Newbie trying to understand Solar Math

[Candela]

Greetings Board Members,

For the last week, I have been reading a lot on solar panels and will like to see if I understand the Solar Math correctly.

Firstly, I want to build a 2000w Solar Generator and here is my plan according to my understang of it:

2x200ah (12v batteries) = will equal 4800wh capacity
I should never go under 50% charge, so I really have about 2400wh capacity
A 2500w invertor to accommodate the 2400wh and
2x200w solar panels @ 5 hours on a sunny day should recharge my batteries at least up to 2000w

Will this setup work and am I understand this correctly?

Sorry, but am totally new to this solar and electrical stuff


Please let me know if I have a correct understanding in the matter and am looking forward to reading/ learning from this forum and its members

Thanks in advance

[NEOH]

Greetings Board Members,

For the last week, I have been reading a lot on solar panels and will like to see if I understand the Solar Math correctly.

Firstly, I want to build a 2000w Solar Generator and here is my plan according to my understang of it:

2x200ah (12v batteries) = will equal 4800wh capacity
I should never go under 50% charge, so I really have about 2400wh capacity
A 2500w invertor to accommodate the 2400wh and
2x200w solar panels @ 5 hours on a sunny day should recharge my batteries at least up to 2000w

Will this setup work and am I understand this correctly?

Sorry, but am totally new to this solar and electrical stuff


Please let me know if I have a correct understanding in the matter and am looking forward to reading/ learning from this forum and its members

Thanks in advance

This does not compute ...
"... A 2500w invertor to accommodate the 2400wh ..."

You need a Charge Controller between the PV Panels and the Battery Bank.
The Charge Controller will be rated in AMPS to handle the 400 Watts of Solar Panels
Example: 400 PV Watts / 12 Volts = 33 Amps, so round up!

Then you need a DC-to-AC Inverter between the Battery Bank and your Loads.
It will be rated in WATTS, to handle your Loads

This does not compute ( unit of measure ) ...
"... 2 x 200w solar panels @ 5 hours on a sunny day should recharge my batteries at least up to 2000w ..."

2 x 200 Watts x 5 Hours = 2,000 Watt-Hours.
Yes, that only occurs on the sunniest & cool days.
But if hot and/or cloudy then less, maybe much less.
That assumes 100% efficiency, which not exist in PV Systems.

There are STICKY NOTES that have good examples, here ...

https://www.solarpaneltalk.com/forum/off-grid-solar/off-grid-solar-panel-systems

[Candela]

Thanks for the quick reply Neoh,

Yes, I comprehend the need for controllers and the amps for the panels, DC to AC and battery banks.

But I just realized your point. Realistically, I will not be using 2500w at a time, so instead of getting a 2500w invertor, a 500w invertor should suffice

Just a little confused in the Solar Math components, the amount of wh I will have from my battery bank, and then the amount of panels required to charge up the batteries on a sunny day, and an invertor to push it nicely.

Load is no concern for me, just using to recharge 2 cellphones and maybe a tablet and am thinking 2400wh a day, if needed in a natural disaster/ emergency (particularly hurricanes here in Florida), should be enough for me

[Tom@SPS]

Candela, the math is a little confusing and we get questions like these all the time from our customers. I think your battery estimate is pretty good as long as you're talking lead acid batteries. We use the 50% depth of discharge rule for those, although it varies a bit by battery manufacturer.

Your projected solar panel output is pretty close. It's best to use average peak sun hours for your area. And depending on how much and when you may use your generator, you'll want to be conservative and use the winter peak sun numbers. Go to http://pvwatts.nrel.gov for that info.

The sizing of your inverter is driven by watt rating of your loads. So you list your loads (which you said are just 2 cellphones and a tablet) and add up the watts. So if you want to power 4 x 100w light bulbs, you'd need 400W of AC. So a 500W inverter would be fine for that application. Since you don't have any pumps or motors for loads, you don't have to worry about surge watts. If you wanted to power a fridge or a pump, then you need to consider the inverter's surge watt rating. A rule of thumb would be to double the running watts of the load to ensure the inverter can handle the surge.

As far as voltage, it looks like you would be building a simple 12 volt system. To keep things simple, if you choose 12V panels, you can wire them in parallel to stay at 12 volts and then use a cheaper 12 volt PWM charge controller to charge a 12 volt battery bank (your 2 batteries wired in parallel) and then a 12 volt inverter.

To size your charge controller, you look at the Isc (short circuit amps) from your solar array and pick a controller that can handle those amps. For example we sell a 160W 12V panel that has an Isc of 9.29A. Two of those panels in parallel means 18.58A. So a 20A 12V PWM charge controller would do the job.

The best plan is to determine your loads and build from there. With only 2 phones and tablet (maybe about 70WH for a charge depending on the models), the system you proposed should be plenty for you.

Hope this helps.

[cebury]

Load is no concern for me, just using to recharge 2 cellphones and maybe a tablet and am thinking 2400wh a day, if needed in a natural disaster/ emergency (particularly hurricanes here in Florida), should be enough for me

Sounds like huge overkill. What am I missing? Why wouldnt you just use your car charger or borrow an "available" vehicle's cigarette lighter plug to charge your phones and tablet? Are you imagining carting this very heavy and wide stuff around or keeping it at home?

Instead of spending hundreds, almost a thousand bucks on panels, batteries, inverter, CC,
just buy something like this, a fresh one every two years : emergency battery
or longer lasting smaller