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Supra-Halbleiter avatar image
Supra-Halbleiter asked

48V battery with only one PV module - any problems to expect?

Hello Forum! I want to build an ESS with 48V battery, but where I'm living now I only have the space for a single PV module which will have direct sun light only for 3 to 5 hours a day. There aren't many modules with a voltage that is high enough under load, but I think I have found one which would do. My idea is, to be able to upscale the system when I move without being stuck to 24V or having to buy new components for 48V.

Do you see any problems with the following combination?

  • Pylontech US3000C 48V
  • Maxeon 3 420W (SPR-MAX3-420-BLK) - it has a Vmpp of 67.7V and Isc of 6.32A
  • Victron MPPT 100/20, for enough room to add another module in parallel without upgrading the MPPT (The 100/20 is recommended by the MPPT calculator)
  • Victron MultiPlus 48/800/9-16

I hope the voltage will be high enough for most of the day.


Solar Panelbattery system voltage
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7 Answers
Michelle Konzack avatar image
Michelle Konzack answered ·
If you have one or more cloudy days, your Solarpanel with a MPPT 100/20 will be not able to charge your batteries. This is why you got suggested to use a 150V MPPT.


Also I would suggest you to use two smaller 180-230V panels which have usually 72 cells and a Vmpp of 36V while the Voc is around 44V (with a 100V MPPT) your panels can not be colder then -14°C otherwise you kill the MPPT.


Hence you should go with two smaller 36V panels (regarding your space problem) and a SmartSolar MPPT 150/35 (the smallest) which allow you to put even more strings in parallel. Generally you can have 2S4P.


The Inverter with 800A will not deliver more the 700W @25°C. However, you can put up to 6 in parallel, but if you try to upgrade over a long period, then you might run into a Hardware version incompatibility.


The suggested 3000VA Inverter would be just perfect, because most bigger household things, like tabletop induction cooker, coffee maker and such have between 1600W and 2000W.


You should realy think about such things before you buy the wrong stuff.


Please note:

I live Off-the-Grid on a 3,7ha Farm in Estonia with 2940Ah of Batteries 24V, 1860Wp Solarpanels plus some 2000W and 700W windmills and I got 4 years enough energy to go even over the winter. And this with a power consumption of 6-7kWh a day.


I november 2022 we decided to buy a MultiPlus-II 24/5000 and use also two Table Top Induction Cooker with each up to 2000W and it is very comfortable...


...but we need to upgrade our Solarpanels with additional 4100Wh using two SmartSolar MPPT 250/100-Tr VE.Can


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Supra-Halbleiter avatar image Supra-Halbleiter commented ·

I have another requirement for the MultiPlus i previously didn't mention, because I was more concerned with the panel and mppt side. I live in a small flat with only one room, so it must be quiet - so i might even have to turn it off at night. I will stay with the MultiPlus 800. It really isn't that important to me. If i happen to want to make coffee, i will use an induction cooking plate on low setting - that will be slow but it will work with 500W.

Regarding panels and system voltage, I'm beginning to be convinced. Also another force turned up, pushing in the 24V system voltage direction - the only dealer where I could source the Maxeon 3 with the high voltages seems to be a fraud.

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Michelle Konzack avatar image Michelle Konzack Supra-Halbleiter commented ·
Apropos Induction cooking:


I have a Phoenix Inverter 24/1200 laying around and it is NOT able to start my Induction cooker, because if I switch it on, it start with 1600W and not with the smallest (200W) one. Can regulate 200, 500, 800, 1000, 1300, 1600, 1800 and 2000, which is a little bit disappointing.


And the small power 200/500/800W are jumping over 1400W regularly.


I hope you have an induction cooker which realy start from the smallest, because in Estonia such thing does not exist. Have tried more then 30 models directly in the shops.

Before you buy one, try it out in the shop.


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Supra-Halbleiter avatar image Supra-Halbleiter Michelle Konzack commented ·

That's interesting. I will see. I might still have a use for the small MultiPlus. For example to charge my power tools or power a low power amplifier. It will be fun getting some experience. Like I mentioned a bigger MultiPlus like the 3000VA version doesn't seem viable for me, because of the fan noise.

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kevgermany avatar image
kevgermany answered ·

The 5V requirement is only for starting charging. After that the panel only needs to be 1V over battery.

Only obvious question is will the panel be sufficient.

