Using 12V power?

[Dimitri]

Anyone run in their homes 12V systems being fed by solar panels?

The girlfriend mentioned building a new home (thankfully so I can build eventually), and I was thinking, although I wouldn't go off the grid, but feeding say the fridge, emergency lighting and back up heaters, on a 400W or so system might be handy due to power outages.

I thought about converting to 120V, etc, but since there are relatively efficient 12V appliances for RV's that might work. I figured the losses might be best if avoided.

Dimitri

[MountainDon]

There's a difference between running the home and having a few backup lights. As for the entire home on 12 VDC, IMO, the home would have to be very small to make 12 VDC viable. For backup purposes, it depends on what is required to be powered when the grid goes down. A small number of lights; sure. But the downside is the need for separate DC wiring as well as the usual AC wiring.


You mentiuoned refrigerator and 12 volt and RV.  Perhaps you already know the following, perhaps not; common RV refrigerators that can operate on 12 VDC can only do so for short periods as a rule. The 12 VDC part of those fridges is really only meant to be used while driving (and making power from the alternator) in order to save the propane. There are refrigerators that use 12 or 24 VDC to run their compressors. They usually cost a lot more per cu ft of fridge and freezer space.

You also mentioned heaters. Electrical resistance heaters are impractical to be run off batteries. This is the same reason an RV refrigerator is impractical to be run off 12 VDC; they use a resistance coil to supply the heat required to make the absorption refrigerator system make "cold".

Before deciding on yes or no make a list of the "must have" items (those that would run on DC) and how much power they would typically use in a day. From that you can get down to how much battery storage is required and from that how many PV modules.

I'm not saying some 12 VDC can't work; but it should be well thought out first. maybe we can help if you can expand on what things you'd like to run off battery and solar.

[Dimitri]

Basically, I want a back up plan for a summer time power failure (remember the black out?) or a winter ice storm. The last one worries me more, but a wood stove will provide most of the heating for a small 2 bedroom home if installed between the 2 bedrooms.

I've found pure 12V DC fridges available, listed as a power consumption of 60-75W, so if I ran a dedicated 200W panel and batteries for it, I am sure I can keep its up time to near 100%.

Lights would probably be LED's or something lower power to light up the rooms of the house of the grid is off. Not too much power consumption at all there. And only use when there is no main power available. I will rig a controller circuit more then likely, so it can detect the main power, then it will flip the lights on in the rooms based on a motion sensor to conserve power.

I think two 200W panels attached to a pole, with a stepper motor to move the panels back and forth during the day to follow the sun would be the best to maximize the power produced. Small shed next to the pole with insulation and a small heater to keep the temperature somewhere in the optimal area for the batteries.

Dimitri

[MountainDon]

If that's all you need to run and if you will be on the grid anyhow, how about not even bothering with the PV modules at all? Simply use a good battery charger running off the grid to keep the batteries up? A good charger that can shift between a true float and an absorb charge rate. Maybe even AGM type batteries so you don't need to worry about the fluid levels? Unless the grid is extremely unreliable that may be more cost effective.

Any idea how many hours out of 24 one of those DC fridges would be running to maintain cold?

[Dimitri]

If that's all you need to run and if you will be on the grid anyhow, how about not even bothering with the PV modules at all?

Well power outages that generally cause the food in the fridge to spoil by definition must last 2+ days, so I'd either need alot of batteries, or a means to keep them full without grid power, hence why I am thinking panels. With a power reserve that can last me a day or 2 of cloudy days.

The 1998 ice storm left people without power for up to a month, the black out lasted 3-4 days depending on the area, and 2 winters ago, the power went out for about a week in some parts around here. So I don't think a ton of batteries to last that long would make much sense.

Any idea how many hours out of 24 one of those DC fridges would be running to maintain cold?

Not sure, but when I was thinking of the math, I figured, a 200W panel, gives me say 180W average, for 8 hours a day, means I get enough power to power a 60W fridge using one panel the entire day. I know its not great math, but its something. The extra panel for the lights, will help compensate for the additional power that may be drawn if the one panel doesn't reach that 180W point for 8 hours. As basic lighting, throughout the house does not need a whole 200W panel.

Dimitri

[Rob_O]

Dimitri, you might get some ideas for your backup power here http://www.whenshtf.com/showthread.php?14032-Whole-house-UPS.

The 1998 ice storm left people without power for up to a month, the black out lasted 3-4 days depending on the area, and 2 winters ago, the power went out for about a week in some parts around here. So I don't think a ton of batteries to last that long would make much sense.

The same storm that takes out your power lines may also take out your solar panels, or cover them with ice, or make them mostly useless because the sky is cloudy for days on end. Build a generator and a 120V charger into your plans