phil.g00

Read up on the risk of Legionnaires disease at 50 as opposed to 60. Legionella bacteria are apparently in all our water, but really get multiplying in 20-45 degree water. 60 degrees kills the buggers, 50 doesn't. Apparently, this can be really dangerous when combined with showering and breathing in water vapour.

No, not so. The maximum allowable voltage on your Pylontechs dictates the maximum allowable voltage of the entire DC side, including your MPPT output voltage. On the other hand if you over panel your MPPT (within reason, I suppose), it won't pop it will just clip the output power to its rating. So you will get very limited benefit from the extra panels. You don't need identical sized MPPT's. The 100A is the output current at the DC voltage. And because your DC voltage is 52.5V, your output power is limited to 100A x 52.5V = 5250W. The 70A will be on the input side at whatever the Vmp voltage is. I never said that, I said with your panels positioned as they are your MPPT is essentially maxed out. You would need to re-position your existing panels, to allow the "electrical room" for more panels.

Yes, just check if there needs to be an additional heat sink. You wouldn't want one. That is a very lossy solution. A variac is a variable transformer, which would work, but would be an expensive solution.

This is a thyristor controlled device, same thing as a light dimmer. Yes, it's safe, if properly spec'd. It's not lossless, but it's not lossy either. I've seen numbers like 1.5W/ amp. There are a few things to know though. 1. It doesn't limit the current to the geyser,( like say a series resistor or a Variac would), it just doesn't allow the whole sine wave through. That portion that it does let through will still peak at the same magnitude as if it was a full sine wave. Everything still has to rated for full current, so it is more correct to say it limits the energy to the geyser. 2. Using one of these on a device that draws sufficient power will cause harmonics on your AC supply that things like inverters may not like.

From what I have gathered on the forum, a CT clamp is not the panacea it seems to be, if you have the wrong type of meter. The lagging response time when a load switches off, means the temporary power export still causes nuisance trips of the meter. I don't have one of these type of meters, so I am sure a CT clamp would work OK for me. If you have any purely resistive heat loads they can be fed by a load diversion DC PWM set up once the batteries are charged. This is what they use to power dump loads with wind generation. This is probably the best solution in your set up to capture the lost production.

If you have Pylontechs at 52.5V, then your MPPT is limited to producing 5250W. Which would suggest you are already pretty much maxed out with a 5.1 kW peak, with your panels in their present position. I pair combinations of E and W and N strings to moderate the noon peak and then I find I can have quite a lot more panels before the MPPT is maxed out. Purely E and W pairings (at the non-ideal roof tilt,) it seems to be about double the number of panels of an ideal tilt North facing array.. Aesthetics is also a consideration, when pairing panels of different manufacturers. I'd like to have same panel type grouped together on one side of the roof and use the other make as a group on another side of the roof. That way people only see one type of panel at a time. This may not bother you though. Then again if you are considering this, then the cost and hassle of re-fitting existing panels would start me evaluating the cost of another MPPT. Depending on your planned expansion, it doesn't have to be the expensive Victron flagship MPPT this time.

First Question: I'd say Yes. Second Question: I'd need more info: 1. What is your present noon peak current when you are tracking? 2. Are all the existing string the same tilt and direction? 3. Will any extra strings be at the same tilt and direction, or do you have other directions and tilts available to you?

No it wont, not automatically anyway. A grid-tied inverter goes full tilt all day long.

Nobody really knows, but I suspect about 30% of the total.

Hmm, now I think you've introduced a third issue. I think a heat pump rating is in terms of its output power. But a heat pump may have an efficiency of 300% or so, then the electrical input power is far less. You should know what your electrical power draw is. In electrical terms, all generation of an under-sized grid-tied inverter will be used and the grid will supply the remainder of the power required. If you can guarantee that your constant load at daytime exceeds your grid-tied capacity, you will not have export issues. Every watt you generate will reduce your electrical bill.

Consider using a Tristar PWM Diversion Charge Controller, it's a lot cheaper.

Is the controller essential or just a nice to have?

This is something I have considered, but it would have to control a relay, so I could automate things. I never got into Arduino's and the like though.

It probably does, what is the quiescent current draw of a unit?