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Supra-Halbleiter avatar image Supra-Halbleiter commented ·

The Pylontech US3000C datasheet says charge voltage is 52.5V-53.5V. So if I understand it correctly, if the panel supplies a minimum of about 57.5V-58.5V the MPPT would turn on - am I correct?

It isn't clear to me, how much light must hit the panel for it to have high enough voltage. As far as I know solar panels should provide the voltage in the datasheet with very little light. It just wouldn't provide a high amperage. Hence my hope that most of the time at least some very little energy would trickle in. Can you confirm this?

Let's say at 10am there is some ambient light, voltage is 60V and 0,1A come in. Is this realistic? With no loads, would the battery very slowly be charged, or would something I'm not thinking about prevent it?

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kevgermany avatar image kevgermany ♦♦ Supra-Halbleiter commented ·
Fully charged, your battery will be around 52.5V. So for charging to start the panel needs to reach about 57.5V. The MPPT will adjust charge current to the max power the panel can deliver in the available light. I've seen charge rates of a few percent of panel power in poor light. In winter, the panel is effectively dead. However charging will continue throughout the day.

I assumed you'd sized the system based on known load. @Kevin Windrem has pointed out that the AC output of the multi is low. Depending on load type and ambient temperature you will see a lot less than 800W. It's rated in VA, not W. Appliances with high start currents may not run. Appliances with inductive loads will reduce output.


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Supra-Halbleiter avatar image Supra-Halbleiter kevgermany ♦♦ commented ·

Thanks for your input! In fact I design it based on possible incoming energy. I want to use most of it with low power appliances and have some backup power left.

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Kevin Windrem avatar image
Kevin Windrem answered ·

You'd be able to add one more panel to MPPT 100/20: 20 amps @ 48 volts is 960 watts. Further expansion would require a second controller or replacing it with a larger one.

Success of your initial build depends on your power requirements. 3 hours @ 400 watts is only 1,200 watt-hours and that 400 watts would be peak with sun angle perfectly perpendicular to the panel. I'd expect 800 watt hours or less per day.

The 800 VA Multi won't run much -- not even a coffee maker.

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klim8skeptic avatar image
klim8skeptic answered ·

@Supra-Halbleiter Just be aware that there is also a SPR-MAX3-420-BLK-R variant that has a Voc of 40.7v and Vmp of 35.5v.

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seb71 avatar image
seb71 answered ·

My idea is, to be able to upscale the system when I move without being stuck to 24V or having to buy new components for 48V.

That's a good approach most of the time, but not if you start with such small components.

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You would have to replace the 800VA inverter anyway for a larger system. Start with at least a 3000VA inverter.

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Adding more Pylontech batteries after a few years is possible, but there might be a noticeable capacity difference between the used and new ones.

---

For a 48V system/battery, get a 150/xx MPPT (or higher than 150V).

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If you do not want to spend that much for now, better make a 12V or a 24V system.

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Supra-Halbleiter avatar image Supra-Halbleiter commented ·

> For a 48V system/battery, get a 150/xx MPPT (or higher than 150V).


What is the reason you suggest to use a 150V+ MPPT instead of 100V? Is it merely for more headroom for the MPPT to have high enough voltage? Or do you see other factors?

My line of thinking was that I won't have more than two panels in the near future and from what I know it is better to connect them in parallel, so shading loss will be less in case of one panel being shaded.

When I upscale the system at a different place, after moving, I aim to have 10+ panels. In this case I will need a much bigger MPPT anyway and I would buy cheaper panels with different voltages than the Maxeon 3, so it would require a second MPPT.

I don't agree with what you said about having to buy a new inverter anyway. If you don't have big loads to drive, it can make it more inefficient.

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seb71 avatar image seb71 Supra-Halbleiter commented ·

What is the reason you suggest to use a 150V+ MPPT instead of 100V? Is it merely for more headroom for the MPPT to have high enough voltage?

You say you want to later upgrade to a much larger system and keep the initial components. In that case, a 100/xx MPPT is not a good choice.

For a 48V battery (nominal), a 100/xx MPPT is not a good choice because with the usual PV panels (at least 2 in series) you get too close to the maximum voltage (and with only one in a string the voltage is too low for a 48V battery). An 150V or 250V MPPT gives you a lot more flexibility on PV panel choice.


That 112-cell panel you want to buy is not a common type. I don't know about the price of that one, but you might want to compare with other options. Usually the 60-cell PV panels have the best price/Watt ratio.



When I upscale the system at a different place, after moving, I aim to have 10+ panels. In this case I will need a much bigger MPPT anyway and I would buy cheaper panels with different voltages than the Maxeon 3, so it would require a second MPPT.

