LP Fridge for Off Grid Application

Re: LP Fridge for Off Grid Application

One way to cycle your batteries that may save you a bunch of fuel costs... Cycle them from 50% to 80% or so every (per cycle)... and let that happen for 5-10 days. On the 6th to 11th day, run enough power in the battery bank to get it back >90% state of charge.

The batteries are more efficient when cycled below 80% SOC (and much more efficient than>90% SOC cycling). And, from what I have read, with good quality flooded cell (i.e., heavy plate, forklift, traction type cells), they will not sulfate as long as they are actively cycling and brought back >90% state of charge once in a while... You might just pick one day a week (or weekend) to do the recharge >90% thing.

And I would study the generator power/current and see what you can do to keep it in the ~50% to 80% range of name plate rating (or prime mover rating maximum).

If you are running the genset at 25% or less of rated power--You should try to do something different.

Good luck on the surgery--Sounds like it has been a tough year for you (and your family) so far.

-Bill

Re: LP Fridge for Off Grid Application

backroad wrote: »

I'm told the the generator is only efficient when charging up to 80% or a little higher.I'm to understand that the rest of the charging needs to come from PV to be efficient.

If this was me... 50% or over for a "standard" genset is fuel efficient... The <80% or so was a derating for "consumer" type generators. Battery chargers that can be programmed to run at near 100% name plate for a consumer type generator--Will probably overheat the alternator head/wiring (anything more than 5-30 minutes or so). Derating to ~75-80% of Watts (really VA) rating of genset is just to acknowledge that only a prime mover rated genset can probably operated (reliably) at near 100% of rated output. Chris Olson has used a number of smaller gensets and finds that many cannot even supply name plate for a very short period of time (not trying to put words in Chris' mouth--just my memory from other posts of his).

If my autonomy is just over a day, am I correct to understand that I can only gain autonomy from a larger storage? I have tried to bring the battery up to 80-90 % in the morning and let the panels "top" the battery off which does not happen.

You can run 50-80% daily cycling with recharging to >90% state of charge every 5-10 days or so for true deep cycle batteries. Charging 80% and especially >90% SOC is not very efficient (or fast).

If the panels are not charging the battery bank as expected (watt array*0.77 derate*1/Vbatt-charging=Amps), then we need to look at the each section of the system.

Is the array voltage/current as expected (Vmp-array, Imp-array)? Is the charge controller in MPPT (maximum current mode) when the battery needs the current? What are the settings for the charge controller (absorb voltage, float voltage, absorb time, charge termination current, etc.)? What is the battery bank voltage (Vabsorb ~59-60 volts for 2-4 hours per day)? Etc.

I do understand that more panels will enable me to top off the battery with other that the generator. Now then, what happens on that particularly cloudy/stormy when the batteries go down and and the generator is not running?

Use the generator directly to power periods of heavy loads (cooking, shop, cleaning). For example, just use the genset to keep the battery bank in the 50-80% range during the week, and fully charge the batteries >90% on Saturday or Sunday.

At his point I believe that the only way to gain autonomy would be conservation, get rid of something that uses enough power, or a larger battery bank.

From earlier posts/discussions--I am not sure I understand your power needs. They seemed to be on the high side (or the generator/solar array was terribly inefficient).

A nice Battery Monitor (Victron is another good brand) can be a good help to understand what you doing to the battery bank (charging, discharging, etc.). With the understanding that you still use the hydrometer as the "gold standard" for estimating battery state of charge (Battery Monitors need programming and can be confused in some cases, and/or drift over time).

A Watt*Hour meter on the genset (there are lots of used utility meters on Ebay--Or here new). If you can, also keep track of fuel use... If you are >>5kWH per gallon of diesel, your genset is being operated efficiently. If you are <<3kWH per gallon, you might be able to "do better" (just some rough guesswork numbers).

I don't see enough conservation happening to make enough difference and with the battery being over two years old I'd really need to replace the battery already in use which would be about $6500 plus another $6500 to upgrade from the "old" battery totaling $13,000. I can"t see that happening. I truly hope that I'm missing something in all this as the only realistic way for me to increase my autonomy would be going back to the idea of the propane refrigerator. This is being a a troubling little circle.

I don't think a propane fridge should make much difference at all... Put a kill-a-Watt type meter on the fridge and see what it is using every day. Even a "poor" fridge at 2kWH per day would use:

2,000 WH per day * 1/0.85 inverter eff * 1/48 volts = 49 @ 48 volts per 24 hour day

That is "round off error" for your battery bank.

THANX from confused again.........................

Start from the basics. Put the battery in the middle and make sure it is running "OK" (specific gravity in the range you need).

Then look at one part of your system. Say loads... Figure out how much you are using per day (AH/kWH/WH, etc.).

Then look at each power source. For example, is the Solar array + charge controller outputting the expected output on a sunny day:

3,100 Watts * 0.77 panel+controller derating * 6+ hours for sunny summer day = 14,322 Watt*Hours per day (from MPPT controllers)
14,322 WH / 48 volt battery bank = 289 AH @ 48 volts useful power from solar array
3,100 Watts * 0.52 system derating * 6 hours of sun per day = 9,672 Watt*Hours of "useful" AC power into your loads per day

If your solar panels are not doing the above--Then either your bank is full (battery+loads do not accept maximum available power), or there is probably something "not right" with the solar power subsection of your power system.

After you get the loads + Solar Power straightened out, then we can talk about genset+AC charger. You have to understand a piece at time. For the most part, the loads+Inverter vs the Charging system do not really interact with each other (other than as battery state of charge).

-Bill