Does anyone happen to have a Prius Prime & live off grid? Need insight, tia!

My house was built with baseboard electric (actually in-wall blowers, same general concept) and a wood stove. The wood is nice in cold weather, but the regional air quality authority now usually bans it (for homes with another form of heat) in the weather where it is nicest to use. Which as actually a good move, we used to suffer from localized winter air quality as bad as any summer forest fire season, due to common poor wood burning practices.

We put in a single zone ductless heat pump for the largest house space over a decade ago, and it provides almost all the heat we need. The far end of the house needs only a little bit of supplemental heat from the original blowers. This was the largest element of our conservation efforts, the heat pump water heater was the next largest. But there were numerous elements too, such as upgraded attic and floor insulation, greatly reduced air infiltration, and better management of winter solar heat gain.

Since adding the heat pump, we've used the wood stove only a few times for longer power outages. The power has a habit of coming back on about the time about the time the fire is well established.

 

Build your battery storage someplace that the temps are pretty consistent such as a basement. Used Tesla Batteries actually make a great storage system and they aren't too expensive.

Also, you'll want to setup your power generation in a east, south, and west facing setup. It's basically overbuilding your panel setup, but this way you'll get power generated all day rather than just in the peak hours. This would give you power generation from dawn till dusk instead of the average 5.5 hours if you put your panels in one direction only. It also reduces your load on the batteries themselves especially in the summer months. Should let you downsize your battery requirements a little as you'll only need them at night instead of all day. I would also add in a bird friendly windmill of sorts so that you can take advantage of any wind that might be around.

 

I would get an electric fireplace as well. One of the ones made for an RV style. That way, if you need heat especially during the day you can run off the panels and not use gas which tends to move quickly during the winter months.

 

MMBH, I think you'll need to see lower cost PV panels and batteries before it'll be cost effective to charge your Prime off-grid. Without charging the Prime is a better hybrid due to it's larger battery.

 

I would normally suggest that off-grid folks making their own electricity, NOT use electric heat. At least not as a primary source. Electric generating capacity is somewhat expensive, and building enough capacity for resistance heat is an inefficient use of those capital dollars.

There are exceptions, of course. The first that come to mind are:
(*) when surplus power or energy must be shed, even if wasted;
(*) micro-hydro with (probably seasonal) surplus capacity;
(*) when using much-more-efficient electric heat pumps, for both space heat and water heat.

 

We were off the grid for 20+ years (starting in 1988, when options were few and pricey). We only used propane for cooking and hot water. We had friends with the propane fridge and freezer options but never thought of them as a good use of propane. Instead we shopped for a very efficient 12v fridge and for the last few years a high efficiency portable 12 v freezer (don't recall the name, but was often used for outback travel). We moved "ongrid" 10 years ago; and with the incredible drop in solar pricing and improvements in accessories in that time I will recommend electric refrigeration even if initial costs to get the efficiency you want are high.

Batteries are a big consideration. Marine grade simply will not cut it long term, auto are not designed for this kind of use. We used golf cart, the low cost option of choice back in the day and we would get 5-7 years of service. The folks who are there now stepped up to heavy equipment lead acid batteries, which can be expected to last twice as long. But there are some newer options to consider. I can't speak to the brands or even the chemistries, but some due diligence on the latest technology is in order. Options may be expensive but consider maintenance (lead acid needs attention, none of which is pleasant and not always safe), life expectancy, ability to function during and after deep discharge, off-gassing if not sealed, and probably more.

We live in an area of cloudy winters, so wind power was a good choice for supplement.

If you can find a bundle of the now-defunct Home Power magazines you will find a wealth of advice and information, some probably trending out of date but still relevant. Or go to their website and download what might help (homepower.com).

 

I'd use it as a hybrid, never charge it from your battery bank, and only charge it from your excess solar capacity during the daytime if you have a really solid AC inverter setup. What I might consider, in addition, is using the Prime as a backup emergency generator for your house power system. On a small, temporary scale (up to 1kW inverter drawing from the Prime 12V battery terminals while the car is Ready) it is a nice perk of owning a Prime. While you can do that with any vehicle, the amount of gas it uses to do that is less in a Prius than any other car. While it's tempting to do it in EV mode and draw the battery down, that really just adds cycles to your Prime battery, so unless you're able to truly recharge it free on solar without going into Charge Mode to recharge it with gasoline, I'd recommend using the "Prime as generator" in HV mode. The bigger sorts of things you can't do with other cars at any cost in gas, I'm not sure you're ready to tackle, and in fact, I'm pretty sure you're not. That would be tapping into the big battery directly at the high voltage end as a solar storage battery or as a power source for 120VAC, 240VAC or split phase AC for both of those, treating it as a piece of 350VDC industrial power equipment. There are off-the-shelf ways to do so, not specific to Prius Prime, but totally suitable for its voltage and capacity. Some are intended for things like city buses, others are intended for expensive military equipment. It's possible to design and build similar systems yourself, but it requires some engineering skills, some electrician skills, and being willing to void your warranty. Even using the military-spec system would probably void the warranty.

Getting back to your question....

Bottom line, there is no way that adding solar capacity of the type you're considering, specifically to charge the Prime, makes sense financially. Some of the hints which make me double down on that are: 1. Using lead-acid marine deep cycle batteries as what you're charging from solar. 2. Having trouble running a coffee machine from your almost 30kWh (600Ah at 48V) battery bank when the sun is down. 3. Considering using a small generator to supplement your solar. (So, if you're going to add solar, do it to avoid needing a generator, when the Prime already can function as one, to some extent. You want the Prime to reduce your need for a generator, not add to your need for one by causing you to have an even bigger battery bank that could fall even farther behind the higher usage it brings.)

Where are you located? Climate can affect your ability to charge the car when and how you want to.

How big is your 48V inverter? Or are you using a 12V inverter tapping just one battery in the string of batteries in series? That would explain it struggling with a coffee maker, drawing it down to be unbalanced from the other batteries strung in series, then getting hammered when charged by something expecting a balanced 48V string.

I figured the 30kWh battery bank based on 48V x 600Ah. Or did the 600Ah refer to adding up the 12V battery capacities, and therefore after you put 4 in series, you only have 150Ah at 48V? With lead acid, you also pay a big price in battery life if you drop it below 50% of the capacity daily, so maybe you really have half that truly available for cycling each day? Which means 15kWh or 3.75kWh? There's a big difference between 30kWh available and 3.75kWh available.


Personally, I'd not even consider charging the Prime by cycling lead acid batteries, though I would consider charging it when you have excess solar coming into the batteries during the day, if you have a nice solid 120VAC (or 240VAC) pure sine inverter that can reliably provide the available charging rates you can choose from in the car. The lowest power charging mode is 8 amps of 120VAC, which takes 8-9 hours to charge empty to full. I'm not sure how well the charger handles voltage dips or cutoffs/resets from your inverter if a cloud passes by while your appliances are on and your inverter coughs.