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A learning-hungry electrician jumps onboard


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Yes that electrician is me. I'm an industrial electrician who mainly do faultfinding on MCC panels and motors. I also on the odd occasion do faultfinding on VSD's, mostly LV ones ( oe oe I should really tell you about our 11kV softstarter, that thing is a beast lolol, filled to the brim with plc's and wizardry but anyways. It mostly idles though but even at idle will burn through my electricity bill in mere seconds minutes if not seconds lol). Why am I telling you this?L Speak your gibberish and techspeak, I can follow :)

Allow me to sketch my prentjie with you. At the evenings I go home and look at my daily usage and cry lol.

On the yard sits three dwellings (which functions as two separate families, main house is rented out to Tony, Tannie and three young men, flat 1 is your truly and his partner, flat 2 is her mother. The three of us (me, wife, mom) eat together and her unit literally uses 25 - 30 units a month, it has a gas geyser  ). So our family average 10 units a day whereby the other averages 30. I have not been able to run proper load tests as I don't have recording equipment but we average about 1.6kw/h over a months rolling average. I have confirmed this both weeksdays and weekends multiple times. 

I am yet to really spend the money to optimize my usage but I now I must really get down and dirty with it, change out Tony's old LP geyser to HP whatever (I really want the other family to be able to shower for both their pleasure and the total cost (top bracket really eats away at money but I can not just tell them, hey you put me in the top bracket, you pay the top bracket for everything, we split the bill percentage wise as I have installed separate kw/h meters in all three DB's subtracting our two from the main as we feed from it to make it truly "fair" since they are paying customers you know). 

So plan/current is : Tony : Gas / solar hotwater, Gas stove and oven already installed (a few years back I lived in there just when I bought it and I can tell you a gas oven is a gift straight from Satan, don't buy that @$%@!) . Old Speed Queen washing machine, two oldish fridges last time I was inside there and had not seen at large boxes so I believe it to be still be there

Me : 50L HP geyser (want to convert to gas / solarelectric), will soon install gas stove and new electric oven as I ripped the old stuff out during remodeling, modern washing machine(not inverter), dishwasher, modern 210L fridge/freezer

Skoonma : Gas already on water, two plate electric portable, no oven, modern washing machine (not inverter), 180L fridge/freezer

I'm leaning towards gas due to conversion cost and it being solidly removed from the bill and it being each unit's own responsibility, unit cost is less too. 

Question

I want to start out with a 5kwh unit (and 10 panels for a start) as I believe it will be sufficient to handle the spikes ( I am open to corrections please, I'm here to learn). For now I'm good on batteries but the plan is to add 7 kwh to get us through the evening and night as ideally I want to be "offgrid" (will still have Eskom just in case). 

From what I understand the only Inverters that can supplement utility with solar are the Victron ones. Am I correct ? 

Thanks for reading my convulsion. Happy days ahead for you. 

 

 

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1 hour ago, gertvanjoe said:

Me : 50L HP geyser (want to convert to gas / solarelectric)

Keep the geyser for now, It is a nice place to store energy. (Set temp to 70C and timer to 12:00-13:00, 2kW element)

1 hour ago, gertvanjoe said:

Skoonma : Gas already on water, two plate electric portable, no oven, modern washing machine (not inverter), 180L fridge/freezer

Replace the fridge/freezer with modern A+++ type as this is almost a continuous load. 

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First, I'd like to encourage you to get the units right, cause it's a little confusing now. The units are kWh (for energy, eg, if you turn on a 2kW kettle and leave it on for an hour, it will consume 2kWh of energy), and kW (a measure of power).

It sounds like you want a 5kW inverter, not a 5kWh one 🙂

Regarding gas: If your goal is to become independent of Eskom, have hot water during  load shedding, or you're running a guest house and absolutely must have hot water at all times, then gas is a good idea. If your goal is to save money, then don't do gas. Gas is the most expensive heating option (unless you have a very efficient "geyser" and a natural gas piped to your estate). A heat pump and or solar water heating (depending on how much sun you've got) saves far more money.

I agree with the comment about installing an A++ rated fridge. Three pluses is even better, of course, but diminishing returns and all that, each + means 10% less energy, but you get to a point where an additional + doubles the cost... not worth it imho. Bosch A++ unit are common and affordable.

As others have said, Victron does not make the only hybrid. But they do make the best one... (yeah, I know... I know... 🙂 ).

