Power outages

[phil.g00]

54 minutes ago, Antony said:

I fact I actually worked out that running a genny during load shedding to power the basics is by far more expensive than having a decent standby.

Petrol (or diesel for the Hulux guys) is far more expensive to run the genny than the grid power needed to recharge the batteries of the standby.

Pure running costs, discounting the sunk costs I'd agree with you.

But, did your calculations amortize the capital cost of the batteries?

Do the calculation writing off 20-25% of the capital cost the battery power needed for say 4.5 hours of peak load. ( Remembering that your battery bank capacity has to be basically double the size you need or it wont last four or five years).  At a 5kW load that's 22.5kWh of availability, the bank would have to around 37.5kWh, if they were proper deep-cycle that could be north of 125K.

Now, if you take the real running cost versus the price of an equivalent generator, say 6-8kVA (a real decent, top of the range, super silent one, that will also outlive your batteries at say 70K), then I think you'll find you have a chunk of change left for fuel to even the playing field.

(We could talk Lithiums, but then the capital cost is higher again to start with anyway).

 

Edited January 15, 2020 by phil.g00

[Antony]

26 minutes ago, phil.g00 said:

Pure running costs, discounting the sunk costs I'd agree with you.

But, did your calculations amortize the capital cost of the batteries?

Do the calculation writing off 20-25% of the capital cost the battery power needed for say 4.5 hours of peak load. ( Remembering that your battery bank capacity has to be basically double the size you need or it wont last four or five years).  At a 5kW load that's 22.5kWh of availability, the bank would have to around 37.5kWh, if they were proper deep-cycle that could be north of 125K.

Now, if you take the real running cost versus the price of an equivalent generator, say 6-8kVA (a real decent, top of the range, super silent one, that will also outlive your batteries at say 70K), then I think you'll find you have a chunk of change left for fuel to even the playing field.

(We could talk Lithiums, but then the capital cost is higher again to start with anyway).

 

this is true for a 5kW load, but if I just want to run the absolute basics with a 1200w system, no hair dryer or kettle loads, then a generator makes no sense.

I have a gas stove, solar geyser with gas backup.

 

[HennieW]

Hi All

 

I have found this product to be relatively cheap and reliable for a 2 to 3 hour outage. It takes care of the power requirements of the entertainment center and some portable lights.  Fridge can stay off for the two to three hours.  Would like to heat from other members what low cost solution they have for the power outages

[phil.g00]

1 minute ago, Antony said:

this is true for a 5kW load, but if I just want to run the absolute basics with a 1200w system, no hair dryer or kettle loads, then a generator makes no sense.

I have a gas stove, solar geyser with gas backup.

I'll admit that convenience, and the ability to absorb the smaller cost differential blur the lines on very small systems. But, just because these costs are not obvious doesn't mean they aren't real. For example:

If you were really comparing apples with apples, to enable you to get by on that very small system, you should also be factoring in the price of your gas conversions, which would've been unnecessary with a capable generator.

 

[___]

1 hour ago, HennieW said:

I have found this product to be relatively cheap and reliable for a 2 to 3 hour outage. It takes care of the power requirements of the entertainment center and some portable lights.  Fridge can stay off for the two to three hours.  Would like to heat from other members what low cost solution they have for the power outages

Now that's a clever little thing. It's only around 400Wh, so in my house it won't make it through load-shedding, but it certainly is sufficient to keep the basics running.

I like to keep at least my fridge running, because it heats up rather quickly.

[phil.g00]

7 minutes ago, Pietpower said:

Solar PV system vs Generator:

We can go there, but no-one was discussing the comparison between a solar PV system and a generator.

It was a comparison between the cost of grid-charged batteries and generator plus fuel.

The addition of solar serves make batteries apparently seem cheaper, but clouds the comparison.

8 minutes ago, Pietpower said:

Generator is pure sunk cost.

That's a truism, any money spent is a sunk cost, including any solar spend.

Generator fuel is a very visible per usage expense, an immediate cost to fill up the tank, it's a running cost if you need to use it.

But, those batteries are a consumables as well. You wont see 12 years without replacing them, it wont be as often, but it's one helluva tank to fill every few years.

And it's a running cost whether you need to use it or not.

