Integrating a Prius into an Off-Grid Home

That is possible, In my region there are many doing it.

There are after market accessories for the Prius that allow you to power your home with your Prius.

As does any battery-bank.

The PowerWall is available on a 10-year lease, It is rated for 50 cycles per year. So if you use it as your battery-bank, it could power your home over-night, for 50 nights per year.

I bet if you over-use a PowerWall 365days/year, you would expect to kill it in a year and a half. The company should charge you the full 10-year lease price for it at that point.

As for cloudy days, you would still need a power source, a Prius could fill that role.

 

I keep thinking about the same problem especially after looking at last month's utility bill. My thoughts:

• traction battery energy storage - very, very risky as you need some sort of battery manager because the Prius battery manager would be off. Minimum requirement: (1) voltage high and low, (2) temperature monitoring, and (3) cooling fan control.
• waste heat capture, exhaust - two solutions: former gas heater fed by exhaust, or wrap exhaust with metal tubing. The gas heater requires: (1) temperature monitoring, (2) exhaust valve, and (3) freezing drain. The metal tubing wraps the exhaust system AFTER the catalytic converter and with high-temperature insulation and water shield. Water is injected at one end and live steam extracted from the other. An insulated, pipe carries the live steam into the home for hot water pre-heat and space heating. Water condensate has to be gathered and hopefully sent back to the car. Requires: (1) temperature monitoring and (2) freezing drain.
• waste heat capture, engine - tap the cabin heater loop to some sort of water heat exchanger. VERY COMPLEX because it must not cool the engine block leading to block warm-up and must also deal with temperature extremes.
  
• electrical - we need to investigate the electrical compressor interface to see if it runs on house voltages, currents, and frequencies. This would be one of two efficient converters from Prius-to-house power. I suspect we are talking about 1-2 kW of power. Not a lot but enough to offload home electrical loads.
• non-gasoline fuel - either natural gas or propane, gas valve that operates when the engine is running to 'enrich' the air stream. There will still be some gasoline burned but a fraction of fully running the engine. This approach minimizes the engine modifications. The other alternative is to 'import' a natural gas or propane fuel system and without bothering the 'powers that be', install, integrate, and use when home. Make your Prius dual-fuel. Alternatively, ethanol/methanol but now we're getting into some tricky stuff getting it non-taxed.

Bob Wilson

 

It'll be very expensive if you go through a battery. As cost to the installer, it adds 12 cents per kWh already.

My solar system is a grid-tied and inter-connectivity agreement is for 15 years. So, I'll look for a solution in 15 years.

For now, I have 600 Watts inverter to clamp onto 12V battery for emergency. That should cover the gas boiler and fridge.

 

It will be my dream house.

 

For an off grid home, using a Prius as a supplemental power generator would be too much hassle. Hooking it up one or two times a year to keep the frig running isn't big deal. If you need to do so once a month because of cloudy days, it starts becoming a chore, and it is probably time to rethink the battery bank size and off grid power options.

Lead acids aren't the most environmentally friendly battery, but are probably still the most economical for a back up battery bank. Not as simple to install as the Power Wall, but it will give more flexibility in design the bank to your needs.

Wind is also an option to supplement or use instead of PV.
Wind Power Your Home | Wind Energy Foundation
While I bet going with the basic electric pump for the well is the most economical, just having it as an option is worth mentioning.
Aermotor Windmill Company - Wind-Powered Water Pumps

It might be seen as sullying the 'greeness' and self-efficiency of the off grid home, but what about using propane. It is clean burning. It could reduce the electric load for heating and hot water; definitely if geothermal isn't an option. It will reduce the load for cooking and the clothes dryer. it could even run the refrigerator. If available for those uses, it could be used for a generator, without the chore of hooking a car up to the house, and having it unavailable as it charges the battery bank. It also allows a smaller bank.

 

For pollution control, a propane engine just produces less than a gasoline one to begin with. People across the street have a generator, and I can understand the noise concern.

I would think the PW would have overcharge protection built in. It reaches full and just stops pulling a charge. The Prius or generator would then idle down, unless wired to allow them to directly power the house.

My point is that if your power system whether solar, wind, or a combination with battery bank isn't enough to meet your needs without leaving you without power one or two times a year at most, then your system hasn't been properly designed to meet your needs. You either need a larger battery bank or more, or varied, generation capacity. I think if you decide to use propane for other uses, like cooking, then installing a back up generator could be a better option vs adding more batteries, PV panels, or a larger windmill. Depends on its price, and installation cost. I would want a noisy one in a separate shed.

If you are looking for a solution for the chance you might be without power one or two days a year, I think a decent pure sine inverter installed in the Prius to power the frig and well pump*. I don't know if charging up the battery bank itself is such a good idea. At least, charging it up to just discharge it right away again. Get it up to where the batteries are happy, and then disconnect it. Its there for when the sun aint shining, or wind blowing. Why put it through another full cycle during an occasional emergency 'power outage' and take some time off its life when you have an emergency back up for the essentials.

