macafrican

There are actually some people making rectifiers in SA - there are all sorts of industrial applications where people need large DC power supply. Those normally assume grid AC : rectifier = DC output. For mine I need high voltage (775V) and yes the Atess is $$$ but I figure in a home setup or small office setup this would ALSO be far preferable than doing the ATS/Bypass usual trick. Was wondering what people’s experience is with generator:rectifier and whether have to be careful about generator type, alternator, voltage regulator, governor, etc. As I have it, the rectifier is set up to present to the generator as a constant load being taken. My other concern is that DC Combiner added to the mix. Basically large DC bus that has the input from the rectifier but also has cables to battery and cables to the battery inverter. Injecting DC there is presumably just same as DC that would have come from grid/solar via the battery inverter / PCS, so the BMS presents either charge demand or takes recharge from that DC busbar? I would set mine up that BMS max charge rate is a little below the rectifier max output. Else the low SOC battery might ask for more kW than the gennie : rectifier can supply and that might get messy.

For tying in a generator to a system, kicking in when battery SOC gets a bit low, has anybody gone DC tied with a rectifier instead of normal generator AC route? In my case I want to keep grid connection if it is around, but severely capped in kVA. Synchronizing generator and grid is tricky and some inverters don’t like it plus many installers just say no quoting nonsensical rules. So alternative method is gennie : rectifier : DC Combiner. That DC Combiner is the junction where inverter picks up DC connection and to which the battery banks are also connected. Concept is -Battery gets to target example 30% - Gennie fires up and supplies DC to the Combiner - depending solar and grid limit and loads the inverter either charges battery or draws it down much slower. -Battery gets to upper target SOC say 75% and shuts down. The nice part is it is fairly clean install, the gennie need not be sized to peak inverter size and there is absolutely no change-over on the AC bus side.

I’d look at how boats handle wind turbines - they could have shore AC power plus DC solar plus DC engine alternator plus wind (AC or DC) and have two battery banks plus battery inverter(s). My gut feeling is a DC charge controller from wind turbine that supplies common DC bus to which you hook the battery inverter and battery. The battery BMS would not know or care who supplies DC or draws DC so view that DC busbar (or DC combiner) as an interchange? I don’t think hooking wind into MPPT solar input of Axpert is a good idea but could be wrong. Very different power management, more than likely the wind charge controller can do a lot of other things to turbine.

By the way, not sure if your supplier allows exporting solar, but if you do, I am 99% certain using three single phase inverters is not allowed. NRS requires you to export equally across three phases. I’m not sure why they require this, as it “costs” power. Eg if you have three phase grid tied inverter of 9kW and at the time when you have 9kW solar you have loads of 1 and 1 and 2, you can’t export 5kW - you can only export 1+1+1

In three phases, should the systems be set up as parallel at all?

256Vac also looks suspect. I have a very large different technology and the data does not always tie up so that even measured over example a week, grid export = Solar + Recharge - Discharge - Loads = Grid. But mine are small % difference not your range.

The BMS prob has in its literature what its factory setting protection shutdown is, sounds like you hit that when inverter thinks it is not there yet. It might be a math and reporting issue? Some inverters show you what they calculate SoC at based on charge and discharge numbers, in others the BMS knows exactly per cel, module and bank and tells inverter what SoC is. To resolve, maybe set at 30% for a while and work your way down over couple of days, and see whether still get an unplanned shutdown. Eventually you’ll figure out that for example 23.5% setting keeps you above protection shutdown. If your BMS data is accessible, can you see millivolt max and minimum per cel? In stable state, that should be small range between the highest and lowest cell. Eg 40 millivolt. If you see a range in the hundreds of millivolt, you may have cel problems that vendor must sort out. What is your max charge and discharge set at? Despite claims by some batteries I stick to ½ C

I presume this for connecting solar to, while on grid? Not sure it is my council or NRS097 rule, but you’re not allowed to connect three discrete inverters onto a three phase utility supply (and remember limit is 13.8kVAac). The three inverters must operate unity - when solar is surplus, equal kVA export to grid, per phase. on your side of the fence, each inverter would be connected to a utility supply phase, so as long as you wire up your phase rotation correctly, a three phase load will work fine. I have a three phase borehole but what I did add is a relay that does not allow borehole to try run unless all three phases operating (I have one three phase grid tied inverter and another battery inverter for loadshed)

Are all your panels on the same orientation? Eg all face NW and at 20 degree angle. You must have, per MPPT, all the panels the same orientation. If half your panels face NE and half NW then you’ll be forced into at least two strings.

At family holiday house we have gas hot water to some bathrooms and it is battle to get to a comfortable shower temp and have it stay there. A plumber told me the problem is the showers have mixer type taps (swing for temp and pull for volume). Do you have a bath with separate hot and cold taps (even if they combine where it runs into bath) and does it also have the problem? Plumber said there is way to have equal hot and cold temp but then the cold supply at gas geyser must also be the cold supply to the point of use and there is a then a gadget that ensures pressure to gas geyser is equal to the cold water that carries on to point of use. We’re considering chopping out the damned mixers and replacing with plain old two tap system.

