24v vs 12v question..

[Steve9R]

Hi Guys..

quick question..

if ive got a 24v system, comprising of 2 x 50w BP panels, a 24v - 240v 1500w inverter, and a 1000Ah 24v battery bank, and ive got a device that draws 50w @240v  does that mean that if tghe device is turned on at the same time that the panels are putting their 50w into the 24v array, 100% of power is used (in the ideal world of course, not taking into consideration inverter requirements and inefficiencies etc)

Im just trying to determine why 24v over a 12v system ? (where there'd obviously be a 50w surplus for charging etc)

thank you

Steve

[Flux]

Voltage doesn't affect the issue. If you have two 50 Watt panels then under perfect conditions, with no losses, it will supply 100W of load with no drain from the battery.

In your 24v case (under theoretically ideal conditions) your two 50W panels should provide 100W to your battery with the panels in series.

If you connect the panels for 12v they will supply 100W in parallel. The current will be twice the 24v case, but watts (volts x Amps) will be the same.

Similarly the 12v inverter will take twice as many amps as the 24v one to supply a 50W load.

Voltage only affects losses from volt drop in wiring, diodes and electronic switches in the inverter.

Flux

[altosack]

I'm not sure I understand the question but I'll take a stab at it.

(Ignoring inefficiencies) 50W is 50W, no matter if it is 12 or 24V DC or 120 or 240V AC. So, with (2)x50W panels, you are getting 100W into 24V or 100W into 12V, and taking 100W out at 240V AC would be 100% of power used in either case.

The advantage to a 24V system is that the inefficiencies are less. While the power is the same, since power is volts times amps (put another way, amps is power / volts), you will have 1/2 the amps in a 24V system than in a 12V system with the same power transfer. Since the power lost in the wire is proportional to the square of the current (loss = amps^2 * resistance), you either have less loss with the same wire or you can use smaller wire.

For example, with a 96W (easier math ;-) panel array, this will be 8A into 12V or 4A into 24V. If you have a wire that has 0.2 ohms of resistance (10 AWG for 30m both ways), the loss of the 12V will be (^2*0.2=13W, where the 24V will be (4)^2*0.2=3W. This is a big difference !

The advantage to 12V is that you can upgrade in smaller chunks (1 solar panel or 2 batteries vs. 2 solar panels or 4 batteries for 24V) and there are more appliances available for 12V.

Stay with 24V (or consider 48V); you won't be sorry.

Dave

[stephent]

well, if you mean you have 2 @ 12 volt panels series to make 24 volts--then you have a 50 watt 24volt panel. (volts add--amps stay same)

If you have 2 @ 24 volt panels (?) and paralleled them for a 100watt 24 volt panel and used them at 50 watts you would have 50 left over..(volts stay same--amps add)

Ignoring losses, etc...as stated.

Using 50 watts of 12 volt demand is 4.16...amps

50 watts of 24 volt demand is of course 1/2 that--- 2.08 amps.

Watts is watts.

Using a 1500 watt inverter for a 50 watt demand is an effeciency loser.

It's probably only getting it's best effeciency at more then 75% of it's rated draw--way lower demand like your example (50 watts) and it's probably way down on effeciency.

[Steve9R]

Sorry Guys..

I was talking 2 x 50w 12v panels.. hooked together to make 24v @ 50w as well.

the background reason for the question, is that ive got a remote security camera / internet router to power while we're not at the property and the 1500w inverter is the normal inverter for the house. .

but obviously if we're not there, we cant rely on our generators to top up batteries etc hence the solar panels..

but i need to be able power this 50w load as well as have an excess into the battery too..

other thing i wanted to do was have some sort of timer that could slot between the inverter and the battery bank as a 24hour timer, to turn the inverter off altogether (eg only leave inverter running for 6 hours of the day whilst there's sunlight)

Only problem with this is of course that breaking the heavy duty battery to inverter wires is not a good idea i would have thought..

thoughts ?

Ideas ?

Steve

[stephent]

ooppss--the watts DO double on the 2 x 12volt to 24

4. amps x 12 = 48 (50) x 2 panels parallel = 100watts
   
4. amps x 24 = 96 (100) series
   
   

but no matter how ya stack it--watts is watts

[Steve9R]

Hi all..

Just an update (albeit it overdue)..

I hooked everything up and it works perfectly..

but the reason for this post.. i actually found a 24v DC Timer that allows me to switch my loads on and off reliably..

www.rpc.com.au (Rainbow power company) here in Australia make them.. and VERY cheap ($55 AUD) .. so if anyone is after timed power on their system make sure you check them out..

I looked at lots of different ones, and even tried building my own by converting a 240v timer before finding this one..

regards,

Steve