1 hour ago, VisN said:

optimum PV array size

In my experience, especially with a small battery (the 4Kwh you have is small), sizing the PV array larger than the peak power of the inverter is a waste. You end  up in the middle of the day with full batteries and an inverter running flat-out (at 2.4kw) and the PV being throttled too. To get better self-consumption you have to take the batteries down to below 50% every night. And a geyser timer becomes a necessity (run it after 11AM).

I'd say the optimum size is between 2.5kWp and 3kWp. My opinion though. I have a very similar setup, 7Kwh batteries, 2.5kWp on the roof right now (pointed in slightly different directions), and a 3KW inverter. I already have this problem: I have to take the batteries down to 50% every night AND do some planning on daytime loads... otherwise the batteries fill up and I have nowhere to put the power 🙂

... plonkster...

so lets say your batteries are charged by 10am... and you geyser/s kick in at 10am, they then charged by 13:00... you now sit with left over PV, other than ye it's there, is there any problem with it... say you have a load in the house of a 1000w and a pool pump at 700w... PV is capable of 9 x 330.... Multiplus II 48/3000/32-35

for now I expect my PV to drop... I'll have top start with 6 x 330w on a BlueSolar 150/35 facing NE (catching early morning sun) and then for now 3 x 330w  on a BlueSolar 150/35 facing N.

Thats simply my roofs for now... will be adding another some smaller panels later in the N direction on a small roof I have or have a idea how to fit some panels next to house on frames... against a double story wall with no windows, good change i can get 6 panels in (might fit them onto their own MPPT) or swop the one N facing 150/35 out for a 150/70 at the time)

G

 

 

 

2 hours ago, plonkster said:

In my experience, especially with a small battery (the 4Kwh you have is small)

@plonkster, thanks for always taking the time to reply 👍. I have 2 x PylonTech US3000, that would be 7kWh, correct? A +/- 3kWp would still be the right size?

What if things really started going pear-shaped and we had extended periods of load shedding, would a larger array make sense then? We've had up to 6.5 hours at a time in Midrand.

1 hour ago, VisN said:

@plonkster, thanks for always taking the time to reply 👍. I have 2 x PylonTech US3000, that would be 7kWh, correct? A +/- 3kWp would still be the right size?

What if things really started going pear-shaped and we had extended periods of load shedding, would a larger array make sense then? We've had up to 6.5 hours at a time in Midrand.

I have 4 off the 2.4kw units and they charge very quickly at 49a from a 4kw Infinisolar plus.

They do tend to drop quickly from 52v to 48.3v where they stay.

With hindsight the charging rate should have been set at 24a. I use mine as a backup with charging from the mains or a generator.

I've never succeeded in emptying them up to the point where  a bms shutdown occurred. Even with a 4 day no power once. I would only top them up now and then with the gennie.

Edited April 28, 20197 yr by Johandup

OK, this is weird.... I cannot quote @VisN's post at all.

I don't have a pool pump. Once the washing is done, the tumble drier's done, and the geyser has re-heated the morning shower's water, I have nowhere else to put the energy (except the batteries). At the moment it works perfectly, as long as I take the batteries down to at least 55% SOC. In winter I will obviously have to raise it a bit. With a pool pump, I could probably add a bit more PV. But right now, adding more PV would require cycling my batteries deeper. Cape Town caps me at 3.5kWp anyway.

I think as a rule of thumb, a 3kWp array with a 3KVA inverter is a good match. Your personal circumstances might push you a bit either way.

Edited April 28, 20197 yr by plonkster

11 hours ago, plonkster said:

In my experience, especially with a small battery (the 4Kwh you have is small), sizing the PV array larger than the peak power of the inverter is a waste.

Plus 1 one that!

And if you do have a large bank, in the city, it costs more per kwh than Eskom. Much cheaper to reduce loads than getting more batteries.

For me, in summer on a 2.1kw array and a very very small bank, I'm struggling to justify more panels. Will see this winter.

I'll be sitting at 9 x 3.3 for now... = 2.93 on a 3Kw Inverter, damm i was good, even un planned atm due to roof space... would like to add a 3rd battery later, but will see how Swambo and kids adjust their usage... tried for 2 weeks to get them to switch off lights as they walked out of a room...  maybe some day...

G

7 hours ago, The Terrible Triplett said:

For me, in summer on a 2.1kw array and a very very small bank, I'm struggling to justify more panels. Will see this winter.

As an actor once said... all these horses and nowhere to gallop.

I think this is still a grey area (for me anyway). 

Logic dictates that one must prevent the battery's dod to go low as it affects its life. We are talking percentages here. 

The way to do this is by preventing loads to be drawn from it by using available power from solar panels in the available daytime. 

If I can get this right by installing panels to the east, west as well as the traditional North sides then so be it. It would be nice to add significant power for 4 more hours per day (my house starts up at 7:00 - 17:30 when the last meal is served). The effect of lower solar radiation from the sun from now (April/May) to the start of the next summer season must also not be underestimated. 

