Possible to use solar panel to run a pool pump?

[hoops10]

My first post but I have been reading a lot. I want to get into this very cool hobby but I do understand there is a lot to learn. I am wondering if it is possible to run an above ground pool pump (which has a 1.5 hp motor) off of a solar panel, or more specifically a solar panel/deep cell battery combo? I am having a tree removed (have to as it's a danger to the house and neighbors too) so I am looking at at least 6-7 good hours of sun. What do you all think?

BTW, I looked for power consumption of the pump but had no luck. Thanks again.

[Mike90250]

Best bacn for your buck, is solar pool heat, then solar house water heat.

Then Grid-Tie, where you don't have any batteries, that is about 95% of harvested power, sold to grid.

bye for a few days

[hoops10]

Thanks for the reply. When you say 'solar pool heat', are you referring to a solar blanket? Something that is black and has channels that the water is pumped through before it gets to the pool? The other two, I don't know that you mean. What is 'solar house water heat'? Meaning I heat the water in my house when solar panels? And is 'Grid-Tie' something that ties the solar panels to the actual electricity grid on my main breaker? Thanks for any clarity.

[slade1977]

Yes it is possible, here are a few numbers:

your 1.5HP pump will draw about 1100W when it is running. One problem with pumps however is starting amperage of the motor. You'll need to look at that. You would need to build approximately 1200W worth of solar panels (about 6 panels) just to handle the power consumption of the pump during sunlight hours. I would think you'd want batteries of some sort between the two as a 'capacitor' to handle that spike when the motor starts. But then again, I'm assuming the pump starts and stops, or does it run continously (I haven't had a pool in my yard since I was a kid)?

If it runs 24-7, you'd need a system to generate 5kw-hr to have a zero-sum power consumption. Your pump would draw about 28kw-hrs/day it was running continously. That would mean, with 6 hours of sun (assuming you get 6 solar hours from that) you'd need approximately a 5kW system capacity to generate enough electricity in those 6 hours to compensate for the other 18 hours the pump is running.

If you went with a non-grid tie system, you'd need about 800 amp-hours of battery capacity at 24V (either directly 24V, or 2-12V in series).

This is all back of the napkin stuff, so i may have missed something.

[hoops10]

slade: Thanks for some good info. Yes, the pump does run continuously. So how many panels and/or batteries do you think I would need? Also, if you don't mind me asking, how did you calculate those numbers (I love math so that is the reason I'm asking)? What do you think a 5kW system would cost (curious because I know that one could be built)? Thanks again.

[slade1977]

I forget the exact conversion number, but I always use 800W=1HP (the actual number is 745.7W=1HP), just easier to work with and provides some fudge factor. So, 1.5HP = 1200W (or close enough)

The largest commercially available panels are around 200W/pannel.

Since it runs continous, you have to calculate the power required for a 24hr period. So, 1.2kW/hr for 24hr = 28.8kW.

So, assuming you get 6solar hours per day (depending on where you are, may or may not be a good number, I'm just using your 6-8 hour period), you need to generate that 28.8kW in a 6 hr period, which is roughly a 5kW/hr system.

The battery part is slightly more tricky. Assuming 24V for the battery system (which is typically what 200W panels are designed to charge) and a 20hr discharge rate, that means you need approximately 1200A-H (28800W/24V=1200AH). Other way to do it is to use your pump to size the capacity. your pump requires a 1200W. A typical 200AH battery can be discharged at a 10A/Hr for it's 20hr rated capacity. So, to convert, each battery can output about 120W in order to reach the 20hr capacity (10A*12V). so, you'd need a total of 20 batteries to do this. Each battery is 120W @ 12V, but you'll need 24V, so 10 sets of of 200AH batteries will do it.

All of this is extrodinarily expensive. I don't like batteries as an option in general when grid tie is an option. They are big, heavy, and environmentally more hazardous than a 100 year old coal plant (at least in my opinion).

If you make the panels yourself, plan on $300-400 per panel. so, 25 panels - $10,000. But the prices on solar cells will make the vary. Additionally, no offense intended, most home made systems have serious longevity issues and start to experience loss of efficiency in just a few years (yes, there are exceptions). Unless you can encapsulate them, it generally isn't worth it to make them yourself for large projects.

