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Central UPS in sectional title apartment building


Nic Roets
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We're a 3 storey building with 45 apartments in Pretoria East. Each apartment get's municipal power, most of them on a post paid basis. Some flats use as little as 200 kWh per month, while other go up to 500 kWh.

Some residents are so fed up with load shedding that they are considering buying battery backup systems costing R3,000+ each.

I think we need to consider a central battery bank to achieve economies of scale. Then supply one socket in each apartment with reliable power. Installing electrical cables is a major hurdle, but that's our problem.

We also have 10+ parking bays getting plenty of sun. We can build car ports with solar panels on top.

At this stage, I just want to draft a discussion document for circulation.

If we aim to supply each flat with 200 W, then it's 9 kW total. Add some spare capacity then we need 3 x 5 kW of inverters. (R70,000)

18 kWh of battery backup to supply us during 2 hours of load shedding. (R125,000)

10 kW of solar panels (R70,000)

10 kW MPPT (R21,000)

45 power monitors so that we can detect if someone is overloading the circuit and / or bill residents (R18,000).

Total R304,000

According to pvwatts.nrel.gov, this system will generate 17000 kWh/Year, saving us R34,000. So the hardware will pay for itself over approximately 10 years.

What have I missed ? How realistic is this calculation ?

 

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That is a very cool idea, if you can convince all the tenants to contribute. Overall your concept looks good. Just make sure you do this will inverters that parallel well and that can also blend power. 

The power monitors will be essential to limit each apartments (over)usage. You will need to do lots of education on this. Also check with your local municipality on how large the system can be. There might be limits there.

My suggestion would be to get a really good system (so no Axperts or clones). Else if you have issues there will be 44 angry tenants knocking on your door and you don't want that.

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It will be sensible for the body corporate to charge an amount each month to replace the batteries when that time comes. It won't be a perfectly fair system, but at least you will have money in the bank when the time comes. 

Get it installed by a qualified person  (and inspected at regular intervals) and get the complex re-certified because if the worst happens then insurers (and other parties) may hold the BC primarily responsible and it will be up to the BC to show that they acted responsibly.

I would consult with an installer up front - or get quotes from people with a good reputation - because I think you've under budgeted. The installation of this little lot and backing up one socket in each unit is going to cost more than little bit.

You also need to be sure that if unit's main breaker is off because somebody is working on the wiring inside my dwelling then they can't suddenly get a shock from the batteries. So you should be able to disconnect each dwelling from grid AND from the alternate source, preferably with one breaker.

Whilst you're at it, what dangers do suicide plugs pose in this scenario? Could somebody playing that game cause problems for the whole building. Probably best to send a nicely worded message to each of the unit owners.

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Thank you Louis. I didn't know that some inverters can be paralleled up. This feature makes it possible to start smaller and scale up.

Bob makes a good point about having a single breaker in each apartment that can disconnect both all the sockets.

I don't know what a suicide plug is. But power to our garages is already supplied by the BC. I once used a bad appliance in my garage and tripped a number of garages in the process. Fortunately the caretaker was nearby and could reset the breaker that I tripped. I foresee similar problems if we have a central battery bank.

It's good to discuss things here before presenting any concepts to the owners.

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Here is some problems. 
 

Firstly you said “some owners” are gatvol. Guarantee this will bring your first problem. Whilst everyone is gatvol, these communal systems seem like a great idea. Like you said, scale etc. But then, loadshedding subsides for a while. Some owners are landlords and want to keep their investment incheck. Other sell after only a year of getting value. Or some start realising that they use power sparingly, whilst your neighbours don’t and you start wondering why did you pay the same. And before you know it you have issues at every AGM. Been there done that.

2 - how you charge, especially when it’s done monthly must be done in such a way that it is not construed as selling electricity, something an HOA cannot do without regulatory approval. 

3 - (on this I only speculate), the legality on wiring another grid on premises, but as you said, your problem. 

