Diverting Grid Tie solar to hot tub
Discussion
Bought a house with a large outbuilding, flat currugated roof - plenty of space for solar- south facing.
I'm going to put up 3.5ish kw of solar with an inverter and run it "grid tie" - i.e. no rebates from the energy co, just using the excess when its there - I run a small business from home and will use at least some of the energy during each working day.
I'd like to harvest the excess and using a diverter to the immersion tank is easy enough - hook it up to the heaving element, with a stat, and off you go.
More complicated is I'd rather the energy go to heating a hot tub - but the catch is all the diverters I see are aimed at connecting to resistive loads i.e. heating elements - but I want to either a) power the hot tub entirely with the excess - though I can't see this as prictical because it would constantly be switching between sources, or b) more likely, tap into the tub heater element, but then I'd also need to power the circulation pump.
Anyone done this?
(p.s. grid tie because I can buy the panels, mounts, inverter and diverter for well under £2k, and do it through my company.)
I'm going to put up 3.5ish kw of solar with an inverter and run it "grid tie" - i.e. no rebates from the energy co, just using the excess when its there - I run a small business from home and will use at least some of the energy during each working day.
I'd like to harvest the excess and using a diverter to the immersion tank is easy enough - hook it up to the heaving element, with a stat, and off you go.
More complicated is I'd rather the energy go to heating a hot tub - but the catch is all the diverters I see are aimed at connecting to resistive loads i.e. heating elements - but I want to either a) power the hot tub entirely with the excess - though I can't see this as prictical because it would constantly be switching between sources, or b) more likely, tap into the tub heater element, but then I'd also need to power the circulation pump.
Anyone done this?
(p.s. grid tie because I can buy the panels, mounts, inverter and diverter for well under £2k, and do it through my company.)
Not exactly the regular meaning of 'grid tie'.
Grid tie just means an inverter synched to the grid, generally one which won't run by itself in the absence of an incoming grid
What you are implying is some kind of 'diverter' system which prioritises running water heating from solar power rather than exporting the excess.
If you want the pump to run 24/7, then look at using something like an Eddi to control the heating side.
Or you could look at a system to turn the thermostat up when the sun is shining?
Someone I know has a bunch of stuff running from a self-installed off-grid solar/battery system, switching to mains when the batteries are low.
That approach offers UPS capacity for his business.
Grid tie just means an inverter synched to the grid, generally one which won't run by itself in the absence of an incoming grid
What you are implying is some kind of 'diverter' system which prioritises running water heating from solar power rather than exporting the excess.
If you want the pump to run 24/7, then look at using something like an Eddi to control the heating side.
Or you could look at a system to turn the thermostat up when the sun is shining?
Someone I know has a bunch of stuff running from a self-installed off-grid solar/battery system, switching to mains when the batteries are low.
That approach offers UPS capacity for his business.
Aye - "Grid Tie" seems to be commonly used by DIY solar users who don't get a FIT.
I'll look at the Eddi. I came across that recently. They show it heating a pool - using the relay to swict on teh circ pump when its heating - just need ot see how to tap into the hot tub (that I've not bought yet) wiring for that, and the heater.
Update: Ahh - found someone online who's done it. Just need to make sure whatever tub I buy gives physical access to the circ pump relay / switch and the heater relay.
I'll look at the Eddi. I came across that recently. They show it heating a pool - using the relay to swict on teh circ pump when its heating - just need ot see how to tap into the hot tub (that I've not bought yet) wiring for that, and the heater.
Update: Ahh - found someone online who's done it. Just need to make sure whatever tub I buy gives physical access to the circ pump relay / switch and the heater relay.
Edited by Griffith4ever on Monday 25th August 09:16
Griffith4ever said:
Aye - "Grid Tie" seems to be commonly used by DIY solar users who don't get a FIT.
I'll look at the Eddi. I came across that recently. They show it heating a pool - using the relay to swict on teh circ pump when its heating - just need ot see how to tap into the hot tub (that I've not bought yet) wiring for that, and the heater.
As I understand it, the Eddi (terrible name) uses phase control or PWM. Therefore it can directly drive a resistive load (such as a heater).I'll look at the Eddi. I came across that recently. They show it heating a pool - using the relay to swict on teh circ pump when its heating - just need ot see how to tap into the hot tub (that I've not bought yet) wiring for that, and the heater.
Driving a pump wouldn't be possible - which is why in your post there is mention of a relay to turn on the pump from the AC supply.
Not sure if the Eddi has an output that can be used to switch a relay - but driving that from the PWM output might not be trivial.
(Quite happy to be corrected if my understanding is wrong)
It may be worth checking out the actual heat demand of various hot tubs.
A friend here is an ex builder with a bad back, very fond of his hot tub.
He reckons it doesn't really cost all that much to run, being a very well insulated version.
Allegedly it's cheaper to have a quick shower and soak in the tub than to have a decent bath every night, in terms of electricity used, or so he claims.
