reducing gas for hot water

[paulthefarm]

Has anyone tried using solar pv panels to drive emersion element in CH hot water tank, without any feed in tarriff scheme, just to heat the water and reduce gas consumption?

Whats the lowest number of panels that could be used?

 

[Y Fan Wen]

First answer would be to just use solar water heaters:

Solar Water Heating Guide: Types And Benefits | Screwfix

Discover everything you need to know about solar thermal panels: how solar thermal systems work, the cost of solar water heating, and advantages and disadvantages.

www.screwfix.com

Modern solar panels seem to be about 400 watts so 8 or 9 panels would be close to 3.5kw immersion. An 8 array would be around a max of 240 volts.

Peimar - 400W Solar PV Mono PERC - Half Cell - All Black

The Peimar OR10H400M is a 400W monocrystalline solar module manufactured in Italy, it is MCS approved and backed by a 30 Year Linear Power Warranty. Suitable for grid tied PV arrays and eligible for the feed in tariff in the UK. These large solar panels can also be used for battery charging in...

www.sunshinesolar.co.uk

 

[Exfarmer]

Any amount of electricity fed into the immersion will produce heat, so hooking a panel to the connections should work.
However panels are DC and normally your average immersion will be made for AC and I do not know the physics.
also panels are generally about 35 volts so would be best ( i think) to stack in series to push voltage up.
to be honest I would speak to some one like this guy, very helpful
Martin Lovatt
Giants Wood solar
07876 357021
he lives off grid and specialises in second hand kit
may be others here on such as @renewablejohn who can tell you more

 

[GEMS]

Has anyone tried using solar pv panels to drive emersion element in CH hot water tank, without any feed in tarriff scheme, just to heat the water and reduce gas consumption?

Whats the lowest number of panels that could be used?

In theory it would work but not very effecient at low power levels . Elements need 240v (single phase) and although your open circuit volts would reach (or exceed ) this in practice 240 v with no power connected to an element would result in a huge volt drop .
Low volts would = low current across the elements fixed resistance - get your physics books back out and research V/I/R. - Ohms law.

Ohm's Law | Electronics Club

Learn about Ohm's Law which shows the relationship between voltage, current and resistance, V = I x R.

electronicsclub.info

Far better to just install solar panels and grid connect (no requirement for feed in tarrif). Any power produced will be used on farm and reduce imported electric.
If you ever get into the situation where you are exporting electricity (unlikely !!!) then install a diversion controller such as a Solic. These divert surplus electricity to your immersion element and monitor production preventing any export.

 

[e3120]

Any amount of electricity fed into the immersion will produce heat, so hooking a panel to the connections should work.
However panels are DC and normally your average immersion will be made for AC and I do not know the physics.
also panels are generally about 35 volts so would be best ( i think) to stack in series to push voltage up.
to be honest I would speak to some one like this guy, very helpful
Martin Lovatt
Giants Wood solar
07876 357021
he lives off grid and specialises in second hand kit
may be others here on such as @renewablejohn who can tell you more

Yes, you'll get heat, but not much, as mains immersions are higher resistance to 'balance' the higher voltage.

Power = V squared/R, so 2% at 1/7 of the voltage.

 

[renewablejohn]

Easiest way is just replace the ac element wirh a dc element. easy job and cheap

https://www.bimblesolar.com/12v-600w-screw-in-water-heater

 

[sjt01]

Easiest way is just replace the ac element wirh a dc element. easy job and cheap

https://www.bimblesolar.com/12v-600w-screw-in-water-heater

What is the difference? The element is resistive, and does not care whether it is AC or DC. What you might need to change is the thermostat, as interrupting DC is rather more difficult than AC. DC forms a stable arc, but on AC the arc is extinguished 100 times a second.

 

[Y Fan Wen]

What is the difference? The element is resistive, and does not care whether it is AC or DC. What you might need to change is the thermostat, as interrupting DC is rather more difficult than AC. DC forms a stable arc, but on AC the arc is extinguished 100 times a second.

That was what I was a bit uncertain about. May have to have the thermostat work a relay which actually breaks the main circuit.

 

[sjt01]

That was what I was a bit uncertain about. May have to have the thermostat work a relay which actually breaks the main circuit.

Chose a relay rated for DC

 

[jasongrantorino]

Using solar PV panels to heat water directly can totally cut down on gas use. Even without a feed-in tariff, it's a solid way to save. You could probably start with around 2-3 panels to see some decent results, but more panels would obviously give you a bigger boost. It's all about finding the right balance for your setup. You can check out this article from the Department of Energy for more details: https://www.energy.gov/energysaver/solar-water-heaters

Using solar energy to reduce gas use would also give you more savings in the long run especially if you’re in the US. States like Massachusetts have great solar programs where they give you incentives for stuff like this: https://massachusetts.statesolar.org

 

[GEMS]

That was what I was a bit uncertain about. May have to have the thermostat work a relay which actually breaks the main circuit.

yes .but .........
Renewablejohn is advocating a 12v DC 600w element -designed for 12v 600w .
You are contemplating a 0-240 v dc from your solar panels on an element designed for 240v and probably 3kw. The current flow at low volts on this approx 30 ohm element is miniscule at low volts and will do little heating.
Do the Ohms law calculations at your volts, compare to your element designed voltage and resisitance.
A 12v element @ 600w will have very little resistance probably 2 or 3 ohms.
Fine but how are you going to limit volts to 12v ? on a sunny day ??
Its not as easy as it appears -thats why i suggested grid tie with diversion controller to maximise energy production.