 

 

[___]

1 hour ago, phil.g00 said:

I'll admit that convenience, and the ability to absorb the smaller cost differential blur the lines on very small systems. But, just because these costs are not obvious doesn't mean they aren't real. For example:

In the past when I did these calculations, I think it always came out around R4.50 per kWh for the inverter-based system and R7/kWh up to R10/kWh for running a generator. But you can get a very very decent Diesel generator that will power the whole house for 15k, and if I consider that my own backup system (sans the PV parts) is on the other side of three times that number, I totally get what you are saying. It's going to take no less than 5000 hours (calculated very roughly) of load-shedding to break even, which is almost 2 years worth of constant stage 6 shedding.

[Richard Mackay]

5 hours ago, HennieW said:

Hi All

I have found this product to be relatively cheap and reliable for a 2 to 3 hour outage. It takes care of the power requirements of the entertainment center and some portable lights.  Fridge can stay off for the two to three hours.  Would like to heat from other members what low cost solution they have for the power outages

 

It's quite a neat product but hardly cheap. It's a camping device from what I can tell..

I go back to my observation that DC systems are far more efficient than AC. So if you don't use an inverter (and  the costs associated with these) you will save yourself plenty!

The question is: Do you really need mains voltage (220Vac) during power outages?

 

[Richard Mackay]

11 hours ago, Richard Mackay said:

The question is: Do you really need mains voltage (220Vac) during power outages?

This question seems to be the elephant in the room! (What elephant? I don't see no elephant!!)

[___]

13 hours ago, Richard Mackay said:

The question is: Do you really need mains voltage (220Vac) during power outages?

I don't have a DC coffee machine. So yes, yes I do need 230VAC!

If all you need to power is an internet router, maybe a laptop or two (or if you are rich and you have a macbook that lasts two weeks on a charge), or you need to charge a cell phone, then a DC system can get you there. I remember Sony used to sell an LCD television that had a DC power supply, so with a bit of effort you could make a DC-to-DC supply for that too. There are outfits who make DC fridges and freezers... but here I draw the line. I have never seen a decent DC cooling device that is anywhere near the price and quality of a Bosch A++ unit.

And while rewiring the house to make your lights DC is a possibility, that is a massive undertaking, as you can't have DC cabling in the same trunking as AC. So if you want the house lights to work at night (instead of several independent DC-powered lamps), you need an inverter.

I will add to your question though, and ask this: Do you really need that BIG inverter? A 500W inverter won't power the fridge, but it is cheap and you don't have to make up DC power supplies for everything. It's of course slightly inefficient, but your laptop plugs in using its original brick, so does the TV...

And talking about laptops. Dell has this thing, they put a 1-Wire memory chip inside the brick, and it has a wire running to the middle pin on the plug. The laptop can therefore check if you have a genuine Dell charger plugged in, and what its wattage is. So this thing about powering a laptop with DC... it is not necessarily as easy as you might think. Not anymore.

[Richard Mackay]

What kind of coffee machine do you have that can't make coffee on a LPG ring burner?

If we are talking power outages of 2/4 hours then the contents of the fridge or freezer won't be ruined (the ice won't even melt if you don't keep opening the door!)

Laptops have well designed battery backup systems and this can be doubled by buying a spare clip in battery pack at a very reasonable price by comparison to all the backup equipment you need to invest in to do the same job.

Edited January 16, 2020 by Richard Mackay

[phil.g00]

3 hours ago, plonkster said:

And talking about laptops. Dell has this thing, they put a 1-Wire memory chip inside the brick, and it has a wire running to the middle pin on the plug. The laptop can therefore check if you have a genuine Dell charger plugged in, and what its wattage is. So this thing about powering a laptop with DC... it is not necessarily as easy as you might think. Not anymore

This is something I didn't know. It might explain why my Dell chargers don't work on my son's non-Dell laptop despite being the identical fitting and ratings as his own charger.

[phil.g00]

17 hours ago, Richard Mackay said:

The question is: Do you really need mains voltage (220Vac) during power outages?

 

I've pondered this myself.

It harks back to the original Tesla - Edison argument.

This is where AC was considered superior to DC because transformers could be used to step up the voltage to transmit the power great distances whilst minimizing the losses that come with high currents. This is the very thing that allowed peoples homes to be electrified in the first place.

That led into our appliances being traditionally AC.

And then the world quickly realized it needed standardized domestic voltages and frequency. 

So getting back to your question, to be of practical use in a domestic setting, domestic wiring would have to have the same current carrying capacity as AC wiring.

All but the smallest power consumers are suitable for low voltage dc.  If this is the point you are making, then you are making an argument for doing without power, not an AC vs DC argument.

