New to Solar.. Want help on pump project.

[cws2011]

Hello.

Here's what I'm thinking of trying to accomplish. We currently have a generator running two sewage/submersible pumps. The pumps are just standard 3/4hp 110volt pumps with on/off floats to control them. What do you guys recommend for me to be too able to run these two pumps. I want to avoid batteries, just to keep the overall maintenance cost low. Running the pumps only when the sun is out is perfectly fine.

Now some of my concerns/questions.
1st off, When the sun is out, and producing power, without batteries, can the system produce the power and it go unused? I understand it will be wasted.
2nd, Is there a controller/invertor that has the capability of doing 110 and 220 in case we ever up to one 220 volt pump instead of the two 3/4 hp 110 pumps?
3rd. Would I be better off trying to find a variable speed pump now? to keep lower power needs since I won't have any battery backup?

Thanks for any help or guidance.

 

[BentleyJ]

Some inverters can operate on solar panels only and do not need a battery, however, due to the variability of weather conditions solar can range from 10% to slightly over 100% of rated output within minutes or even seconds. This is the absolute worst case scenario for induction motors and you would be setting yourself up for a completely unreliable system. IMHO, there is no scenario where operating pumps without a battery as a buffer is a good idea. Maybe if the system was grossly oversized but that makes no sense.

 

[Rednecktek]

Hello.

Here's what I'm thinking of trying to accomplish. We currently have a generator running two sewage/submersible pumps. The pumps are just standard 3/4hp 110volt pumps with on/off floats to control them. What do you guys recommend for me to be too able to run these two pumps.

Tough question as pump HP are NOT equal to the 735w/hp in engineering so you'll need to throw a kill-a-watt or an amp-clamp meter that can read surge and running watts to find out exactly how much each pump calks for. Motors often need 3x or more their rated wattage to get started so if you can't get a startup surge measurement, factor 5x for startup surge. Figure worst case scenario that both pumps try to fire up at once and give yourself 10%+ on top of that. That'll be your inverter size.

You'll want to find a low frequency inverter if you can, they handle the startup surges better than high frequency inverters.

I want to avoid batteries, just to keep the overall maintenance cost low. Running the pumps only when the sun is out is perfectly fine.

That's not going to work for pumps. Even if you had a zillion gigawatts of solar, the pump would try to start up, the controller would start tracking its power point, hopefully there's enough sun to feed the pump, but by the time that all happens your pump has either given up and stopped or the motor has burned up.

You're going to need a battery, it doesn't even have to be that large, just to provide for that startup surge and give the inverter and panels time to start feeding in the juice to the motor.

Now some of my concerns/questions.
1st off, When the sun is out, and producing power, without batteries, can the system produce the power and it go unused? I understand it will be wasted.

Panels don't PUSH power, the load ASKS for power and the panels PROVIDE what they can. If there's no load, the panels just sit there doing nothing. If you have a 10kw array and only need 50w, your panels will only produce 50w. So, nothing is wasted.

2nd, Is there a controller/invertor that has the capability of doing 110 and 220 in case we ever up to one 220 volt pump instead of the two 3/4 hp 110 pumps?

Nope, inverters are built to convert a single DC voltage in to a single AC voltage out. Whether that's 12vDC to 110v DC or 48v DC into 220v DC, they have to be 2 completely differently built pieces of equipment.

3rd. Would I be better off trying to find a variable speed pump now? to keep lower power needs since I won't have any battery backup?

Good luck finding a variable speed sewage pump, I've never heard of such a beast. Even if it exists, you'll spend way more on it than a solar system to feed a bog standard plug into the wall pump.

Thanks for any help or guidance.

We're here to help.

 

[cws2011]

Tough question as pump HP are NOT equal to the 735w/hp in engineering so you'll need to throw a kill-a-watt or an amp-clamp meter that can read surge and running watts to find out exactly how much each pump calks for. Motors often need 3x or more their rated wattage to get started so if you can't get a startup surge measurement, factor 5x for startup surge. Figure worst case scenario that both pumps try to fire up at once and give yourself 10%+ on top of that. That'll be your inverter size.