Plan on $600 per panel. That doesn't include the cost of batteries or inverters for the grid tie variant.

Now, some more things to look at.

I've assumed worse case on the motor. I seriously doubt your motor is pull 1200W constantly. To better size your system, you may want to try to meter your pump to figure out just how much it is drawing. Poor man's way of doing this is to trip every breaker in your house except for the pump. And then watch your power meter. I would guess your pump is probably only pulling 500W/hr. I say this because my heating system is a force hot water with a 1.5HP motor on the pump, and no way does that pump pull 1000W/hr.

So, if the pump is pulled significantly less power, then you can see how drastically the system can be reduced.

Another solution to consider, and again I'm no pool expert, but is there any major harm in not running the pump except during daylight hours? If not, then the system is even smaller and more simple.

[hoops10]

slade: Wow, man you are giving me some great info. I really appreciate all of it. Running the pump for only like 12-15 hours is something that I have thought about. According to what you have described to me, let me see if I can get this (BTW, the pool is not installed yet so the pump will be brand new):

1) Let's go with your 500W/hr figure. At 15 hours, I would need 7.5kW/day.
2) Again using my 6 hour figure, I would need a 1.25kW/hr system.
3) How many batteries would I need for the above calculations (if they are indeed correct)?

Finally can you explain how the grid-tie thing works? Also how do my figures look above? Thanks again.

[russ]

pump sizing

I suggest you check with your pool people on how many turn overs you need per day to filter the water. That will give you the correct pump sizing then see if you can make solar fit.

To little recirculation would not be a good thing regardless of power cost.

[slade1977]

To size batteries:

Still going to use the 20Hr discharge rate. For a 200AH rated battery, it can discharge up to 120W/hr to get to the 200AH rating, which means each battery has approximately a 2.4kWh capacity (or just take the 200AH rating multiplied by 20 Hours, and you end up with the same number).

So, for 7.5kWh, divide 2.4kWh into it for 4 battery sets (gotta round up). Since you need two-12V batteries per set, you'll need 8 batteries rated at 200AH.

I would look into the circulation requirements. Also, the pump manufacturer may be able to get you realistic power consumption rates. The motor is likely oversized for the pump, as is standard practice for pumps.

[Mike90250]

Grid Tie:
Grid tie solar are systems that consist usually only of solar panels and a grid-tie inverter, with no batteries. The solar panels feed a special high voltage input inverter (usually 140 to 600 volts DC), which converts that directly to AC power. Any power produced by the solar panels subtracts from what you are using from the power company.
from http://store.solar-electric.com/gridtiesolar.html

Batteries will cause a huge increase of loss in your system. Forget batteries, unless you have
lots of $$ to spend every 8 years.

Grid Tie is about 95% efficient, the modern inverters are very good.

A swimming pool seldom needs more than 8 hours of pump/filter time, unless it's full of kids.

A 5KW grid tie system will start about $40,000 installed.

[slade1977]

I am in complete agreement with Mike on the battery issue. To me, they are not worth the effort if you have the ability to tie into the grid to act as your 'battery'.

[hoops10]

mike: isn't there also state and/or federal rebates that u can get to bring that $40,000 figure down to something more reasonable? I thought I remember reading about a 30% discount or something like that. Thanks.

[Mike90250]

mike: isn't there also state and/or federal rebates that u can get to bring that $40,000 figure down to something more reasonable? I thought I remember reading about a 30% discount or something like that. Thanks.

here's the US database: http://www.dsireusa.org/

[slade1977]

It varies from state to state, but many are cutting the rebates out due to the economic problems most states are having.

For instance, I was talking with some of my electrician friends in CT, and they just stopped their rebate program.

[PoolGuy]

A swimming pool seldom needs more than 8 hours of pump/filter time, unless it's full of kids.

Mike is correct. If your pump and filter are a matched pair and the correct size for your pool, you should not need to run the pump day and night. 8 to 12 hours will be enough depending on the water temperature, amount of debris (dust, leaves etc) and the bather load.

This will mean you can probably reduce your solar system size by at least half.