I don't agree with what you said about having to buy a new inverter anyway. If you don't have big loads to drive, it can make it more inefficient.

So you plan to have a 10+ panels system and keep that 800VA inverter?

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Of course, for your current low-power system you would be better of with a 12V or at most a 24V system.

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

As I said, i intend to connect the panels in parallel. I know they are not common, but that is not an argument. I have tight space requirements.

Regarding the inverter, I don't see a reason to upgrade unless i need to charge faster or use more AC power.

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seb71 avatar image seb71 Supra-Halbleiter commented ·

As I said, i intend to connect the panels in parallel.

So what has this to do with what I wrote?


Also price/Watt is not important?

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

What does it have to do with what you wrote? When the panels are connected in parallel, they won't exceed 100V, so i don't see the need for a bigger MPPT. You say the voltage will be to low, but i'm not convinced yet. You make a lot of statements without explaining why you think it is that way.


The ratio is important, but my space requirements trump it and the 48V pylontech battery is cheaper by a similar amount than the 24V variant.


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Michelle Konzack avatar image Michelle Konzack Supra-Halbleiter commented ·
For such small Inverter, it create to many headaches with 48V.


Why not use highly reliable SOPzS Batteries which cost a fraction of your Pylontech UP3000?


I pay 2500€ for 17,6kWh SOPzS batteries while a Victron 25,2V/200Ah (5kWh) cost 4800€.


I can give on my Battery a load of 300A while your Pylontech would shout down your whole house.


P.S.: the biggest load I ever gaved on my 2940Ah 24V Batteries was 700A.


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seb71 avatar image seb71 Supra-Halbleiter commented ·

Obviouslly you missed the "later upgrade" part.

And this:

So you plan to have a 10+ panels system and keep that 800VA inverter?

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A single 112-cell panel in a string won't reach 100V (I did not even said such a thing), but the PV voltage might not be optimal for a 48V battery.

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

No, i did not miss it. I answered: "Regarding the inverter, I don't see a reason to upgrade unless i need to charge faster or use more AC power."


You did not say a single panel will exceed 100V, but i understood it from your suggestion to use an MPPT which can handle more than 100V. Why would i need a bigger MPPT, if my voltage does not got over 100V?

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seb71 avatar image seb71 Supra-Halbleiter commented ·

PV voltage will not always be Vmpp, depending on Sun position, panel temperature, any shade.

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No, i did not miss it. I answered: "Regarding the inverter, I don't see a reason to upgrade unless i need to charge faster or use more AC power."

Then for what you will use a 10+ PV panels system?

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

> PV voltage will not always be Vmpp, depending on Sun position, panel temperature, any shade.


In understand that, but i have no data on it and people are saying the voltage is a lot less dependent on sunlight than amperes and a voltage near Vmpp will be reached with ambient light. It would help to have some real data. Unfortunately the datasheet doesn't have it.


I have a feeling you just want to contradict myself, instead of helping me to understand your point.


> Then for what you will use a 10+ PV panels system?

I may be drawing hundreds of watts DC base load for a computer cluster.

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klim8skeptic avatar image klim8skeptic ♦ Supra-Halbleiter commented ·

@Supra-Halbleiter Panel Imp is (almost) proportional to the insolation that the panel receives.


Vmp is (mostly) stable and independent from insolation levels. Any shade / shadows nerfs voltage levels up. Avoid shade.

A Sunpower doc from 2012, similar Imp to your proposed panels.

sunpower-e19.png

Note, the power @ insolation equals the point on the IV curve that yields the greatest chart area. (fill factor)

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seb71 avatar image seb71 Supra-Halbleiter commented ·

That's correct: PV voltage rises faster than current, as you get more light on the PV panels.

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seb71 avatar image seb71 Supra-Halbleiter commented ·

I won't have problems drawing hundreds of watts DC base load from a computer cluster.

Ah. Cryptomining or similar?


I assumed a home/domestic/household system. Where you mostly need AC power.


Anyway, for a larger system (10+ PV panels you say), you do not want lots of PV panels in parallel (on an MPPT). You do not want to deal with large currents and other possible issues.

Also you probably don't want lots of small MPPTs.

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

Yes, similar. AI model calculations and I'm a cloud engineer with my own toys on premise.


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Michelle Konzack avatar image Michelle Konzack Supra-Halbleiter commented ·
Hmmm, a bunch of 230V Computer PSUs?