You'll want to find a low frequency inverter if you can, they handle the startup surges better than high frequency inverters.



That's not going to work for pumps. Even if you had a zillion gigawatts of solar, the pump would try to start up, the controller would start tracking its power point, hopefully there's enough sun to feed the pump, but by the time that all happens your pump has either given up and stopped or the motor has burned up.

You're going to need a battery, it doesn't even have to be that large, just to provide for that startup surge and give the inverter and panels time to start feeding in the juice to the motor.



Panels don't PUSH power, the load ASKS for power and the panels PROVIDE what they can. If there's no load, the panels just sit there doing nothing. If you have a 10kw array and only need 50w, your panels will only produce 50w. So, nothing is wasted.



Nope, inverters are built to convert a single DC voltage in to a single AC voltage out. Whether that's 12vDC to 110v DC or 48v DC into 220v DC, they have to be 2 completely differently built pieces of equipment.



Good luck finding a variable speed sewage pump, I've never heard of such a beast. Even if it exists, you'll spend way more on it than a solar system to feed a bog standard plug into the wall pump.


We're here to help.

Guess I should have been more clear on the pump. Its is just pumping water from a farm drain tile pit. The sewage pumps from harbor freight were just the cheapest/most flow option at the time. So I believe i can find a variable speed water pump. Just not sure what type of equipment would be required to run the variable speed part. I have found some pump controllers that are a lot more money than I was hoping to spend.

 

[OzSolar]

It's not about horsepower, it's about how many gallons per day you need and total dynamic head.

Once you've determined those you can start shopping for battery-less solar direct pumps. There's a lot of option. Top of the line is the Grundfos SQF but there's all sort of options on Amazon, Vevor, etc. The cheaper ones actual specs are hard to determine so it's a bit of a guessing game.

RPS Solar has all sort of options as well. Some folks haven't been happy with them but it reads more like folks jumped into something head first without understanding what they were after.

Whatever option you choose you'll be happier if you spend some time educating yourself first.

Not a recommendation and I have no association with them but The Solar Store has got some good resources.

Submersible Solar Well Pumps | The Best Selection Online

thesolarstore.com

 

[Cmiller]

Guess I should have been more clear on the pump. Its is just pumping water from a farm drain tile pit. The sewage pumps from harbor freight were just the cheapest/most flow option at the time. So I believe i can find a variable speed water pump. Just not sure what type of equipment would be required to run the variable speed part. I have found some pump controllers that are a lot more money than I was hoping to spend.

If you are only pumping relatively clean water, look at the Grundfos flex pumps such as the 6SQF-3. The "flex" (designated by the F in the model#) pumps will accept 30-300Vdc and/or 90-240Vac. We have often set these up "solar-direct" on well pumps to fill a cistern during sun hours. I would recommend a minimum string voltage of around 120V of solar panels, so if you were to use 60 cells panels, you would need minimum of 4. If you would use 72 cell (or 144 split cell) panels, you would need minimum of 3 panels. We haven't set one up recently, but we would usually have between 1kW to 1.5kW of solar on these setups.

These pumps will usually start pumping at around 70-90 watts of available solar in the morning and just ramp up to follow the solar curve, then ramp back down as the sun goes lower in the evening.

There are also a few other solar-direct pumps out there, such as the Lorentz pumps, but we had by far the best success with the Grundfos lineup! Also, the Grundfos lineup has all the controlling built into the pump, so you can run it with literally no other controller involved. But I would recommend using the CU200 pump controller with a float, so the pump shuts off before running out of water. These do have a low water sensor right on the wires coming out of the pump, but if the pump often runs out of water, it will eventually be damaged, as that sensor doesn't seem to be very reliable.

So what you would need:

• Grundfos 6SQF-3 pump (or one of the flex models)
• Grundfos CU200 pump controller and low water float
• 1-1.5kW of solar panels