Tiny House (ADU) Battery ? Grid Tie ? Hybrid System ? VS Rewiring ?

[nifty-stuff]

California made some really big changes to state laws regarding ADU's (Accessory Dwelling Unit), making it MUCH easier for people to add a small house onto their existing residential property.

We're in the process of evaluating a few companies (sonderpods and habitat adu) to have a pre-manufactured 750 sq. ft. unit placed onto our yard.

These units are 100% electric, including a HeatPump hot water heater & mini-split HVAC.

... but it will cost $8,000 to run electricity (240 v) to this new "house"!

Well, here's the BIG Question:
I'm wondering if I should allocate that $8k from running a whole new line, and put it towards a battery/inverter system instead?

Another idea: Could I "trickle charge" a battery system with a 120 v, 20 amp circuit that is already close to the unit (so, still avoiding the $8k for the new service line) to a battery / inverter system that could then run the entire house? For example, it would trickle-charge 24/7 on 120v, but then be able to provide massive power bursts throughout the day.

I think there would be lots of ways to do this, but seeing the new videos for the BLUETTI EP500 got me thinking, "Hey, I could buy two of these units and a handful of solar panels for less than running a new electrical line... and BONUS, it would provide backup power during a blackout."

Really looking forward to your guys' thoughts!

[oregon_phil]

Your ADU is 100% electric. Make a spreadsheet of your electric devices, specs for each device (volts, amps, starting amps if appropriate). What is your predicted daily run time for each device? And what devices are going to be used at the same time.

The mini-split probably takes quite a bit of power, not to mention the electric cook top. How many equivalent BLUETTI EP500's would it take to start up a heat pump? Or run your 4 burner cooktop?

A short exercise like this will help you wrap your mind around this problem.

[nifty-stuff]

Make a spreadsheet of your electric devices, specs for each device (volts, amps, starting amps if appropriate). What is your predicted daily run time for each device? And what devices are going to be used at the same time.

Thanks for this! I've actually been working on a spreadsheet just like this!

As I do so, I am a little concerned that the output will outpace what most of the "smaller" (i.e., non-powerall size) units can handle. The big three being: Heat Pump / Mini Split
Electric Range / Oven
Heat Pump Water Heater
In a scenario where just those three are going at the same time creates really high consumption.

That said, I know that there are systems out there that can handle this kind of output, but they start getting really REALLY expensive.

[oregon_phil]

Keep going on the spreadsheet. If you are so inclined, buy a Kill a Watt and figure out all of your proposed energy use. Yes the big three are going to rack up the power, but the small loads add up fast too!

One burner on my electric range is 1500 watts; 7800 watts if all four burners are going. If it's Thanksgiving and the oven is going too, that's another 2600 watts for 10,400 watts.

After you complete your exercise, then you can start pricing potential systems. You are going about this the right way. i.e. get data, then make an informed decision

[nifty-stuff]

Keep going on the spreadsheet. If you are so inclined, buy a Kill a Watt and figure out all of your proposed energy use.

I've got one and love it! I've also got the Emporia trackers on an existing "conversion JADU" where I'm tracking how much power is used in that unit as a proxy for this 2nd unit. The big unknown is that as a rental, each tenants usage will probably vary a bit. For example, one tenant we had was barely home and rarely cooked... vs. one that might be home all day, cranking the HVAC, cooking all the time, etc.

One burner on my electric range is 1500 watts; 7800 watts if all four burners are going. If it's Thanksgiving and the oven is going too, that's another 2600 watts for 10,400 watts.

After you complete your exercise, then you can start pricing potential systems. You are going about this the right way. i.e. get data, then make an informed decision

Ya, great stuff!

... and it's here that I start seeing the $$$ go up and up and up for a system that can support those kinds of concurrent watts output.

[SunEagle]

I've got one and love it! I've also got the Emporia trackers on an existing "conversion JADU" where I'm tracking how much power is used in that unit as a proxy for this 2nd unit. The big unknown is that as a rental, each tenants usage will probably vary a bit. For example, one tenant we had was barely home and rarely cooked... vs. one that might be home all day, cranking the HVAC, cooking all the time, etc.


Ya, great stuff!

... and it's here that I start seeing the $$$ go up and up and up for a system that can support those kinds of concurrent watts output.

Unfortunately it will cost about $1500 for every kWh a solar/battery system can produce. So for $8000 you can get maybe 6kWh a day which is very small amount of energy. You will also have to replace the batteries when they die and baby sit the system to make sure you don't shorten their life span.

IMO I would pay the $8000 for a grid power connection, because even if the price of power is $0.35/kWh a grid tie will pay for itself and a solar / battery system will not.

[nifty-stuff]

Unfortunately it will cost about $1500 for every kWh a solar/battery system can produce. So for $8000 you can get maybe 6kWh a day which is very small amount of energy. You will also have to replace the batteries when they die and baby sit the system to make sure you don't shorten their life span.

IMO I would pay the $8000 for a grid power connection, because even if the price of power is $0.35/kWh a grid tie will pay for itself and a solar / battery system will not.

I'm kinda sad to say that I think you're probably 100% correct

Ugh. I guess I'm not the only one waiting for some amazing breakthroughs in batteries to REALLY drop the prices down.

[SunEagle]

I'm kinda sad to say that I think you're probably 100% correct

Ugh. I guess I'm not the only one waiting for some amazing breakthroughs in batteries to REALLY drop the prices down.

I believe battery prices will come down but unless you can perform the work yourself the price of installation will go up. Labor costs in the US will only go up.

[Ampster]

I believe battery prices will come down but unless you can perform the work yourself the price of installation will go up. Labor costs in the US will only go up.

Furthermore NEC 2020 requires the use of UL approved Energy Storage Systems so the ability to assemble a DIY battery systems will be difficult to get approval wherever that version of the NEC is adopted.

[SunEagle]

Furthermore NEC 2020 requires the use of UL approved Energy Storage Systems so the ability to assemble a DIY battery systems will be difficult to get approval wherever that version of the NEC is adopted.

Sad to say but you are correct. It is getting harder for those people that can DIY a battery system but are not allowed to do so. While I feel it may be safer for people this way it certainly will be more expensive.