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help needed to explain very basic termonology


Chippy

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I am a complete novice on all things solar etc,

I have been to a company who have designed a system that they say will cover everything I need but I want to install this all myself.

I have a fair understanding of electronics form about 35 years ago but everything has changed so much since the time of resistors and transistors.

First question is; The panels recommended are 330w at 48.06V, this bit I understand but then they are rated 1000V Vdc, can someone explain the meaning of this as I seriously doubt they are 1000 volts.

Second question is the inverter is a 24 volt  2000w model,  It says on the spec sheet that @25 C it puts out 2000 VA  continuous power, 1700watts for 30minutes and 1300 watts continuous and  @40 C

its 1200watts, does this sound a reasonable output for a 2KVA system.

Last for the moment is batteries,  4 120ah batteries are included in the quote I got, (Lithium are out of my price range so I'm going for lead acid deep cycle for now,)

I don't need a lot of power as we don't run much, about 250 to 300 watts per hour so is the battery backup good enough for maybe two days?

I would like peoples opinion as I have a naturally cynical nature when it comes to sales people. they are going to say it is fine just to get  a sale from my experience.

 

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6 minutes ago, Chippy said:

First question is; The panels recommended are 330w at 48.06V, this bit I understand but then they are rated 1000V Vdc, can someone explain the meaning of this as I seriously doubt they are 1000 volts.

The 1000V could refer to two things. The one is the maximum system voltage, in other words, you are not allowed to put more than 20 of those PV modules in series, otherwise the total system voltage will exceed 1000VDC. The second thing it could be referring to is insulation levels. The PV-cabling is usually rated for up to 1000VDC. Unless you're installing more than 20 modules, I wouldn't worry about this part 🙂

9 minutes ago, Chippy said:

Second question is the inverter is a 24 volt  2000w model,  It says on the spec sheet that @25 C it puts out 2000 VA  continuous power, 1700watts for 30minutes and 1300 watts continuous and  @40 C

its 1200watts, does this sound a reasonable output for a 2KVA system.

That sounds like a Victron Multiplus Compact. They are rated at 25°C and the peak power they can do continuously depends on ambient temperature, down to 60% (1200W) when it is really hot. If you drive it outside these parameters it will simply overheat and shut down, then restart when it's cooled down.

I once had a case in Turkey where the inverters would regularly shut down after an hour at full power... except if it was cold in the morning. At -10°C it can run full power continuously 🙂

Inverters are usually sized for the peak they need to cover, and they rarely need to cover the peak for more than a few minutes, so the quoted numbers are not unreasonable. If you have continuous loads over 1200W, then get a 3kva.

14 minutes ago, Chippy said:

Last for the moment is batteries,  4 120ah batteries are included in the quote I got, (Lithium are out of my price range so I'm going for lead acid deep cycle for now,)

So two strings of 2 batteries, 240Ah at 24V. That's 5.76kwh, of which you ideally want to use only half, 2.88kWh.

15 minutes ago, Chippy said:

I don't need a lot of power as we don't run much, about 250 to 300 watts per hour so is the battery backup good enough for maybe two days?

The "per hour" part is confusing. If I assume that your loads is in the 250W to 300W range, then every 3 hours roughly equates to 1kWh (300W times three is 1000... ish), and you have 2.8kWh (maybe three) to use, so you have 9 hours of backup (9*300 = 2700, ie 2.7kWh).

If you run the batteries right down to zero, then 5760/300 ~= 19 hours. If you do this daily your batteries will die an early death.

Getting back to the inverter size: Your batteries should not be discharged at more than 20% of their capacity (48 Ampere), so the maximum load your batteries can handle is also only around 1kw (48*24). So the design balance in this system is not bad.

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Thanks Plonkster, the Vdc makes sense now,

the inverter is aTBB energizer apollo, I can't find any negative reviews of them but then I can't find any positive ones either.

Where I am at the moment we have a smart meter and it shows what power we are using , the normal reading on it is 0.1 kw during the day with occasional peaks of 2kw but as we are changing to solar geysers and a gas stove our biggest consumer of power will be a hairdryer that gets used for 5 minutes of the day.

You say the design balance seems ok, thats the main thing I was wanting to know as I'm allocating about a 6th of my renovation budget into the solar  aspect of the place I'm renovating

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1 hour ago, Chippy said:

You say the design balance seems ok, thats the main thing I was wanting to know as I'm allocating about a 6th of my renovation budget into the solar  aspect of the place I'm renovating

It's a small system, but not small-small if you get my meaning. I used a 1.6kva inverter for years and it ran all the important stuff, but it could not run the hairdryer. I upgraded to a 3kVA about two years ago and that makes a significant difference in the appliances that can run: Washing machine, dishwasher, microwave... just not all at the same time. But I already had the big batteries.

Also, the system you're looking at doesn't sound as if it has much in the way of future-extensibility. You will keep the PV modules, and maybe the batteries, but everything else will likely get swapped at some point.

