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New Micro grid system on BYD batteries going in @ 11.6kWp

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Solar PV, the generation part happens here.

How many panels and what Wattage do we need to support these loads. There are a few angles to consider. Let’s start with the batteries, Since I will end with 48kWh worth of storage, I need to be able to charge them during Winter time in less than 8 hours as that is all the Sun I have available. That means 6kW worth of panels (48kWh storage capacity divided by 8 hours gives you 6kWh) during the 8 hours should charge from a 20% SoC to 100%, system losses and efficiencies accounted for. But I want to support my shifted loads during daytime on those panels, so now what? Basically double the panels to 12kWp and you will have 4 hours to support loads and 4 hours to charge batteries for nighttime use. This is on average. You will end up with too much power generation during low demand times. Store that as Heat in the Geyser. A general rule of thumb would be to charge your storage in as few as 2 hours to allow for crappy weather. If you are in a Winter rainfall area or get lots of clouds and crappy weather, as few as 2 hours to recharge storage may be a good idea. If you dwell in a less cloudy less crappy weather area, just rejoice and charge over a longer period, period. Its a balance with some uncertainty, thumbsucks, assumptions and nuances plus the unpredictability of your usage patterns and the predictability of the weather, hahaha.

Another consideration is how much space you have to fit the panels. That may limit the total number you can install. In urban areas ground level may not always be the best, rooftops may be better for various reasons. Theft, shadows, or just plain space availability. Do you have enough space to install the required number of panels? My 11.6kWp system needs 30 panels in total. 6 panels are for the Black start MPPT capability at 2.3kWp and will supply DC charging to the system. The balance will be on the Fronius string inverter. It will take up a surface area in two rows on my roof, of 102m2 The Fronius priority is to support the loads and charge batteries. In general we will limit the loads in the mornings until batteries are at least 80%SoC. Then the loads will be added, Dishwasher, Laundry, Geyser, cooking etc. There should be enough capacity to carry the charging and some loads as the loads will be managed one after the other so as to allow charging.


One point to note, most designers design and sell these systems for capacity, big sexy numbers and all the power to them, pun intended. More bigger, more better ne. It may however not be the smartest move. We will get to that later. In general we have now determined more or less that a 6kWp panel system is what we need and guessed that it may b a good idea to double that, right? Right. So lets model.

This is a 2.2kWp system we have modelled here with my actual consumption included. You may say buy hey, the generation is skewed, panels don’t generate such a flat performance across the seasons, and you may be partially right, it depends but we’ll cover that. More importantly for now is the fact that we consume way more than we generate, time to fix that! Let's go…. But first, if we multiply this install capacity by 3, we have a ~6kWp system. So for the most part then, except June, July, August and parts of September we are good to go as we have excess energy (with a 6kWp system) to charge batteries and do the time warp again ;) Remembering always that we collect sunshine and time warp it to after dark by storing it in batteries. Your day vs night, morning vs evening loads will largely determine if the above is true.


Now you clever lot may notice a 2.2kWp system modelled here covers 35% of consumption. If multiplied by 3 that will be 105% of consumption over the calendar year. Yep indeed, would have wasted some there, yes Siree. Wasted is such a misnomer here…. But what the heck. Over dimensioning for energy independence is worth it. Or just use less to start with, cheaper both ways. But who gonna be called cheap on here 😳😉

Now way, you still messing with us I can year ya all complain. We will get to that, I promise, for now ignore the flat panel generation, pun intended.

This below is a 10kWp system and it covers most of my consumption, but not all. Remember the system above, the 2.2kWp one, yes that will be the MPPT black start DC coupled system that will charge batteries. I fully expect the Quattro to help the Fronius with supporting the loads. The daily generation will be partially consumed during the day, and partially time warped again. So the back of napkin calculation done to size the storage for supporting nighttime operations, is a good way to calculate you panel sizing requirements, too boot.