OK, some confusion of terminology here. Firstly as already pointed out, is that kW do not equal kWh. (We should have a sticky for this). Kilowatts are a rate of energy usage which we call power, kilowatt-hours reflect the amount energy used over a time period. @Natal_Nic, your inverter is rated at 3kW, but your usage in a day is 10kWh, not 10kW. For example, 10kWh could be used either using a constant 1kW of power for 10 hours or a constant 10kW of power for one hour in your daily usage. Whether an inverter can handle your peak demand depends on you usage pattern. You have not supplied the correct information for anyone to answer that question. Secondly, @Bobster, the term "grid-tied inverter", is being confused with "hybrid inverter". An hybrid inverter combines and "off-grid inverter" with "grid-tie" capabilities. It is positioned as a series device that passes grid current through it. A grid-tie inverter, which was asked about, has no batteries. A grid-tie inverter is a parallel device, it adds to the grid supply, the grid supply is not supervised by it. If there is sufficient solar yield, a grid-tie inverter will pump its 3kW worth of power into the grid all the time. If your loads constantly demand more than 3kW the shortfall will be made up by the grid, and nothing will trip (in normal operation). Likewise if the loads are less than 3kW the excess generation will flow back into the grid. Now @Natal_Nic, when you generate excess power to your usage you are exporting power just like a power station does. Exporting power can create regulatory and supply point issues depending on your meter ( a pre-paid will trip) and national/local restrictions.

@ewertb, This whole answer isn't necessarily to address your set up, but to rather address panel positioning in general. Your " less than ideal" orientation and numerous different aspects is not a disadvantage, and no you don't need numerous smaller MPPT's if you do things right. I'll explain: The maximum voltage threshold that an MPPT can deal with, will dictate the number of panels you can have in a string. Every panel in this string should be of identical spec and pointing in the same direction at the same tilt. Now the current capability of your MPPT will dictate the number of strings you can deal with. So you can parallel your similar strings to match this current capability. Now, I want you to be aware of something, a solar panel with very little light still basically outputs full voltage. It may not be capable of supplying current at low light but its operational curve is such that it is very close to full voltage. This in turn means that it wont drag down the voltage of a panel with good light that can output a decent current. Which means a shaded panel can be paralleled with an un-shaded panel with impunity. The common misunderstanding I am trying to address, is that it is often thought that all strings to a single MPPT have to all be at the same tilt and direction as each other. As long as each string contains the same number of identical panels, and within each different string the panels are the same tilt and direction, then the strings can be paralleled. Between the strings themselves, they can be at a different tilt and direction to each other on the same MPPT, without an operational detriment to speak of, in fact this has a considerable upside. The tilt and direction of a string determines when in the day a string has its peak output. If all the strings pointed in the same direction they would peak together, and that peak current versus your MPPT's capability would determine the number of panels you could have. Your MPPT will have to be sized to deal with a big peak of current for a short period of the day. This is inefficient, because the other 92% of the solar day, that MPPT is idling. The cost of that MPPT is a production overhead. Paralleling strings with different directions means you can match waxing and waning strings together and spread their peaks. This softens the noon peak. This in turns means you could either use a smaller (cheaper) MPPT, or alternatively increase the number of panels and get more useable units of power throughout the day. The MPPT still isn't overstretched at noon, but at least it is working at a reasonable pace throughout the day. I mix and match strings like this, and you'll be surprised how many more strings of panels you can add before you reach your MPPT's capability. Paralleling low tilt E and W strings, anecdotally, I estimate it is about twice the number of panels, of an ideal tilt N - facing array. My loads are such that I can use every watt I make in a day, in other words my MPPT's do not back off when then batteries are charged. You might argue that this is just trading panel efficiency for MPPT efficiency. So, I'd like to point out two further advantages that I have noticed: 1.Getting the power throughout a longer solar day also makes the power more useable than having schedule my loads to match a massive noon peak. 2. On an overcast day, when you really need the power, a panel will still produce say 10% of its output, largely regardless of it's tilt and direction. Having twice as many panels under those circumstances makes a welcome difference.

It would be better with two balancers and still not to join the mid-point.

I don't think you are asking the difference between 2S2P and 2P2S (which are identical), but you are rather asking if you should common the mid-points of the batteries or not? Both commoned or un-commoned will work, I'd advise against commoning though. If you join the midpoints a faulty (or unbalanced) battery will affect the whole bank to its detriment, as opposed to only its own string if un-commoned.

Yes, these numbers must be identical.