 

[br jones]

i boost

 

[suffolksmallholder]

All way too complicated. Fit a solar thermal panel and the control unit. Sorted.
SS

 

[renewablejohn]

yes .but .........
Renewablejohn is advocating a 12v DC 600w element -designed for 12v 600w .
You are contemplating a 0-240 v dc from your solar panels on an element designed for 240v and probably 3kw. The current flow at low volts on this approx 30 ohm element is miniscule at low volts and will do little heating.
Do the Ohms law calculations at your volts, compare to your element designed voltage and resisitance.
A 12v element @ 600w will have very little resistance probably 2 or 3 ohms.
Fine but how are you going to limit volts to 12v ? on a sunny day ??
Its not as easy as it appears -thats why i suggested grid tie with diversion controller to maximise energy production.

Actually suggesting getting a dc element which matches the dc voltage of the panel not necessarily 12v that was just an example. ie if solar panel 48V then get a 48V element.

 

[C.E.S]

MY-PV ELWA DC Immersion Heater​

IMO this would be your easiest option with built in MPPT tracker and thermostat plus the option to boost off AC if you ever needed. Great bit of kit

 

[Y Fan Wen]

yes .but .........
Renewablejohn is advocating a 12v DC 600w element -designed for 12v 600w .
You are contemplating a 0-240 v dc from your solar panels on an element designed for 240v and probably 3kw. The current flow at low volts on this approx 30 ohm element is miniscule at low volts and will do little heating.
Do the Ohms law calculations at your volts, compare to your element designed voltage and resisitance.
A 12v element @ 600w will have very little resistance probably 2 or 3 ohms.
Fine but how are you going to limit volts to 12v ? on a sunny day ??
Its not as easy as it appears -thats why i suggested grid tie with diversion controller to maximise energy production.

I was told by my installer that the voltage increases rapidly to the rated voltage as it gets light and then the wattage increases as the light gets stronger. 8 panels at 30v will give 240 so most of the day it will be roughly the same as the standard immersion but the wattage and heat will vary through the day.
As I said at first, solar water heating is better.

 

[2wheels]

we have an immersun connected to the immersion heater in the tank. the gas boiler heats the water when no sun . the electric immerser is not used otherwise. saves a bit on the gas bill. the cost of the immersun was £450 installed, thought it was dear at the time but wouldn't be without it now.

 

[Wisconsonian]

I was told by my installer that the voltage increases rapidly to the rated voltage as it gets light and then the wattage increases as the light gets stronger. 8 panels at 30v will give 240 so most of the day it will be roughly the same as the standard immersion but the wattage and heat will vary through the day.
As I said at first, solar water heating is better.

Except solar water heaters are expensive and unreliable compared to PV. Easiest way to heat water with PV is probably grid tied and use the standard load controls to avoid export.

Running a resistance heating element on DC direct from the panels is a classic case of the advantage of Maximum Power Point Tracking. If the light is weak, then the heating element will draw too much power and the panels won't reach their MPP. Then in full sun the element won't draw enough and the voltage will be slightly high, as the amperage will be below MPP. The panels might be able to be sized to the load so you achieve 80%? or maybe only 50%? It wouldn't need a MPPT, two or three heating elements, or banks of elements would achieve most of the efficiency gain. Say one small element, then another two relays that connect another two larger elements for full load.

 

[hollister]

we have an immersun connected to the immersion heater in the tank. the gas boiler heats the water when no sun . the electric immerser is not used otherwise. saves a bit on the gas bill. the cost of the immersun was £450 installed, thought it was dear at the time but wouldn't be without it now.

Same but dumb oil boiler which relies on heat coming back from coil, wish we had a double immersion element tank as it heats the top but doesn't heat whole tank so runs out quickly. Thinking about a DIY solar water panel to circulate the tank as well as heat to even put the temperature.

Certainly makes it more noticeable when there's an issue with solar tripping.

 

[2wheels]

Same but dumb oil boiler which relies on heat coming back from coil, wish we had a double immersion element tank as it heats the top but doesn't heat whole tank so runs out quickly. Thinking about a DIY solar water panel to circulate the tank as well as heat to even put the temperature.

Certainly makes it more noticeable when there's an issue with solar tripping.

ok, ours heats the whole tank.