One can easily obtain direct drive swimming pool pumps. They are mostly AC but DC ones are out there.

I would like to put a solar powered pool pump in parallel with my existing mains powered pump. I can easily make sure they do not run simultaneously. However, it seems to me the economics of pool pump plus solar panels, plus batteries, plus controller seems to make this route not viable.

Any ideas on direct solar panel to DC motor connections or the feasibility of this route will be gratefully received.

 

Perhaps use a DC-DC buck/boost converter module (widely advertised online) to create a fixed voltage for the pump from the variable voltage of the panel?

 

Your existing pump should have name plate data on it. Look at the power r5equired to run it. Look at the cost of your mains power delivered from your power company. Note the daily run time. Knowing your current cost of operation you should be able to figure out where you get a turnaround on an investment of solar power.

Ron

 

I would investigate running existing pump off panel + battery + inverter. The plumbing for parallel pumps is not trivial.

 

Your existing pump should have name plate data on it. Look at the power r5equired to run it. Look at the cost of your mains power delivered from your power company. Note the daily run time. Knowing your current cost of operation you should be able to figure out where you get a turnaround on an investment of solar power.

Ron

Already done that. It's a 900W pump. In June, July and August, it runs non-stop. So call it a kW and with electricity plus all the taxes they add, running around 20 cents a kW hour (off peak about half that and 6 hours a day), its getting on for €4 a day, so peak months, €350. With solar and no batteries, I guess I can save 40% of that. Batteries don't make any financial sense here.

 

Well having crunched the numbers and done your homework if you see a turnaround on investment I would do it. Just remember for the most part solar panel ratings are in direct sunlight and on overcast or rainy days have little to no output.

Ron

 

Direct solar to motor systems are more involved then a first glance will show.

As the sun rises and the panel begins to supply power the motor will be stalled and draw all the current it can, acting as a short. And it will stay that way all day long as a short is completely inefficient at consuming power.

The trick is to be able to supply a possibly high starting power to the motor briefly as it starts.

 

After investigating just such a setup, I decided to install a straightforward grid-tied solar as the most cost effective solution.

Normally when the pump is running the grid-tied panels are at maximum output so my panels are supplying both the pump motor plus most of the house demand. The pool pump clock is set to only run the pump during the middle of the day.

I think it achieves everything you are aiming to do, has no maintenance overhead, no plumbing complications, switches demand between solar and grid power as needed, and as a bonus returns me a small credit on my power bill for exported excess.

By my estimate, my payback should be around 5 years or so at current prices- from your figures perhaps quicker for you.

 

One can easily obtain direct drive swimming pool pumps. They are mostly AC but DC ones are out there.

I would like to put a solar powered pool pump in parallel with my existing mains powered pump. I can easily make sure they do not run simultaneously. However, it seems to me the economics of pool pump plus solar panels, plus batteries, plus controller seems to make this route not viable.

Any ideas on direct solar panel to DC motor connections or the feasibility of this route will be gratefully received.

It's a question of current. Actually, there are several questions from a problem-solving/design standpoint- but the first is: How much current and volts do the DC pumps draw?

 

Really, i is a question of POWER, with current being one problem. Short of using a brushless DC motor, one will be stuck with either having a custom motor created or using a standard voltage DC motor. So the very first question becomes what is the available voltage from the solar array. 90 volts is one common DC motor voltage, and for 900 watts then the current is ten amps, So is ten amps and 90 volts a reasonable output from an acceptably sized and priced solar array?
The good news is that the starting inrush for a universal, (brush type) motor is less because a series motor makes torque even at zero RPM.
Unfortunately the cost to benefit ratio for an adequate solar power filter pump is probably not acceptable if mains power is available. Except in California.