Regarding sizing, Victron inverters can be paralleled if the are identical hardware units, with identical firmware. The firmware compatibility is crucial, as there has been iterations of the firmware chip, and two different chips are incompatible, and there are no workarounds. Know up front that specifying a 3kVA Victron when you make a purchase is not enough, you must specify the first four digits of the firmware chip as well, if you want to parallel a unit. If the firmware matches paralleling two units is a piece of cake. Your local authority will probably specify a maximum size and a list of approved inverters. Cape Town seems to have taken the lead in this, I expect other local authorities will adopt Cape Town's practices, so you'd be as well to make your system "Cape Town compliant", even if this isn't an issue that isn't pushed where you are at the moment. In that case, the size limit is 25% of your incoming MCB size. This is a good stage to do your sums, to see if getting a larger municipal supply ( so you'd qualify for a bigger inverter) would be worth it. You could also consider a combination of hybrid inverter and one of many 3rd party grid-tied inverters, just to optimize your size allowance. This also works well and is cheaper, but it is not as rock solid a union as two hybrids.

DC is a must for control circuitry, you cannot use AC to control equipment that controls AC, because you couldn't turn it back on if it went off.

I think you have to consider data centres as a special case, far removed from the domestic application and I'll explain why.. Data centres use DC for a very good reason, it guarantees a much cleaner, more reliable supply for very sensitive equipment. Data centres still use plenty AC power, but they can (and do) ditch the grid seamlessly and quickly and run off their own batteries/ generation, if there is a hint of a problem with the grid power quality. But, using the good traits of DC is not cost-free, you still have to deal with the bad. Google, Microsoft, Amazon, Paypal, Facebook and others have data centres in Ireland. Why are all these big names in Ireland? Well to be honest, Ireland ticks a few boxes for them. But one reason that is often stated is because these data centres can massively reduce their power costs on the cooling requirements on all this equipment using Ireland's temperate climate. So low voltage DC ( and it's heat losses) has in part decided in which countries these boys have to set up shop. Whilst, thee and me in a domestic scenario, would consider moving country in order to use DC a tad inconvenient.

I took the video to represent an aspiration. It doesn't represent a practical solution for people unless they are willing to do without. The voltage standards talked about intra-home were between 5V and 48V, touting it to be inherently safe. This is neither true nor practical. I'll expound on why the low voltages mentioned ( 5V -48V) are impractical to use in a standard domestic setting. Lets look at the best case scenario: 48Vdc represents a voltage, 230Vac (rms)/48Vdc = 4.79 times lower than conventional AC. That means for the same power, to your standard 16 Amp wall socket, you need 16*4.79 Amps = 77Amps. Remember that electrical losses are I2R, they are not proportional to the current, they are proportional to the square of the current. Which in turn means wiring that plug with 16mm2 cable there and back = 32mm2, instead of 2.5mm2 x 2 = 5mm2. ( Well, I'll give my AC plug socket an earth wire, so 7.5mm2 in total, it is still less than a quarter of the copper needed for the DC equivalent). That's at 48V, which is the highest voltage mentioned, voltages like 5V,( also mentioned), require a ludicrous amount of copper. A 5V plug socket equivalent of today's AC standard would need over 600m2 of copper. It gets into the realms of cable size that isn't even made. Then we have to consider the "inherent safety" of this voltage, sure you wont get shocked, but that's not the only danger, with current comes heat, with heat comes the risk of fire. A loose connection in the right place, with current this high and your house will burn down. Sure, that can happen with AC as well, you are just massively increasing the risk of it happening, because every electrical connection in your house would be a potential welding machine. So to get reiterate my original post, a DC standard is needed, and it has to be a higher voltage than what is good for camping. The low voltages mentioned in your video don't cut it.

You can use grid-tied charger to help charge the off-grid batteries. As long as it wasn't a bi-directional inverter/charger the off-grid system would still be considered off-grid. What I am getting at is, there is still legally a way to use excess from your 4.4kWp by changing it to dc, which in turn can add to the 5kWp system.

I am certainly an advocate for maxing out on panels. You don't want drive it so hard, that it is clipping often, so you are losing out on a lot of available power, but you don't want to under-size the array, so that you not making full use of that MPPT you paid so much for. Try to aim for a sweet spot. I would also suggest you consider combining E and W strings if you can, ( as you can have more panels without clipping), that you can with a North facing array. That might seem like a strange thing to say, but it is much more useful to spread your power production over the day, the the W array picking up as the E array is dropping off. A N facing array may possibly provide an unusable excess of power at noon.