How big of a battery do I need for a 160 Watt solar panel?

[poot_traveller]

I understand I need a deep cycle 12V battery. And I also understand that a battery shouldn't be used below 50% power. 

If I get one too big I might not be able to charge it up much past the 50% power mark, I might be only able to charge it to 60% then only have 10% use of it.

My question is; how big of a battery do I need for a 160 Watt solar panel?

 

[MrNoodly]

A 1-to-1 Watts-to-Amp Hour ratio is about the maximum, with more wattage being preferred. As an example, I have a 270W panel feeding 208AH of batteries.

 

[Natgreen]

100ah would be a solid battery for that. You 1to 1 is a good general rule but it's good to have more wattage because you won't be in peak sun conditions all the time

 

[regis101]

Do you mean to say 1:1 is the min ?

 

[B and C]

This really needs to be approached from the opposite end. How much electricity do you plan on using each day? Everything else is based on this. It is called a power budget since you are now the power company, you need to figure out how much you need. All of your devices will say how much power they draw. Multiply this times the number of hours each day you plan on using them and then add them all together. This will tell you how big your battery needs to be and that will dictate how much solar you need. There needs to be some padding of the numbers to account for those days that don't produce much solar energy too. That being said, it is cheaper to cut back on your power requirements.

 

[highdesertranger]

yes you are figuring this all wrong, start with,

1. figure out your daily usage
2. select your battery bank to according to number 1
3. select your solar panels according to number 2

10 years ago 1 to 1 solar to amp hours was the minimum recommendation, now a days 2 watts to 1Ah is considered the minimum starting point. this is one area where more is better, as in more solar.

poot you really need to brush up on how this all works. if you only charge your battery to 60% your battery will have a very short life.

highdesertranger

 

[tx2sturgis]

Now and then, sometimes the budget and/or existing hardware can define the route we take in sizing our system.

Poot, if you already have the 160w panel and need to buy a battery and solar controller, I think a 80-100ah AGM battery would be a good choice.

I would not go much above 100ah rating, unless you have alternate charging sources, such as a generator or shore power hookup, or a tie-in with the vehicle alternator.

With this setup you should have enough power for modest uses: Charging a phone and laptop, running a few LED lights, maybe a radio and a hotspot or wifi booster. In other words, small electronic devices. You will not have enough power to run power-hungry items like a microwave oven, or an induction cooktop.

You might end up with enough energy to power a small 12v fridge, but only in mild (but sunny) climates and limiting the other items to a few hours a day.

 

[B and C]

limiting your power usage to the available power is an option. As TX2 says, this will work, you will just need to keep an eye on battery charge level. It is cheaper to conserve energy, whether it will fit your needs is another story.

 

[lenny flank]

A 1-to-1 Watts-to-Amp Hour ratio is about the maximum, with more wattage being preferred. As an example, I have a 270W panel feeding 208AH of batteries.

Minimum. 

Ideally, you'd want probably twice as much panel, to cover periods when there's not as much sun. Me, I have a 100w panel and 100ah battery, but my needs are minimal and I don't use more than maybe 10-15% of the battery, so I don't have any trouble recharging each day.

But the real calculation that matters is how much power you actually plan to use. THAT is what determines how much battery bank you need, and in turn how much panel you need to charge it.

 

[jonyjoe303]

The bigger the better, just keep the bulk / float voltage above 14 volts all the time. The reason a big battery is better is there are times when a smaller battery will be quickly charged up and then you will be wasting available sunny weather doing nothing. Bigger battery fully charged will last you several days during cloudy conditions, a small battery will barely make it a day. 

160 watts will get you about 8 amps of power when the sun is overhead. If you use alot of power, you will always struggle to fully charge a lead acid on solar no matter how big or small the battery is, thats why I recommend to keep the float at 14.4 volts all day long. The sun will go down before you ever fully charge it (absorb for several hours at 14.4 volts).  Only if you plan to store the battery for months connected to a trickle charger is when you float under 14 volts.

 

[tx2sturgis]

The bigger the better, just keep the bulk / float voltage above 14 volts all the time. The reason a big battery is better is there are times when a smaller battery will be quickly charged up and then you will be wasting available sunny weather doing nothing. 

If the OP is using surplus solar power to operate devices and loads such as laptops and internet hotspots then the sunlight is not 'doing nothing'...

Once the battery is fully charged (or approaching fully charged) that surplus energy can be used to recharge mobile battery packs, laptops, smartphones, etc...and the battery that is fully charged will not begin to be used (drawn from)  until the available solar energy is gone with late evening and nightfall.
 
I agree that bigger batteries are fine, IF (as I stated above) the OP has an additional way to charge them. 