4 - 200W per unit (did I read it right)? What are you going to do with that? Good LED TVs can be up to that alone.  What about DSTV, wifi and some lights, although small it adds up. Put at least 600W per Flat and do your calc again.

5 - Liability. This damn plug that the HOA supplied surged and killed my R70,000 OLED TV I bought last week. Please replace. 

If it was me I will do 2 things:

1 - Spec a good 3kW inverter, 2.4kW/h battery package. An “approved by HOA” of some sorts. 1 Consult, 1 Electrician etc. Then use the bulk buying power of the group of individuals who are truely gatvol to secure these items as 1 purchase. 
 

2 - Find a fairsish way where indiciduals can use common space to errect 1 or 2 panels of their own that feeds their individual inverter to charge the battery and carry some of the backup off grid load. 
 

in closing, I just cannot see how a Grid Tried communal backup system will be worth the hassle and regulatory effort

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20 minutes ago, Nic Roets said:

 

I don't know what a suicide plug is. But power to our garages is already supplied by the BC. 

My understanding:

you take a lead with a 3 pin plug on both ends. One end you plug into your alternative source (like a generator or ups), the other you plug into any other plug in your house. 
 

You so power all your circuits with this suicide leade (you can turn of the CB of that house plug to limit it somewhat). 
 

so 2 things can happen. 
1 the lead itself is to thin an can can catch fire. Your DB was desinged on a 60amp supply for example, and that is not a 2.5mm2 house lead 

2 Eskom comes back on and sparks can literally fly and those sparks can be your communal inverters

Edited by daniemare
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9 minutes ago, daniemare said:

you take a lead with a 3 pin plug on both ends. One end you plug into your alternative source (like a generator or ups), the other you plug into any other plug in your house. 

There are many many reasons a suicide plug is a very very bad idea.

1. The danger of turning on the main breaker before removing the "alternative supply", thereby energising the grid. This can get you in serious legal trouble, especially if someone dies because of that.

2. Part 2 to the above, turning on the breaker and forgetting the generator/inverter is still connected... and blowing it up.

3. Leaving either end disconnected while energising the other end can cause someone to be electrocuted. Again, legal trouble could be in your future.

4. You're feeding energy in on the wrong side of the RCD. While doing this, you have no earth leakage protection.

5. With many generators, the supply is floating. This means there is no protection against a single earth fault because your TN bond is disconnected with the main breaker.

In general, the best thing is to never ever even suggest to anyone that this sort of thing is possible. I mean literally the only time I would even consider it is if I'm snowed in in some remote cabin and it's an emergency, I'm literally going to die unless I get the power on NOW... then maybe. Otherwise, just no.

🙂

 

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2 minutes ago, plonkster said:

There are many many reasons a suicide plug is a very very bad idea.

1. The danger of turning on the main breaker before removing the "alternative supply", thereby energising the grid. This can get you in serious legal trouble, especially if someone dies because of that.

2. Part 2 to the above, turning on the breaker and forgetting the generator/inverter is still connected... and blowing it up.

3. Leaving either end disconnected while energising the other end can cause someone to be electrocuted. Again, legal trouble could be in your future.

4. You're feeding energy in on the wrong side of the RCD. While doing this, you have no earth leakage protection.

5. With many generators, the supply is floating. This means there is no protection against a single earth fault because your TN bond is disconnected with the main breaker.

In general, the best thing is to never ever even suggest to anyone that this sort of thing is possible. I mean literally the only time I would even consider it is if I'm snowed in in some remote cabin and it's an emergency, I'm literally going to die unless I get the power on NOW... then maybe. Otherwise, just no.

🙂

 

2 things......

clearly many many many things. Thanks, luckily my neighbour listen to me with my 2 reasons. I will now share the others with him as well. 
 

Back to the topic. This type of possible behaviour is why I will definitely not get involved as an HOA.
 

Supplying electricity is not the job of an HOA, and I think @plonkster’s use of the word “die” and “electrocuted”  should make that clear. 

