I got a free solar panel and want to use it to supply off-the-grid

>>1157453
Your batter can't run a 350w space heater most likely. That's 30 amps, not counting any loses.

You may want to think about doing the new grid tie thing. Where the inverted electricity gets back fed into the house, but you need special stuff so if the power goes out it stops working and doesn't kill a lineman.

>>1157590
> You may want to think about doing the new grid tie thing. Where the inverted electricity gets back fed into the house, but you need special stuff so if the power goes out it stops working and doesn't kill a lineman.

I have a 3.3Kw grid-tied system on the roof already. That is not the purpose of this extra panel.

> Your batter can't run a 350w space heater most likely. That's 30 amps, not counting any loses.

But what's the solution? Shorter and thicker cables?

>>1157593
First you should figure out where your losses are.

The type of battery matters much.. A lead acid battery, is not just a lead acid battery.
The way they are constructed determines their performance in specific applications.
Some are made to have high crank current, some low self discharge or high capacity. You will not have all at once..

And drawing 350w from a 40 Ah battery will not last long..
350w/12 = 29A
That is ideally 1 hour 20 min on full charge..The capacity is most likely defined at 0.1C or lower. So more likely 30-40 min.

Load a battery and the voltage drops, remove the load, and it will increase to open circuit voltage. This is due to internal resistance and chemistry. Go Google..
The voltage potential of a battery tells very little of the Charge stored..

File: GET A REAL BATTERY.jpg (361KB, 900x900px) Image search: [Google]

361KB, 900x900px

>>1157593
>But what's the solution?

>>1157453
my 1500 watt 110v inverter says it will pull 157 amps at full load. 1500/110=13.63_ amps ac (so say 13.5), 157/11.629_ amps dc (so say 11.5). so basically expect to draw approximately 11.5 amps dc per 1 amp ac. if you have a 350w heater on a 110/115/120v inverter you can expect it to draw 3.2-2.9 amps ac (so just average 3) and 3*11.5=34.5 amps dc. 40ah/34.5a=69.5 minutes run time absolute best case scenario but more likely the inverter will have low voltage protection or just wont work at low voltage so thats time to shave off of your run time.

>>1157453

Going from 12 volts to 120 volts then dumping that into a restive load is extremely inefficient. Get those 12v defroster heaters for cars and a bigger battery.