Doing both parallel and series connection on a single PV array

[Dunkirk]

What would happen if I have 8 panels of 40v 10amp and I connect them in 4s2p configuration to power a dc water pump. On the other hand, I connect the same array in a series 8s configuration to charge batteries via mptt scc. I will have a switch between the two that I can flip to use the pump and flip the other way to charge the battery.

Would there be any potential damage to the panels?

 

[rmaddy]

Why not run the pump off of the batteries that are being charged via the solar? No switching or complicated wiring required.

What do you plan to have between the panels and the pump? Panels do not provide a constant voltage.

 

[timselectric]

That does seem like a lot of extra effort.
Not saying that it can't be done.

 

[MisterSandals]

configuration to power a dc water pump.

How many volts will your dc water pump accept?

If you hook up 4x 40V panels in series, that makes 160V. It its a 12V pump, it will run REALLY fast but maybe not very long.

 

[Dunkirk]

How many volts will your dc water pump accept?

If you hook up 4x 40V panels in series, that makes 160V. It its a 12V pump, it will run REALLY fast but maybe not very long.

The pump is rated for that configuration 4s2p.

 

[Dunkirk]

Why not run the pump off of the batteries that are being charged via the solar? No switching or complicated wiring required.

What do you plan to have between the panels and the pump? Panels do not provide a constant voltage.

I have thought about running the pump off the battery. I am afraid that on overcast days, the pump will discharge the batteries by evening. I am not available to monitor the pump during the day. Its supposed to fill a tank that then drains via sprinklers. On overcast days the pump will use up the battery storage thus affect other battery dependent operations.

 

[rmaddy]

I have thought about running the pump off the battery. I am afraid that on overcast days, the pump will discharge the batteries by evening. I am not available to monitor the pump during the day. Its supposed to fill a tank that then drains via sprinklers. On overcast days the pump will use up the battery storage thus affect other battery dependent operations.

What is the pump voltage? I ask because you state you were thinking about running the pump from the battery but you also stated you wanted to run the pump from 160V of solar panels.

As for the pump running down the batteries you could use something like the Victron Battery Protect. This could be used to turn off the pump if the battery voltage gets below a certain voltage that you can set.

 

[Dunkirk]

What is the pump voltage? I ask because you state you were thinking about running the pump from the battery but you also stated you wanted to run the pump from 160V of solar panels.

As for the pump running down the batteries you could use something like the Victron Battery Protect. This could be used to turn off the pump if the battery voltage gets below a certain voltage that you can set.

Thanks for the battery protect idea. The pump has an mppt controller that receives 160v from panel but can also use 48v from battery.

 

[Dunkirk]

Thanks for the battery protect idea. The pump has an mppt controller that receives 160v from panel but can also use 48v from battery.

According to the manual, I have dc 72 and a dc 110 pump. So it looks like I need a 72v or 110v battery. Seeing that this is not practical, it leaves me with only 2 options. Buy extra panels to power the inverter even though the pumps are only used 4hrs a day on average or figure out how to use the pump panels to also power an offgrid inverter.

 

[Dunkirk]

My main concern is will I damage the panels if I wire them both in series and in parallel? What would happen if by mistake both pump in the parallel conformation and the inverter in series were to be left on simultaneously?

 

[timselectric]

My main concern is will I damage the panels if I wire them both in series and in parallel? What would happen if by mistake both pump in the parallel conformation and the inverter in series were to be left on simultaneously?

There will be a dead short between half of the panels.
Probably smoke at first, but eventually fire.

 

[Dunkirk]

There will be a dead short between half of the panels.
Probably smoke at first, but eventually fire.

Thats my fear. But I also know my fear may be unfounded. How do they test the short circuit current in panels?

 

[timselectric]

With a volt meter. The results are on the label.

 

[sunshine_eggo]

Why switch?

Would 4S2P not work on the MPPT?

 

[brum]

Look for a simple solution - no switches to modify the panel configuration. Simple is reliable and reliability matters. If the charging controller and the wiring are supposed to work fine with 4S2P go with that option.

If not - use DC boost converter directly from the battery and put in front of it a DIY or adjustable voltage sensitive relay that triggers when battery voltage is a bit below the float charging voltage (if having stored energy is with higher priority compared to running the pump). Or go for a pump that works on the same voltage as the batteries and skip the DC boost converter.

 

[pollenface]

You won't kill a solar panel unless you throw a brick at it.

Leave your panels in the configuration required by your controller to charge your batteries.

Run the pump as needed from your batteries.

 

[Dunkirk]

Why switch?

Would 4S2P not work on the MPPT?

It would. The MPPT has 120v as minimum starting voltage. 4s2p gives me a 160v configuration. During hot sun, I get 144v from the panels. I guess the difference is due to the panels heating up. So my secondary question would be how much less efficient would a 4s2p (160v, 20a) configuration be compared to a 8s setup ( 320v 10a) for a 5kw inverter with max volt 450v and minimum 120v and max amp 18a? The MPPT enables me to utilise direct solar energy to 240v ac without use of a battery. Will this function be impaired by using 140v dc rather than 320v dc?

 

[timselectric]

No
It will shift the power point to only produce 18 amps.

 

[timselectric]

It will probably be rare that you produce more than 18 amps, anyway.

 

[Dunkirk]

No
It will shift the power point to only produce 18 amps.

I dont understand this answer