I guess the tub is going to lose a lot of heat when the lid is off, which generally won't be when the sun is shining...
A friend here is an ex builder with a bad back, very fond of his hot tub.
He reckons it doesn't really cost all that much to run, being a very well insulated version.
Allegedly it's cheaper to have a quick shower and soak in the tub than to have a decent bath every night, in terms of electricity used, or so he claims.
I guess the tub is going to lose a lot of heat when the lid is off, which generally won't be when the sun is shining...
I run two 5000va victron inverters, 19kwh of pylon batts and a modest 3.5kw array on the shed. System is set to never export. It runs the hot tub easily in the summer months - with some off peak battery charging as well.
Tub tends to go off october because even with a full charge overnight, the batteries will be depleted by early evening (in addition to supplying the entire household)
I should really fit a heat pump, but the tub itself is about 15 years old and apart from a couple or recirc pumps - refuses to die (master spa with steel frame)
Tub is heated overnight off-peak (about 5kwh) and daytime for 4 hours (4kwh) - as it gets colder outside that will go up to 13kwh and is usually the point i turn it off
Tub tends to go off october because even with a full charge overnight, the batteries will be depleted by early evening (in addition to supplying the entire household)
I should really fit a heat pump, but the tub itself is about 15 years old and apart from a couple or recirc pumps - refuses to die (master spa with steel frame)
Tub is heated overnight off-peak (about 5kwh) and daytime for 4 hours (4kwh) - as it gets colder outside that will go up to 13kwh and is usually the point i turn it off
Griffith4ever (I miss my Chim!) - you might find it easier if you wired it up with a decent control mechanism/system. Something like HA might be overkill, but it would make it trivial to control your systems. e.g. "when excess power is > 200w, power the pumps" and "when excess power is > 3000w, power the heater".
Modulating the power of immersion heaters is slightly harder, there are off-the-shelf tools like Eddi etc which do this.
As I said, HA (open source Home Automation) is perhaps at the geekiest end of the scale; in the midrange, Victron may have the ability to do all this using their control systems.
Modulating the power of immersion heaters is slightly harder, there are off-the-shelf tools like Eddi etc which do this.
As I said, HA (open source Home Automation) is perhaps at the geekiest end of the scale; in the midrange, Victron may have the ability to do all this using their control systems.
No ideas for a name said:
Griffith4ever said:
Aye - "Grid Tie" seems to be commonly used by DIY solar users who don't get a FIT.
I'll look at the Eddi. I came across that recently. They show it heating a pool - using the relay to swict on teh circ pump when its heating - just need ot see how to tap into the hot tub (that I've not bought yet) wiring for that, and the heater.
As I understand it, the Eddi (terrible name) uses phase control or PWM. Therefore it can directly drive a resistive load (such as a heater).I'll look at the Eddi. I came across that recently. They show it heating a pool - using the relay to swict on teh circ pump when its heating - just need ot see how to tap into the hot tub (that I've not bought yet) wiring for that, and the heater.
Driving a pump wouldn't be possible - which is why in your post there is mention of a relay to turn on the pump from the AC supply.
Not sure if the Eddi has an output that can be used to switch a relay - but driving that from the PWM output might not be trivial.
(Quite happy to be corrected if my understanding is wrong)
All looks very doable
OutInTheShed said:
It may be worth checking out the actual heat demand of various hot tubs.
A friend here is an ex builder with a bad back, very fond of his hot tub.
He reckons it doesn't really cost all that much to run, being a very well insulated version.
Allegedly it's cheaper to have a quick shower and soak in the tub than to have a decent bath every night, in terms of electricity used, or so he claims.
I guess the tub is going to lose a lot of heat when the lid is off, which generally won't be when the sun is shining...
I'm driven to it principally as we won't use all the solar during the day time, and hot tubs cost "from" £35 a month to heat. A friend here is an ex builder with a bad back, very fond of his hot tub.
He reckons it doesn't really cost all that much to run, being a very well insulated version.
Allegedly it's cheaper to have a quick shower and soak in the tub than to have a decent bath every night, in terms of electricity used, or so he claims.
I guess the tub is going to lose a lot of heat when the lid is off, which generally won't be when the sun is shining...
biggiles said:
Griffith4ever (I miss my Chim!) - you might find it easier if you wired it up with a decent control mechanism/system. Something like HA might be overkill, but it would make it trivial to control your systems. e.g. "when excess power is > 200w, power the pumps" and "when excess power is > 3000w, power the heater".
Modulating the power of immersion heaters is slightly harder, there are off-the-shelf tools like Eddi etc which do this.
As I said, HA (open source Home Automation) is perhaps at the geekiest end of the scale; in the midrange, Victron may have the ability to do all this using their control systems.
I run a full HA setup! - however, when there are 1 box solutions for under £400 then I'll always lean that way (Eddi) - still, food for thought!Modulating the power of immersion heaters is slightly harder, there are off-the-shelf tools like Eddi etc which do this.