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Just now, daniemare said:

clearly many many many things. Thanks, luckily my neighbour listen to me with my 2 reasons. I will now share the others with him as well. 

Your point 1 is actually a good one too. I can just see someone wire up his 5kVA gennie (because that's quite a common size at your hardware stores), and grabbing the nearest 10A cabtyre to wire up his connection... 🙂

 

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10 minutes ago, plonkster said:

Your point 1 is actually a good one too. I can just see someone wire up his 5kVA gennie (because that's quite a common size at your hardware stores), and grabbing the nearest 10A cabtyre to wire up his connection... 🙂

 

Sad thing was that my neighbour’s system MSW inverter power trolly was set up like this. 

To charge - take plug A (AC feed into inverter) and plug in wall socket labelled “inverter” (in garage). Then, when Load shedding start, unplug plug A take plug B (AC feed from inverter) and plug into same socket. The socket is on its own CB in the DB labelled inverter. 

My neighbour said the installer gave some other instructions about turning things on and off but he can’t remember. 
 

The installer - the a registered sparkie according to my neighbour.

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18 hours ago, Nic Roets said:

I think we need to consider a central battery bank to achieve economies of scale. Then supply one socket in each apartment with reliable power. Installing electrical cables is a major hurdle, but that's our problem.

I see this as something that could happen more and more in the future as we are getting closer and closer to that blackout, I had a similar discussion with my neighbour on diverting extra solar power from my system to there house during load shedding, even if it’s just by throwing a extension over the wall and limiting them to a small 5A circuit breaker. 

In my case a bottle will do!

 

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1 hour ago, Gerrie said:

even if it’s just by throwing a extension over the wall and limiting them to a small 5A circuit breaker.

I've done that, a little differently though. There is a small business run by a friend next door, and we literally have an extension cord doing duty. I wired in a Sonoff POW in the head of the cable, configured it to allow 500W max for 30 seconds. This is a tad better than a 5A breaker, because a breaker only trips instantly at 5In (5 times the nominal rating), which means people can overload it by as much as 200% for several minutes.

To assess how a communal setup would work, one should look at existing shared setups. Back in 2008, I had an Adendorff leaflet advertising a nice large generator, showed it to the boss... he showed it to the guy next door, and by the next day they had ordered two generators, to be delivered in one shipment. The generators arrived... and only then we realised they were three phase. We had enough power for three offices...

So they sold one, walked over to the office one down and offered for them to buy in. And ran three offices from one generator... and that is when you realise it is not as simple as you thought. It works for the most part, but many days you had to walk over, ask them what they are doing because the generator is dropping RPMs and your laser printer cannot work...

🙂

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There is a reason why Utility Companies, like Eskom, start out tax payer funded, large and public. (A pity some stay taxpayer funded). It is because they have to be big, and at first, charging only per unit will make it unaffordable, hence the need for tax or debt funds. 
 

Problem is with HOAs, that upfront unfairness will be to much to overcome 99% of the time. Never mind the actual complexity of running, maintaining and administering of such a scheme. 

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11 minutes ago, daniemare said:

There is a reason why Utility Companies, like Eskom, start out tax payer funded

Eskom unfortunately abuse these hundreds of millions received from tax payers and have no real interest in solving the crisis, but I am sure the next profit driven mogul who will take over Eskom when it have been split into three will quickly realize the enormous opportunity in selling electricity generated on tax payers rooftops, they don’t have to lay-out a cent but just be the middle man and collect profits on rules that please them again.

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It occurs to me that we're dismissing the OPs idea rather than doing what would probably be expected of a bunch of solar power enthusiasts, that is to promote it... 🙂

Of course the pitfalls needs to be carefully considered.

Truth be told, unless this is no more than 3 or 4 flats in your own backyard, I'd spend the money on a large Diesel generator and roll the cost pro-rata (on the overall electricity use) into the rates. Much more capacity for much less money.

