Battery capacity

AJMike · 01-04-2019, 08:23 AM

I was reading the beginning of Mobile Solar Power Made Easy and it contained the following statement:

For every 100 watts of solar panels you have on your roof, you should have around 75-100 amp hours of sealed lead acid battery.

My Fuse came from the factory with 2 type 24 NAPA lead acid batteries and 2 100 watt flexible solar panels on the roof. I had just ordered a 3rd panel to add when I saw that statement and wondered if the batteries had enough capacity to make adding a 3rd panel a practical thing to do. Based on the statement they would need to have 225-300 amp hours capacity. Do they? Or am I wasting my time and money for these batteries? Or is the statement incorrect? I understand that AGM batteries would probably be better, but I was planning to wait until I needed to replace these batteries.

BobC · 01-04-2019, 09:45 AM

It's not an issue of necessity, it's just that your panels may be capable of charging more battery capacity than you have.

You may be "wasting" some of your added solar power in ideal conditions, but, in less than ideal conditions, your existing batteries will charge more quickly which will be a big improvement. At some point you'll be replacing your batteries anyway.

When you do so, I'd recommend two 6V golf cart batteries in series, something else to research.

I don't see any real downside of doing it now other than the cost of the panel may drop a bit in the future.

AJMike · 01-04-2019, 01:59 PM

Quote:

Originally Posted by BobC

It's not an issue of necessity, it's just that your panels may be capable of charging more battery capacity than you have.

You may be "wasting" some of your added solar power in ideal conditions, but, in less than ideal conditions, your existing batteries will charge more quickly which will be a big improvement. At some point you'll be replacing your batteries anyway.

When you do so, I'd recommend two 6V golf cart batteries in series, something else to research.

I don't see any real downside of doing it now other than the cost of the panel may drop a bit in the future.

The panel and all of the stuff I need for the installation is due in sometime next week and I was wondering if I should just return them to Amazon, but you are surely right and I will be better prepared for the AGM batteries when I replace our current wet cells. I assume the solar controller that came installed on our Winnebago Fuse will only supply what are batteries need and so it will not hurt anything. And I got a great price on the solar panel.

cj_calva · 01-04-2019, 02:55 PM

Hi!
Here you find a battery charger calculator: Battery Charge Time Calculator

Let's say that a roof installation goes up to an efficiency of 80% in summer in Southern California.

With an additional panel you charge the actual battery capacity faster.
With additional batteries you can stay longer with the same devices or you can use more devices for the same time.

So you see it's not really necessary that you install additional batteries. The amount of installated battery capacity shows you how long you can use a certain need of power.

So this need of power is that what you have to ask yourself first before you spend money in additional equipment.

You can also use the direct power from the solar panel. So perhaps you can have your espresso only when the sun is shining. But if this is ok for you, due the fact that you take your espresso always after lunch on a sunny day, you do not have to install extra battery capacity for the espresso machine.

Knowing that moving the vehicle or being connected to an electrical hook-up charges your batteries too. And there are certain other limits like the water supply (that's our "limit"). An empty fresh-water tank and full grey/blackwater tanks let you move your RV too and you charge the batteries with that. So having a battery capacity for 7 days is too much if your tanks are full after 3 days.

Concerning AGM batteries: certainly they are better due they have a long life and are not sensible concerning vibrations etc. You should not use different types of batteries.
If you add one or two batteries and don't need really much more capacity I recommend the same type that you already have built in. Also those batteries can fulfill your needs up to 10 years.

powercat_ras · 01-04-2019, 03:50 PM

In particular if you are flat mounting panels on the roof of the RV, so they are not tilted and turned to maximize their sun exposure, then solar panels put out less than their rated output and I suggest to up that formula. Also there is less daylight between October and March and the sun sits lower in the sky, further reducing daily output. Personally I have 400 amp-hours of golf cart batteries, 600 watts of flat mounted solar panels, and a MPPT solar charge controller. That seems to work out about right for me.

On a Fuse I would suggest starting with 300 watts solar panels, a MPPT charge controller, and 2 $ 80 Costo 6 volt golf cart batteries, for 200 amp-hours storage, with 100 amp-hours actually usable if you want to make the batteries last about 3-4 years if you do boondocking.