More later

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A Quick summary and crystal ball view. We have this far looked at the following:

  • Reliability and Availability of energy
  • Types of systems
  • Available Sun 
  • Energy demand
  • Generation and capacity planning
  • Panel layout and orientation is next
  • Summary this far (this bit) and then to follow
  • Inverter choice for micro grids
  • Storage selection
  • Diagrams and layout of components
  • Build and install
  • Commissioning
  • Beer 🍻 

This far the batteries are in place, well first phase of that. We have started making the roof mounting struts, done about 2/3 of them. Monday we continue with that and start the install on the roof.

The damn roof is sloped South by 5 degrees, oh the joys...


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Hi Sarel.


This is truly well done.

I'm running a dual system switchable through Arduino's. One for daytime use and one for nightime use. Power is on 24/7.  It is kind of a self thought out Frankenstein system. I just wish I had your knowledge. Hoewver, being retired I have the time to research and test new ideas.

My motivation for buiding this is the same as yours. Fat middle finger to the looting government we have.

I was pointed to your thread by someone else this morning. As I am in Cape Town and we've had the worst weather in 20 years, I was a bit on edge if we would make it. We did.

Yesterday was the first full day of sunshine in a few weeks. Both my battery packs were full by 13h00 and running through the night, this is what my PylonTech shows at present.



Considering the fact that the night time system is charged through household grid the result figures on usage and efficiency is escewed. I am looking into how to get these accurate. It's really immaterial though. Fact is we suffer no inconvenience.

Nevertheless, I'd rather spend R300k wisely than throw it to the sharks, if you know what I mean....

Disconnected is the way I will stay in future.

Following this thread keenly!



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@Sass Nicely done man, kudos to you and the system! Same objectives for sure, different roads to get there. Certainly your way is very efficient in every way, more so than mine, especially on the capitol front 👍 That is the real intelligent way to achieve energy independence! You have just proven that fact. Even with the efficiency losses of your system, you still managed to stay off grid and be self sufficient for a long period, irrespective of the weather. 🙇‍♂️

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23 hours ago, Sarel said:

@Sass Nicely done man, kudos to you and the system! Same objectives for sure, different roads to get there. Certainly your way is very efficient in every way, more so than mine, especially on the capitol front 👍 That is the real intelligent way to achieve energy independence! You have just proven that fact. Even with the efficiency losses of your system, you still managed to stay off grid and be self sufficient for a long period, irrespective of the weather. 🙇‍♂️

Hey thanks @Sarel. A really most appreciated compliment from someone as experienced in energy matters as you are!


Just like you I also run machines in my home workshop. A similar compressor, a lathe etc, etc. The only item I never use on my batteries is my MIG welder. For that I use a generator. No way will I bring that kind of load near the batteries. I also build cars, even my own design, with fiber moulds and a jig for the frame. Frames are literally all I weld.

I suppose ultimately I will upgrade mine with more lithium batteries. I truly have no need for bigger inverters.


When it comes to relying on SA government to supply anything? No thanks. I learnt that lesson decades ago. 


I am really keen to see your long term results!


Have a lovely Sunday.

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Let's time warp again but stay on panels, panel orientation design layout.

What direction should your panels face and at what angle should they be installed at? It depends, on a number of things. Where will they be installed is likely a big factor. On the ground, then they can be installed facing in the ideal direction and at the ideal angle. If its on a roof, mostly your roof angle will determine the panel angle and direction as well. When you have a flat roof or one tilted in the wrong direction (hey thats me, 5 degrees south facing roof here), your generation will be sub optimal, same for facing in the wrong direction. It may really really be worthwhile to invest in getting the orientation and tilt optimised. Remember the flat generation curves above? To get there for me means making custom mounts.

Here follows an interesting animation: You can see the Sun angle in the sky for the same time of day as well as the shadows cast. And below that another view.

