Solar Pool Pump System Questions

[markpj23]

Just getting started in the solar world. I've got a long electronics repair & computer science background plus many years of DIY plumbing and electrical work behind me so I'm not completely clueless (I hope).
We're buying a house in an area served by Duke energy, and that means higher rates than we're used to. Our current pool system is a single-speed 230v power hog, but at least it has solar heating panels on the roof. Pool is roughly 15 x 30, pretty standard.
I have been soaking up info about DC powered pumps running off of solar. It seems to me that the risk comes in a scenario where it's cloudy for consecutive days and the solar panels just can't produce enough to keep the pool clean. That means either a battery bank, a hybrid system or just plumbing in a DC pump in parallel with the existing pump to manually select when the sun is out.
Trying to spend as little as possible (of course). I came across a thread where the solution was to install a grid-assisted inverter:

Growatt 2.2kW 3HP Solar Pump Inverter l Water Pump Inverter | Grid-Assisted | SPI 2200TL2-HV​

Several questions about adding this to my system:
- Do you run into permitting issues since this inverter is connected to the grid? Or is this incapable of feeding back to the grid such that an AC service disconnect box is all that you need? Growatt manual does not address this. I know that grid-tie inverters used for net metering are a whole different ball game.
- If the power needed to run the pump is say, 1800w, and the solar panels are producing only 1000w, will the grid-assist feature pull the other 800w from the grid? Or is it an either PV or grid equation?

If I go the straight DC pump & solar panel route:
- Are the DC pumps powerful enough that I can just forgo the AC pump & inverter complexity all together? My sense is that they are not...
- Since most of these pumps run at higher voltage (72v or 90v) is there an MPPT or DC-DC converter that would pull from a lower voltage battery bank and provide the needed voltage? My thinking is that the cost of building a 72v battery bank is way more than a 24v bank.
- A 'standard' MPPT has output voltages of 12/24/48v. Is there a reliable / quality solar pump controller that can be set to the pump voltage needed? Not looking to buy a chinese knock-off headache box...

TIA for any insights.

 

[SamDeleted]

Just getting started in the solar world. I've got a long electronics repair & computer science background plus many years of DIY plumbing and electrical work behind me so I'm not completely clueless (I hope).
We're buying a house in an area served by Duke energy, and that means higher rates than we're used to. Our current pool system is a single-speed 230v power hog, but at least it has solar heating panels on the roof. Pool is roughly 15 x 30, pretty standard.
I have been soaking up info about DC powered pumps running off of solar. It seems to me that the risk comes in a scenario where it's cloudy for consecutive days and the solar panels just can't produce enough to keep the pool clean. That means either a battery bank, a hybrid system or just plumbing in a DC pump in parallel with the existing pump to manually select when the sun is out.
Trying to spend as little as possible (of course). I came across a thread where the solution was to install a grid-assisted inverter:

Growatt 2.2kW 3HP Solar Pump Inverter l Water Pump Inverter | Grid-Assisted | SPI 2200TL2-HV​

Several questions about adding this to my system:
- Do you run into permitting issues since this inverter is connected to the grid? Or is this incapable of feeding back to the grid such that an AC service disconnect box is all that you need? Growatt manual does not address this. I know that grid-tie inverters used for net metering are a whole different ball game.
- If the power needed to run the pump is say, 1800w, and the solar panels are producing only 1000w, will the grid-assist feature pull the other 800w from the grid? Or is it an either PV or grid equation?

If I go the straight DC pump & solar panel route:
- Are the DC pumps powerful enough that I can just forgo the AC pump & inverter complexity all together? My sense is that they are not...
- Since most of these pumps run at higher voltage (72v or 90v) is there an MPPT or DC-DC converter that would pull from a lower voltage battery bank and provide the needed voltage? My thinking is that the cost of building a 72v battery bank is way more than a 24v bank.
- A 'standard' MPPT has output voltages of 12/24/48v. Is there a reliable / quality solar pump controller that can be set to the pump voltage needed? Not looking to buy a chinese knock-off headache box...

TIA for any insights.

, DC pumps are loud and don't move much water , and like you pointed out , you're going to struggle to make 72vdc

I think your best bet is an inverter and an AC pump , and then either manually switch between grid & off grid power depending on cloud cover, or get yourself an automatic transfer switch


An AC pump isn't that big a draw , maybe 200w/300w ? So you won't need a big fancy inverter, cheap and cheerful will do

 

[SamDeleted]

Solar pool pump

Not technically a solar "build" per se, and not yet in showroom presentation state like the others featured here, but it's functional and alive (when the Sun's out). This transplant replaced a 1.5 hp pump mated to a 900-sf cartridge filter that circulates a 15,000-gal pool in Florida. If you're...

diysolarforum.com

 

[sunshine_eggo]

- Do you run into permitting issues since this inverter is connected to the grid? Or is this incapable of feeding back to the grid such that an AC service disconnect box is all that you need? Growatt manual does not address this. I know that grid-tie inverters used for net metering are a whole different ball game.