I run my Servers with DC PSUs from http://www.mini-itx.com and the efficiency is much higher.


I suggest you to go with a 24V System

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Supra-Halbleiter avatar image Supra-Halbleiter Supra-Halbleiter commented ·

Regarding inverter efficiency, apparently the MultiPlus 3000VA versions efficiency peaks at 400-800W load. That's much lower than i expected. I couldn't find data about the 800VA version though.1691826095223.png

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Supra-Halbleiter avatar image Supra-Halbleiter Supra-Halbleiter commented ·

Whoever downvoted this, could you explain why, please? I don't get it.

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kai-fuchs avatar image
kai-fuchs answered ·

we got the Multiplus 800 in a Van and it´s doing s great job. enough for small power tools, laptops, the "anti snore machine" for my dad. Depends your use case for us it's plenty enough. I think your base system should work. If you don't draw lots of power every day. We got 2x100W and travel with that setup since over 1,5 years and we have enough energy to run laptops intensively and small kitchen appliances every once in a while. But anyway think of the biggest load on 230V you want to run in your system, and size the inverter or multi accordingly. Inverter are not cheap therefore it can be better to oversize a little bit.

Normally you get with quite little light on the panel to the rated voltage, but as said before your Amps will be low with little light. shouldn't be a problem.

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seb71 avatar image seb71 commented ·

What's your battery nominal voltage (12V/24V/48V)?

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Supra-Halbleiter avatar image Supra-Halbleiter commented ·

Thank you. That's good to hear and about what I expect from the system. Of course I can't use power tools or a heater with the small MultiPlus like others warned, but in my scenario it makes no sense to me, to use a huge MultiPlus which will then most of the time run with bad efficiency, because I will only power small appliances from it.

I didn't say it, but I mainly want to have emergency backup power for my laptop, mobile phone and an LED lamp, etc. with the little sunlight I have access to. Most of my loads will be DC - i plan to power these devices directly and not with their 230V power supply.

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kai-fuchs avatar image kai-fuchs Supra-Halbleiter commented ·
A lot of DC appliances take only 6-30V might be easier to go with a 24V system in this case. Otherwise you would need a DC-DC Charger to run your loads on 24v or even 12 V if
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Supra-Halbleiter avatar image Supra-Halbleiter kai-fuchs commented ·

I know. I'm in a predicament - whatever I choose, I will have to accept some conversion loss. One of my bigger permanent loads is a PoE-Switch, which requires 51,8V. So my devices required voltages are all over the place. It feels like 48V is a good compromise, when i want to power something from 230V every now and then too.

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seb71 avatar image seb71 Supra-Halbleiter commented ·

I asked kai-fuchs what is his battery voltage. He did not reply.


In one of his threads, he said he has a 24V system.


So his experience of charging that 24V battery with 2x100W PV panels will not translate to a 48V battery.

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kai-fuchs avatar image kai-fuchs seb71 commented ·

Hey I run Systems on 12 and other on 24V depends the use case. The one with a Multiplus is running of 12V.


Yes, it always depends the panels, and so on. @Seb71 Correct me if I’m wrong, I made the experience doesn’t Matter if I have a single 12V a single 24V or 2x12V series connected. As soon as I’m having a little bit of light my voltage is at or just below the Rated V of the panel. The more light I get the higher the A that go into the charger….

There for I strongly believe his array should work even if it doesn’t harvest lots of power. As said before. I assume nobody can’t 100% say it works or not if he/she doesn’t have the same system running. This is highly unlikely and therefore not really helping.

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seb71 avatar image seb71 kai-fuchs commented ·
The MPPT always tries to track the Maximum Power Point for the panel illumination from that moment. Meaning it tries to find the voltage & current combination for which it can output the maximum power. If the PV array voltage is too close to the battery voltage, the MPPT might not be able to adjust for maximum power in certain situations.

When buying a new system it is better to configure it so that you avoid such sub-optimal setups and get the most for the money you spend.


His plan is to start with a single 420W PV panel which is supposed to power the loads and charge a 3.5kWh battery, while having 3-5 hours of Sun each day. He needs to collect all the energy he can.


Also in this case OP said he intends to later upgrade to a much larger system, while keeping the initial components. This changes what components are better to be purchased.


Of course, there is the option to just make a system optimized for the current needs (at lower cost) and replace most of it (if not all) when upgrading to a larger system. But OP said he does not want to do this.

