Question Mixing Solar and Shore Power - Time vs. State of Charge?

[Neal]

I'm at a CG for two months and long term stay pays for power usage. As I have a good solar setup (1800W) on the roof I'm going to blend solar. My dilemma is do I set solar to only be used during the solar time of the day, I'm going to have solar come on at 9 AM and go off at 5 PM, or should I set AC to come on only when the batteries are below a certain percentage (State of Charge) such as 50-60%?

By telling the system to use solar in a time window the batteries will likely stay at or near 100% SOC.

By setting the shore power to only take over when the batteries get below a certain level such as 50-60% I'll use less shore power as I may be able to remain on batteries until the next solar period but the batteries will drain to a much lower level such as overnight.

Are batteries better off being at or near full charge all of the time or is it good for batteries to let them cycle to 50/60% and then go back to full charge daily?

Batteries are meant to be used so I have no problem if this shortens the lifetime slightly but what is the preferred handling of battery charge? What do you suggest for solar use in a long term campground setup such as this where you're paying for shore power yet you have solar?

 

[Chuggs]

The easiest method with the ME-ARC is to use CC/CV mode. One of the settings is the "Rebulk" voltage. The other methods would be to set AC-IN to a SOC.

Ideally, you experiment with the two methods. Most of these parks have a meter on the pedastle, so you can see exactly what your kWh usage is each day using the varying methods.

Yes, deeper cycles on the batteries are paid back on shorter life expectancy...but the math of computing which is more economical... utility charges vs battery replacement is difficult to quantify. You can study battery cycle curves based on Depth of Discharge...to see what if you can quantify the amount by which your battery life is reduced.

I would leave solar on all the time. Anything it produces is free.

If you leave your battery type in Lead acid/AGM 1 or 2/or Custom...you will be using more utility power. The batteries stay in a co continuous float. When solar starts up with sunrise, little will be accomplished. Letting the other methods use some battery overnight will save utility power...and if you balance your requirements...the Solar will provide more of the power. If the Magnum goes into bulk charge...solar may cut out completely...so the AC-IN or using CC/CV with a lower rebulk voltage will prevent this.

I have noticed the Magnum wakes up alot of times following shore power interruptions in Bulk charge mode. If you notice this...you can go into control, and where it says Multi...dial in Start Float. This will cause the charger to cut back to Float or Silent depending on the mode you've set.

Lead acid chemistry does need to be cycled to full charge to redissolve sulfates...this will help extend the life of the batteries. LiFePO4 do not need a full charge like that...but may need it occasionally if the BMS uses top balance method vs bottom balance method.

 

[Neal]

Thanks, I'll give the SOC connect a try and get the most out of solar + battery to avoid shore power for inverter source.

 

[Neal]

I've decided to use TIME CONNECT (solar use between a start and stop time) as using solar based on state of charge puts you in conserve mode. With home theater, home office, under glow by morning if I used the coffee pot it would hit LBCO with the voltage spike. Not how I want to do this for two months. I want to use solar to offset costs and electricity use/waste so the time connect will be the good balance providing the inverter demand during daylight hours.

 

[Chuggs]

You can just set SOC to a higher number for AC-IN...

It almost doesn't really make such a difference that it would make it worthwhile. When I dry camped at FMCA rally...I probably produced 6 kWh on a good day. At a utility rate of .105 /kWh...your not saving much more than .63 per day. It would take a week to save enough for a Starbucks coffee...

Solar earns it's stripes when dry camping...no shore utilities to be had...and generator cost per kWh is higher and comes with the added noise penalty. Or when trying to squeeze in a few more amps to run two 15kbtu a/c's off a 30 amp outlet. I've never been on metered electric...where you pay for kWh used...but I don't think I would be very aggressive on my batteries in order to save a few bucks. If you kept the SOC cycling between 80% and 95%...you could balance the savings with less chance of LBCO triggers during a spike...and putting more cycles on the batteries...while still saving a couple of bucks.

 

[Neal]

Good point. I just want to put those hard earned solar dollars to work but it's probably futile. I'll see how time connect works out simply to get some use out of it but may just abandon this and stay on shore power.

 

[Jim]

LOL, RV's (Class A especially) are a funny bunch, myself included. Not an issue to drop $200K on a motor home, cover the costs of insurance, storing, maintenance, etc. And then try to save $3.00 on electricity.

 

[Chuggs]

LOL, RV's (Class A especially) are a funny bunch, myself included. Not an issue to drop $200K on a motor home, cover the costs of insurance, storing, maintenance, etc. And then try to save $3.00 on electricity.

I held off making the same remark...I knew someone had to say it...

It's just too hard not to...

Somethings, however...are just worth the academic exercise. I am the same way. The things we kids will do for brain stimulation...

 

[Neal]

The flip side is you paid $5K for your solar setup you sweated through installing and now you want to use it every chance you can. If I can save some electricity usage to simply avoid waste in a hugely sunny area such as I'm staying now then it sure seems like all homes in the area could save the power generation if we all did this. Yeah, save some money too but again, I have the "stuff" on the roof I sure would like to use it. I turned off solar but I'm itching to use it as it's so dang sunny here right now!!! But the down side is the power is not as clean/pure than being on shore power and that's the reason I'm really opting out.

 

[Chuggs]

Just pull anchor and head back out to BLM land...

The solar will produce the power, and the savings will be the lack of monthly resort fees. Of course, you have to get inventive if you want to play pickleball.