R1458 just to be connected. My town has charged high availability for ages, but they do charge lower kWh. It is a clever strategy to try and compete against solar. Eg at my factory we now pay R441/kVA for highest half hour kVA but 144c energy charges. So on a 300kVA peak demand, the cost before one kWh is R132k per month…. The only way to beat that is to add storage to solar and have an inverter that caps your grid draw at say 100kVA. That battery, ignoring any increased solar use, generates R1m a year in direct savings. It also means solar runs 100% during loadshed. I haven’t used diesel since September 2023

We can expect that the fixed costs per month will escalate, some people in some towns on prepaid only pay kWh! In my town for example, that 50A three phase would cost R1,458 ex VAT… A lot of old era homes had enormous electricity supply, far more than the home needs unless you also run a welding shop. Downgrading connection and even changing from three phase to a small single phase is possible but it will all depend on your setup, how much solar, etc. If have big solar, then split up that you have a minor public board and a battery between it and your existing board with most loads.

I briefly looked at converting a LandCruiser FJ40/45. It would not be possible to register for public road use, as the regulations have not been sorted. Have a look at www.evconvert.co.za

Edit : missed that roof is thatch

It isn’t a gas geyser as such - the gas system watches the water on its way out solar geyser, which runs through system like a radiator inside gas system. If temp needs it, it fires up gas and the water is heated on its way through. Pressure should be fine, but at family holiday home my experience of gas is that you should avoid mixer type taps, those ones with an arm that swings for temp and volume. I would rather have two taps and water mixes post tap on its way to shower head. Our non automatic is a Bosch one, probably stick to quality brands… The gas systems come in different sizes, down to small undercounter ones for example at an island counter basin. The gas itself must just be securely piped through house and you will need electricity there too.

I think you said it is not permanent home, so presume weekends/holidays. You prob expect to be popular so at times many people. Solar PV works well with permanent use but not occasional use because of high capex relative to days used per year) so I would go: 1. Big Solar thermal and a small pump off battery that circulates water from collector to large reservoir/tank whenever temp differential is enough. This should keep te reservoir well above the disease temperatures while you are away, which can happen if not warm enough. 2. A gas inline system that kicks in automatically if exit water from tank when somebody opens a tap is less than for example 45 degrees. You will likely anyway have other gas appliances. With gas you cannot run out of hot water even with 25 guests. my perm home has solar thermal + heat pump which is fine warm times of year but takes AGES in cold times. If I could re-do it I would do as I described above.

Thanks, will look. Also noticed it is only IP44 protection and I’d probably install outdoors, so also budget for an enclosure

I mostly charge my EV at work which has lots of solar so charging EV just reduces our exports. At home I have three phase solar grid tied that is allowed to export and separate from that a loadshed backup on one phase. Home battery is too small to consider charging EV during loadshed as my solar is anyway dead during loadshed. So I’ve made peace with : if I charge EV at home it increases my net home grid kWh by either using grid or reducing exports. Going to sell the i3 and get that new little Volvo and when I do, will get three phase charger at factory. Then I’d almost never need to charge at home as 2-3 hours at factory will do full recharge. Single phase charging at factory sometimes means it takes couple of days to get to 250km if I’m also using i3 a lot during day. I see Victron has a 22kW three phase EV charger for about R10k which is reasonable and I trust Victron

Btw in the setup of PCS there is the max charge rate to battery, which we’ve set to ½ C or 300kW - for battery health longevity sake. One could set it higher but in my case even if I had low battery then I’d have 400 solar and 100 capped grid and then minus loads we would not have 500 available to charge battery with. Whether grid on or not, the PCS charges the battery at up to that 300 but we prevent problems by changing the SolarEdge power percentage to follow load when battery is over 95% So in loadshed on say a sunny Sunday when loads are 75, battery is almost full and solar could be 250, we restrict solar to 75kW. There is obviously nowhere for the potential solar to go at that point. Other than this scenario the PCS dynamically changes battery charge rate. In the PCS setup you define the generator max and you define the battery charge rate when on gennie. That is static in Atess. So if you set it at 75kW and your gennie max at 350, then it does the 75 so if your loads push 275 the bypass cabinet opens generator contactor. If you tap dance outside you can use DataGuru to change that setting every second but that is a difficult tap dance and Atess warned that some interface component was designed for x number of changes and would not last for thousands of changes. No idea if that is true but we anyway rejected that approach. When I need to help battery I don’t want to help it at 50 or 75 kW, I want the most I have available going to battery.

Yes the controller starts gen, nudges voltage and freq to match what it sees on load busbar, then closes breaker. It also governs Scania at fixed output instead of load-following, Atess is not involved and there is no need to prioritize because remember I only do this when battery is very low. Atess does not even know gennie is running, all it sees is loads dropped a lot or became negative. Therefore, PCS runs normal mode, which is to charge battery at variable rate up to our configured max of ½ C while capping grid draw at for example 75kW. So capped 75 grid + say 100kW solar + 300 gennie - 250 load = puts 225 into battery. If there is loadshedding it would be 100 solar + 300 gennie - 250 loads = 150 into battery. If it is bad loadshed and it is evening, my loads are low so it would be 0 grid, 0 solar, 300 gennie, 40 loads and after about 80 minutes battery should be back at 75%

We do use the PCS for peak-demand-shaving. The generator only becomes relevant when battery is too low, for example loadshed and bad solar. Generator then must put back 300 kWh and help with carry loads to extent the capped grid and small amount of solar are insufficient.