The copper to wire a house would be too expensive, if the DC voltage wasn't pitched so that equivalent wiring couldn't transmit the same power. And that DC voltage is much higher than the pseudo- standards of 12, 24 or 48V dc. (There is also the matter of switching DC and standard AC motor speeds, but we wont go into that now).

Could be done, of course, but then the world would have to settle on a new standard DC voltage or there would be no mass market for our toys.

Nobody would make the domestic appliances we so crave in China, because what voltage would the Chinese design them for?

And this is the real reason, historically the world decided to do something a certain way because of a particular technical reason.

I accept that your own on-site generation with solar today, means the problem of electrical transmission over distances doesn't affect you today.

However between then and now, massive industries and economies have geared up to supply consumers with a selection of products based on AC conventions of specific voltages and frequencies.

So asking if we could get by with DC, is essentially the same thing as asking if we could get by a different AC voltage or frequency, or a different octane of fuel.

Of course we can, but it would be very inconvenient in terms of product choice.

So the world is saying "if it ain't broke don't fix it".

 

 

 

[___]

3 hours ago, phil.g00 said:

This is something I didn't know. It might explain why my Dell chargers don't work on my son's non-Dell laptop despite being the identical fitting and ratings as his own charger.

It is literally a memory chip, and it contains a text string. Start reading here. You can literally buy a DS2502 chip and program it with the text "DELL00AC090195046CN09T2157161543835EAL03" and the laptop will think there is a 90W PSU there.

But my point of course is that it takes work to adapt your appliances to work on DC, because they all ship with AC->DC SMPS bricks that makes some kind of DC voltage, not necessarily standardised.

How I came to know about it, is my old PSU has a problem with the cable, and intermittently it cannot read that chip. Then the laptop refuses to charge the battery and it won't run at full speed. There is a hack for writing the right stuff to some file sysfs (if you're running Linux that is), and then it overrides the BIOS and charges anyway, but I can't remember what that is.

The other sign is that when you boot the laptop, it stops right after the power on self-test and tells you that the PSU can't be identified.

With my old laptop I can also get it working by wiggling the cable a bit. Once it's read the chip once it works fine.

[Richard Mackay]

2 hours ago, plonkster said:

It is literally a memory chip, and it contains a text string. Start reading here. You can literally buy a DS2502 chip and program it with the text "DELL00AC090195046CN09T2157161543835EAL03" and the laptop will think there is a 90W PSU there.

But my point of course is that it takes work to adapt your appliances to work on DC, because they all ship with AC->DC SMPS bricks that makes some kind of DC voltage, not necessarily standardised.

How I came to know about it, is my old PSU has a problem with the cable, and intermittently it cannot read that chip. Then the laptop refuses to charge the battery and it won't run at full speed. There is a hack for writing the right stuff to some file sysfs (if you're running Linux that is), and then it overrides the BIOS and charges anyway, but I can't remember what that is.

The other sign is that when you boot the laptop, it stops right after the power on self-test and tells you that the PSU can't be identified.

With my old laptop I can also get it working by wiggling the cable a bit. Once it's read the chip once it works fine.

If you have a one of these laptops and the power supply packs up don't throw it away because it will be useful if you want to power your laptop from a DC source.

The ID chip is located close to the output of the PSU so it's easy to supply an external DC supply to the output circuit that includes this ID chip.

[___]

1 hour ago, Richard Mackay said:

If you have a one of these laptops and the power supply packs up don't throw it away because it will be useful if you want to power your laptop from a DC source.

You can also get cheap knock-offs from drop-shippers on BidOrBuy (I don't really like drop shippers, but they can be useful). I have such a knock-off, but it has a problem: Unlike the original PSU, this one has an earth!

The old one is isolated and has no earth. The chinese knock-off has an earth and it earths the chassis of the laptop, which apparently it was not designed to handle. This earthing creates complete havoc with the touchpad. If you touch an exposed metal part while operating the touchpad (such as the outer part of a usb port), then it works correctly, otherwise it jitters all over the place. In the end I used the knock-off at my work desk (where I have an external mouse) and the jiggle-the-cable original for travel purposes. It's an old Latitude E6410 from 2012, still amazingly capable despite its age, especially once you fit an SSD.

Edited January 16, 2020 by plonkster

[Richard Mackay]

15 hours ago, phil.g00 said:

I've pondered this myself.

It harks back to the original Tesla - Edison argument.

This is where AC was considered superior to DC because transformers could be used to step up the voltage to transmit the power great distances whilst minimizing the losses that come with high currents. This is the very thing that allowed peoples homes to be electrified in the first place.

That led into our appliances being traditionally AC.

