Hello,
I have a 900L inflatable HotTub which costs a small fortune to heat, I have recently lifted it off the floor onto some pallets and rubber matting on top of the pallets to reduce the heat lost through the floor.
I then built a small solar thermal box with around 30 metres of 1/2in pipe, sprayed black and plexi cover. I use a 100w panel, PWM controller and 12Ah battery to power a small 18w submersible pump which I dropped straight in the tub. I have left a hose end on the return so I can control the flow, the idea been when the sun goes down the battery runs out of power and it stops pumping during the night.
I am using "shade" to allow the thermal box to get some sun before the solar panel which has to bring the battery up to charge before the pump kicks in and we are off again.
With lots of sun it actually works surprisingly well, it managed to bring the water up to 32C after several days of sun but next to nothing with little sun obviously. But I was thinking I have some panel watts and battery capacity spare so can I improve it.
I have found a couple of small heating elements around 12v dc 20w each which I could build into a insulated box and join that into the mix.
Cold water out of the tub > thermal box > heating element box > warm water back to the tub.
My concern is the panel, is their enough power
Panel is 5.55a at 18v 100% sun
Pump is 1.5a
Elements are 3.22a
PWM controller can only output5a just read it might be 10a so this is just under the limit and I would be pretty much maxing the panel out even at 100% so very little charge going to the battery.
I just ran the numbers through a calculator I found online and it says 900L of water from 20C to 30C over 2,100mins (5 hours sun for a week) would need 359wh of heating and that's not accounting for it dropping temp during the night.
Do the heating elements output at a reduced power if they cant get all the power they need, or do they just not work ?
Is there a way to calculate the wh for the thermal box ?
Are these small elements going to add even 1C of heat to the water ?
Cheers
I have a 900L inflatable HotTub which costs a small fortune to heat, I have recently lifted it off the floor onto some pallets and rubber matting on top of the pallets to reduce the heat lost through the floor.
I then built a small solar thermal box with around 30 metres of 1/2in pipe, sprayed black and plexi cover. I use a 100w panel, PWM controller and 12Ah battery to power a small 18w submersible pump which I dropped straight in the tub. I have left a hose end on the return so I can control the flow, the idea been when the sun goes down the battery runs out of power and it stops pumping during the night.
I am using "shade" to allow the thermal box to get some sun before the solar panel which has to bring the battery up to charge before the pump kicks in and we are off again.
With lots of sun it actually works surprisingly well, it managed to bring the water up to 32C after several days of sun but next to nothing with little sun obviously. But I was thinking I have some panel watts and battery capacity spare so can I improve it.
I have found a couple of small heating elements around 12v dc 20w each which I could build into a insulated box and join that into the mix.
Cold water out of the tub > thermal box > heating element box > warm water back to the tub.
My concern is the panel, is their enough power
Panel is 5.55a at 18v 100% sun
Pump is 1.5a
Elements are 3.22a
PWM controller can only output
I just ran the numbers through a calculator I found online and it says 900L of water from 20C to 30C over 2,100mins (5 hours sun for a week) would need 359wh of heating and that's not accounting for it dropping temp during the night.
Do the heating elements output at a reduced power if they cant get all the power they need, or do they just not work ?
Is there a way to calculate the wh for the thermal box ?
Are these small elements going to add even 1C of heat to the water ?
Cheers
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