As I said, HA (open source Home Automation) is perhaps at the geekiest end of the scale; in the midrange, Victron may have the ability to do all this using their control systems.
Griffith4ever said:
I'm driven to it principally as we won't use all the solar during the day time, and hot tubs cost "from" £35 a month to heat.
Is that '£35 a month in August, and 'all your money' in January', or £35/month averaged over a year for a small one?I'd guess if you've got the lid off for several hours a day in the winter it's going to have a fierce appetite for heat, but most people don't do that(?).
£35 a month doesn't go that far in memberships of places with pools etc.
I have 6KW of solar on the roof since 2015.
All surplus goes via a PVmate switch to the hot tank and then a 3.2kw storage heater. Works perfectly hot water all year and for most of the colder months a raging hot storage heater in the hallway warming noticeably the central portion of the house.
Summer months and the surplus once hot water is at 70deg the switch puts the surplus into a 2.2kw water heater in the hot tub. Simple resistive device. Again it just all works.
Ps Love the PVmate in ten years we had three Solar Iboost one of which threatened to burn the house down. Last four years the PVmate just gets on with the job -Iboost too hot or too cold and it switches off -its in the loft after it literally started to catch fire in the airing cupboard.
All surplus goes via a PVmate switch to the hot tank and then a 3.2kw storage heater. Works perfectly hot water all year and for most of the colder months a raging hot storage heater in the hallway warming noticeably the central portion of the house.
Summer months and the surplus once hot water is at 70deg the switch puts the surplus into a 2.2kw water heater in the hot tub. Simple resistive device. Again it just all works.
Ps Love the PVmate in ten years we had three Solar Iboost one of which threatened to burn the house down. Last four years the PVmate just gets on with the job -Iboost too hot or too cold and it switches off -its in the loft after it literally started to catch fire in the airing cupboard.
Griffith4ever said:
I'm driven to it principally as we won't use all the solar during the day time, and hot tubs cost "from" £35 a month to heat.
“£35 a month” is a meaningless figure usually made up by the people selling them or people in denial. You will note above that i provided the actual kwh consumption of mine - which you can multiply by your day rate and get a result.My tub uses between 8-13kwh a day depending on the outside temperature (I have months of graphs to back it up)
Today which is a pretty warm day it used 8.4kwh - which at the current price cap of 25.73p equates to £2.17 for the day or £65 a month minimum.
Now again in my case, I have solar, batteries and octopus go - which is 8.5p overnight and the house runs on batteries all day - so my actual rate is around 9.8p (as you still pull a little from the grid even when 100% batts)
So my tub costs 8.4kwh x 9.8p = 82p x 30 days = £24
so as you can see, the cost varies massively depending on the cost of your electricity
Winston Wolf said:
I have 6KW of solar on the roof since 2015.
All surplus goes via a PVmate switch to the hot tank and then a 3.2kw storage heater. Works perfectly hot water all year and for most of the colder months a raging hot storage heater in the hallway warming noticeably the central portion of the house.
Summer months and the surplus once hot water is at 70deg the switch puts the surplus into a 2.2kw water heater in the hot tub. Simple resistive device. Again it just all works.
Ps Love the PVmate in ten years we had three Solar Iboost one of which threatened to burn the house down. Last four years the PVmate just gets on with the job -Iboost too hot or too cold and it switches off -its in the loft after it literally started to catch fire in the airing cupboard.
Did you add the heater to the hot tub, or is that the existing one?All surplus goes via a PVmate switch to the hot tank and then a 3.2kw storage heater. Works perfectly hot water all year and for most of the colder months a raging hot storage heater in the hallway warming noticeably the central portion of the house.
Summer months and the surplus once hot water is at 70deg the switch puts the surplus into a 2.2kw water heater in the hot tub. Simple resistive device. Again it just all works.
Ps Love the PVmate in ten years we had three Solar Iboost one of which threatened to burn the house down. Last four years the PVmate just gets on with the job -Iboost too hot or too cold and it switches off -its in the loft after it literally started to catch fire in the airing cupboard.
Griffith4ever said:
Batteries = money. I just want a low cost way of diverting unused energy, used, or not.
i’m not going to go into the technical details of how you might achieve that - as it’s domestic electrics and the “pro’s” will jump all over me (rightly to an extent).I suggested batteries because it’s a universal simple solution for dealing with excess power that you can use throughout your home - yes it costs money, but the costs have come down substantially in the few years i’ve had mine.
Your solar isn’t producing anything in the winter - whilst I charge my batteries at 8.5p and run the house at all other times over the winter.
I’ve got enough space for 6-8kw of solar on my roof, but the roi in my case isn’t worth it. The only time it would be worth it, is if cheap overnight goes away (which it will eventually imo)
Winston Wolf said:
Griffith4ever said:
Did you add the heater to the hot tub, or is that the existing one?
I place in the hot tub a submersable heater unit off Ebay - £10. The inbuilt heaters on HT's would require the pump to be working which the switches do not allow.Its really quite simple.
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