Battery watts vs solar panels watts???? - Ram Promaster Forum
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post #1 of 9 Old 06-14-2019, 02:51 PM Thread Starter
Oso
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Battery watts vs solar panels watts????

How much or many will a lithium 100 watt battery will hold from a 100 or 160 watt solar flex panel? Or do I need 2 100 battery’s for a 160 panel? What does this equal into amps??
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post #2 of 9 Old 06-14-2019, 03:25 PM
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I would suggest learning some basic concepts about DC electrical systems then coming back and asking questions. There are tons of videos on YouTube that can bring you up to speed.
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post #3 of 9 Old 06-14-2019, 04:24 PM
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Garage
Van electrical is a pretty big challenge to most folks, most will have to watch and read a lot before you come to have a safe understanding of it.

First, I am pretty sure you mean a 12v 100 amp lithium battery. Lithium is becoming more popular as the cost lowers and easier off the shelf chargers and other lithium friendly components are available. Lithium batteries can be charged quicker and you can take more of the energy out of them, i.e. a lower SOC (State of Charge, how much of the 100 amps is still available) than lead acid batteries (no more that 50% for their SOC).

Solar Panels are listed in watts since the voltage and amps you can have coming out is a function of how you hook them up.

So for my needs I have 200 amps of 12V lead acid batteries which I try to keep above 75% SOC or 150 amps. Since I have 200 WATTS of solar panels I can normally get them close to 100% SOC every sunny day.

So 100 amp lithium is pretty happy going down to 25% SOC or lower so if I had them I would be okay with running it down to 30% or 30 amps which meant I consumed 70 amps overnight, this is unlikely since I normally consume about 40 amps.

SO for me I would be okay with 100 amps 12v lithium battery with at least 160 watts of solar. This would allow me to run my fan all night or if it was cold my heater which cycles on and off all night (thermostat) and watch a DVD on my TV and charge my phone. I do have a "smart" switch which allows the engine to charge the battery if my usage is too high or it is cloudy, etc.

I would recommend taking a look at Faroutride website, they have good tips on all things for vans and a DIY guide for electrical.
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post #4 of 9 Old 06-14-2019, 05:51 PM
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post #5 of 9 Old 06-18-2019, 08:57 PM Thread Starter
Oso
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Still doesn’t answer my question..
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post #6 of 9 Old 06-18-2019, 09:11 PM
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Oso,

Your question doesn't make much sense. How much or many will a lithium 100 watt battery will hold from a 100 or 160 watt solar flex panel?
What is your 100 Watts battery? Watts = I (amps) x V (Volts) So if your battery is 100W, and 12V, your amps are less than 10 Amps!.
Your other question: Or do I need 2 100 battery’s for a 160 panel? I guess your implying 2 x 100 Amps batteries?
I suggest you watch some youtube about basic electricity so we can help you better.
Good luck!
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post #7 of 9 Old 06-18-2019, 11:14 PM
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Oso,

We assume your proposed lithium battery is 100 amp-hours (implying it will deliver 100 amps for an hour). This is pretty common for drop-in lithium batteries.

100 amp-hours is equivalent to approximately 1,300 watt-hours (implying you can put a 100 watt appliance on it for 13 hours or, at the other extreme, a 1300 watt appliance for 1 hour - - or any combination of watts x time (hours) that equals 1300 watt-hours).

If you use a 100 watt solar panel, the most that it will 'output' is 100 watts. But it will only do this under the best of conditions - - mainly, that the sun is directly overhead. The sun doesn't stand still. It moves across the sky and, even at noon, will not be directly overhead unless you happen to be parked on the Tropic of Cancer on June 21st.

So here are some of our experiences (we have 800 watts of solar, but will work our numbers out assuming we have just 100 watts).

The most we've ever 'collected' is 560 watt-hours of energy in a single day for a 100 watt solar panel. If you have a completely discharged a 100 amp-hour lithium battery (1300 watt-hours), it will take you over TWO PERFECT DAYS to recharge your battery. Thus, easily, you could attach 200 watts of solar (or more, since, again, you rarely get 560 watt-hours/day from a 100 watt solar panel). In fact, you could use 300 watts of solar.

Most people on this forum suggest working from another angle. They suggest deciding/determining what your power requirements will be . . . what appliances do you intend on running . . . then spec solar panels, if possible, to meet that requirement. LED lighting draws little power, a compressor refrigerator is good, but can draw more power - - we probably use 750 watt-hours/day on our refrigerator. Thus, a single 100 amp-hour (1300 watt-hour) lithium battery can supply such a frig and any LED lighting you may have. But, if a 100 watt solar panel can only, in perfect conditions, provide 560 watt-hours/day . . . you'll need another source of charging (alternator or shore-power) to meet the difference. And we'd caution to assume something more like 250 watt-hours/day (rather than the perfect 560) for your 100 watt solar panel expectations. And even that won't be met if it's overcast or you choose to park under a tree.

Bottom line, go for 200-300 watts of solar . . . and don't rule-out alternator and shore-power alternative chargers.

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post #8 of 9 Old 06-19-2019, 06:30 AM
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Well said Winston.
So Oso, what do you have that uses amps? Have you figured how much amp/hours you need?
Energy storage is lead acid, glass mat, lithium, so there are limits in how much they hold, how much you can get out of them.
12, 24, 48 or 110 volts? How much do you need of each?
I'm figuring this out now as well, so much to consider. I just bought a 300w solar panel that produces 24v. What to do.....

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post #9 of 9 Old 06-19-2019, 11:07 AM
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Oso. What some folks here are trying to tell you is that you are not using the engineering terms in a way that makes sense. I would suggest looking up a primer on BEE. Basic electrical and electronics. I took a course on that in the Navy years ago and it made me dangerous enough to do my own car work successfully.

This is how they used to explain electricity to mechanics.
Voltage is the water pressure in the pipe.
Amps refers to the volume of flow of water thru the pipes.
A diode is a check valve.
There are other explanations like that and they can really help. When the power triangle was first explained to me it really opened my eyes.

A larger more powerful solar panel will charge a battery faster because it provides more amps at a given voltage. The battery can only hold what it is designed to hold. That is often expressed in amp hours. How many amps per hour at a given voltage can you withdraw from the battery before it requires recharging.

Even simpler is to think of the system as "Goesintos" and goesouttas". If the solar system is is putting amps into the faster then your loads withdraw them, then the goesintos are larger than the goesouttas. And that will keep the battery charged. And having enough battery to make it thru the night means you have enough battery. That depends on the loads you have put on it. Its all a balancing act. Some batteries will accept a charge faster than others, and that makes them more efficient. My new AGM golf cart batteries recharge faster than my old flooded cell batteries did.

I'm just touching on basics here. Hope it helps.

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