[IslandCrow]

Having ordered a wood-burning stove (but not yet installed), I am turning my attention to other projects that would help make my powering-down an acceptable experience.

Soon I would be able to cope with several days of electricity cuts, but as I work from home and need a computer for work, any lengthy power cut means I cannot do my job while the grid is down.

Reading some pages that I have 'googled' on home power, I seem to be coming up with more and more questions, about what would be the right way for me to go. (solar and/or wind ? etc).

From my reading it seems that small systems (eg for boats, rvs, small cabins) are DC systems, whereas larger set-ups involving heavier electrical use tend to be AC systems. I am not sure what to make of this, and was wondering if people here have thoughts about the issue that they might like to share.

Thank you

[gg3]

Use AC.

Even if you were to try to install all DC appliances (another expensive change), and most of them ran on 12 volts, you would still have some devices that had differing voltage requirements. For each of those devices you would need a DC to DC converter. Those converters are inefficient and rather more expensive than AC to DC converters.

If you use AC, you can keep all of your present appliances (and replace with more efficient AC units as needed, which will be less costly than DC units that aren't manufactured in such large quantities). And for those devices that require DC, for example LED lighting, inexpensive AC to DC adaptors will do the trick.

Note, you also want to be able to unplug those AC to DC adaptors when not in use, otherwise they are "parasitic" and keep up a constant low level of energy consumption that will cost over time.

If you're rewiring your house I would also suggest putting in "all-room" switches. That is, a switch on the wall near the door that shuts off everything in the room, so you don't have to run around unplugging all the things that might be on standby. There would obviously be exceptions for outlets connected to your fridge in the kitchen, your clock radio in the bedroom, etc.

Also I would suggest installing a whole-house power meter in the living area. This could be done as an analog ammeter, or as a digital ammeter. It will show you the total current consumption at any given moment, which is good for finding various subtle ways to save more power. The digital ones are better at displaying small values that might be lost on an analog dial scale. If it was my house I'd install both for a user-friendly interface that can be read easily from a distance.

The only situation that justifies installing a whole-house DC system is where you have designed your entire electrical infrastructure around it and haven't bought any AC powered appliances yet. At that point you can converge the designed voltage with the appliances, for example standardizing on 12 volts DC all'round. However you would still need DC to AC inverters for powering items such as computers, answering machines or other telecom, and so on, and those should also be factored into the design.

Meanwhile, if you're moving to a high conservation lifestyle, be sure to include clothes lines or clothes drying racks (indoor as well as outdoor, to deal with inclement weather). These will pay for themselves quickly by saving the approx. 2.5 KWH per load of laundry that would otherwise be used by the tumble dryer. However it's still useful to have a tumble dryer for the rare but unavoidable instances where you have to sanitize laundry that can't be bleached, by heating it to a high temperature during drying, for example when dealing with contagious illness.

[Niagara]

I can't speak for Finland, but here in Canada/USA 12 volt systems are popular for trailers and motorhomes.

However they have very limited usefulness. With 12V you can only power some basic appliances, like lighting, portable TVs and mini stereo systems. There are 3-way fridges available that accept 3 types of power (120VAC, 12VDC and propane) however these are absorption fridges and far less efficient than standard compressor fridges.

There are also a small number of electronic gadgets that are designed for 12VDC, like laptops, PDAs, etc.

One problem with 12V DC circuitry is the limit on power available. Forget about running a microwave, toaster, kettle, hair dryer etc.
Electrical power = volts X amps

So to get 1200 watts of electric power you only need 10 amps @ 120V,easily carried by 14-gauge domestic wiring. (Only 5 amps in Europe @240V)
But at 12V the current would be 100amps, requiring HUGE cables.

In my opinion it would be far more useful to invert the low voltage DC and run standard AC wiring.

[EnergyUnlimited]

$this->bbcode_second_pass_quote('IslandCrow', '
')Soon I would be able to cope with several days of electricity cuts, but as I work from home and need a computer for work, any lengthy power cut means I cannot do my job while the grid is down.

