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  Reply # 1835296 1-Aug-2017 21:42
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you still need to transform the incoming AC to DC, or the generated HVDC to LVDC.

 

 

 

given the efficiency of inverters these days i cant really see a use case personally, given everything else you need to buy to make it work would cost you a bit


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  Reply # 1835309 1-Aug-2017 22:40
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What will you do for room heating, cooking, and hot water? As they are your 3 main power users. If you are going to use a ELV DC system, you are going to need an alternative for the big 3. Which will pretty much mean gas heating, hot water, and cooking. If you have piped natural gas where you live, it will probably be cheaper than electricity for a large household.

 

12V fridges are expensive. Let alone a full size 12V fridge. Be cheaper just to get a mains fridge, and get a refrigeration tech to replace the compressor with a 12V one. (motor and compressor are a sealed unit, you can't replace just the motor)

 

 

 

But first of all, see what the council say. They will probably ask for massive development contribution fees, on top of your building consent fees. And that is assuming that the unitary plan for your area will allow 3 dwellings on your section. Otherwise you will need a resource consent. And Watercare will probably ask you to pay an infrastructure growth charge as well. Council fees will almost certainly be at least $50,000 for what you want to do. And expensive upgrades to the rest of the house for things like fireproofing, insulation (both thermal and noise).

 

You will soon see why house prices are so expensive. And why there are so many illegal household units out there. The council normally use the presence of a kitchen as the test of whether you are creating separate household units Vs just extending an existing house. If you want to do things legally, far cheaper to have just 1 kitchen, and add on lots of bedrooms. And take in lots of flatmates. Also means that you don't have to spend heaps separating out the power, water, and installing extra self contained hot water systems. Otherwise you can't bill separately for water and power.






 
 
 
 




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  Reply # 1835626 2-Aug-2017 12:27
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Aredwood:

 

What will you do for room heating, cooking, and hot water? As they are your 3 main power users. If you are going to use a ELV DC system, you are going to need an alternative for the big 3. Which will pretty much mean gas heating, hot water, and cooking. If you have piped natural gas where you live, it will probably be cheaper than electricity for a large household.

 

12V fridges are expensive. Let alone a full size 12V fridge. Be cheaper just to get a mains fridge, and get a refrigeration tech to replace the compressor with a 12V one. (motor and compressor are a sealed unit, you can't replace just the motor)

 

 

 

But first of all, see what the council say. They will probably ask for massive development contribution fees, on top of your building consent fees. And that is assuming that the unitary plan for your area will allow 3 dwellings on your section. Otherwise you will need a resource consent. And Watercare will probably ask you to pay an infrastructure growth charge as well. Council fees will almost certainly be at least $50,000 for what you want to do. And expensive upgrades to the rest of the house for things like fireproofing, insulation (both thermal and noise).

 

You will soon see why house prices are so expensive. And why there are so many illegal household units out there. The council normally use the presence of a kitchen as the test of whether you are creating separate household units Vs just extending an existing house. If you want to do things legally, far cheaper to have just 1 kitchen, and add on lots of bedrooms. And take in lots of flatmates. Also means that you don't have to spend heaps separating out the power, water, and installing extra self contained hot water systems. Otherwise you can't bill separately for water and power.

 

 

Water Heating

 

Looking at heat pump based system with a couple of large capacity tanks outside. Could also utilise solar and potentially AC elements as backup. The heat pumps should be able to be converted to DC.

 

Cooking

 

Looking at induction cooktops and not sure yet on the oven. Not a high priority but conceptually both can be modified to DC.

 

Heating

 

Heat pumps as above with the water.

 

 

 

Planning

 

Yea looked at this. We really want a separate kitchen so we have our own complete living space. The sleep-out shouldn't count as a minor dwelling as it has no cooking facilities. If we can keep the square meterage under 99m2 then the council tool is estimating $~21,000 for contributions exclusive of the building consents.

 

The land is mixed housing suburban under the unitary plan and a minor dwelling is allowed with no additional resource consent.






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  Reply # 1835732 2-Aug-2017 13:50
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also, start looking at Mobile homes (especially the bigger and more expensive ones).

 

 

 

Most there are doing the exact opposite from where you seem to be heading... they all run Solar/alternator/generator (DC) inputs and then invest in inverters to get it to change back to standard 240VAC to run more standard equipment (think washing machines, Nespresso, etc.)

 

some higher capacity (600AH Lithium/1200W Solar) bus conversions are even proponents of using standard Samsung refrigerator units as they are now very efficient running and MUCH cheaper than equivalent native DC fridges....

 

 

 

http://www.nzmotorhome.co.nz/NZMotorhomeForum/viewforum.php?f=55


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  Reply # 1835771 2-Aug-2017 14:41
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Zeon:

 

To be very clear this is not about saving money - rather to see what is possible technically. I am fully aware and expect this will be a multitude more expensive than a traditional AC system.

 

 

I don't understand. You admit this will cost you considerably more than a standard AC setup, why make your mortgage larger for what seems like purely academic reasons? What is the benefit of doing this?


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  Reply # 1835787 2-Aug-2017 14:55
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I followed a blog type of thing about a couple who went off grid in their house over the north shore. They used a mixture of AC and DC - essentially using  the voltage native to the appliances - 12v for all their modems, cordless phones and other plug-pack gadgets and mains from an inverter for the 240 volt stuff. Admittedly it was a few year ago before LED's where so plentiful. I tried running all my 12 volt stuff off of solar and a battery for a year but gave up after the first set of batteries wore out. Bill savings were hardly noticeable but it was an interesting project.