Getting back to gas again, seriously. 14.6MJ of energy in a kg of LPG. Convert to kWh, that's around 113kWh in a 9kg bottle. Divide the cost up, around R2/kWh per unit of energy. Compare yo what you pay for electricity, chances are it's very close (Cape Town is R2.56/kWh, so gas is technically a tad cheaper). But a resistive element inside a tank of water is close to 100% efficient, and gas is nowhere near 80%... so it's a simple high school physics question that some teacher really should slip into the matric paper: Gas is not cheaper.

🙂

Edited by plonkster
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27 minutes ago, gertvanjoe said:

From what I understand the only Inverters that can supplement utility with solar are the Victron ones. Am I correct ? 

Others are also able to blend, but just confirm it as there are some claiming to be Hybrid or whatever the exact term should be, but that definition has lost its meaning and it is now also seen as being able to power from either grid OR PV and not mix grid AND PV. But the Victron inverters like the MultiPlus-II does blend.

1 hour ago, gertvanjoe said:

I want to start out with a 5kwh unit

Is the plan to have all 3x units connected up to the Inverter? I'm guessing that everything will then be on AC Out 1 seeing how each unit has their own meter, DB etc. so it won't be possible to have something like the ovens, geysers etc. on AC Out 2? Although you could of course have yourself on AC Out 1 and then put Skoonma and Tony on AC Out 2 which means that they'll go down when the grid goes down and you'll carry on from the batteries (or just cut Tony as it seems like Skoonma doesn't really have big loads). That's sneaky, but something I'd do as it's most likely not possible to have everyone running off batteries.

1 hour ago, gertvanjoe said:

I believe it will be sufficient to handle the spikes

I think so too, yes. If I have it correctly the MultiPlus-II 5000VA unit can use ~4000W from PV / battery and also blend in another 50A from the grid which is 11 000W at 220V - 12 000W at 240V.

You will have to keep in mind that the inverter can only do ~4000W when the grid has failed. Yes, it can spike to 9000W for a second or so, but will generally only handle a maximum constant 4000W or less depending on the temperature. (Which is why I mentioned still giving Tony loadshedding)

1 hour ago, gertvanjoe said:

For now I'm good on batteries

Just make sure that the batteries that you have are able to reach the 9000W peak of the inverter. The MultiPlus-II can peak at 9000W for example which is 187.5A at 48V.

I think the more technically inclined folk like @plonkster & @Jaco de Jongh will be able to answer in more detail and confirm or deny my statements. :) 

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2 hours ago, gertvanjoe said:

I want to start out with a 5kwh unit (and 10 panels for a start) as I believe it will be sufficient to handle the spikes

Depending on the inverter that you go with, you don't aim to handle the spikes but rather the base.
1) If you ever want to go fully Off Grid your inverter will need to handle any spike, so if your highest spike is at 8kW, you need an inverter that can handle that 8kW.
2) If you just want to save money and still keep using Eskom power (when available) as well, then you can go for a much smaller inverter that can blend the power.

It does sound like you are more on the 2) option side. In that example if you use a Victron Multiplus II 3k it will be able to cover up to 2.4kW from solar/batteries (I think it can handle few second spikes up to 6kW <- not sure the exact value) with the rest of the power you get from the grid. Later on you can add more MPII 3k as they can parallel. Same goes for the 5k model and also for many other inverters (not the normal Axpert and their clones)

Also to give you a bit of an idea (but this vary depending on your environment where your are) you can work on Every 1.3kW of solar panels with a 20-30A MPPT to give about 5kWh of power on a sunny day (less in winter, more in summer, etc, etc. Just a rough idea). So if you use 10kWh a day you will need 2x this and battery storage to last you through when the sun is not available. 
And then tomorrow is a rainy day and all your nice calculations are out the window and you use some extra eskom power :) 

 

PS. I also agree about the gas. It's not cheaper and a bit more hassle. But it does more the tenants from your bill

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1 hour ago, plonkster said:

First, I'd like to encourage you to get the units right, cause it's a little confusing now. The units are kWh (for energy, eg, if you turn on a 2kW kettle and leave it on for an hour, it will consume 2kWh of energy), and kW (a measure of power).

It sounds like you want a 5kW inverter, not a 5kWh one 🙂

Regarding gas: If your goal is to become independent of Eskom, have hot water during  load shedding, or you're running a guest house and absolutely must have hot water at all times, then gas is a good idea. If your goal is to save money, then don't do gas. Gas is the most expensive heating option (unless you have a very efficient "geyser" and a natural gas piped to your estate). A heat pump and or solar water heating (depending on how much sun you've got) saves far more money.

I agree with the comment about installing an A++ rated fridge. Three pluses is even better, of course, but diminishing returns and all that, each + means 10% less energy, but you get to a point where an additional + doubles the cost... not worth it imho. Bosch A++ unit are common and affordable.