Solar globe and analemma animation with shadows (video)



PV Watts calculator NREL (video)


Now we can start to answer the questions on the flat panel generation response. You can pause the video and look at the effect of different facing panels as well as different angles. By using these simulations, if you can precisely position your panels in angle and direction, is how you can make em flat panels balanced or tuned to you demands. Simple eh? Yes.

Solar PV Angles, what are the options (video)


Here is the crux. If you are only looking to get maximum yield in a year, by all means follow the recommended tilt angles, normally same as your latitude. If however, you want to generate your energy to your demand curve, ie. more during Winter to help carry the heating load or for Summer to carry cooling load, if that is your biggest demand, simulate and tweak your orientation and/or tilt. For my use, I skewed my results to get a close to flat curve with a Winter balance. my Latitude is close to 26deg, but my tilt ended at 33deg to achieve this. Overall, I am not loosing much compared to the maximum overall energy at a different tilt angle, maybe 40 -100kWh.

This is an easy way to simulate and model your generating capacity, add your address and a few parameters and click away.


Let’s model and simulate the PV rows and get the numbers down for how far apart the panel rows needs to be apart, the inter row distance, to prevent shading. We at 26deg, the panels are 2m tall, and I calculated that the optimal tilt angle is 33 deg. See detail above as to why 33deg tilt as my Lat is 26deg. 

Note: Tilt angle number below is from Vertical.



Percentage shading with no obstruction far away on horizon or near like trees etc. 


Power generation. Some power will start to be generated from about 7:00 -7:30 depending on the shade on your panels and other factors. The below is a best case scenario. Power will be produced till about 17:00 All of these input parameters can be tweaked to lengthen the production time or to skew things to suit your demand.


Some info to help make sense of it all, visualising sure helps.

Later more


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Hi Sarel

Interesting information. Thanks

For my installation, what I did is install the north facing panels on the flat roof to proper north, as the flat roof made the angle possible. This meant building a frame from steel, bolted to the parapet walls and then got the angle correct by adding cross sections with the correct orientation. Here I also installed the panels on a hinged adjustable frame that I adjust according to the azimuth for the particular season. There are three heavy duty adjuster rods with stainless steel threaded bar welded which makes it a real simple operation. I achive between 19 and 27 degrees easily and it is a simple case of usine my laser level to get the angle, then raise or lower the frame depending on the season.

My North West facing panels is fixed to the pitched roof. At a 25 degree angle it is not always giving the best yield but being far south I do get satisfactory results in winter days. Hence there is no reason to tweak or re-engineer the mounting system which is also home made.

Thank you for your post. This is sure to assist many in making better decisions when installing their PV arrays.





Edited by Sass
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Today I had to kill a tree, well kinda. It was rotten. to the core, no really, it was.


The tree sucking up my kilowatts are to the right.


Rotten core


The front row structure, still need a lot of work. The parts closer are angled a few degrees to the east on purpose, for the MPPT DC coupled black start panels. Time was about 16:20, still with no shade on the far side and some shade on the near side panels.

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A Summary for the design part

There are many tools available to assist in extracting every Joule of energy from your investment. The best one tool in your toolbox is to reduce consumption and peak demand. Consumption not happening pays forever into your savings. The second best tool is to not waste your hard earned money on the thievery and thuggery of the cities and utility, don’t support their corrupt people, get energy independence.

The next steps are to understand your energy consumption. Below are two product example types that can assist. The efergy system monitors and tracks whole house consumption and the kill-a-watt measures individual plug outlets or devices.





All of this is about voting with your wallet, saving your money by installing a system that will reduce your monthly expenses. A Rand saved is worth 2 earned.

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22 hours ago, Sarel said:

A Summary for the design part

There are many tools available to assist in extracting every Joule of energy from your investment. The best one tool in your toolbox is to reduce consumption and peak demand. Consumption not happening pays forever into your savings. The second best tool is to not waste your hard earned money on the thievery and thuggery of the cities and utility, don’t support their corrupt people, get energy independence.

