Hot Water Energy Source - Solar vs Street Gas

Forums › Home Workshop DIY › Hot Water Energy Source - Solar vs Street Gas

lende

27 posts

Geek

#303799 10-Mar-2023 00:53

Hi all,

Currently, I have a Solar panel installed at my home and an electric (indoor) hot water cylinder.

I want to reclaim the space currently occupied by the hot water cylinder.

I have two options,

Buy an outdoor hot water cylinder (solar panel): Cost ~3k + labour charges

Use piped (street) gas: Vector cost 7.5K (meter, digging, piping, etc.) + 3k for Rinnai unit + labour charges

Which one has better ROI and is economical?
any experience, feedback, or input is welcome...

1 | 2

12348 posts

Uber Geek

ID Verified

Lifetime subscriber

#3048378 10-Mar-2023 05:41

solar because its free power but it will still take a while to pay for itself, you will never get a saving on gas and the price will keep going up over time

where in the country are you?

is reclaiming that small about of space in the house worth it?

TrendMicro

Best TrendMicro deals for antivirus and malware protection(affiliate link).

BlargHonk

77 posts

Master Geek

#3048402 10-Mar-2023 08:40

How good are the outdoor hot water cylinders in the colder parts of the country? (i.e. Canterbury and South). Just in terms of energy transfer it seems odd to put a big mass of stuff you want to keep hot outside, when the outside temp can be below zero. Is the insulation on them just really good? Is there any comparisons of the energy use between an uninsulated HWC at a 20deg ambient, vs a insulated outside HWC with a 0deg ambient?

wellygary

7381 posts

Uber Geek

#3048404 10-Mar-2023 08:48

You'll never pay back the gas install and on going fixed costs if its your only gas appliance..

As well as a standard electric outdoor cylinder,

I would look at doing the numbers on a outdoor heatpump water heater. they look to be about $7K but have a much lower power consumption...

Silvrav

366 posts

Ultimate Geek

ID Verified

#3048451 10-Mar-2023 09:25

following as we have a similiar idea, but being in the south we might have to put it in the roof.

lende

27 posts

Geek

#3048478 10-Mar-2023 10:44

Jase2985:

solar because its free power but it will still take a while to pay for itself, you will never get a saving on gas and the price will keep going up over time

where in the country are you?

is reclaiming that small about of space in the house worth it?

Based in Auckland.

Not sure whether it is worth or not but it is an order from my wife so don't have an option :D

lende

27 posts

Geek

#3048479 10-Mar-2023 10:45

wellygary:

You'll never pay back the gas install and on going fixed costs if its your only gas appliance..

As well as a standard electric outdoor cylinder,

I would look at doing the numbers on a outdoor heatpump water heater. they look to be about $7K but have a much lower power consumption...

Have not found any comparison yet but will try again...

lende

27 posts

Geek

#3048480 10-Mar-2023 10:46

wellygary:

You'll never pay back the gas install and on going fixed costs if its your only gas appliance..

As well as a standard electric outdoor cylinder,

I would look at doing the numbers on a outdoor heatpump water heater. they look to be about $7K but have a much lower power consumption...

oh okay let me find out more about outdoor heatpump water heater

Scott3

3340 posts

Uber Geek

Lifetime subscriber

#3048497 10-Mar-2023 11:25

Last place that I lived that had street gas (a decade plus back), the gas was about 7c/kWh, and the daily fee was about $1 per day. For the amount we were using (4 students gas hot water & gas cooktop), we were at roughly breakeven point. I.e. everything we saved from gas being cheaper than power, was canceled out by the daily fee for the gas connection.

Just for hot water (unless you use an obscene amount), you are never going to pay back that $7,500 connection fee.

Having a street gas connection, only really makes sense if you are going to be using a heap of it. (i.e. house central heating, hot water, cooking, perhaps clothes dryer...).

In modern times, heat pumps on a cheap standard user power plan typically work out cheaper to run than a heater on street gas, and residential gas clothes dryers are pretty much unavailable in NZ, so it is harder than it was 25 years ago to use a lot of gas.

---------

Next thing to be aware of is the Climate Change Commission’s draft plan to cut New Zealand’s emissions.

