want to keep pestering people lol.

Apart from that I am fairly sure I will not burn down the house (it is a brick house so I have that going for me) or electrocute myself which is quite nice. Most of my questions revolve around wire thickness though,

You are right, the 4 awg was for the SPF 3500 the SPF 5000 calls for 2 awg (as per the manual), in fact I ordered 2 awg cable (it arrived today) I don't know why I mentioned 4 awg...

The manual does mention 8 AWG cable as for the AC output (as well as input, but I won't be tying it to the grid so it does not matter to me), so this should be the cable that connects to the sub panel right?

So, as I see it, 12 awg will be fine to use from the panel to the outlets as it will have a breaker that will not allow it to draw more than 20 amps (which in reality will be 16 as I want to leave some room). Is this assumption correct?

 

[WYtreasure]

Well for now I have 2 questions, but I don't even know what I don't know, after these two questions I am sure I will be left with two more, but I don't want to keep pestering people lol.

Good one, yep we don't know what we don't know.
Offer up as much valid info as you can when you have a question about something. A bunch of Q&As is silly.

Apart from that I am fairly sure I will not burn down the house (it is a brick house so I have that going for me) or electrocute myself which is quite nice. Most of my questions revolve around wire thickness though,

You are right, the 4 awg was for the SPF 3500 the SPF 5000 calls for 2 awg (as per the manual), in fact I ordered 2 awg cable (it arrived today) I don't know why I mentioned 4 awg...

Alrighty then, 2 awg it is.

The manual does mention 8 AWG cable as for the AC output (as well as input, but I won't be tying it to the grid so it does not matter to me), so this should be the cable that connects to the sub panel right?

Yep, sounds like inverter to sub panel.

So, as I see it, 12 awg will be fine to use from the panel to the outlets as it will have a breaker that will not allow it to draw more than 20 amps (which in reality will be 16 as I want to leave some room). Is this assumption correct?

Yes, pretty much. As I understand "headroom" 80/20 works, I like 60/40. BUT now I will contradict myself considering 12 awg from the panel. It depends on things like appliances, vacuum cleaners, led lighting and so on.
I've considered dedicated led lighting circuits of 14 awg, while knowing the appliances will get 12 awg.

I picked up an EATON 2 space, 4 circuit, 70 amp main lug panel at Menard's for $18. I think 2 breakers cost more than that but now I have a dedicated box to stick to the wall with everything else.
Do you have your sub panel yet?

 

[Spelunking]

Good one, yep we don't know what we don't know.
Offer up as much valid info as you can when you have a question about something. A bunch of Q&As is silly.

Alrighty then, 2 awg it is.

Yep, sounds like inverter to sub panel.

Yes, pretty much. As I understand "headroom" 80/20 works, I like 60/40. BUT now I will contradict myself considering 12 awg from the panel. It depends on things like appliances, vacuum cleaners, led lighting and so on.
I've considered dedicated led lighting circuits of 14 awg, while knowing the appliances will get 12 awg.

I picked up an EATON 2 space, 4 circuit, 70 amp main lug panel at Menard's for $18. I think 2 breakers cost more than that but now I have a dedicated box to stick to the wall with everything else.
Do you have your sub panel yet?

Thanks a million for your answer. Right now the system will be just for backup meaning it will only run some basic stuff, but I want the upgradeability in the future, this system has the potential to be upgraded fairly seamlessly from what I have read/seen. This also means I will not be drawing large amounts of power.

I can get a good deal on 12awg at a local store (they are going out of business and are clearing stock) so I will stick with that gauge.

I do not have a sub panel yet, I was thinking of getting one from the same shop where I am getting the wire as well as the breakers

 

[WYtreasure]

Thanks a million for your answer. Right now the system will be just for backup meaning it will only run some basic stuff, but I want the upgradeability in the future, this system has the potential to be upgraded fairly seamlessly from what I have read/seen. This also means I will not be drawing large amounts of power.

I can get a good deal on 12awg at a local store (they are going out of business and are clearing stock) so I will stick with that gauge.

I do not have a sub panel yet, I was thinking of getting one from the same shop where I am getting the wire as well as the breakers

Good thinking. Sometimes there will be DC breakers left on the shelves which could go cheap. Read the fine print.