The next steps are to understand your energy consumption. Below are two product example types that can assist. The efergy system monitors and tracks whole house consumption and the kill-a-watt measures individual plug outlets or devices.

All of this is about voting with your wallet, saving your money by installing a system that will reduce your monthly expenses. A Rand saved is worth 2 earned.

Hi Sarel.

Over the last two years I have sourced some prime tools similar to the above from Amazon. Sometimes the items sold there are in many ways superior.

Brilliant advice though. I could not agree more, especially about preventing the thievery from central and local government. 

That part is really massively painful to bear.


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Inverters charging and AC vs DC coupling and back to the Micro grid.

From previous posts we know our demand profile. Now comes the selection of the Inverter Charger and other goodies to make this work. We will cover panel selection and other items later in a separate post. 

For any given kW class, there are a multitude of manufacturers up and down the price performance and quality spectrum. You know your budget and needs (wants). The payback and breakeven point will show you how good an investment you made at the end. There is also the set and forget or convenience factors to consider, never mind the SWAMO and long haired approval effect. Remember always, what are the problem(s) you want to solve. This drives all your decision making and investment. Are you a hands on man, or do you want to be hands off wrt the system and just monitor and manage your energy consumption?

Always, always consider the future capacity and upgrades of your system (we always change things in the future). My original design was only the start, compare the two images below.


Current Design in the process of being build.

The new layout to allow future proofing in the space where this is to be installed. (PS: The spacings and layout are not 100% correct here, just done for planning purposes as a rough guide). It's not to say the I will be doing this, but I want to have the option to do so in the future, especially for the dual Quattro's. Maybe have more solar with a second Fronius at that time or later.


For me, I may want to have the option to double up on my Inverter/Charger and parallel a second 8kVA unit for 16kVA total. This can then support a second 8kW string inverter if required, not that I have much ideal roof space for more panels left. The place for the 3rd battery is ready as well. All wiring, especially the DC busbar is designed and build from day 1 to allow for seamless expansion.


More to follow. The major components next.

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Oops, I forgot to add the AC vs DC part above:

This below is the AC coupled system where the Solar panel energy is converted from DC directly to AC for self consumption during the daytime. This is the most eficcient way with least losses to power the loads. This is not a grid tied system as the Inverter/Charge can form a Grid  for the String Inverter when the Utility grid is switched off or failed. This will happen as long as in this case, the battery can supply the inverter and keep it running.



A DC coupled system is where you use a Charge Controller to charge a DC battery system from the DC Solar panels. This is the most efficient way to get batteries charged as the losses are reduced compared to first changing the Solar DC to AC and then again to DC to be able to charge batteries.



You can combine the two types of systems and this is what I did. When the AC coupled system are hooked up to the output of the Inverter Charger, you form a Micro grid. I have a more complete post under Electricity Fundamentals on Micro grids.



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For me seamless means expansion while the system is still in operation and not switched off, ie live. Concurrent maintainability (to add, subtract or maintain) while in operation, is a key consideration for me. See later. (There are lots of danger here, will write about arc flash later). The idea is to pre-wire and build everything so that the unit my be isolated and bypassed, or isolated and worked on safely. The Inverter/charger will have a manual bypass for the utility mains, the DC side will have isolators. On the battery side there will be isolators for each feed as well. The DC distribution will have 6 items connected. The two Inverters on each end and the MPPT charge controller and batteries in the middle part.