 

I do a lot of DC installations in boats & motor homes. I have also done appliance repair in the past. Cool idea, however IMO you are just not going to get away from AC - it will be too restricting - for example while LED's are DC devices, a lot of LED light power supplies to straight from AC to a current regulated DC feed - not 24/12 volts. Also igniters in gas heaters, stoves etc could require a ground up redesign to work from DC. I think you will struggle to find anyone who can replace motors in fridges and heat pumps, and you will likely struggle to find DC motors for these appliances.

 

Additionally even if you could convert fridges, it may be false economy - 12v native fridges tend to be better insulated than mains fridges where the intended power supply is essentially unlimited and the maker is cutting costs. It could cost you more in extra solar and battery power to make up for the poor insulation than buying the proper fridge in the first place.

 

Before you commit, be sure to research batteries, the amp/hour capacity you will need, the cost to buy, the life expectancy (it probably won't be 10 years) and cost to replace the batteries. I have seen several similar projects change direction dramatically after the people realise true annual cost of the batteries. Lithium is still coming on line, is quite expensive and I don't know much about its life. Lead Acid is usually far more expensive than people anticipate. The reason is that your typical deep cycle battery is good for about 300 cycles (assuming a 50% discharge depth) which means for a house you'll be replacing them annually - spending (conservatively) $2K or $3k per year on batteries tips the scales firmly in favour of grid supply. If you oversize your battery bank so that you're only discharging to 20% you can get better life, however you will probably be surprise how big and expensive such a battery bank will be.

 

If you want a DIY project to reduce electricity dependence, I suggest going for solar hot water, and solar PV's with a grid tied inverter.


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  Reply # 1836162 3-Aug-2017 01:32
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Zeon:

 

 

 

Water Heating

 

Looking at heat pump based system with a couple of large capacity tanks outside. Could also utilise solar and potentially AC elements as backup. The heat pumps should be able to be converted to DC.

 

Cooking

 

Looking at induction cooktops and not sure yet on the oven. Not a high priority but conceptually both can be modified to DC.

 

Heating

 

Heat pumps as above with the water.

 

 

 

 

 

 

Heatpump hot water - HW heatpumps will still draw at least 1KW when they are running.  This model draws 7.1A at mains, equivalent current at 12V is 136A or 34A at 48V - so no, not going to happen from a battery system.

 

Induction cooking - you will need at least 32A at mains for a 4 cooking zone induction cooker - That is 613A at 12V. There is another thread where someone said that the starter motor in their Mitsi Pajero 4WD draws 450A in comparison. Yet that starter motor is unlikely to be used for more than 10 seconds at a time. - No way at all can you run an induction cooker from 12V.

 

Heating - A well insulated house of your size will need at least a 6KW heater to keep the whole house warm. When it is really cold outside, you probably won't get better than a 2.5COP on a heatpump. So it will use 2.4KW/Hr per hour. Run it for 8 hours per day - that is almost 20KW/Hr for just heating alone. I have been quoted $2700 for a 2.4KWhr of capacity Li-Ion battery. You will need 8 of them just for heating. And you will still need more for your other loads, let's say 10.

 

So $27,000 for battery storage alone, plus the cost of a custom designed heatpump. That is some ridiculously expensive heating.

 

 

 

Now lets look at exactly what the power company provides with a grid connection. Standard capacity is 15KW. Now price up a 15KW rated inverter, that alone will probably cost 10K. If you are on a low user plan, you pay just 33c per day to "rent" the equivalent of a 15KW rated inverter, that the lines company will fix at their cost if it breaks. Even over 20 years, you have paid only $2409 for the equivalent of a 15KW inverter. Far cheaper than actually buying one.

 

And for the actual electricity itself - you only pay for what you use. No need to invest big $$$ in batteries and solar panels, that either won't be enough, or if you usage goes down. Will be a wasted investment.

 

There was a thread on trademe forums where someone who has been living in an offgrid house for over 10 years. He said his system maintenance costs worked out to $75 per week averaged out over 10 years. And that was including managing to make his first battery bank last over 8 years - which is a massive achievement. Starting today $100 per week would be a more realistic figure to allow for an offgrid system maintenance and parts replacement budget. 

 

Still keen? $50,000 at least setup + $100 per week ongoing? That would buy alot of grid power.

 

Myself - I have a small scale battery system for running my router ect. I will be adding solar PV to it in the future. Does it recoup it's costs - no. It's main purpose - as a backup power system. Although I may get close to break even. But only because Im on a peak / offpeak power plan. So I only need to offset the peak charges. And I benefit by then getting cheap offpeak power. Most of those savings will only be due to taking advantage of loopholes in how charges are billed on the power price plan that im on. Only one company offers that plan, if they disappear, or stop offering that plan. Goodbye to my savings.






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  Reply # 1836168 3-Aug-2017 07:03
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@aredwood you forgot solar panels to charge batteries, which will probably be in the realm of 75kW worth of panels to cope with heating on cloudy winter days




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  Reply # 1840529 7-Aug-2017 12:56
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Hi all, thanks so much for the feedback - really useful. From what I can see, the battery tech is limited at the moment. Probably it will be a piece by piece approach. The way the construction is being made will make running new cables exceedingly easy and can make decisions further down the line.

 

Will focus on the lights for the moment and then look at the others as the next step.






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