My goal would be to extend the life of a R60k battery investment. 

 

think you missing point of the Lithium Ion batteries, they want to be discharged daily, they like going down to 80% SoC.

I'm going to try and setup my system that during day it run's primarily off Solar, with added when required from grid, in the night it runs primarily off Batteries, added by grid as needed,

of course, I want to leave some in battery, should we wake up and suddenly run into a load shed, need enough in batteries till bout 9-10am... when I will be able to be fully on PV again.

G

1 hour ago, plonkster said:

As an actor once said... all these horses and nowhere to gallop.

When we had a pool pump, before the drought, different story.
Or if the 8 year old EV tube system decides to go.
Or if I can get to cooking food daytime for evening consumption.

 

53 minutes ago, Johandup said:

Logic dictates that one must prevent the battery's dod to go low as it affects its life. We are talking percentages here. 

What George said ...

39 minutes ago, georgelza said:

think you missing point of the Lithium Ion batteries, they want to be discharged daily, they like going down to 80% SoC.

 

1 hour ago, plonkster said:

As an actor once said... all these horses and nowhere to gallop.

Found it 🙂

44 minutes ago, georgelza said:

think you missing point of the Lithium Ion batteries, they want to be discharged daily, they like going down to 80% SoC.

Aaah I know... but let's say I take them down to 80% DoD (not SoC). That gives me an additional 2kwh of energy I can take out at night and put back in during the day. Divide by 5... that's 400W of extra PV, above the 2500Wp I have now.... so pretty much bang on 3kWp.

Let's talk theoretical max. If I run that inverter at full power for 24 hours, that's 24*2.4 = 57kWh. Divide by 5 (ish), that's 10kWp. So that is the absolute maximum that you could ever get through a 3kva Multiplus in a day, so 10kWp is the theoretical maximum you could install IF you had a large enough battery to store at least half of the energy you'll be making... 🙂

But it is extremely unlikely that you will do that. Let's say you have half the battery space to do that, and half the loads... that puts you at around 5kWp.

So the answer is somewhere between 2.5kWp and 5kWp depending on your local conditions.

9 hours ago, The Terrible Triplett said:

Plus 1 one that!

And if you do have a large bank, in the city, it costs more per kwh than Eskom. Much cheaper to reduce loads than getting more batteries.

For me, in summer on a 2.1kw array and a very very small bank, I'm struggling to justify more panels. Will see this winter.

That really depends on how your system is being used. Many people, in the cities, have off-grid systems, where it helps to have a larger PV array, in order to recharge your batteries while the house still consume power as well. 

1 hour ago, georgelza said:

think you missing point of the Lithium Ion batteries, they want to be discharged daily, they like going down to 80% SoC.

I'm going to try and setup my system that during day it run's primarily off Solar, with added when required from grid, in the night it runs primarily off Batteries, added by grid as needed,

of course, I want to leave some in battery, should we wake up and suddenly run into a load shed, need enough in batteries till bout 9-10am... when I will be able to be fully on PV again.

G

A sweet spot might be to run it down to say 70% or 60% and then go back to grid?

1 hour ago, Johandup said:

I think this is still a grey area (for me anyway). 

Logic dictates that one must prevent the battery's dod to go low as it affects its life. We are talking percentages here. 

The way to do this is by preventing loads to be drawn from it by using available power from solar panels in the available daytime. 

If I can get this right by installing panels to the east, west as well as the traditional North sides then so be it. It would be nice to add significant power for 4 more hours per day (my house starts up at 7:00 - 17:30 when the last meal is served). The effect of lower solar radiation from the sun from now (April/May) to the start of the next summer season must also not be underestimated. 

My goal would be to extend the life of a R60k battery investment. 

 

@RichieRich this is what I was referring to when using 2 MPPT's

something that will be experimented with, via the MQTT streams... will run MQTT and NodeRed on my HomeAssistant/HassIO host and modify these settings from there.

In addition to monitoring and switching Sonoff's...

Looking at replacing the breaker+timers on Pool and 2 x Geysers with Contactors controlled by sonoff - Basic's getting commands from HomeAssistant. That way I have better remote control over them instead of just a on/off time.

G

48 minutes ago, plonkster said:

Found it 🙂

Aaah I know... but let's say I take them down to 80% DoD (not SoC). That gives me an additional 2kwh of energy I can take out at night and put back in during the day. Divide by 5... that's 400W of extra PV, above the 2500Wp I have now.... so pretty much bang on 3kWp.

Let's talk theoretical max. If I run that inverter at full power for 24 hours, that's 24*2.4 = 57kWh. Divide by 5 (ish), that's 10kWp. So that is the absolute maximum that you could ever get through a 3kva Multiplus in a day, so 10kWp is the theoretical maximum you could install IF you had a large enough battery to store at least half of the energy you'll be making... 🙂

But it is extremely unlikely that you will do that. Let's say you have half the battery space to do that, and half the loads... that puts you at around 5kWp.

