Hello from Alaska

[funinalaska]

I found this forum while searching for solar information for a home my wife and I are in the process of planning to build in the next year or so.
We are building a small cabin on a piece of property near Fairbanks, AK.
The reason we are looking into solar is because the power grid in the location we are looking at is questionable at best.
Power outages are common and often long lived.
We are doing everything possible to be able to survive without power at all but we decided that a 12V lighting system is probably the way to go.
We are looking at using LED strip lighting around the perimeter of all rooms for light and since these are all 12v native then we don't have to do any inefficient conversion AC to DC or the other way around. Also using a small RV type water pump for potable water use in the house from a tank in the house (yes this is a dry cabin, no utility and no well).
There are a couple big pieces of information I am looking for that I hope this forum will help me find.
One of which is something to help me keep my battery bank charged during the dark winter months here.
I was wondering if some sort of stand by charger existed.
Something that ties to grid power but will only charge if your batteries get below a certain level.
I don't want something that will always be charging my batteries, that kind of defeats the purpose of putting PV on my roof.
I simply want a charger that will stay plugged in to the grid and connected to my batteries and if the battery reaches a set "low" limit that the charger will kick in and charge them to full then go back into it's standby mode.
Does such a beast exist?

[inetdog]

I found this forum while searching for solar information for a home my wife and I are in the process of planning to build in the next year or so.
We are building a small cabin on a piece of property near Fairbanks, AK.
The reason we are looking into solar is because the power grid in the location we are looking at is questionable at best.
Power outages are common and often long lived.
We are doing everything possible to be able to survive without power at all but we decided that a 12V lighting system is probably the way to go.
We are looking at using LED strip lighting around the perimeter of all rooms for light and since these are all 12v native then we don't have to do any inefficient conversion AC to DC or the other way around. Also using a small RV type water pump for potable water use in the house from a tank in the house (yes this is a dry cabin, no utility and no well).
There are a couple big pieces of information I am looking for that I hope this forum will help me find.
One of which is something to help me keep my battery bank charged during the dark winter months here.
I was wondering if some sort of stand by charger existed.
Something that ties to grid power but will only charge if your batteries get below a certain level.
I don't want something that will always be charging my batteries, that kind of defeats the purpose of putting PV on my roof.
I simply want a charger that will stay plugged in to the grid and connected to my batteries and if the battery reaches a set "low" limit that the charger will kick in and charge them to full then go back into it's standby mode.
Does such a beast exist?

Hi funinalaska and welcome to Solar Panel Talk.

If you have grid but it is unreliable, you may find that it is more economical to avoid the battery bank and go with a small generator instead.

Power from batteries charged by PV will cost you far more per kWh than the same amount of power from your utility.

[Naptown]

Hi funinalaska and welcome to Solar Panel Talk.

If you have grid but it is unreliable, you may find that it is more economical to avoid the battery bank and go with a small generator instead.

Power from batteries charged by PV will cost you far more per kWh than the same amount of power from your utility.

The kicker may be the cost of diesel fuel there and getting the generator to start in winter.
Chris Olson will have more on maintaining generators in butt cold conditions

[Sunking]

We are looking at using LED strip lighting around the perimeter of all rooms for light and since these are all 12v native then we don't have to do any inefficient conversion AC to DC or the other way around.

Right there is your first major mistake. 12 volt losses are far greater and requires a copper mine to do what you want. Forget 12 volts that is for toys and RV, not homes. Go with 24 or 48 volt and use an inverter. You will thank me later.

Second huge problem is your location In winter you have no sun, thus no solar power. Summer is not much improvement because thesun circles around you and no way to get direct exposure without very expensive high maintenance 2-axis tracking. Even with tracking sun angles are so low you only end up with a few modest Sun Hours of power.

If you do this buy a commercial grade diesel generator as you are going to need it about every day.

[funinalaska]

Ya, forget a generator.
Where I am with Gasoline costing over $8 a gallon and diesel about the same, NOT going that route.
Remember this is a modestly basic system running ONLY lighting and an RV water pump that draws about 5 amps.
This is for a one room cabin, not a full time home.
It will be used a couple months in the winter and most of the summer.
as far as non viable solar collection. I am in the area in Alaska where there are more stationary PV arrays than I have ever seen.
I have done the math and I don't need much for the system.
I will be running a total of 150 watts of 12V lighting and a 5 amp (60 watt?) pump that may see a total of an hour or two of usage a week when the cabin is occupied
To me this doesn't seem like enough to justify a multi-thousand dollar investment in a generator plus the absolutely stupid cost of fuel.
Even a small (4000 watt) generator will consume about a quart of fuel an hour with no load so call it a minimum of 2 gallons of fuel a day
Times 7 days week 4 weeks a month times 6 months of usage (4 summer and 2 winter)
So 2X7X4X6=336 gallons of fuel a year times $8 a gallon is about $2688 just in fuel for the generator and that is stopping it when sleeping and not at the cabin.
I think a $2000 investment is justified.

Considering my expectations are:
150 watts of lighting estimated expectation of use 4-6 hours per day, at 6 hours that comes to 75AH per day and that is probably a gross over estimate based on having EVERY light on in the house at all hours when we are home
A 5-6 amp 12V water pump, used for one sink only estimated total usage 2 hours a week Say a third of an hour a day (20 mins) and call it 1AH per day

So total daily consumption will be 76Amp Hours per day I am looking at a 150 watt panel to be mounted on the roof facing south which based on angle of effectiveness calculations I will get 11 months of greater than 2 hours of useful charging from the sun. and in the summer about 6 hours of direct rays in the shortest days of the year about an hour or a little less.

So yes, In my mind, very doable. Oh and I already own a 300 AH 12V battery bank, so I don't even need to purchase that part.

So back to the question at hand, Is there such a thing as a charger that only turns on when the battery absolutely needs it and then turns off instead of always trickle charging?