I modified my Lynx In DC busbar unit to accept fuses as well. Everything is isolated and covered to stay safe from making shorts. Considering peak currents at 48-50 volts of 1080 Amps and maybe much much more, that is seriously dangerous. See previous post on the BYD packs for peak currents. As a general rule: The maximum available short-circuit current is 10 times the 1 minute ampere rating of the system, ie ~10 000A in my case. This is deadly serious!  I am planning for 70mm2 cables between batteries and busbar, and dual 70mm cables between + and - busbars and the Inverters. This means very low resistance as the length of cables are very short. No cables as fuses here 😮


Documented cases of low voltage DC killing people here (one was at 69 Volts DC: https://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=775742&id=14295083

These are the potential risk factors for Batteries:

  • Chemical 
  • Electrolyte 
  • Shock 
  • Thermal – Molten splatter 
  • Arc Flash: Heat, light, sound, pressure 

The busbars are good for a 1000A, not that the two Victron’s can draw anywhere near that at 640 Amps combined for a few seconds, normally half that. 

Currently there are two towers, but I will wire the 3rd one in as well. Since the cables will have isolators and isolated connectors on the ends, the 3rd set of wiring will be included on day one as well. This means that the busbars will not be opened to install the new battery at the time. Only maintenance will be on fuses and that circuit can be isolated, minimising risk. However the second Inverter will not be pre-wired as the cable ends are lugs, open and not insulated.

Since most of my consumption is based around 0.5 - 6.5kW with short peaks sometimes to 12-13kW, an Inverter of 6-8kW should handle the bulk of my needs, time will tell. Considering that I am planning to time warp the bulk of my usage to daytime (apart from lights, kettle and heating/cooling during the seasons), the String inverter will be mostly used to carry the loads. The Fronius is 8kW purely from solar with the arrays being 2 strings of 5.0kWp each we should mostly have enough energy during mildly sunny days to support the 6-7kW loads. This includes the geyser now set to ~2kW. If any peaks above this level happens, the Inverter can support the higher loads from battery. This is the Micro grid with the Fronius string inverter sitting on the Quattro Inverter/Charger AC out.

All of the equipment, battery system, Inverter/Charger and String Inverter will be cabled for networking to ensure reliability. See items below. There are Apps for all devices as well as Internet Cloud portals where monitoring can happen. All this data will be integrated to my Home Automation system for local Control and monitoring. Nothing will depend on the cloud for operations. The Victron Cerbo GX device will be the main management and control system. It has Wireless capability for fallback in case of network failure, as does most of the equipment. My home network consists of Ubiquiti Router, switches and Access points for the WiFi.






Because of our intermittent internet, I am planning to have all of my data locally.


More on this to follow.

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In building my system I discovered just how violently a DC current shock can be. Truly painful. I was nailed by PV panels though I thought in my ignorance DC won't harm. 

Luckily I was unharmed but since the I ensure proper insulated gloves and other safety gear.

As for DC flash protection, I found and imported my breakers from the USA to ensure these are capable of not being damaged by the arc.

Everyone must take note of your comments. That is my advice. One can never be too careful. We are talking some serious amps with our respective equipment.

My motto is rather too much protection than too little, hence my AGM batteries are in a seperate room back to back behind the  inverters with a brick wall between them and proper ventilation. And inadequate cabling is another definite danger

The PylonTechs don't really need venting. But what is scary is the installations I have seen where there are no proper venting of hydrogen gases with flooded batteries and arc breakers in the same location.

Everyone, please take note


Edited by Sass
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On 2021/07/22 at 3:15 PM, Sarel said:

And as if on que, while I am typing this all up, a new round of loadshedding announced......... 🥶

Edit added: Eskom just explained to my earlier point that a unit at Tutuka (old plant) and Medupi (NOT old Plant) went down. And on top of that, the previous 2 units at Tutuka and  Medupi that were supposed to be returned today, are still down.



They blew up Medupi unit 4. Sheer incompetence. As I wrote earlier at the beginning of this thread, not even the new Plant will withstand the incompetence.


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Posted (edited)

So about 7 years ago, Duvha station Unit 3 boiler exploded due to no maintenance being done. It was a coal dust explosion and it destroyed the boiler and building. Eskom estimated repairs to be done by 2019 or 2020. Today, that unit is still down and apparently nowhere close to be rebuild. This happened on 30 March 2014.


edit: added date

Edited by Sarel
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And to jog your memory, just for the record, Feb 2011 Duvha Unit 4 was tested and exploded during the test. This was a controlled overspeed test, but the geniuses disabled all overspeed safety systems, go figure.



this shaft piece does not belong here, its place is way down there….