And then the world quickly realized it needed standardized domestic voltages and frequency. 

So getting back to your question, to be of practical use in a domestic setting, domestic wiring would have to have the same current carrying capacity as AC wiring.

All but the smallest power consumers are suitable for low voltage dc.  If this is the point you are making, then you are making an argument for doing without power, not an AC vs DC argument.

The copper to wire a house would be too expensive, if the DC voltage wasn't pitched so that equivalent wiring couldn't transmit the same power. And that DC voltage is much higher than the pseudo- standards of 12, 24 or 48V dc. (There is also the matter of switching DC and standard AC motor speeds, but we wont go into that now).

Could be done, of course, but then the world would have to settle on a new standard DC voltage or there would be no mass market for our toys.

Nobody would make the domestic appliances we so crave in China, because what voltage would the Chinese design them for?

And this is the real reason, historically the world decided to do something a certain way because of a particular technical reason.

I accept that your own on-site generation with solar today, means the problem of electrical transmission over distances doesn't affect you today.

However between then and now, massive industries and economies have geared up to supply consumers with a selection of products based on AC conventions of specific voltages and frequencies.

So asking if we could get by with DC, is essentially the same thing as asking if we could get by a different AC voltage or frequency, or a different octane of fuel.

Of course we can, but it would be very inconvenient in terms of product choice.

So the world is saying "if it ain't broke don't fix it".

 

 

 

Good points!

However the traditional (Eskom) model of remote power stations generating electricity which is then transmitted to distant users is on the way out. It makes a lot of sense to generate flexible power locally. These systems are called micro grids and DC plays a big part here.

Standards are being developed so these systems can be integrated if required. Check out this webinar:https://www.youtube.com/watch?v=bIB1_TZ9MbI

(What I found particularly interesting is the DC voltage standards that they are setting. The last question at the end of the webinar addresses this)

 

[phil.g00]

4 hours ago, Richard Mackay said:

Standards are being developed so these systems can be integrated if required. Check out this webinar:https://www.youtube.com/watch?v=bIB1_TZ9MbI

(What I found particularly interesting is the DC voltage standards that they are setting. The last question at the end of the webinar addresses this)

I took the video to represent an aspiration. It doesn't represent a practical solution for people unless they are willing to do without.

The voltage standards talked about intra-home were between 5V and 48V, touting it to be inherently safe.

 This is neither true nor practical.

I'll expound on why the low voltages mentioned ( 5V -48V) are impractical to use in a standard domestic setting.

Lets look at the best case scenario:

48Vdc represents a voltage, 230Vac (rms)/48Vdc = 4.79 times lower than conventional AC.

That means for the same power, to your standard 16 Amp wall socket, you need 16*4.79 Amps = 77Amps.

Remember that electrical losses are I2R, they are not proportional to the current, they are proportional to the square of the current.

Which in turn means wiring that plug with 16mm2 cable there and back = 32mm2,  instead of 2.5mm2 x 2 = 5mm2.

( Well, I'll give my AC plug socket an earth wire, so 7.5mm2 in total, it is still less than a quarter of the copper needed for the DC equivalent).

That's at 48V, which is the highest voltage mentioned, voltages like 5V,( also mentioned), require a ludicrous amount of copper.

A 5V plug socket  equivalent of today's AC standard would need over 600m2 of copper. It gets into the realms of cable size that isn't even made.

Then we have to consider the "inherent safety" of this voltage, sure you wont get shocked, but that's not the only danger, with current comes heat, with heat comes the risk of fire.

A loose connection in the right place, with current this high and your house will burn down.

Sure, that can happen with AC as well, you are just massively increasing the risk of it happening, because every electrical connection in your house would be a potential welding machine.

So to get reiterate my original post, a DC standard is needed, and it has to be a higher voltage than what is good for camping. The low voltages mentioned in your video don't cut it.

 

[___]

1 hour ago, phil.g00 said:

So to get reiterate my original post, a DC standard is needed, and it has to be a higher voltage than what is good for camping. The low voltages mentioned in your video don't cut it.

There is one possible case one could make for a low-voltage standard, and there is even some precedent in data centers. In some data centers there is the option of a 48VDC supply. Servers and other equipment get a DC/DC power supply that feeds from 48V. Of course we're talking a specific application with well-understood power needs.

In a house there are many appliances that could run from DC just as well, and technically already do (they either have a PSU brick or a built-in SMPS). Computers, especially laptops. Televisions (now that we're leaving the CRT behind), charging cell phones, lights. Almost anything that doesn't have an induction motor or a heating element

If one were to make such a case, then it would not be a replacement for the AC system, rather it would be a second "rail" in the house for appliances that are supported.