AJMike · 01-04-2019, 05:54 PM

Quote:

Originally Posted by powercat_ras

In particular if you are flat mounting panels on the roof of the RV, so they are not tilted and turned to maximize their sun exposure, then solar panels put out less than their rated output and I suggest to up that formula. Also there is less daylight between October and March and the sun sits lower in the sky, further reducing daily output. Personally I have 400 amp-hours of golf cart batteries, 600 watts of flat mounted solar panels, and a MPPT solar charge controller. That seems to work out about right for me.

On a Fuse I would suggest starting with 300 watts solar panels, a MPPT charge controller, and 2 $ 80 Costo 6 volt golf cart batteries, for 200 amp-hours storage, with 100 amp-hours actually usable if you want to make the batteries last about 3-4 years if you do boondocking.

The current wet cell batteries that we have are rated at 120 amp-hours each so it seems to me that they provide more power reserve than 2 golf cart batteries, but then perhaps I do not understand battery usage well enough. I planned to use these until they died which, in the Arizona heat, may not be all that long, and then replace them with either AGM or lithium batteries, provided I can match the physical size. There is not much room for batteries in our RV and there is no place for extra batteries unless I use some of our limited storage.

BobC · 01-04-2019, 07:50 PM

Rather than re-create a discussion on various battery choices, I suggest you research previous threads on the topic. As you've surmised, there's no need to replace your current batteries unless they're failing or otherwise not meeting your needs.

Most likely your 12V batteries are the "marine" type batteries which are hybrid starting/"deep cycle" batteries. Golf cart batteries are true deep cycle batteries, are more robust and will perform better in the long run. If your battery specs list cold cranking amps (CCA) they definitely are such a hybrid.

There are also "true deep cycle" 12V batteries. Either these or golf cart batteries are going to be a better choice than your current batteries.

powercat_ras · 01-04-2019, 07:54 PM

You said you have OEM Winnebago NAPA Batteries. The 120 you saw is another parameter: Battery Reserve Capacity (minutes). This divided by 2.4 is Amp-Hours. == They are ONLY 50 Amp-Hours each.

They are NOT designed for true deep cycle operation. Golf Cart batteries are. Why does Winnebago use them? They are the cheapest batteries they can get and for most RVers who that camp plugged into shore power they work OK.

Assuming you can fit two golf cart batteries where the 2 NAPA batteries are (they are taller so make sure you can handle their height) you can DOUBLE your storage for about $ 160.

Li batteries like Battle Born are great, too if you have $ 1,000 laying around to spend.

rarebear.nm · 01-04-2019, 08:21 PM

Total wattage of the panels does not always match the power delivered to the batteries. Solar controllers have a maximum wattage they'll accept from the panels. My MPPT Morningstar 65 limits itself to 800 watts. So if my 1050 watt panel array produces say 900 watts, only 800 watts will even enter the controller. The advantage in over configuring the panel output is that if panels are set flat or a panel is shaded (assuming parallel connections) I still see perhaps 400 to 600 watts usable. Plenty to meet our needs.

Cost of some panels alone seem to be under $0.50/watt. I've seen one panel with costs at $0.25/watt. With these low prices there's little reason not to max out your roof space. Present tariffs drive solar costs higher at least for the short term.

AJMike · 01-05-2019, 05:42 AM

Quote:

Originally Posted by rarebear.nm

Cost of some panels alone seem to be under $0.50/watt. I've seen one panel with costs at $0.25/watt. With these low prices there's little reason not to max out your roof space. Present tariffs drive solar costs higher at least for the short term.

While I do not wish to spend any more than I have to, I had two other considerations in mind when I chose which flex panels to use. First, I wanted to buy panels that would not fail and I have seen posts on these forums about cheap flex panels that failed quickly and, second, I wanted the installation to look as professional as possible and that meant installing the same type of panel that came from the factory. Since Winnebago used SunPower flex panels I decided to use them as well.