Hell guy, don’t insult people trying to help you. Especially when you were confusing kW and kWh! Obviously they’ll start at the bottom to figure what you actually have

You’re confusing kW and kWh. KW is power, kWh is energy over time. Think of it like water in a pipe. You have a 10cm pipe (10kW) that delivers 10 liters per hour (10kWh). After three hours you have 30 liters (30 kWh) but obv still have a 10cm pipe. With solar, that 10cm pipe has low pressure in the morning and it might only deliver 2 liters per hour at that time. You take your solar DC capacity (sum of adding the watts of all your panels) is say 16000 Watts. That might have for example a 18kW grid tied inverter. Over a year unless you have odd tree or mountain shade, you should expect around 1525h of output at AC level. 16kW * 1525h = 24,400 kWh. That will not be linear over year. For rough math work on 6.1h per day in summer and say 2.6 in winter. You can use these ‘solar hours’ and ignore that your 16kw system is only doing 1kw at 8AM and 1.8kWh between 8AM and 9AM and it might do 17kW on a cool sunny day. Solar hours are basically a conversion of the solar exposure per sqm and the 1525h I gave you is based on what I’ve seen across many MW in the area and is measured after conversion, so it is your alternating current hours. Forget about the DC Watt hours and conversion losses - solar hours the way I gather them is your AC output to expect. If you switched off all your loads then you’d be generating about 3MWh in Dec/Jan in Cape summer (16kW x 6.1h x 31days). In Winter generating about 1.3MWh in July. What you export is entirely a function of generation and your loads and the timing of your loads. If you add more solar then the added solar is likely to nearly all be added to exports because your old solar export was after loads deducted. Despite all the theory, if you can, try and do your new solar that a portion faces ENE, a portion N, and a portion WNW. What you lose in solar hours vs all North is minor compared to the benefit of a longer flatter kWh curve. Think of it this way : with a longer flatter curve you get more solar earlier, and later, even if you export less in middle of day. As mentioned, you CANNOT add more in conventional grid-tied solar if you are LV connected on a shared LV feeder which I am 99% certain you are. There are rural connections where one client is on one pole mount transformer and he can do different. You cannot, COCT can detect you in an instant and importantly your AC setup might not cope with 30kW which is say 150Amps! Very few homes are wired for that. What you could do is split your AC board. So put more solar down, this time put a hybrid inverter with that new solar and add a battery bank and move everything that you would like to have backed up during loadshed/power failure onto this second DB. Your other AC board has the loads that will go down if grid goes down and it has your existing solar and it will export when old solar exceeds the loads that stayed on the public board. So it will prob export more and depending how you size your private AC board and what you put on it in terms of loads, that would never export to council but always have 3 to 5 hours of stored energy. (There are cheat methods that if your private AC board and new solar has full battery to supply some of that DC to your old grid-tied inverter but now getting very tricky. You would add a small breaker in your public AC board and program the new hybrid inverter on your private AC board to (1) only charge the battery (2) at a throttled kW and (3) not export to grid and (4) only when that battery is in trouble say 20% SoC. You could cheat a bit and allow export after battery full but be careful to cap that at what the public AC board’s middle of day loads are. You mentioned your new inverter is paid for : if I were you I would really ask the guys if you can upgrade that to a hybrid inverter and add batteries. You have so much solar, you really should have all lights and plugs at minimum able to run almost indefinitely. You will go insane if you have 30kW residential solar and no power during grid problems.

I see where we are missing each other : you are confusing kW and kWh You said “No 30KW inverters I have more than 30KW solar panels and it is for my HOUSE. Soon I will add another 30KW plus. Iw ill stop when I have about 65KW that I can push back” What you meant is you want to push back 65kWh per day. That would mean a three phase home with about 12kW worth of solar capacity in CPT in summaer and not using much in terms of loads. A 65kW solar system would be outputting 350kWh+ per day. If you are three-phase connected you can legally and safely do around 16kWdc solar even if COCT argues that the limit is 13.8kWdc. You could do say 25kWdc and convince them that your inverter will throttle grid export at 13.8kWac. That way your loads get solar and you export the most solar you are legally allowed to.

The presidential proclamation was about limits lifted to 100MW for very big systems. I am MV connected to the grid through my private MV:LV transformer so I could go big solar. You are LV connected to the grid, could be single phase or three phase. There are very good technical reasons from grid perspective why people on a shared LV feeder (you and say 100 houses around you are connected to one MV:LV transformer) should be individually subject to limits. You can go read NRS97:2 and argue with them if you disagree. At a more practical level, you will have an instant disaster if you try and connect 65kW solar on a 60A single phase connection!