As others have said, Victron does not make the only hybrid. But they do make the best one... (yeah, I know... I know... 🙂 ).

Getting back to gas again, seriously. 14.6MJ of energy in a kg of LPG. Convert to kWh, that's around 113kWh in a 9kg bottle. Divide the cost up, around R2/kWh per unit of energy. Compare yo what you pay for electricity, chances are it's very close (Cape Town is R2.56/kWh, so gas is technically a tad cheaper). But a resistive element inside a tank of water is close to 100% efficient, and gas is nowhere near 80%... so it's a simple high school physics question that some teacher really should slip into the matric paper: Gas is not cheaper.

🙂

True about the efficiency, but R2500 (gas) and installation vs R11000 (solar electric. We have lot of overcast days and they are paying tenants so "deal with it" will likely not go well. If it was just me, sure, my SO.. maybe... Paying tenants nah) and installation does make a difference. It also means I can safely have a smaller system without needing to worry that two 2kW elements kick in at the same time and sends the system belly up. 

 

To the other poster chastising me on my units, sorry, it came out as a flood of text but I'm sure you yourself understand the concepts just as well as I do so I hope it was not too confusing. 

 

To another poster, I don't have any batteries currently. lithium battery packs will be phase 2

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16 hours ago, phil.g00 said:

Is separate metering not an option?

Nowadays you can get kWh meters that take up the space of an MCB in a db for dirt cheap.

Well from utility side it likely will not be an option as they are very reluctant to install a second feed around here and the municipal electrician told me he won't connect a second prepaid. It would have worked a charm though as the cost involved would likely be covered in the first 4 months of not have such a high max bracket usage since there will now be two meters registered. Will try and push harder on that one

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14 minutes ago, gertvanjoe said:

Well from utility side it likely will not be an option as they are very reluctant to install a second feed around here and the municipal electrician told me he won't connect a second prepaid. It would have worked a charm though as the cost involved would likely be covered in the first 4 months of not have such a high max bracket usage since there will now be two meters registered. Will try and push harder on that one

Might be a bit of family politics involved, but what I am suggesting is you install a kWh meter in each dwellings DB and agree a rate between yourselves and implement your own meter reading schedule.

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29 minutes ago, phil.g00 said:

Might be a bit of family politics involved, but what I am suggesting is you install a kWh meter in each dwellings DB and agree a rate between yourselves and implement your own meter reading schedule.

That's what I did already. 

Usage get distributed between the three units. Unfortunately running all of this from one metered connection puts an awful lot of the kwh used in the maximum price bracket. (I average about 1100 kwh) 

Tony 700 kwh

Skoonma and me 400

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1 minute ago, gertvanjoe said:

That's what I did already. 

Usage get distributed between the three units. Unfortunately running all of this from one metered connection puts an awful lot of the kwh used in the maximum price bracket. (I average about 1100 kwh) 

Tony 700 kwh

Skoonma and me 400

And everyone want's to claim the full discounted rate, I can just imagine.

It can still be done fairly and proportionately, that's easy, but having to justify it on a constant basis will be more than life's worth.

 

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38 minutes ago, phil.g00 said:

And everyone want's to claim the full discounted rate, I can just imagine.

Just split it down the middle... Poor Tony's gonna get the brunt of it, but it's probably fair?

49 minutes ago, gertvanjoe said:

Skoonma and me 400

Ek en my skoonma... bly in 'n woonwa... 🙂

 

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2 hours ago, phil.g00 said:

And everyone want's to claim the full discounted rate, I can just imagine.

It can still be done fairly and proportionately, that's easy, but having to justify it on a constant basis will be more than life's worth.

 

I do it fairly. The bill is based on percentage used (which probably puts hurts me, but I'd rather have renters and a bill hurting than no renters and a small bill). For me it is also not worth the hassle of sub-metered kwh units (unless I can get two metered connections directly from the municipality). 

 

Back to the main topic, thanks for everyone's input so far. I have had my eye on a few inverters so far but had been mis-informed about only the Victron being able to blend. I will go and see which one best suits my needs and go with that far now. I have a feeling that the savings from getting the two geysers off the grid alone (included its running cost) alone will pay for itself in a time-span I am quite happy with. Add to that the fact that the blending will lower it even more and top it off with the fact that I would be able to pocket the included portion of the rent that has been added as a base cost for electricity (before metering was installed, I now bill them and subtract their base cost ) it'll be swell. I will think of it as their rent increase (something I hate discussing, never had to as the previous renters moved before I really could justify a proper increase, but seems like Tony wants to grow old here, which I don't mind at all)

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