Edited by plonkster
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I am with @daniemare on this  - even ignoring all the possible legal pitfalls the communal setup admin will be more headache than load shedding.. Get all interested parties to gather for a meeting on Thursday evening 19:42. Arrange all present in 5 rows -  each row according to length (short people in front, taller to the back). Now ask them to re-arrange in 3 rows alphabetically based on first name. Now ask each group to discuss and agree unanimously on a single appliance that should be plugged into a backup plug socket... 😉 . 

 

On 2020/09/08 at 11:38 AM, Nic Roets said:

Then supply one socket in each apartment with reliable power.

If the system gets off the ground a major problem will be abuse/control...

Multiplug2.jpg.90f90ee4ca31fa4fb8a0816e18db82bc.jpg

What is the penalty for abuse? Who will enforce it? ("I will not pay any "fine".....I did not overload anything...your meter is faulty...show me the calibration report...this system is unfair...pay back my share of the setup costs I no longer want to be part of it").

On 2020/09/08 at 11:38 AM, Nic Roets said:

We're a 3 storey building with 45 apartments....

If we aim to supply each flat with 200 W, then it's 9 kW total. Add some spare capacity then we need 3 x 5 kW of inverters

45 x 2000W kettles switched on  = 90kW. You must size inverter for peak load (and you will have close to no control what is actually plugged into any socket/s).

Do 1 person occupied units get the same power supply as the 5 occupant units?

On 2020/09/08 at 11:38 AM, Nic Roets said:

According to pvwatts.nrel.gov, this system will generate 17000 kWh/Year, saving us R34,000. So the hardware will pay for itself over approximately 10 years.

What have I missed ? How realistic is this calculation ?

Batteries are probably unlikely to see 10 years..

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On 2020/09/08 at 11:38 AM, Nic Roets said:

We also have 10+ parking bays getting plenty of sun. We can build car ports with solar panels on top......

What have I missed ? How realistic is this calculation ?

Think the car port building costs are not included?

18 minutes ago, plonkster said:

It occurs to me that we're dismissing the OPs idea rather than doing what would probably be expected of a bunch of solar power enthusiasts, that is to promote it... 🙂

Of course the pitfalls needs to be carefully considered.

Truth be told, unless this is no more than 3 or 4 flats in your own backyard, I'd spend the money on a large Diesel generator and roll the cost pro-rata (on the overall electricity use) into the rates. Much more capacity for much less money.

not so much dismissing as not wishing that task on even my worse enemy. But in the spirit of finding solutions not problems and promoting solar... a good sized generator is maybe better suited and adding grid-tied PV could maybe help claw back some costs.. (spitballing here)

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3 hours ago, plonkster said:

It occurs to me that we're dismissing the OPs idea rather than doing what would probably be expected of a bunch of solar power enthusiasts, that is to promote it... 🙂

Of course the pitfalls needs to be carefully considered.

Truth be told, unless this is no more than 3 or 4 flats in your own backyard, I'd spend the money on a large Diesel generator and roll the cost pro-rata (on the overall electricity use) into the rates. Much more capacity for much less money.

I used to work for one of the big three national healthcare groups, and we would have one generator backing up essential circuits for a whole hospital campus (multiple buildings). This is an easier implementation for a complex that, like the hospital, will have a single point of connection to the grid for the whole property. 

Downsides:

1) You will need to have somebody tasked with keeping the diesel topped up.

2) At the hospital we had two sets of sockets. The red ones that took a plug with a chamfered earth pin were backed up, the others were not. This was intended to reduce the load on the genny, but you can guess how it ended up and how it will end up in a residential complex. Some people would get red plugs from builders warehouse and make sure their heater or coffee urn was backed up. Of course one person doing this doesn't make too much difference, but the knowledge gets around. At one point management had to issue a list of types of devices that were not considered essential - this included toasters and waffle machines.

I suppose that lower rated circuit breakers on the essential plug circuits might solve the problem, but then you're potentially looking at rewiring each unit. Not impossible, but there's a cost to that. 

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