Can you provide a picture of the inverter? Sometimes one can recognise them as a clone of something else.

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https://sinetechstore.co.za/shop/inverters/hybrid-grid-interactive-inverters/tbb-energier-apollo-inverter-24v-2000w-50a-pwm/

Link to the inverter, for some reason I can't get any attachments to work so I'll put this instead

 

We don't need a big system as we are going back to a lifestyle where we have no TV, Internet electric kettle or microwave etc. as I said we will have a solsr geyser and gas cooker .

The two biggest users of power will be a washing machine that will be used maybe twice a week at 1100 watt for an hour at a time and a hoover for maybe a few hours a week.

our only constant will be the fridge freezer which pulls less than 0.1 kw according to the meter

Thanks for the input though

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16 hours ago, Chippy said:

That has a PWM charge controller. That makes me a little concerned about the 300W PV modules you mentioned.

An MPPT charge controller works a bit like a DC transformer. If you put in 42V at 8A (which would by typical for a 330W PV module), it converts that to 24V at 14A so you get the full 330W from PV. If you use a PWM controller, the panel voltage is pulled down to the battery and there is no increase in the current, so you get 24V at 8A, that is less than 200W. You will literally lose a third of your PV power with this charge controller.

I found the manufacturer's site though: http://www.tbbpower.com/productDetail_6.html

I can't say anything about the quality of this unit. The website indicates that they have offices in China and in Germany. It looks good to the eye, I'm just concerned about the PV-module mismatch with the PWM solar charger. You'd be better off either pairing this with 60-cell modules (250Wp or 275Wp usually), but even then there will be some losses. Perhaps try to find an inverter/mppt combo in your price class?

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Plonkster, i really appreciate the advice,

I have found this, it's at least a mppt/ inverter. would this be a better option?

Solis 3.0kW 4G Dual MPPT - Single Phase.

It's specs are as follows; Weight: 11.5 kg.

Rated Power: 3,000 W

Min PPT Voltage: 100 V
Max PPT Voltage: 500 V
DC Startup Voltage: 120 V
DC Shutdown Voltage: 100 V
Max Input Voltage: 600 V
Max DC Power: 3,500 W
Max AC Power: 3,300 W
Max DC Current: 22 A
Max DC Inputs: 2
Has DC Fuses: 0
Connector: MC4 Compatible
Included Connectors: 2
Euro Efficiency: 97.1 %
Transformer: None
IP Rating: IP65
MPPT Trackers: 2
Has Integrated DC Switch: No
Warranty: 5 years

Solis_Dual4G.jpg

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13 minutes ago, Chippy said:

I have found this, it's at least a mppt/ inverter. would this be a better option?

Quality wise I like it more. But it's a grid-tied inverter. No batteries. No backup if the power goes out, which I assume is what you are after.

Why not use the 2.4ka Voltronic inverter (aka Axpert)? I don't particularly like that inverter, just before my fellow forumites think I have defected. I would much rather sell you something blue, such as a Victron Multiplus Compact with an external MPPT. But it's not the worst thing in the world and it does come with an MPPT option if I recall.

If your budget allows for it of course.

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2 hours ago, plonkster said:

Quality wise I like it more. But it's a grid-tied inverter. No batteries. No backup if the power goes out, which I assume is what you are after.

Why not use the 2.4ka Voltronic inverter (aka Axpert)? I don't particularly like that inverter, just before my fellow forumites think I have defected. I would much rather sell you something blue, such as a Victron Multiplus Compact with an external MPPT. But it's not the worst thing in the world and it does come with an MPPT option if I recall.

If your budget allows for it of course.

My budget is already near it's limit so  a victron is only an option if I didn't have to buy anything else.

I think I'm getting the hang of the type of inverter that I need, I found this ;        Voltronic Axpert MKS Hybrid off-grid inverter 3kVA/3kW 600W MPPT 24V

It's cheaper than the original one so to my pocket it looks good.

Am I getting nearer the mark with this one?

Edited by Chippy
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1 hour ago, Chippy said:

Am I getting nearer the mark with this one?

Left column is 1kw, so the middle column would be the one to look at. Just note that that one is limited to 75V on the solar charger, so you can't put two 330W PV modules in series (that would put you at around 90V), they'd have to go in parallel.

Also, start saving for a better setup immediately. This one has no extensibility, and I'm not a fan of the Voltronic. It's a good "placeholder" until you can afford something better.

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5 hours ago, Chippy said:

My budget is already near it's limit so  a victron is only an option if I didn't have to buy anything else.

I think I'm getting the hang of the type of inverter that I need, I found this ;        Voltronic Axpert MKS Hybrid off-grid inverter 3kVA/3kW 600W MPPT 24V

It's cheaper than the original one so to my pocket it looks good.

Am I getting nearer the mark with this one?

Bite the bullet and get the Victron. If you shop around you can get better prices than you see online.

I think Afrikaans speakers would say "goedkoop is duurkoop".

Edited by VisN
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