Of course this doubles up all sorts of costs, double the wiring, and so on and so forth, so it's still not going to be easy to argue for it.

[phil.g00]

2 hours ago, plonkster said:

There is one possible case one could make for a low-voltage standard, and there is even some precedent in data centers. In some data centers there is the option of a 48VDC supply. Servers and other equipment get a DC/DC power supply that feeds from 48V. Of course we're talking a specific application with well-understood power needs.

I think you have to consider data centres as a special case, far removed from the domestic application and I'll explain why..

Data centres use DC for a very good reason, it guarantees a much cleaner, more reliable supply for very sensitive equipment.

Data centres still use plenty AC power, but they can (and do) ditch the grid seamlessly and quickly and run off their own batteries/ generation, if there is a hint of a problem with the grid power quality.

But, using the good traits of DC is not cost-free, you still have to deal with the bad.

Google, Microsoft, Amazon, Paypal, Facebook and others have data centres in Ireland.

Why are all these big names in Ireland? Well to be honest, Ireland ticks a few boxes for them.

But one reason that is often stated is because these data centres can massively reduce their power costs on the cooling requirements on all this equipment using Ireland's temperate climate.

So low voltage DC ( and it's heat losses) has in part decided in which countries these boys have to set up shop.

Whilst, thee and me in a domestic scenario, would consider moving country in order to use DC a tad inconvenient.

Edited January 17, 2020 by phil.g00

[___]

51 minutes ago, phil.g00 said:

have to consider data centres as a special case

I did...

3 hours ago, plonkster said:

Of course we're talking a specific application with well-understood power needs.

I think many of us have considered the inefficiency of taking 48V up to 230V, only to convert it back down to 19V for a laptop, 5V for a USB charger, 12V for some downlights (though admittedly MR16s are no longer popular), and so on. These are all relatively low power applications. Now of course just because we've thought of it, and just because it is more efficient, doesn't mean it is a good idea. For example, I've decided long ago that making peace with the inefficiency of the loop is much easier than modifying the house to have two circuits! I also knew that one day I might move, and I wanted to keep things as standard as possible.

Edited January 17, 2020 by plonkster

[Richard Mackay]

I spent much of my 'corporate' career in industrial automation. Years ago we had many different control voltage standards: AC 120 or 250. Also many DC standards: 5, 12, 24 etc.

I recent years this diversity has reduced to one: 24V 

These days you cannot buy any other voltage for an input module for a Siemens controller (the biggest player in this field).. Like the model T Ford you could only get in black, the same applies to 24V in control voltages. (The output modules were available with potential free contacts so you could use 220V to energise a contactor if required) 

So here is another DC standard that has developed. Not only is 24V used for control, it is often used to power instruments, controllers etc. in electrical control systems.  

Edited January 17, 2020 by Richard Mackay

[phil.g00]

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

 

 

[Jaco De Jongh]

On 2020/01/16 at 10:23 AM, Richard Mackay said:

On 2020/01/15 at 10:26 PM, Richard Mackay said:

The question is: Do you really need mains voltage (220Vac) during power outages?

This question seems to be the elephant in the room! (What elephant? I don't see no elephant!!)

If I read your comments correctly, you want to steer this conversation in the direction of "DC microgrid" type of backup systems to at least keep the electronics live. I guess there is a market for that, but it will be a selected market... most of the guys here wants a bit more luxury during Load shedding. 

All of my esencial electronics run directly off a DC bus that's been installed a few years back. so even if my inverter fails, they will still be live.  

[Richard Mackay]

45 minutes ago, Jaco de Jongh said:

If I read your comments correctly, you want to steer this conversation in the direction of "DC microgrid" type of backup systems to at least keep the electronics live. I guess there is a market for that, but it will be a selected market... most of the guys here wants a bit more luxury during Load shedding. 

All of my esencial electronics run directly off a DC bus that's been installed a few years back. so even if my inverter fails, they will still be live.  

I'm an electronics tech. When I started we still had thermionic valve technology. This used high voltage DC. Then the transistor appeared and voltages dropped and have kept on dropping. Electrical power reticulation was always AC since this was the way electrical power was managed and still is.

However these small but powerful electronic gizmos that we depend on run on DC (with a battery) and we will see this will influence the grid in the 'energy mix' going forward. I don't believe we will see one system dominating since it won't be the ideal solution for all applications.