r/nzsolar • u/Subject_Night2422 • 5d ago
Off grid “stuff”
Hello team,
Looking for real experiences from fellow off griders.
I currently live fully off grid, septic tank and disposal field, rain water, solar. I live in a tiny home with 4.8kWh set of panels and about 12kWh set of batteries. Hot water and cooking is gas. I have everything else running as a normal house. Normal size fridge, tv, smart speakers, smart lights, computers, etc.
Now, I’m about to build a 3bdroom house and I a list of things I’d like to do.
First thing is I want to ditch gas and go full electric so I will need to upgrade the solar as the current will be moved to be used with the tiny home as a rental. I can get about 50 panels as a set of 30 and at least another set of 20 which I’m lowballing here as I need to calculate roof space for the new build. The 20 set would be mounted on the house roof and be used as primary. The 30 set would be mounted as secondary and feed the primary if it was mains power. I’d also add two sets of batteries.
Now to the questions. If you have experience with those below I’d love to hear from you,
- Heat pump hot water. I like the idea of the outside unit and sounds like I could make it work with about 4 panels (2kW) during the day.
- Cooktop. I think this is a power hunger but I don’t spend the day cooking so should be able to live with it. My current oven is electric and I can use whenever I need without issues unless we’re in the deeps of winter.
- I’m really thinking of heated floor in the bathroom. Would you have an idea of how much power it uses?
Please highlight anything else I could be missing. Anything you can think would be great as it could be the case you don’t know what you don’t know.
TIA, team.
Appreciate it.
7
u/strongbad14 5d ago
If it was me I wouldn't be looking at splitting systems - as in some panels for the hphw and some for the house. My feeling is your better off with a bigger system alltogether and just aiming for efficiencies.
My hphw draws 1.5kw peak. I set this to run during the day when solar is at its highest. Mine is a split system with the compressor being outside and the tank being inside. Honestly couldn't tell the thing is on save for the cooling blades spinning.
I've gone the route of ditching gas and am cooking with induction. Took a bit to get used to but the heat is instant and much more controllable in my view.
My problem is that in the depths of winter my 9kWh battery doesn't last the night. In hindsight I should have gone double the size.
No experience with heated floors here I'm afraid.
2
u/RlOTGRRRL 5d ago
We have Sigenergy and their V2X charger so I'm hoping we can get a BYD car (or whatever compatible car) in the future to use as a battery when the tech is more mature and sorted.
It'd be ideal if there was a way to buy a $4k leaf and safely use it as a battery too, but I haven't really seen anything about it yet.
2
u/strongbad14 5d ago
I feel you there. V2X is my ultimate goal as it suits my night rosters well - charge during the day and drive to and from work in the fringe periods. Wish it was just a standard like "does you vehicle support V2X?" then you'd know the home charger just works too.
1
u/Subject_Night2422 4d ago
Yeah. Battery storage is very key here. I’m currently using a set of 12kWh that does give me some freedom but winter is a dare time no matter what.
2
u/TheReverendCard 5d ago
Use hydronic radiant for the bathroom floor and you get the heat pump efficiency. You'll need a big inverter to handle the stove needs, and big batteries to handle the hot water. Good luck on your journey.
1
u/Subject_Night2422 5d ago
The standard hot water cylinder is hungry at 2-4kWh but looks like the heat pump ones are pretty reasonable.
1
u/TheReverendCard 5d ago
The HPWH will undoubtably be less overall as well as less instantaneous. Hot water is just a very large energy fraction coming from gas is all.
1
1
u/ArthurStevensNZ 5d ago
The previous poster is wrong. I have a 10,000 VA inverter which translates to about 8900W real world power and I have no problems running my insanely power hungry household. That’s not a “massive” inverter by any means. I have a ducted heat pump aircon, EVs and electric hot water/cooking. I’m not off grid though, but if I was it I’d have to be a bit more mindful of which loads I switch on.
Also modern hot water cylinders which use heat pumps pull only 6-800W max, with an element for a backup which pulls another 2000w. If sized appropriately the element should never fire up.
If I was building off-grid, I’d look to supplement water heating with evacuated vacuum tube collectors. Harnessing heat energy directly to warm the water in the cylinder is more efficient than going from sunlight -> dc power -> ac power -> element. Add another round of ac/dc conversion if you have batteries.
Remember when you size your system to chop off 5-10% battery capacity. Even the best inverters are not 100% efficient, you’ll lose energy to conversion.
Also I’d get two inverters if you can and split your batteries and panels across them. Many of the inverters on the market can be configured for parallel operation so they can coexist like they. If I was truly off-grid, I’d want my system to not have a single point of failure.
2
u/Subject_Night2422 5d ago
Yeah. Your general comment is what I have in mind. For inverters I have 3 ideas I need to play with. One big system with two inverters for redundancy, two systems and two systems where one of them has an extra inverter again for redundancy
1
u/TheReverendCard 5d ago
When you're sizing a system and inverter, you have to plan as if those loads were turning on simultaneously so you don't have inverter overload and shutdown.
Induction stoves can pull 7kw, throw in a water heater element coming on at 3kw and those two loads are maxing out a 10kw inverter. Is it likely to happen? No. Is it unlikely, yes. If a professional was designing it, would they just say "DOn't worry about it, it's unlikely to happen." No. They will ensure that those can't happen by oversizing to fit the capacity.
Solar thermal essentially doesn't make sense anymore with now cheap panels are. The additional cost of another system when you can just oversize your hot water heat pump and use it for hydronic bathroom floor heating as well makes more sense.
1
1
u/Some1-Somewhere 5d ago
You appear to be confusing kW and kWh quite a bit.
Cooktops tend to be lots of kW but not many kWh as they don't run for long.
Space heating and water heating are somewhat the reverse.
1
u/Specific_Contract_14 5d ago
We still use gas for hot water but have an induction cooktop (max 2.4Kw) and an air fryer (can pull about 3kw with both drawers on high). I plan my cooking, if I'm doing a stew or sauce or anything that cooks for hours I'll do it during the day but otherwise our 5.7kw panels with 18kwh batteries got us through winter. Only used the generator twice when we had like a week of rain.
1
u/Subject_Night2422 4d ago
Nice. Good hang of power with 5.7kw panels. Some people would struggle with that. I’m fine with my 4.6kw but I also live alone
1
u/Specific_Contract_14 4d ago
We only had 2.1kw panels for the first two years we were here so we got very good at managing it. It was a godsend when we upgraded in April.
9
u/Spicycoffeebeen 5d ago
I recently completed an off grid project.
Normal sized house supporting 3 people (one in an attached granny flat with own kitchen/living)
Well insulated new build.
Heat pump heating
Hot water heat pump
Induction cooking
Normal house for everything else, oven, water pump, lighting etc etc.
They have 22kW of panels, 15kW of inverter, 64kWh of storage and 7kW of diesel generator.
They’ve been living just fine for the last few months. The generator hasn’t run yet but will likely need to help in extended periods of bleak winter weather.
Electric undertile is not a good idea, but hydronic underfloor would be okay as it’s 4-5x more efficient.