The draft includes a ban on new gas connections in 2025, and then a phase out / disconnect of existing connections by 2050.

https://www.stuff.co.nz/business/green-business/124127933/choosing-gas-for-new-homes-could-be-money-down-the-drain-says-consumer-nz

Note this hasn't been adopted by the government, who are working to release a gas transition plan by the end of the year.

https://www.mbie.govt.nz/building-and-energy/energy-and-natural-resources/energy-strategies-for-new-zealand/gas-transition-plan/

Unclear what exactly will be adopted by the government, but there is a substantial risk that your expensive street gas connection will be disconnected in 27 years. And if your gas water heater dies in say the last decade of that, it will be hard to justify replacing it with another gas appliance, so you might not even be able to use all those years.

Don't pay too much attention to the big money "Gas is chaining" campaign by various vested interests.

Some of what they are proposing is technically questionable. i.e. "Phase 3: Conversion, Stepwise conversion of network branches to 100% H2". As an engineer who has worked on hydrogen piping systems in the industrial space, this is questionable. Hydrogen is a real pain to work with. It will embrittle metals, leak through solid steel etc. The design needs to consider this. You need special valves, and you cannot use threaded connections, due to how easily hydrogen leaks through stuff.
Lets face it, in most cases we use gas because it is cheap. Often the unwanted byproduct of oil drilling. The nonfossel gases they are talking about are likely to cost a heap more.

-----

Final thing to consider is your solar setup. Going electric would allow you to better optimize for this. As you know, you get peanuts selling power back to the grid, so you are much better to self consume.

Getting a big duel element cylinder, and a solar diverter / timer will assist you with self consuming. For example:

https://hotwatershop.co.nz/product/rheem-optima-300l-outdoor-mains-pressure-cylinder-580-x-1820/

https://digitalassets.reecegroup.com.au/m/a64b14965c96b1af/original/Specification-Sheet-Optima-Dimensions.pdf

Bottom element is connected to the solar diverter / timer, and is only operates at times of day you are likely to have lots of solar production. Top element is connected to regular power, meaning in the event that in the event it is not already heated by the lower solar element, the secondary element will kick in to heat the top bit (47L for the 300L cylinder, 90L for the 400L), much reducing the risk of running out of hot water.

----

Also note that the gas infinity hot water heaters don't tend to last as long as electric cylinders.

----

Final thing to note is that by moving the hot water location, typically the plumber will run a pipe from the outdoor location to the old cylinder location. If this is a long way, it will increase the amount of time that it takes for the water to run hot when you turn on a tap, reducing convenience and efficiency.

nickb800

2699 posts

Uber Geek

Trusted

#3048551 10-Mar-2023 11:48

Completely agree with @Scott3

Just to add a few more points:

- If you (or your wife) really must have gas and want to free up that cupboard space, go for LPG bottles not piped. As above, you just wont pay back the cost of piped gas installation or daily fees.

- First Gas is proposing to have a bunch of plants around the country generating hydrogen from electricity, and running this through existing gas lines to replace natural gas. If this actually happens (i share Scott's skepticism) this would mean modification or replacement of your gas water heater in approx ten years time. In generating hydrogen they will face an efficiency challenge with potentially 50% (I've seen round trip efficiency estimates from 20-90%) of the electricity energy put into this process coming out as energy in the hydrogen. This means that to make one unit of hydrogen energy they would need two units of electricity energy. There's lots of variables, but in any case I can't see how hydrogen powered water heaters would be cheaper to run than electric water heaters in this scenario.

- If you are going to keep a cylinder, consider going night rate or night rate plus afternoon boost which has the benefit of fairly low operating costs and fairly low upfront cost too

Newtown

128 posts

Master Geek

ID Verified

#3048618 10-Mar-2023 12:33

Have you looked at these CO2 heat pumps for water?

https://www.reclaimenergy.co.nz

I wouldn't go near gas, just the daily fixed costs that keep increasing are a major deterrent. We have a solar system and we're moving away from fossil fuels to electrify everything. I haven't got a Reclaim system yet, but will in due time.

eonsim

262 posts

Ultimate Geek

#3048643 10-Mar-2023 13:45

So when you say solar panel are you meaning solar hot-water heating panel or a solar electricity panel? As there are significant differences in options between the two.

