I’m 100% in agreement with you, my average loads are <1000 with 7 adults, and when all sleep <500w which is taken care of by the batteries now … IF I can recharge them.
My challenge comes in, the 4-5 hours of heating 2 geysers with each a 2kw element daytime between 11-3pm.
Geysers need about ±2h each to get to 65deg, and the family showers wisely, so once a day is perfect.
And IF there is bad weather, bah, Eskom is there.
Hence my “standing loads” of 2kw x 4h per day coupled with the pesky detail of also recharging the battery bank during a sunny day.
EDIT: I don’t care about the MW, kettle, induction plates, air fryer nor the convection oven. They go on and off all the time during cooking, overshooting all the time as the panel production is throttled back, with like max 500w coming out of the batteries during those times. Par for the course.
That probably means, maybe 700-800W during the day, constant background load.
This is the load a PV inverter can service very efficiently. There is no round trip into the batteries and out again. The object of the exercise is to use it as you make it and to try and match that during the day.
You probably want a PV inverter that can give you 700W from about 9:30 - 4:30. That way you’ll probably get 1300W+ when your geysers are on.
What you don’t really want is to use a PV inverter excess power to charge batteries, as that is probably less efficient than MPPT charging. (Although it is still not wasted, and better than nothing).
Now THAT is why forums are such an excellent source! Those titbits that someone mentions and the readers read that and think … I never knew/thought of that!
I started off with the idea of a 355w and a 420w panel fitted to a 700w Solis, direct to the main DB. 700w Solis is in stock at Segen. Got very excited, direct into the main DB. Not even a Carlo to link it to the Victron.
Tell me, your thoughts, the scenario:
Daytime load 1000w average
heat 2 x 2kw x 5 hours
recharge a 560ah bank from say a min SOC of 50%
How far will I get with a 700w Solis and 2 x 350w panels added to the system?
Firstly, “Average” could mean 10kW for 1hour and 0kW for 9hrs. What I am talking about is the “Mode”. That is the mathematical term for the number it is mostly at. So if you are mostly likely at 1000W during the day we are on the same page. However, if you are mostly likely at 600W, and have a 2000W load for 4 hrs, that is not the same thing. So we have to be clear what we are talking about.
(This applies for a no-export situation). The PV inverter should supply your “mode” load for as long as possible throughout the day. I would achieve this with a two MPPT inverter with an East string and a West string on an MPPT respectively.
That equates to an early start & late finish of production.
This would still give you a midday peak, albeit a long shallower one.
The Victron MPPTs are for charging the battery, and combined with the Multi, for those heavier loads during the day.
I would use a geyser timer, combined with one of those load management relays ( to sequence the geyser loads) and turn them on, say at the time the batteries are usually charged. ( Or even better use SOC supervision).
Then if there was sun you’d use it for the geysers, and if there wasn’t you’d use ESKOM.
( You don’t really have a choice).
Unless you expect load-shedding I wouldn’t use ESKOM to charge batteries for nighttime use. I would just use straight ESKOM at night.
( You have a choice about this, so maybe the geysers should be priority over the batteries being charged and not vice versa?)
8 am - 5 pm: 600w = ±5.4kWh per day.
11am to 3pm: An additional 2kw x 5h = ±10kWh per day
= ±15.4kWh per day.
I can get, on good days, 27kWh from the panels.
This month more like 20kWh per day.
Hence me thinking, Solis 2kw to cater for the 10kWh per day.
The rest of the day, taking care of some of the ±5.4Wh.
The main system focussed on the difference, main production going towards the batteries, which is nowhere in the above sums.
Just remember, the efficiency benefit of the PV inverter over a Victron MPPT is by matching your daytime loads, not by pumping 10kWh into the batteries, so you can use round trip power later.
I’d rather look at the long game.
You have the itch to go for the 700W inverter now because you already have the panels, plus it’s in stock, seams like a quick and easy, cheap solution.
In a year things change again and you might need another 700W.
I’d rather add at least a 2 kW Solis now, the price difference between a 700W, 1 kW and 2 kW isn’t that much if I remember. Even if you then only add the 700W of panels you already have now and add more at a later stage.
Eventually you can get the Solis PV up to say 1.5 kW to comfortably cover the 1 kW base loads you have during the day.
I thought it was an excellent idea yes, the 700w Solis, last night I ended up with a 3kw one with 5 x 545w panels as one will not sell a 700w one easily, need to consider that, so to upgrade later one has to get another 700w and then maybe a 3rd. I’m not sure of multiple Solis on the same system, will find that out.
And each time panel mounting costs.
So, THAT call is based on: Phukkit, have the panels, get a 700w as it is “cheap” shave off the baseload and see where that gets the numbers in real life.
Yes, I agree. My impression is that the current MPPT will have more than enough from the 4.2kw array for recharging the 560ah bank, having less of a load to handle if there are no geysers to heat peak sun hours.
Matter of fact did a “test” and switched off the geysers a day or two (not-so-good weather days) … man, those were tense days as there was little hot water, no matter that I told everyone I’m doing it.
I see Sat and Sunday are clear days. I think I’m going to switch off the geysers, with the existing loads, and see what happens, irradiation-dependent.