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Cloud computing and its issues.

Nowadays every business are using Cloud services, and it has its merits. You can access your data in the Cloud from everywhere, yay. Because of poor Internet availability, it does not always work. No fault of the Cloud services, just connectivity issues.

One concern with Cloud services, Big Tech has your data, they can cut you off for whatever reason, any time. They can also use this data to track you if they wish (yes they do as your data has a monetary value). Even worse, they can learn all sorts of things from your data about you. So be careful.

I for one, would rather have my data available locally and under my control. I have a home automation system and use that to manage my home and keep track of and store my data. My Solar production and home consumption will be monitored and managed by the HA system.

Currently I use the Efergy Energy hub system to monitor my Utility grid consumption. This will change to a system that I can read and store the data from locally without going via the cloud. I will monitor my energy production and compare it to the theoretical daily production predicted to keep tabs on the eficciency. It will also be programmed to help optimise my self consumption from Solar.

Next is the construction of the system.

I started about a week ago to install the Solar panels.

Made this hoist to carry the panels up 6 meters to the roof.



A video here to show how the lift works https://youtu.be/1ZALDwz3jJQ

Second set of panels installed


In the above we are busy aligning them panels, the closest one not done yet. My OCD almost made me edit the closest panel out of the image 🤔🤭🤪

First row of panels done. There are two sets in this picture. The front set are the 425W x 10 panels and the frame behind the people are the 385W x 6 panels. The back row will have the rest of the 14 x 425W panels.



At 07:20 on 7th August we were already measuring 1 Amp at 40Volts per panel for the easterly set of 6 panels and 0.5 Amp at 45 Volts per panel for the North facing panels. The 6 panels on the eastern side are rotated and extra 7 degrees East to get more and earlier sun to boost batteries early morning as this string will only be DC charging the batteries directly.


Yes they are dirty as heck, but we still installing. 

See later for more....

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On 2021/07/26 at 8:32 AM, Sarel said:

My setup is in a very old house. I still have the original copper Ryalco geyser. This thing is fitted with a ~4kW element. I am not planning on replacing this for various reasons. The current setup in preparation for the Solar install is as follows:

A timer and a Sonoff switch combined that controls a SCR controller driven by a little adjuster that changes the duty cycle of the SCR from 0 - 100%. I will leave out the gory technical details for now. This allows me to control absolute times with the timer that the geyser must be switched off. The Timer has a NO and NC contact set. I am using reverse logic (to help ensure that if timer fails, we have a chance that the Normally Closed contact will remain closed under no power condition) and the Sonoff can still control the geyser heating. The timer and Sonoff only controls the mains feed to the power supply for the control gear, so a few milliamp's at best. The life and reliability of the Sonoff and timer is improved. When the timer is active, ie. closing the contacts, the SCR control voltage is interrupted via the NC contacts, now open (24V for a 4-20ma control.) Thusly ,when the timer switches on, it inhibits the power supply to the PWM and no heating. So I am setting the timer for when the geyser cannot be warmed. 

The SCR is a zero point crossing time proportional control ,so much gentler on the element. It will duty cycle switch power to the element.



SCR proof of concept video

Now this allows me to control and dial in the energy consumed from 0 to the full kWh of the element. Each cycle of the mains will still consume the full kWh but on average the load will be what we set on the dial. My timer enabled the geyser at 13:00 and switched it off at 16:00. My base load was ~600 Watts and the 4kW element was fed about 2kW via the SCR control. There were most likely a voltage sag at that time or the element is not really a full 4kW unit, likely consuming only 3.5kW or so. This control is done to allow me to tweak my Fronius and Quattro load and allow better control over charging and keeping my feed in to 0.