Like the others I'd strongly recommend going traditional Electric or Heat Pump electric hot water cylinder. If you have solar power (photovoltaic) then the electricity generated by the solar panels can be used to heat the water by adding either a Timer or Solar Diverter to the hotwater cylinder and solar system. These will significantly increase the proportion of your solar power you use improving the pay back period and significantly reducing your power bill.

If you have a solar hot water panel (and want to keep it) that may complicate things as the system will need to be hooked up to the new hot water cylinder, potentially limiting the placement of the new cylinder outside.

billgates

4624 posts

Uber Geek

Trusted

#3048644 10-Mar-2023 13:55

@Newtown I have looked at the Reclaim system and the Sanden (Rheem in NZ) are the best heat pump hot water systems you can get from COP and firsthand experience of hundreds of Australian homeowners' point of view. The compressors for both the Reclaim and Sanden are made in the same factory in Japan. Their differentiation is the cylinder manufacturer and controller. Reclaim is releasing their new V2 compressor and V2 controller which will add WiFi and a smartphone app in April in Australia/NZ. The pricing for Reclaim is around $10k installed with a 315L cylinder.

A good 400l to 500l hot water cylinder with 2 x 3.6kW elements is around $4k installed which is now what I am more inclined towards as the $6k difference can go towards buying a battery setup for the solar PV system.

Do whatever you want to do man.

Newtown

128 posts

Master Geek

ID Verified

#3048653 10-Mar-2023 14:20

@billgates – I know that the Reclaim unit is a white label Chofu unit, but not sure if Sanden is too.

Tell me more about the v2 units, that's more than I know? Link?

What about the lower PV generation in winter? This is the reason I wanted to go down the hot water heat pump for efficiency? At least you'll have time to monitor this winter and reassess.

billgates

4624 posts

Uber Geek

Trusted

#3048657 10-Mar-2023 14:36

@Newtown I will be ok with the 2 x 7.47kW PV arrays split across two phases as I will be looking at installing a 3.6kW element on each of the phases. The batteries will also help top up any extra power required during rainy/winter days. Our lowest winter period generation prediction is 750kWh. I am thinking of adding another 4kW inverter and 5kW of panels (11 or 12 more) on the 2nd phase where the ducted aircon, laundry and where the primary element might be for the hot water cylinder, but this is the last Wishlist option until we get our batteries sorted first followed by some landscaping around the home. Not to mention, it will take a lot of convincing of our installer to get on top of that 35-degree roof pitch to install more panels hehe.

While the $6k savings in your case will not result in a full upgrade to your existing PV system but I reckon for another $10k ~ $11k you could add another 4kW or 5kW SMA inverter along with more panels to your existing setup which will help with your EV, winter, and rainy days?

Reclaim-QuickStartGuide-v2Release-Issue03-Jan2023-art-Web.pdf (reclaimenergy.com.au)

The v2 heat pump has a more powerful compressor which increases the thermal output to 5.24kW (with better COP)

The reason why I am also more inclined towards the traditional hot water cylinder is because you can get a solar diverter like myPV AC.Thor9 which integrates with SMA Home Manager and you can configure it to heat up automagically using excess solar only whereas with Reclaim you will need to set a timer to use your Solar PV excess but cloudy/rainy times can be an issue. Saying that the WiFi app will make controlling the unit a lot easier now and the low power consumption even using grid power won't be a huge deal breaker.

Do whatever you want to do man.

Newtown

128 posts

Master Geek

ID Verified

#3048793 10-Mar-2023 17:38

@billgates – thanks for the link, the new unit looks pretty good and I've emailed the NZ Reclaim office to get a sense of availability. My intent is to add more panels at some point to get another 4-5kW as you mentioned.

I've never heard of myPV AC.Thor9 before, and it looks promising that it integrates into Home Manager. With the Reclaim system, there's an option to control it via dry contact/modbus then potentially glue it into HM via SmartApplicationEnabler.

How will you get AC.Thor9 when it's only available in DE? I guess you could use a parcel forwarder.

I'm liking where you're heading with your system. You should contact SMA AU to write up a case study of your exemplar set up. The installer will moan about the roof pitch, but at least you're a serious customer :D

1 | 2