Larger battery banks that are being charged by limited solar (only) will take much longer approaching and staying above 14 volts if those batteries were deeply discharged the previous night.

 

[poot_traveller]

A 1-to-1 Watts-to-Amp Hour ratio is about the maximum, with more wattage being preferred. As an example, I have a 270W panel feeding 208AH of batteries.

I had my eye on a 120AH battery for my 160 Watt solar panel.  Do you think that would be fine?

 

[poot_traveller]

100ah would be a solid battery for that. You 1to 1 is a good general rule but it's good to have more wattage because you won't be in peak sun conditions all the time

What about a 120AH battery?  I've been advised to buy a certain brand of battery (Century) and this particular brand doesn't sell 100AH batteries, the next closest size is 120AH.

 

[poot_traveller]

yes you are figuring this all wrong,  start with,

1.  figure out your daily usage
2.  select your battery bank to according to number 1
3.  select your solar panels according to number 2

10 years ago 1 to 1 solar to amp hours was the minimum recommendation,  now a days 2 watts to 1Ah is considered the minimum starting point. this is one area where more is better,  as in more solar.

poot you really need to brush up on how this all works.  if you only charge your battery to 60% your battery will have a very short life.

highdesertranger

I've already purchased the solar panel and according to my calculations, it is the size I need for my daily power usage *touch wood*

I just need the right size battery so the battery and the solar panel play nice with each other. 

Yes I do need to brush up on how this all works, but I originally thought a deep cycle battery was a deep cycle battery and all I had to do is buy a big bad ass battery. But then it dawned on me I might need a particular size.  I'm hoping a 120AH battery will go well with the solar panel.

 

[maki2]

I only have enough roof space for one 160watt panel. I do have an AGM 160amp deep cycle battery. So therefore I take along a small 1000 watt generator as a backup power source.

Eventually when I have the funds I will add a portable solar panel for a second source because some days I will need more panel area if it is overcast and some days I might want to park in the shade and put the portable panel in the sun. I have already added a plug port through the side of my trailer for that someday portable panel acquisition as part of my build.

 

[poot_traveller]

The bigger the better, just keep the bulk / float voltage above 14 volts all the time. The reason a big battery is better is there are times when a smaller battery will be quickly charged up and then you will be wasting available sunny weather doing nothing. Bigger battery fully charged will last you several days during cloudy conditions, a small battery will barely make it a day. 

160 watts will get you about 8 amps of power when the sun is overhead. If you use alot of power, you will always struggle to fully charge a lead acid on solar no matter how big or small the battery is, thats why I recommend to keep the float at 14.4 volts all day long. The sun will go down before you ever fully charge it (absorb for several hours at 14.4 volts).  Only if you plan to store the battery for months connected to a trickle charger is when you float under 14 volts.

I'm going to have a 12V battery. Could you please explain what you mean by "keep the float at 4.4 volts all day long"?.  Sorry for my lack of understanding.

 

[poot_traveller]

I only have enough roof space for one 160watt panel. I do have an AGM 160amp deep cycle battery. So therefore I take along a small 1000 watt generator as a backup power source.

Eventually when I have the funds I will add a portable solar panel for a second source because some days I will need more panel area if it is overcast and some days I might want to park in the shade and put the portable panel in the sun. I have already added a plug port through the side of my trailer for that someday portable panel acquisition as part of my build.

And the panel can charge up the battery just fine?

 

[maki2]

And the panel can charge up the battery just fine?

Sure, even a 50 watt panel can charge up a large battery given enough time.

The issue is not can the source of electrical coming in get a charge put into the battery. The issue is will you drain the battery down faster than it is getting charged? People keep telling you this in comments. You need to wrap your head around the concept. It is like a water faucet, low water pressure with a small trickle will still get a drinking glass or even a swimming pool filled but it will just take longer than if you had really high water pressure with a strong stream of water.  If you only have a small glass you will quickly use up the water if you drink faster than it is getting filled. If you have a swimming pool sized container it will last quite a while even if you are drinking faster than it is getting filled but eventually it will get empty because speed of input is less than your out take. When that happens you either have to slow down your drinking or find a secondary water source to fill the container.

You need to remember that you must adapt your lifestyle to what you have for resources or else you have to adapt your power resources to meet your needs. There is no magic bullet here, it is just basic math. Power coming in and the storage capacity should always be able to exceed your draw on the battery bank. If you don't have the ability to have enough panels to meet that power need then you have to figure out what must change and maybe that means an alternative source of power or maybe it means changing your everyday lifestyle to reduce the need for power.

 

[B and C]

^^^Well said

 

[Mrcap]

...but a 160w panel would be commonly be matched with around a 100ah battery.


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