One 100 watt panel cost me $218, so that is more than $2.00/watt, but in truth I never saw a panel that cost less than about $1.25/watt and most were $1.70/watt so $2.18/watt did not seem like much more. All of the reviews of the SunPower panels were positive and it seemed like the cheapest way to go in the long run. Only experience will tell me if I chose correctly or not.

WinnieView · 01-05-2019, 07:55 AM

We bought the Renogy 200 watt RV kit, and replaced our two type 24 lead acid batteries two days ago with the 6 volt GC batteries from Costco. They were about $200 out the door with cores and fit into the existing battery tray. We will need to use different 'hold down brackets' such as tie down straps.
Our solar goes on next week before our first trip to Bartlett.

rarebear.nm · 01-05-2019, 01:48 PM

Quote:

Originally Posted by AJMike

While I do not wish to spend any more than I have to, I had two other considerations in mind when I chose which flex panels to use. First, I wanted to buy panels that would not fail and I have seen posts on these forums about cheap flex panels that failed quickly and, second, I wanted the installation to look as professional as possible and that meant installing the same type of panel that came from the factory. Since Winnebago used SunPower flex panels I decided to use them as well.

One 100 watt panel cost me $218, so that is more than $2.00/watt, but in truth I never saw a panel that cost less than about $1.25/watt and most were $1.70/watt so $2.18/watt did not seem like much more. All of the reviews of the SunPower panels were positive and it seemed like the cheapest way to go in the long run. Only experience will tell me if I chose correctly or not.

My cost per watt was for standard rigid panels. Bluesun has a 500 watt panel for $0.25 to $0.36/watt. These are larger sized panels (like 72 cell) and will not fit every application.

If you want flex panels then Sunpower does make some of the best on the market. Suggest you look for panels with ETFE coating and not PET coating. Big difference in expected life span and cost. At $2.18/watt I'd "guess" they are ETFE coated. Check the warranty.

AJMike · 01-05-2019, 03:51 PM

Quote:

Originally Posted by rarebear.nm

My cost per watt was for standard rigid panels. Bluesun has a 500 watt panel for $0.25 to $0.36/watt. These are larger sized panels (like 72 cell) and will not fit every application.

If you want flex panels then Sunpower does make some of the best on the market. Suggest you look for panels with ETFE coating and not PET coating. Big difference in expected life span and cost. At $2.18/watt I'd "guess" they are ETFE coated. Check the warranty.

I was not looking at anything bigger than 100 or 110 watts so I never noticed the much lower per watt cost of the larger panels. I was only looking at flex panels and I do not think they come in larger sizes than 170 watts.

Ret.LEO · 01-09-2019, 04:32 PM

Other things to consider. If you take a wet cell battery below 50% you have hurt it. Golf Cart batteries the same way along with AGM's
AGM's are a good budget friendly solution plus they can be installed anywhere.....no fumes.
Lithium is the very best but expensive initially. BUT they can be drained safely to 10% with no harm, can be recharged for 3,000-5,000 times. It does seem finally Lithiums are coming down some.

rarebear.nm · 01-09-2019, 05:01 PM

Quote:

Originally Posted by Ret.LEO

Other things to consider. If you take a wet cell battery below 50% you have hurt it. Golf Cart batteries the same way along with AGM's
AGM's are a good budget friendly solution plus they can be installed anywhere.....no fumes.
Lithium is the very best but expensive initially. BUT they can be drained safely to 10% with no harm, can be recharged for 3,000-5,000 times. It does seem finally Lithiums are coming down some.

I think Lithium batteries are very good in many conditions. But you should be aware of the recharge temperature limits. Discharge and recharge temperatures are not always equal for any one type of battery and between different types.

Lead acid: Discharge range (-4 to 122F) Recharge range (-4 to 122F)

Lithium Ion: Discharge range (-4 to 140F) Recharge range ( 32 to 113F)

Whereas the discharge range fits with most RV use the lower recharge limit of lithium is 32F. This may or may not be an issue depending on RV construction and location where its used and stored. I'm not trying to argue for or against any battery type, just be aware.

Source:

https://batteryuniversity.com/learn/...w_temperatures