Herewith my consumption. (the peaks are from other loads.)1534014308_Screenshot2021-07-26at08_14_31.thumb.png.7909673a2c2c1737b479f2f646601c5b.png

I will describe in a future post how I will use an Arduino to control the heating periods and then the duty cycle based on a few parameters form the Solar system.

Geez Sarel , just when I think I beginning to understand heavy current rollout philosophies, you come with this micro grids and AC and coupled system. Sigh. So much to learn. But I am following this thread with interest, a bit above my pay grade , but nonetheless.


I have particular interest in your solid state element chopper.  I will , weather,covid and funds permitting , invest in additional geyser, to act as what I call a 'water battery'.


So I will drive both geysers  with 5kva inverter, downgrade elements to 2kw each and then multiplex the power with something like you have here. So I am looking forward to your sessions on this product as you promised.


I have a question so long for you. Instead of  slicing/multiplexing  the power cycles between geysers as you explained, would it be viable to chop energy on a per cycle basis , ie triac phase control. It will allow me to turn a 3kw element into a continuously variable element between 0 and 3 kW. Like a house dimmer. But this is a powerful one, will it upset the inverter , and will the resultant EMI/RFI issues be hell to deal with?

My rationale is based on the fact this arrangement will have a lesser impact on instantaneous inverter power demand. Or am I wrong.?


Kind regards 

Dropkick Murphy.






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@dropkick Your assumption on lesser demand is correct. My system simply do half cycles of mains on a ratio basis, on vs off. Every half cycle crosses Zero Volts and thusly would switch off at that crossing. The instantaneous demand is still the element demand when the cycle is on. What you looking for are phase angle control vs my time proportional controller. It's basically what are used to dim lights as you correctly stated. The advantage would be that you will be reducing the instantaneous demand.

Both Phase angle and Time proportional will deliver the same result, but in very different ways. EMI/RFI for both systems are not too bad and can be controlled well. Most commercial controllers will manage that already. Because the time proportional system will do whole cycles (or multiple whole cycles) it can cause some issues with lights flickering due to voltage fluctuations based on current draw. You will normally see much less of that with phase angle control because the power (Amps) required for each switch will be less per cycle and each cycle will be equally affected.

Phase angle control are more sophisticated and normally a bit more expensive but with better control. Think of Time proportional as being a blunt instrument in comparison. See Phase control below.


I would think that the Phase angle control would be ok on any inverter as its being used in Industrial situations that are running off of Solar power for such installations.

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Geyser control

There are many ways to get your Hot water boiler to be usable and heating from Solar power. All of these strategies are once again driven by your needs. How much energy do you need to heat up the water to the set temp? How big an element do you have and how much water do you need to heat? How long do you want the process of heating to last? You can use SSR’s (Solid State Relays), Phase angle or Time proportional control, use a smaller element or go to a stand alone DC Solar direct system to name a few, to manage the water heating process from Solar PV. All the methods have advantages and disadvantages, choose your poison.

As part of the Open energy monitor system, clever people have developed open source PV Diverters https://learn.openenergymonitor.org/pv-diversion/mk2/index (simply a way to use excess Solar energy to heat water instead of feeding into Eskom grid). Another strategy would be to use Space heating/cooling by Air Conditioner. Commercial units like the Ohm Pilot and the Myenergy Eddi and others, are available.

For my system of 3.5kW, we are used to it being ready on full power after about 40 minutes or less. As my strategy is to time warp my loads to daytime use for all the heavy users like the geyser and some others. The geyser is the single biggest consumer in my case. For now we are having my worksop out of this :D To help get the average load down (this is not the total load, just the average over a period) I decided to use the Controller I had in hand. This: https://ccipower.com/products/controllers/1020-ac-zero-cross-single-phase-power-controller It is not ideal but will certainly achieve my goal to have less of a continuous peak load on the Inverter. The Quattro can do short bursts of up to 16kVA or ~12kW. In my total house load this should be fine.


