Pump and solar panel help

If you could tolerate a system that follows sun intensity over a day, it could be very simple. Something
like a 100W 12V panel would provide about 18V mid day, 12V several hours different, and nothing at
night. A capacitor should be placed across the motor to supply the current spikes of a brushless motor.

If the motor must cycle continuously over 24 hours, a complete battery and charger system would be
needed, might be more practical to run on grid power. Bruce Roe

The pond location isnt near any outlets and I cant run a line to the pond.

The problem is that you won't get that 5 - 6 hours of useful sunlight every day. So you have to figure a battery system to safely run your daily loads that is big enough for 4 days of little to no sunlight.

So if you want 15 min on and then 15 min off all day long you are talking about 12 hours of run time with a 5 watt load. That is only 60 watt hours so it is pretty small but you should add in some fluff due to the timer and other losses. So round it up to 100 watt hours a day.

100 wh daily will require a 12V battery system about 50Ah (100wh / 12v x 4 = 33.3Ah). A 100 amp panel (~ Imp = 5.5a) with a 15amp PWM CC gets you a balanced system.

Now if you have under estimated your daily watt hour usage you will need a bigger battery and solar panel wattage. Also if you want to use that battery to it's full life you really don't ever want to discharge it more than 35%.

So you have to decide if believe what the pump manufacture is telling you for watt hours is correct. If not then go with a bigger battery and panel wattage that will get you a C/10 charge rate.

My solar hot water circulator pump has a March brand DC pump fed from an old Siemens 45 watt panel. It has been running like this for at least 15 years. It originally had no controls at all except for an on/off switch. I eventually put a loop powered controller that compares the temperature at the outlet of the panels to the tank temperature and cycles the pump on and off to improve the system efficiency. The March pump has brushes and I expected I would need to replace them by now but its running fine. It was not a cheap pump and expect a amazon special may wear out qicker and be less tolerant to voltage swings.

Would using a mppt benefit more than a pwm?

Shopping list:
100 watt panel
12v 100 ah battery
Pwm or mppt

A MPPT is definately better if you have more than 200 watts of panels or if you have panels with a high Vmp. If you are going to use only one 100 watt panel or even one 200 watt panel you really don't lose much in charging amps if you have a PWM type.

A quick rule of thumb: PWM - Amps in = Amps out., MPPT - Watts in = Watts out.

So if you have a 100 watt panel with a Imp = 5.5 amps then you should see that 5.5 amps ( under perfect conditions) being sent from the PWM CC to charge the battery.

Now with a 100Ah battery you should be using 2 x 100w panels with Imp ~ 5.5amps. Those two wired in parallel to the PWM will still get you about 10 amps output for charging.

I see okay thanks!

Sorry can you explain why I should be using 2 panels instead of 1 for 100 ah battery.

Thank you

Edit:
Oh i think i know. Is it because the battery needs a certain amount of voltage?

A battery needs a charge rate around 1/10 of its amp hour (AH) rating. So a 50 AH battery needs around 5A, a 100 AH battery needs around 10A. One of your panels puts out 5.5A, about right for a 50 AH battery. Two panels in parallel would be 11A, about right for a 100AH battery.

Thanks for all the help but I decided to go no battery and just have it only run during the day time.

If I was to use the same pump and connected it to the solar panel would I need something inbetween? The seller says no but I want other opinions

Using enough 12V panels with considerably more current capacity than the roughly 1/2A
motor drain, will keep the motor running faster (nearer Voc) and longer. Use a capacitor
in parallel with the motor to supply the current spikes of a brushless motor, the panels will
do the average. I would say try a 20,000 mfd or larger, 20VDC cap, observe polarity.
Bruce Roe

I connected a 24V solar panel directly to a 24VDC marine pump for irrigating a garden from a nearby pond. It's worked for years with the exception of pump failures due to dry running and dirt. The best part is that when the sunshine is not perpendicular to the panel, it doesn't stop - the pump continues, just slower.

The pump I used is a "Seaflow" and it has a cutoff switch that disconnects electricity when the head reaches 60 PSI. This works out well, as I use battery-powered timers to control water to multiple stations. When the timer opens a valve, the pressure drops, the pump turns on and water flows.

I saw those. But was looking for a submersible. Think im going with this

12V-18V DC Brushless Submersible Water Pump 898 GPH for Solar Fountain Koi Pond and Waterfall (1 Pack) https://www.amazon.com/dp/B01KC3UAN6..._g8EWCb9QRY320

With a 50 w panel