Solar Pool pump and heating

Possibly a bit late in the year to post about solar pool heaters and pumps, but i would think many people are looking at reducing the cost of owning a pool or a hot tub, and the costs for heating and filtering. here is how…

There are two ways to heat your pool, or you could combine them, but this is thermal ( we don’t do thermal) or electrically. Solar inverters will provide you with mains voltage to run your pool and hot tub but you need to take into account “British weather” as well as the load total and match the inverter.

The British weather part, refers to clouds as a cloud can drop power instantly, and therefore I would suggest a battery capable of powering the load for a few minutes to a few hours; or go grid tied. IF you do go grid tied, your excess would power your home, and power your home when the pool is not in use. but if youre not making solar power you will be using grid power to power the pool.

The Solar Diverter.
if you have solar, there is nothing worse than backing down the power or sending it to the grid for free, a diverter will divert excess power to your pool or tub, there are a few different types and how they work, but they simply measure the solar and the loads and send the rest to something else. its best to use the heater which is independent as the power is modulated ( changes) so that only the excess is provided.

Off Grid.
If you are going off grid to power the pool, then you would need to have enough solar and battery to run the system. most pool ( on ground) will use around 2kw of power, but usually less than 3.6kw in most events. You would want around 5kw from the inverter, which off grid costs are low and around £500. However the battery will need to cope with clouds and run the system into the evening and also recharge, this would mean having a bigger solar array. it is ideal that you pre heat the water and also insulate your pool correctly as this will reduce the power demands over all.

THE MATH…..
The heat pump should be able to heat the water by approx. 0.20 – 0.25 degrees per hour. It takes 1.16 Wh to heat one litre of water one degree, In other words, one kilowatt hour heats 862 litre of water by one degree Celsius.
( Pool Litres x 1.16 = Wh per degree)

Water unheated may be around 15oC and you want to raise this to 22oC, this means that you would want to heat 7 degrees, therefore you would multiply the Wh by 7.

Here is an example:
My small pool is 1800L x 1.16 = 2088Wh x 7 =14,616wh
I can use a 2.1Kw pool heater, which will use 14.6kwh of power per day. (excluding losses).

Cheating.
If you wish to cheat, you can use irrigation pipe ( which is black plastic) and make coils on a black box that the sun shines into, you can then have a small pump that slowly circulates the water and the sun would heat the water and the pool. This can take the load off a solar electrical system as it can be fed into the heater/pump to add “heating power” the sun is typically 1kw m2 to give you some idea, however the transfer of heat is less effective.

Here is a guide and talk about that…. ( LINK)
So I bought three 500′ lengths of 1/2 inch tubing on amazon for $40 each and a submersible pump for $45. PVC connectors for the pump were another $20. So $185 total for about 60 square feet of solar surface area.

First I tried just running 500′ of hose around on the grass. I got about 5000 btu at noon on a sunny day.
Then I tried 500′ in one of those hot boxes they make on youtube and got about 7000 btu at noon on a sunny day. Better, but still no buano.

Then I split the hose in half (2×250′) and ran that through the hot box and got 8500 btu.

Then I split another spool and ran both halves back and forth across the roof and got 17k btu!! Why you ask? My roof and attic are very hot during the day so it’s getting a ton of conduction heat in addition to the direct solar energy. That said I decided to run the other spools on the roof as well.
So for $185 (and a bunch of time and effort) I’m getting around 50k btu/h into my little 4000 gallon AGP (at noon on a sunny day). My pool was averaging around 71 degrees (here in Florida), now it’s almost 90. Love it.

If anyone else wants to try, here’s some things I learned:

Have two ladders at different ends of the house in case you knock your ladder down while pulling all that tubing up to the roof (or take your phone with you so you can call someone to set your ladder back up lol)

• Don’t bother with the hot box idea if you have a hot roof.
• The hot box cost $50+ plus time and effort to build. For that cost it would have been better to simply buy more tubing and run it across the grass.
• Cut the 500′ rolls in half (250′), to get twice the gpm and more overall btu. (Yes I have six 250′ tubes running from the pump, across my roof, and back into the pool).
• Don’t spiral up the hoses. This causes slower water flow. Water moves fastest in a straight line.
• Put gaps between the hoses on the roof and don’t let them overlap. Most of the heat is coming from the hose touching the roof. If hoses are placed too tightly together, it will make a cold spot in the roof and you won’t get as much benefit from the heat of the roof.
• They make a pvc fitting called a manifold (normally used for spa jets). I connected it to the pump and used slip compression inserts to connect the tubing.
• Don’t wear running shoes on a hot roof, the sole glue melts after a bit.

If you have gone to the link for this you may agree that the pipe on the roof is a no go. you can coil on the ground and keep it smaller to take up less space in some form of hot box. or black board..

RECOMENDATIONS
For pool or hot tub heating start off with good insulation, build a frame and insulate, it can look good!
Find the solar panel location firstly to ensure you that you can fit solar panels in the space.
Think about power totals, and duration. you may want to run the pool when the sun shines, but after hours (night heating) will need a bigger battery to heat.
Don’t forget once it is heated the losses (insulation) will restart the heating process.
A 5kwh battery will give you 2.5hours of heating a 2kw heater, adding 2kw of solar will extend this to up to 15 hours a day.
charge your battery, this means a load and recharge must be met by solar. use 5 hours as a base.

Solar and the battery.
Battery charging is pretty much essential and you can calculate this in a simple way.
lets say your power use is 2.4kwh you have a 10 kwh battery. We know that the sun is around for 8 hours during the summer ( sometimes) so we run the system for 10 hours.
Pool reaches temp in 5 hours.
We then say 2kw x5 heating the pool. (2kwh)
We need to recharge the battery, this is 10kwh /8 (1.25kwh)
Therefore we would need to have 3.25kw of solar as a minimum. 4.4kw is recommended.

COST.
£500 Inverter
£2200 Battery
£765 Solar
£190 Electricals
£3655 ( off grid)

Our mini off grid kit can be found here.. £1694

£800+ (grid tied)
A slight difference in price, however the system is entirely different as there is no battery
The grid tied system can be a single inverter or micro inverters. You would simply match or slightly over over provision for the load of the pool ( 2.4kw) which includes heating and pump, and that is that.

For example 6 410w solar panels (2.46kw) (link to the 4 pack) is £252 including delivery, add two more panels for £150.
You could have a string inverter 3.6kw sunsynk £750. we do offer other inverters, which are not shown in the website, for example the 1.5kw growatt would reduce the power demand to around 500w (£232)

There are many ways, including the micro inverters, we offer the 800w and 1200w as well a 2kw. the later two being 4 panels per micro inverter. Micro inverters are suggested for difficult installations where you may have panels placed in different places. A Growatt 3.6kw string inverter is around £400 bringing the cost to £802 with 6 solar panels (2.6kw).

Panel considerations.
Most string inverters will have 1 mppt, meaning you can have one array connected, the Growatt above has two, meaning that you can split the array to have them in two different places.
You have to account that solar panels would need a space of 1.75 meters by 1.15 meters each. which is why it is important to ensure that you can mount the panels, typically in no more than two places. with micro inverters you do not need to, you can mount the panels individually as they have MPPT per panel.