Permitting requirements vary. It does not feedback to the grid, so risk of discovery is very low.

- If the power needed to run the pump is say, 1800w, and the solar panels are producing only 1000w, will the grid-assist feature pull the other 800w from the grid? Or is it an either PV or grid equation?

The product description implies it will use available PV and supplement with grid.

If I go the straight DC pump & solar panel route:
- Are the DC pumps powerful enough that I can just forgo the AC pump & inverter complexity all together? My sense is that they are not...

A pump is a pump. A 1hp AC pump is no different than a 1hp DC pump as pumps are rated by their output. They may have different efficiencies and consumption, but the output is the same.

- Since most of these pumps run at higher voltage (72v or 90v) is there an MPPT or DC-DC converter that would pull from a lower voltage battery bank and provide the needed voltage? My thinking is that the cost of building a 72v battery bank is way more than a 24v bank.

Correct thinking. I don't think a battery bank on a higher voltage DC powered pump is practical.

- A 'standard' MPPT has output voltages of 12/24/48v. Is there a reliable / quality solar pump controller that can be set to the pump voltage needed? Not looking to buy a chinese knock-off headache box...

If the Growatt operates the way it says, it seems like the most cost effective and practical solution. Simply wire it to your pump, PV and grid, and you get to offset your pump use with PV.

 

[markpj23]

thanks for the replies - all very helpful

 

[BentleyJ]

I ran across this same issue a few years ago when installing a pond with a waterfall feature, looking for the most efficient way. Ultimately I chose a Pentair 1.5Hp variable speed pump. Its works great at lower RPM settings only drawing 200W while providing a nice steady flow for the waterfall which is about a 7' lift. These pumps are expensive but so far it has worked perfectly for 7 years and it has inputs for external control so is connected to our Insteon home automation system.

HOWEVER, at lower RPM the pressure is not high enough to effectively push water through a conventional pool cartridge filter. I ended up abandoning the pool type filter and just put 3 x 7" bag filters up at the top in the open receiver and let the water fall through the bags. With a pool you need much better filtration and that takes power.
When selecting a pump you really need to understand the true Wattage at the pressure and flow required to keep the pool clean. A DC pump even in the 72 to 90V range is still less than half of 240V AC meaning its going to require more current.

 

[hwy17]

An AC pump isn't that big a draw , maybe 200w/300w ? So you won't need a big fancy inverter, cheap and cheerful will do

Full size single speed pool pumps run about 500-3000w, and up from there but usually only 3kw+ for commercial equipment.

 

[sunshine_eggo]

An AC pump isn't that big a draw , maybe 200w/300w ? So you won't need a big fancy inverter, cheap and cheerful will do

Huh? A small 1hp pool pump is going to have a ~1200W draw and a big surge.

OP indicated 1800W (likely from experience) this is typical of a 1.5hp pump, which sounds about right for his pool size.

 

[SamDeleted]

Huh? A small 1hp pool pump is going to have a ~1200W draw and a big surge.

OP indicated 1800W (likely from experience) this is typical of a 1.5hp pump, which sounds about right for his pool size.

Your American pools are clearly bigger than mine !

 

[sunshine_eggo]

Your American pools are clearly bigger than mine !

Yep. We colonists are all overweight and need big pools.

 

[wattmatters]

Pool is roughly 15 x 30, pretty standard.

I'm assuming those dimensions are in feet, not metres. For comparison I have a 50,000 litre salt water pool (~13,000 US gallons).

Perhaps consider putting in a modern variable speed AC pump. Older style single speed pumps consume way more energy than is necessary for pool sanitation.

My old single speed pump would suck ~1200 W.

I replaced it with a Hayward variable speed pump about 6 years ago. Once it's finished it's initial 5-minute primer cycle at 3000 rpm it drops the revs back to all day pumping mode and sucks ~ 320 W. It made an instant and massive saving on the energy required for our 50,000 litre pool. Yes you might have a longer duty cycle to achieve the desired water throughput for the day but they are still going to use a LOT less energy overall. They are also much quieter.

Since we have both grid-tied and off-grid solar PV, I can run my pump from either and the duty cycle is during the daytime when solar PV is available.

You could use a smaller off-grid PV inverter with a utility input to cover for times the PV is inadequate but it seems like a waste of PV & inverter to be dedicated to one job only.

This is the power draw for my pool pump and chlorinator:



Whatever pump you have, they are a bit of a bugger of a load and motors tend to require very large short term current draw, so whatever is powering it will need to be able to cover for that. Having the inertia of grid supply available to start it is helpful. Once up and running it's no big deal, nice steady draw.

My pump has a pretty soft start which helps.

 

[markpj23]

I figure that I'll have to measure actual starting current once I get my variable speed pump. Then I can spec the PV & inverter.

 

[hwy17]

Inverter VS pumps probably have a possible way to tap solar DC straight onto their DC bus like an inverter heat pump. Warranty voiding, of course.