I remember a post by someone off grid recommending leaving occasional use, high draw items like power tools out of the calculations for the PV and battery size, and just using a portable generator for them. It saves money on overbuilding the system for such items. Prius and inverter could also be used for such.

*Be sure to have a plug installed to power the pump from such a source. Co-worker was without power for days after Sandy, and didn't have a way to get their portable generator to power their pump.

 

I am interested in the propane solution too but live in a city where local ordinance may forbid any except the small tanks used for gas grills.

I'm looking at the Prius plug-in to the house as a co-generation as well as keeping the car at operating temperature. With heat recovery, the system becomes competitive with utility power and the house and hot water stay warm. Then when I need to take a trip, unplug from the house and start at +52 MPG instead of paying the warm-up price.

Of course you my realize that if I could fuel the car with natural gas when plugged-in and recover most of the heat for the house. The electricity generated could 'charge a Leaf' and be cheaper than the grid. The reason being grid electricity throws away over half of the heat.

So I pay for the gas to heat the house but first 'burn it' in the car. The previously lost heat from the car, some fraction of it, heats the house. The electricity generated by our 38% efficient, Prius is powered in the parking place by the untaxed, natural gas I've already paid for. Gas company is happy; my utility bill is happy, and; the electric company is wondering 'How'd they do it?'

Bob Wilson

 

That sounds complicated for the gains when home cogen units are on the market.
http://green.blogs.nytimes.com/2009/04/29/a-winters-tale-my-first-season-with-micro-combined-heat-and-power/?_r=0
Honda Worldwide | Technology Picture Book | Cogeneration I don't think it's available in the US, but Honda has one that is an actual Atkinson engine.
There are also home fuel cell cogen units out there, but the likely fall in the too expensive range.
The warm up penalty is reduced for the gen3, and should be more so for the plugin, because it can lean on the battery for more during the warm up cycle.
Hooking up and disconnecting an exhaust heat recovery system everytime you need to take the car out will make the 'plugging in takes too much time and work' crowd faint.
If cargo space loss isn't a concern, converting a PPI to CNG or even bi-fuel isn't a technical challenge. I think home refueling it while providing power, some of which will go to the refuel compressor, will be the challenge. With a 8GGE CNG tank, the Civic GX took overnight to fill up with home refilling. If not actually refueling at home, but just running the engine, will the residential supply be high enough pressure for the engine? I'm guessing probably.
Then what do you do when the mobile cogen unit is out an about?

That said, I can appreciate doing a project for entertainment reasons.

 

I wish Toyota offers a home off-grid package with PiP2.

 

Isn't it available in Japan now?

They probably won't to reduce comparisons to the Mirai.

 

Yes, PiP has the plug out cable in Japan. Not sure of the power rating.

Mirai's plugout can supply 9kW. Much more than Tesla Powerwall 2kW.

 

It just needs a ready supply of hydrogen.

If your home use really is a steady 9kW, then the Mirai will be empty in under 7 hours.

2kW steady output from a Powerwall should be plenty for most homes.

This is amusing: Recharge Your Nissan LEAF Via Toyota Mirai Fuel Cell Sedan

 

This actually makes perfect sense and is not that complicated. All you need to do is run PEX tubing in your house and run the engine coolant into a hot water tank.

For extra credit, I would opt to use a liquid cooled diesel generator fueled with biodiesel. Then, I need to control the discharge of the battery and engine coolant temperature with information from the thermostat at my house. The hardest part will be writing the software, but I think I am capable of the virtualization/networking for IoT tunneling to protect the thermostat and Prius from hacking.

It would also be cool if there were a self flying kite that could turn the flywheel of the generator.

You mention "an exhaust heat recovery system."

If I had a liquid cooled biodiesel generator, I would use the engine exhaust from that generator to heat the engine block of the Prius. I could pipe the exhaust in through the exhaust gas recirculation circuitry. This would force the exhaust gas from that diesel generator through the catalytic converter improving emissions of the generator. I don't expect more than a few hundred watts from a 15kw generator from the exhaust, but I would also be able to heat the engine coolant of the car with the generator, and I expect to find at least an extra 15kw of energy from the generator's engine coolant. 100% improvement on the efficiency of the generator is a conservative estimate.

So, 38% thermally efficient E85Prius*(x) + 50% thermally efficient BioDiesel Generator*(z) = system efficiency

 

Also, look at the cost of using the generator. If the fuel is $6/gal but the thermal efficiency is 12-25% better than the Prius, it is still not competitive. I would apply for a road tax refund, but I think there also needs to be a higher road tax on road fuel.