So the answer is somewhere between 2.5kWp and 5kWp depending on your local conditions.

The problem with solar panels is that they never produce at 100% so having extra solar panels available would help getting more energy in the mornings and afternoons when the sun is lower, as well as in winter, and on cloudy / rainy days. 

5 minutes ago, SilverNodashi said:

That really depends on how your system is being used. Many people, in the cities, have off-grid systems, where it helps to have a larger PV array, in order to recharge your batteries while the house still consume power as well. 

Yes, we know that. 🙂 

But you know maybe a few whom have grid tied systems with a 2.1kw array and a 4 x 6v T105RE battery bank, all the horses with nowhere the gallop.

You don't need to go 5/4/3 solution all the time. (cwl)
(5kva Axpert, 4kw array, 300ah battery bank)

Long story short, past a certain point there will be diminishing returns. That point could be anywhere between 2.5kWp and 5kWp depending on your battery size and assuming the inverter is a 3KW Multiplus-II. I see no point in sizing my array over 3kw unless I also add more battery capacity. That's my subjective situation though 🙂

15 minutes ago, plonkster said:

Long story short, past a certain point there will be diminishing returns. That point could be anywhere between 2.5kWp and 5kWp depending on your battery size and assuming the inverter is a 3KW Multiplus-II. I see no point in sizing my array over 3kw unless I also add more battery capacity. That's my subjective situation though 🙂

You and I have debated this issue, my gut told me limit array to inverter max, you thought about it and then some more.

Have a question: You have a small cheap "Leisure Deep(sic) Cycle" battery bank set to Always Keep Charged in ESS - only there for adhoc load shedding.
You have 3 geysers (2kw each) and a pool pump (1kw) with general loads of say 500w.
A geyser and the pool pump with general loads can run together = 3.5kw
So you install a 4kw array, scheduling when the geysers come on during the day.
4kw array making sense or not?

Edited April 29, 20197 yr by Guest

5 minutes ago, The Terrible Triplett said:

4kw array making sense or not?

Well, how many hours can you get out of that...

A 150 liter unit, assuming you have to reheat a full tank from cold, will need 3.5 hours to get to hot. And a pool pump, if I am not mistaken, needs to run 6 hours a day, right? Then it seems you can schedule these to run during the peak sunlight hours and 4kWp might just be justifiable.

I can't do that. My single geyser runs less than half of that, and there is no pool.

7 minutes ago, plonkster said:

I can't do that. My single geyser runs less than half of that, and there is no pool.

Same here, loaded question for future people reading the thread. 🙂

I find with the quick showers being the norm here in Cpt, that they 200l geyser we have, 3 people using it, seldom goes below 40deg. So 2 hours on should be ok.

Winter, different story.

We have 3 geysers, 150l, 200l and a 50l.
50l - basta that. On Eskom.
150l on solar between 1-3pm on a timer.
200l EV system started having issues.

The 200l Geyserwise will beep, as in it resets itself, evenings mostly, after 12-6am the most. Quotes to have it fixed came in substantially high. 

Then it stopped, no more rebooting. I THINK it was bad Eskom power but I could not prove anything using the Victron data.

So the idea was born, why spend thousands on a EV system that has served it's purpose, spend that on more solar panels, schedule the geysers.

Edited April 29, 20197 yr by Guest

11 hours ago, georgelza said:

think you missing point of the Lithium Ion batteries, they want to be discharged daily, they like going down to 80% SoC.

I'm going to try and setup my system that during day it run's primarily off Solar, with added when required from grid, in the night it runs primarily off Batteries, added by grid as needed,

of course, I want to leave some in battery, should we wake up and suddenly run into a load shed, need enough in batteries till bout 9-10am... when I will be able to be fully on PV again.

G

I'll have an opinion on lithium batteries in six years from now. 

Until then we rely totally on what manufacturers tell us. 

Though there is a longterm trial running in Aus. Where there were a few fatalities so far amongst the participants. Nothing like a spotlight to get cooperation. 

7 minutes ago, Johandup said:

Where there were a few fatalities so far amongst the participants. Nothing like a spotlight to get cooperation. 

50 per cent of the various types under performing from what I hear.

Edited April 29, 20197 yr by phil.g00

14 minutes ago, Johandup said:

I'll have an opinion on lithium batteries in six years from now. 

Until then we rely totally on what manufacturers tell us. 

Though there is a longterm trial running in Aus. Where there were a few fatalities so far amongst the participants. Nothing like a spotlight to get cooperation. 

so you want to spend the money on lithium-ion and then run them SoC/DoD as if they are Lead Acid's...

I'm pretty sure if you look at say your cell phone... which is  a lithium ion, which gets drained to 5-10% daily and it survives...

ye sure Lithium-ion is not as old as lead acid, come on people, they not exactly 1 year old... they have been around for a couple of years, and all the mfg's run 1000's of cycles on various config's to test what works and what not... allot more testing that any of us combined can imagine.

G