EDIT: See, I want to draw about 1kw per hour out of the batts from ±6pm to when the sun takes over.
Doing that with 500w per hour gets me to about ± SOC of 75% by 8am.
Hence the min SOC of 50%.
If I drawdown to 50% SOC and daily loads and recharge with the 4.2kw array without geysers … will try
Yes, they can operate independently, without being aware of one another. At one time I had a 3kW ABB aurora and a 1.5kW Solis both on the output of my 5kVA Phoenix.
Both respond to frequency-shifting independently, and the Multi actually isn’t aware the power is coming from 2 inverters. It just responds to the total power generation of the two.
I re-jigged things recently, and probably will re-jig a few things again.
Just be aware the total PV inversion sum cannot exceed the Victron inverter capability.
(1:1 rule)
Question: My idea is to put the Solis direct onto the Main DB, independently of the Victron.
Thinking is the main DB, although supplied by the Victron being grid-tied as is now, will now “draw less” from the Victron setup. Does that make a difference?
Did you see my earlier philosophical remark? You have to heat the geysers daily, that is a given to maintain domestic bliss.
So you are prepared to use ESKOM to do that.
But lets rephrase this:
My question was why not heat the geysers as a priority for solar energy?
You do not have to charge the batteries to maintain domestic bliss.
Doesn’t make sense to charge the batteries with ESKOM, why not just use ESKOM at night?
Maybe they can wait for a sunnier day tomorrow?
Why do the batteries get the first bite of the cherry?
I thought one of the advantages of this new battery chemistry is that is quite happy at a lesser SOC for a while?
If there is Load-shedding that is a different situation.
Looking at your situation, I can’t help but feel what you need is not more panels, but rather a heatpump.
You currently have 4KW’s worth of resistive heating going on (2x2KW elements for 5 hours as mentioned in your previous post) that’s 10kWh per day per heating element, so about 20kWh per day for both.
If you replaced them with a single 5KW heatpump (Should probably cost around R25K) you would need about 4 times less electrical energy for the same amount of heat, given they have a COP of around 4.
That means only a 1.25KW peak instead of you current 4KW peak. and only 5kWh of consumption and not 20kWh of consumption.
I may have been unclear, was referring to the 1:1 rule, if connecting to the main DB, will make that rule null and void?
They don’t currently, geysers do. Yes, I can use more Eskom at night, when I did the sums on the back of a cigarette box, I would "run into the red " faster than more panels.
BUT, you understand what I’m saying … and each time we seem to come back to the baseload of 600w with me having the 2 panels onsite now AND access to a 700w AND the fact that I can probably connect more than one Solis to the main DB … why NOT start there.
Yes, that is an option. Got prices recently, as well as Geyserwise PV option, compared that to a 3kw Solis with 5 x 545 panels with the install, is cheaper, lasts longer and has more benefits to the home overall.
Always trying to think “down the line”:
Take the 4.2kw array and get a Solis to match it, as it is all about daytime loads.
Donate the 700w Solis to a child.
Then, because Victron is staying, get 8 x 545w panels for battery charging to shave off some serious evening loads, like cooking too … not a WANT nor a NEED most DEFINITELY a HOBBY.
Yes it is void if you are upstream of the Multi, but then I think you need a CG so the Multi knows about it. But so long as you are less than 1:1 there is no issues downstream either.
My point is the batteries can wait a few days until a sunny day fills them from empty til full. The geysers are kWh’s that must happen daily.
Yeah, do what you can do now. Ever bit helps if it’s in the right direction.
Well, at this moment in time, for 700W you can connect it and another couple like it wherever you want.
You will have to do your sums, but more MPPTs ( ie multiple smaller Solis’s) may suit your roof and will be easier to tailor to your usage pattern. That part only you will know.
I have been buying cheap second-hand PV inverters from eBay for a few years now and taking them back to ZA with me, when I go on holiday.
I have 5 installed in ZA at my mother’s. I think 4 in the cupboard in ZA, and I think 11 or 12 still with me in Ireland.
They are all under the stairs and I am not getting them out just to count them.
Oh!, and 1 took to ZA was a dud. (a Delta)
But, to be honest I don’t really know exactly how many I have.
I think I have 7 or 8 Victron MPPTs as well.
Anyway, should be enough for the BIG build when I retire.
Put the Solis on the input side of the Multi (ie directly into the DB, with its own breaker, that is regulation anyway). It has to feed in AFTER the grid meter.
Fit the optional current transformer to ensure no feedback. It is cheap enough and covers those days when your baseline is lower than what the PV-inverter can make, for whatever reason.
The 1:1 rule does not apply if the Pv-inverter isn’t on the output of the Multi. You can fit as much as you want (subject to whatever other regulations apply to the area).
Configure Victron ESS with a grid setpoint that is higher than whatever the Solis wants to zero at. That way the Multi will always import energy from the Solis if your loads are not using it, because it can SEE it going out with the grid meter.
Unless you fit an additional energy meter (and set the role to PV inverter) to measure the PV-inverter, your “AC loads” will be incorrect in the Victron overview.
The cost of the 1kW Solis is around 4k and the 2kW is around 7k. The 700W unit is R2.7k (quick google). That makes 2 x 700W not all that unattractive.
