Enough power?

mkirsch wrote:
Well, if the 55W "can't quite" keep up, and you're more than doubling your solar capacity, I would hazard a guess that you are good to go.

Worst case you can add the 55W panel back in by changing your solar controller.

You've got nothing to lose, and everything to gain, by trying with the 120W panel. You can't add the 55W or any other panel in without spending money on a new controller anyway. If you don't need it, you're money ahead.

+1
And a controller capable of just a 55W panel would be very inexpensive. Here's a link to one from a reputable brand for $33. I'd get one and hook both panels and controllers up to the batteries.

tvman44 wrote:
I would not waste my money on anything less than 200 to 400 watts. :)

And I'd buy a generator and forget about it. ;)

I would not waste my money on anything less than 200 to 400 watts. :)

Size a battery bank and PV array properly
Rule of thumb SWAG (scientific wild ass guess), about 75 to 130 watts of panel for every 100 AH of house battery, or about one watt per AH that you have. Nothing substitutes for knowing your actual needs or wants (not necessarily the same thing). Know the actual measured loads and do the math.

After 1 year of service (and maybe not even then), it is NOT advisable to enlarge a battery bank by adding new batteries to it, because a batteries voltage response changes with age. Internal resistance changes causing losses and failure to equalize. A weak cell will "steal" from the surrounding cells. The battery “chain” is only as strong as its weakest link).

Solar if it is the primary energy source, should be sized to produce more energy than the load requires, that stormy day, shady camp site, solar charging battery loss thing.

Buy high-quality batteries, you get what you pay for. Good deep-cycle batteries can be expected to last for 5 to 15 years, and sometimes more particularly with proper care and feeding. Cheap batteries can fail in half that time, and good batteries can fail with poor care and feeding. 6V batteries are not better than a good quality 12V (but may be easier to lift).

The ideal battery bank is the simplest, consisting of a single series of cells that are sized for the job. Fewer cells will reduce the chance of defects (parts left out don’t go wrong).
According to the Concord/Lifeline battery company based on their research you can mix battery sizes but not age and type i.e. AGM to AGM is OK AGM to Wet Cell is not, (lower internal resistance in AGM).

When wiring a battery bank the goal is to maintain all of the cells at an equal state of charge. Cells that receive less charge are likely to fail prematurely. This can take years off of the life of the battery bank. A fraction of an ohm of added resistance in one battery string can reduce the life of the entire string.

(1) Connect the two main cables to opposite corners of the battery bank, and maintain symmetry in wire size and lengths. This will help to distribute current evenly through the bank.
2) Arrange batteries to maintain even temperature distribution throughout the bank. Avoid uneven exposure to heat sources. Leave at least 1/2 inch of air space around each battery, to promote even cooling.
(3) Apply a finish charge at least every 3 weeks (bring every cell to 100% charge).

Use temperature compensation
When batteries are cold, they require an increase in the charge voltage limit, in order to reach full charge. When they are warm, they require a reduction in the voltage limit in order to prevent overcharge.
Bring the batteries to a full state-of-charge (SOC) at least every 3 weeks. This reduces internal corrosion and degradation, and helps to insure equalization, so that any weaker cells do not fall continually farther behind.

Install a System Monitor
Would you drive a car with no dashboard? Metering is not just "bells and whistles". It is necessary to help you to read the status of the system. Many charge controllers have indicator lights and readouts built-in. Their effectiveness for the most part very from creating false security with essentially meaningless ‘idiot lights’ to it gives “some” idea of what is happening. They are not a substitute for a system that actually measures what goes into and comes out of your battery(s) using a shunt. Two well respected systems Victron http://www.victronenergy.com/battery-monitor and the Trimetric from http://www.bogartengineering.com

brholt wrote:
How long do you batteries last now? Knowing that it would be easier to estimate.

We find camping that a 150 watt panel often will not keep up in winter for us. The problems seem to be:

1) It's cold out in winter and the furnace uses significant power.
2) The batteries are cold so less current available.
3) when it's sunny the sun is still low and the daylight hours are short so we don't get near the solar contribution we get in summer
4) being in the PNW we are cloudy a lot and often in forests which restricts sunlight even more.

You will still get hurt by 2 and 3, and it sounds like 4 isn't a problem. The real wild card is 1, how much heating you do. (I am assuming you have LED lights, otherwise the lighting draw may be more than you think)

I only sometimes turn on heat to take chill out, runs about 10mins.
I am in the PSW sun is really not a problem :)
No LED's but like I said, really don't use the lights, maybe 15mins at night.

How long do you batteries last now? Knowing that it would be easier to estimate.

We find camping that a 150 watt panel often will not keep up in winter for us. The problems seem to be:

1) It's cold out in winter and the furnace uses significant power.
2) The batteries are cold so less current available.
3) when it's sunny the sun is still low and the daylight hours are short so we don't get near the solar contribution we get in summer
4) being in the PNW we are cloudy a lot and often in forests which restricts sunlight even more.

You will still get hurt by 2 and 3, and it sounds like 4 isn't a problem. The real wild card is 1, how much heating you do. (I am assuming you have LED lights, otherwise the lighting draw may be more than you think)

Well, if the 55W "can't quite" keep up, and you're more than doubling your solar capacity, I would hazard a guess that you are good to go.

Worst case you can add the 55W panel back in by changing your solar controller.

You've got nothing to lose, and everything to gain, by trying with the 120W panel. You can't add the 55W or any other panel in without spending money on a new controller anyway. If you don't need it, you're money ahead.

My understanding is that the furnace fan can suck some power. The water heater can be run on propane so I don't see that being a drain unless you purposely want the WH to run on electric. I think a lot of folks in your position look for more efficient room heaters so that the furnace isn't running as much. Doubling your solar with the 120W certainly will make things twice as nice as you have it now at a minimum.