DIY solar using Sonoff

[Dirk]

The solar diverter valve is OK as long as it is below the level of the panels, does that sound accurate?

Not sure what you're asking. It doesn't have to be. If it is, then that's fine, too. If the valve is a drain-down model, it must be below the panels to allow them to drain through it.

 

[Dirk]

So I set it to turn off at 65 or sunset. Seems to work.

You might get into trouble at some point with that. It will work, but maybe not as effectively. If the pool is at a comfy 85°, and the air drops to 66°, your "heater" will still be running and will actually end up cooling the pool, until the air hits 65. Heating a pool with solar can be additive over a few days. By that I mean, maybe that cooling period won't affect your swim that day, because you got out early, no big deal. But it could affect the next day or two, as maybe the pool will not get as warm as it would have because the heater has to make up for that loss.

You don't necessarily "start fresh" each day. The heater starts adding degrees to whatever the temp of the pool is in the morning. It'll be warmer sooner, and/or end up warmer later, if the pool was 75° in the morning as opposed to 65°.

That's another feature of a solar controller. It not only turns on the flow through the panels only when they can actually make the pool warmer, it also turns off the flow before sending water through the panels could make the pool cooler. Additionally, the controller modifies the pump speed, too (if you have a VS pump), such that the pump ramps up only when the solar heater is engaged, and then runs slower when the panels are not heating the pool. So the controller maintains a warmer pool using as little electricity as possible. (Pardon if I already made that point.)

 

[strategy400]

At this point I'm happy if it doesn't run after dark. I'll be adding more logic as I go. Still trying to find a safe water sensor to add into the mix. I'm seeing that a pentair sensor uses a "10K ohm thermistor" and I'm not sure if this can connect to my sonoff device. The sonoff uses a ds18b20 sensor. I may end up scrapping the sonoff devices and getting a solar controller. I can use the sonoff for other purposes...

 

[Dirk]

There is a chart available that translates the resistance read from those Pentair sensors into temperature. I think @JamesW might have a link.

I can't advise how one might get a Sonoff device to make use of the numbers.

My pool water temp sensor is digital, based on a commonly available chip. You can make your own sensor, or they are available in waterproof housings. You apply 5V to the chip and it returns the temperature. I mentioned already: I housed a waterproof sensor in another layer of insulation and stuck that in my pool. You'd still have to solve for the Sonoff "talking" to one of those. I use that sensor for a temperature display. I also have the Pentair sensor that is used by my solar controller. So I have both.

Sorry, that's not particularly helpful.

 

[Dirk]

This might be some help:

Temperature Sensors - Further Reading

www.troublefreepool.com

 

[strategy400]

I believe the pentair type sensors are NTC/analog and as such will not work with sonoff which uses a digital type sensor eg - DS18B20. Bummer. I'll have to keep using a more primitive controller scheme for now. Ewelink has claimed they are going to release a way to compare temperature values this June or July, but I'm not holding my breath. I don't think the solar controllers available are good for me because of the way they interface with the pump. This is how my relay is operating now just by sensing outdoor temp:

 

[Dirk]

Are you monitoring the air temp, or the roof top sensor temp, when you get those "ON" events? They seem pretty late in the day, even the 09:06:37 would be late where I live. Of course, it's April and still cool out that early, so maybe that's all you can get right now.

 

[strategy400]

Sensor is in the sun near the panels. We are at 3500 feet so maybe it's still a little cooler than closer to sea level. It's also been cooler the past few days.

 

[strategy400]

Ordered a pentair solar valve. There's something that I'd think would be a smaller valve inside but I can't see anyway that it opens and can't see any light coming through it.

 

[Dirk]

I've never looked at mine, but I wouldn't expect to see light through it. I think it would be normally closed, and the weight of the water from the panels would push it open. Pretty sure you've got the right one. Should look something like this:

 

[strategy400]

I pushed on it a little with a blunt punch and it wouldn't move or open at all. I don't see how any water would ever get through that thing.

 

[strategy400]

Disassembled the entire valve. Reassembled. The little check valve ball now moves freely....

 

[Dirk]

Disassembled the entire valve. Reassembled. The little check valve ball now moves freely....

Good job catching that. That would have given you some problems later.

So can you see light through it now, or is it spring-loaded closed? Or does the ball flop around freely (no spring)?

 

[strategy400]

Ball flops around freely, only moves about 1/8 inch. I guess it needs pressure behind it to seal so I'd imagine a little squirt of water gets through initially, and not much comes through the other way during "drain down". Next weekend I'm going to try to splice it into my system. I hope nothing goes terribly wrong and I end up with a green pool

 

[strategy400]

How long after gluing pvc can you put pressure in the system?

 

[Dirk]

From the google machine: "Between 15 minutes and 2 hours is the standard range for PVC glue drying."

I'd wait hours. Some glues are fast drying, so it's not a universal answer.

 

[strategy400]

The glue is holding so far.

 

[Dirk]

Not sure you'll appreciate this or not, but here's some data points for your consideration. I turned on my solar heater on Thursday. I'm pretty sure it added at least 5° each day. It's hard to know how much my pool temp is benefiting from sun on the water vs sun on the panels. But to my point:

I noticed my solar heater came on this morning while the pool was at 76° and the ambient air temp was only 52°! It's almost 10am now and the air temp is still at 68°, 6° cooler than the pool.

And yesterday the heater kicked on at 7:00am, right when my pump fired up for the day. But today the heater didn't come on until 8:00am.

Just some examples of how a solar controller can calculate on the fly when best to fire up the heater, while waiting on a fixed air temperature spec can cost you hours of pool-heating goodness. Yesterday the solar heater was able to heat my pool at 7:00am. Today it couldn't until 8:00am. So just setting a regular start time isn't efficient either, because yesterday my pool benefited from the heater at 7, but today the solar panels would have been cooling the pool off between 7 and 8.

So while a few degrees here or there doesn't matter all that much in mid-summer, this time of year every degree makes a difference in wanting to get in or not. I appreciate that my controller is eking out every bit of heat I can get into my pool, but not wasting pump energy when it can't.

 

[strategy400]

Thanks for the info. I just yesterday connected the panels to the equipment pad. Hard work. So I ran it just to my spa for 3 hours (1 to 4pm). Took it from 72 to 84. The spa never gets more than 1 or 2 degrees from direct sunlight. The ambient temperature was 76. I've used an IR thermometer on the panels with no water in them on a warm day (can't remember the ambient temp) but the panels read 140. So there is energy there. Today I'm trying the whole pool to see what happens.

 

[Dirk]

Wow! 12 degrees in the spa, nice. I wish I could get that in my pool! Here's another consideration, for the future. I may have mentioned: my EasyTouch pool automation controller handles everything pool, including the solar. It has a nice feature regarding heat. I can schedule the pool to be heated with only the solar system, or only the gas heater, or both! The EasyTouch determines which heater can do the best job given the conditions, and of course, which body of water receives the heat. In your case, you could set it up where the pool gets heated with solar during the day, then late afternoon the controller concentrates the heating on the spa, to get it ready for you for the evening. It'll figure out which heat source to use, so maybe for an hour or two it'll heat the spa with the solar, then as the sun is setting it'll automatically switch over to your gas heater to finish the job and get it up to 100 (or whatever you set).

Full automation systems are considerably more expensive than the solar controller I recommended, but they do have their advantages that might make them worth the money to you (someday)...