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

I said it in the extreme form that I don't want to buy new components, but I want to add an 'ideally', because I know it is not possible to stick to that 100% and have a perfect setup in all cases. After all we're not living in a dream world. I meant that I don't want to buy 24V components first and then have to replace everything with 48V components. I'm okay with having to replace _some_ components - just not the most expensive ones like the battery, if possible.

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seb71 avatar image
seb71 answered ·

But what's the purpose of that starting system anyway?

You have frequent power outages (or expect to have frequent outages)?

If the purpose is only to reduce the power bills, it's a bad idea. It will take years to "recover" the money the system from your first post will cost.

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With a small system you can start with a 12V or at most 24V battery (LiFePO4 or even lead-acid). Much cheaper than a Pylontech 48V - which you can't fully use anyway (not enough PV power).

Stick with DC-only (no inverter at all) and it would really make sense.

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Supra-Halbleiter avatar image Supra-Halbleiter commented ·

Many purposes, but it is not about saving money. Maybe you should have asked earlier instead of assuming a lot of things

  • I like to play around and learn this stuff so I can advise others
  • I want to gain some autarky in the case of outages - i will judge for myself if it is necessary, or worth it to me, thank you
  • I want to develop a different mindset by involving myself in this, because I think the process opens the mind to some forms of wasting energy
  • I am an idealist wishing for decentralized infrastructure and I'm making a first step

I disagree about not being able to use the Pylontech fully. I may want to leave more reserves for backup than you think. I'm not even sure about it myself at this time.

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seb71 avatar image seb71 Supra-Halbleiter commented ·

I disagree about not being able to use the Pylontech fully. I may want to leave more reserves for backup than you think. I'm not even sure about it myself at this time.

A 420W PV panel can not completely recharge a 3.5kWh battery and power loads during each day (each 24h). That is what I mean when I say you will not be able to fully use the Pylontech 48V battery.

Even with a second 420W PV panel (so 840Wmp in total) you will not have enough power.

Let's say you only use 80% of the battery capacity of that Pylontech each night. That's 2.8kWh. A single 420W panel would take about 6 hours and 30 minutes to charge that (assuming it always outputs maximum power and also assuming it only charges the battery and you have no loads and ignoring the loses).

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

Of course. Then i may just decide to not power any loads from the battery until it is charged. You assumed it, but I never said i want to power loads and charge at the same time. I don't care, even if it takes days. I want to make use of the little solar power I have access to.

When i have a power reserve i'm comfortable with, the Pylontech is put to good use!

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Supra-Halbleiter avatar image Supra-Halbleiter Supra-Halbleiter commented ·

I wonder what is wrong with people down voting this. You may have other goals with your PV or disagree, but downvoting this seems destructive. Maybe you want to explain?

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Supra-Halbleiter avatar image Supra-Halbleiter Supra-Halbleiter commented ·

LOL... here is another post for you to down vote, to give you an occupation on this lovely sunday evening.

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kai-fuchs avatar image kai-fuchs seb71 commented ·
Hey @Seb71 assuming that everyone is living of a daily battery circle might be wrong. I e.g. have a big battery in one of my systems to power a Phoenix 24/1200 but only one panel. Cause my use case is to have power during the weekend, when I’m in the garden using a fridge and a pump, power tools etc.. then the system has a week to recharge until the next weekend.

Franks system can make sense if it fits his purpose. It might not be a problem for him that he needs 3 days to recharge the system after he has drawn more than normal (e.g. power outage). I think this System having an oversized battery makes sense especially if the solar is not reliable do to low solar hours or frequent cloud coverage

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Supra-Halbleiter avatar image Supra-Halbleiter kai-fuchs commented ·

Exactly, you get it! Thanks for sharing your opinion.

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seb71 avatar image seb71 kai-fuchs commented ·

Cause my use case is to have power during the weekend, when I’m in the garden using a fridge and a pump, power tools etc.. then the system has a week to recharge until the next weekend.

That's an off-grid system. For an off-grid system you do want a larger battery (with more energy stored than you consume in 24h), which can power your normal loads for a few days.

His system would be used in a flat, where he has grid power.

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Supra-Halbleiter avatar image Supra-Halbleiter seb71 commented ·

I'm thankful for your input, but please stop telling me what i want - it's exhausting.

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seb71 avatar image seb71 Supra-Halbleiter commented ·

I am not telling you "what you want".

It's just a proper design for an off-grid system to "want"' to have a larger battery. Just an expression to convey an idea.


In any case, my replies included explanations for the technical reasons for my recommendations.

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