[EnergyUnlimited]

$this->bbcode_second_pass_quote('Niagara', '
')One problem with 12V DC circuitry is the limit on power available. Forget about running a microwave, toaster, kettle, hair dryer etc.
Electrical power = volts X amps

So to get 1200 watts of electric power you only need 10 amps @ 120V,easily carried by 14-gauge domestic wiring. (Only 5 amps in Europe @240V)
But at 12V the current would be 100amps, requiring HUGE cables.

[IslandCrow]

Thank gg3 and niagra.

I have found both your replies very helpful in understanding the issue. I have saved your replies in my files on alternative energy.

I know that the next step in looking at backup electric systems is to reduce the amount of electricity that I am using. I have started to use 'power-strips' so I can turn off most of my office equipment from one point.

[IslandCrow]

$this->bbcode_second_pass_quote('EnergyUnlimited', 'W')eird, as it may sound, but you will not need your computer anymore (unless you are using it for games playing...), once blackouts became common...

[tsakach]

If you are off grid, it doesn't make sense to go from DC to AC and back to DC if you think about it.

I run a satellite modem, wireless routers and weather station. These devices draw 40 watts 24/7. AC/DC conversion efficiencies were measured by plugging the device into a Killawatt meter, and measuring the DC load with an amp meter. The inverter efficiency was taken from a chart in the inverter documentation, which shows the efficiency curve dropping off for smaller AC loads. I am currently using golf cart batteries, which are only 70% efficient.

Calculating efficiency losses at each step results in the following:

40 watt load
56 watts AC/DC conversion, 70% efficient
68 watts inverter DC/AC conversion, 82% efficient at 68 watt load
100 watts on battery, 70% efficient.

2.4 kwh total (winter, 10 hours on sun, 14 hours on battery)

In addition, the inverter required 20 watts, which adds another 0.6 kwh, so the total on AC comes to 3.0 kwh.

Calculating efficiency losses for the same 40 watt load powered on DC results in the following:

40 watt load
44 watts DC/DC conversion, 90% efficient (17 watts DC/DC + 23 watts direct 12vdc)
63 watts on battery, 70% efficient.

1.3 kwh total (winter, 10 hours on sun, 14 hours on battery)

Switching a 40 watt load from AC to DC resulted in a 230% increase in efficiency. At first, I found this hard to believe, but my batteries are now fully charged every day by 1:00 pm compared to sometimes going weeks without being able to fully charge the batteries. My inverter now runs on standby mode, only drawing 1.5 watts, so AC power is still available like normal.

[MD]

AC won because of transformability and therefore transportability.
In a post-grid word of precious watts a total DC system becomes much more attractive.

[RonMN]

Just a suggestion...definately temporary but it would get you by for quite a while running only your pc and a couple of light bulbs.

Get a gasoline generator & try to keep you car filled with gas. If a blackout happens, that could keep your computer running for a couple weeks. (computer...not the entire house).

And if it goes beyond a couple weeks...well, chances are the bank wont have the electricity to process your paycheck anyway

[IslandCrow]

Thank you for the latest input. In reading them I realise that I have to get serious about the question of "what is the minimum amount of electricial power that I need to keep my office and other equipment running?".

I know that it is a lot less than the amount of electricity that I am currently using, partly because of the need for electricity to run the heat exchange pump, fridges, freezers and stove. In a prolonged period of blackout, we would have a wood burning stove for some heat and cooking, meaning that if it happened in winter we would have to 'abandon' the bedroom (and probably the office) and sleep/work in the kitchen.

[tsakach]

If you need to keep a wood stove burning it is possible to build a "wood burning generator / turbine wood-stove."

This outfit sells plans for converting an automobile turbocharger into a gas turbine engine. It supposedly can generate up to 2kw so you might be able to recharge a battery bank from a load of wood. It requires a high pressure oil pump and the turbo is noisy. I don't know about camping out in the kitchen with this thing. This is definitely in the experimental prototype stage.

[Bytesmiths]

$this->bbcode_second_pass_quote('EnergyUnlimited', '')$this->bbcode_second_pass_quote('Niagara', 'N')ot so huge...my welder cables can carry 300 A and they are not really huge.

[MacG]

$this->bbcode_second_pass_quote('Niagara', 'H')owever they have very limited usefulness. With 12V you can only power some basic appliances, like lighting, portable TVs and mini stereo systems.