This was the demand for my geyser prior to managing it with the controller. The largest peak.



And this is with the controller. The sawtooth part after 12:00. My Energy monitoring system only looks at 6sec averages. I do see the full Amp draw on the clamp meter, but they are slow as well 😕 As you can see in both images, the base load at about 2kW.


With the Micro grid, we have the Fronius string inverter at 8kW (on 10.2kWp panels) combined with the Quattro at 6.5kW with ~12kW available on peak for a second or so from the Quattro, for a theoretical 14.5kW total load capacity. The over dimensioning of the panels on the Fronius was deliberate (its still far from its Max inputs) to allow the longest flattest power curve to be available during all times, including Peak Winter as can be seen in the image below. This was deliberately engineered this way by manipulating the panel angle, to get an even seasonal generation balance. Obviously there is a compromise, the total annual generation capacity is a few percent less. Most systems are engineered not like this but to deliver the maximum annual energy. I chose to do it otherwise, for reasons.

The below image are my system’s modeled and predicted values for the percentage of kWp panel generation including losses due to soiling, wire losses, cloud cover and losses due to heat etc. If we look at the 10:00 column for all the months, we should have about 8kW, or close to as a minimum available generation until 14:00. These are obviously averages across the month but still a good general indicator for planning and sizing. It’s the same distribution for any time of day for the year. For a 10.2kWp panel output and a 8kW Inverter, 80% generating capacity input to the inverter after losses, should get us to about 8kW output on the Inverter, or close to that.


MORNING.png.fbc6b516513eaaa20d515007636d778a.pngMy aim in general are to use Solar during sun hours to increase my self consumption and keep my total load under 7kW where possible. As is clear, I have headroom. Between the 2 Inverters we have more than enough supply available to support any load combination up to at least 10kW conservatively. The load total can be managed by sequencing the daytime use combinations. My base load varies between 0.5kW and about 2kW normally, big load items excluded.


Since I have 2.3kWp panels on the MPPT charge controller only charging the BYD batteries full time, the demand for charging from the 10kW Fronius side are reduced meaning less energy are diverted away from managing daytime loads vs battery charging. I do not mind my batteries SOC only reaching 100% late in the day.


One thing I researched, but could not find any answers on at all, was the effect on inverter regulation due to the nature of the load switching from the phase angle or time proportional controllers. There are many research papers on Small signal and Transient response for various Inverters and micro grids. The issue at hand is we do not know the topology of the inverters (we can guess, but also guess wrong) or anything really about their small signal control mechanisms. Also, not much info is available for this type of load. This aspect is anyways above my pay grade and knowledge. From a pragmatic view, I will rely on experiments and empirical data collected. As long as my Inverters are not loosing regulation and remain stable, all is well ;) If shi7 happens, there are other solutions to follow.

My geyser management currently consists of a SCR Time Proportional Zero crossing controller. It is capable of switching 20A loads and the control input is 4-20mA. The 4-20mA controller is a manual setter where I can dial in a percentage between 0-100% (any value between 4-20mA) This is translated to half cycles switched on and off. The switching scheme goes like this: a few cycles on followed by a few cycles off to make up the ratio. This may be 2 cycles on and 11 cycles off for example.

Later on I want to use an Arduino with 4-20mA output to control the % supplied to the element. I can then use my home automation system to control the Arduino based on available Solar PV and battery SoC to set the %. While battery is charging and no extra Solar available for example, the % will be set to 0%. The availability of Solar will drive the % between 1 and 100%. There is a time that will switch on during times where I do not want to heat water, normally between 18:00 and 08:00 to not use battery power. The Timer switch does have a NO and NC contact set. When the timer is off, or not powered, the NC contacts are closed. So I use the NC contacts to open and inhibit the ability of the geyser element. The timer is not in the element circuit and only switches a small load, so life should be fine. The SCR is the only high current switch.

More updates follows

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