My energy back-up

I have been toying with the idea of setting up rack shelves with deep cycle batteries charged by solar panels in our detached garage. There won’t be an issue with battery off-gassing since it is behind the house. Getting the electrician to install on an automatic transfer switch for the house wouldn’t be a problem either.

Guess I need to break out P-Calc and run the numbers verses the whole home generator.

Some key things to consider:
Max power
Max startup power
Time to “refill”
Availability of “refill source” during an outage


I think it’s worth clarifying here that there really is no comparison here because the bluetti and similar units are not generators at all but rather batteries for energy storage. The generator in this scenario would be the solar panel.

I would add that at least as it pertains to my original post, in my scenario, my interest was not keeping a whole, standard-sized house running with the usual daily high-energy appliances. Rather, my focus was/is having a small system that would work in a low energy scenario, primarily as a computer/lighting back-up during an outage.

With a 200 watt solar panel and 650ish KWH battery, this system is more about staying online and having lights which in my experience are the two primary ingredients to my tiny home being comfortable. For the higher energy tasks in my scenario I have propane for cooking/coffee and back-up heat if needed.

I’ll add that for me I do actually prize having solar energy as a part of my solution. Though it’s only 200 watts (160 in terms of what my battery can take), I’m interested in what such a small, micro-energy system can do for me in terms of daily use in my tiny house (my full time residence). On a typical day I have 3 lights on during the day and into the evening. In some ways this minimal set-up is also a test-run for me. Will it generally be sufficient, day-to-day, in keeping my lights on and my iPhone/iPads charged? I suspect only on successive cloudy days, especially in winter with shorter days, will this potentially be a problem. By the end of February I’ll have a better idea of how it works for day-to-day use for this purpose.

I’m also considering (based on what I learn with this experiment) whether I might expand to a second, larger battery and 2 additional panels… 1500 to 2000 WH of storage and 500 watts of input. For me this is a short term, real world solution for some of my low-energy daily needs with thought being given to possible longer-term, more comprehensive solution for day-to-day power generation.

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Yes. A million times yes. It’s borderline fraud to market a battery pack as a “generator” - the word has a meaning, and “battery pack” isn’t part of it.

This is absolutely true - but for people who live in apartments (raises hand) the traditional generators are a far less practical option. Even if you’re at ground level, the generator has to be outside, fuel needs to be stored, etc. and there are frequently local regulations about whether you’re even allowed to do that sort of thing.

The batteries definitely have a place, even if they’re less efficient. :slight_smile:


Or heat in the winter. It still gets damn cold here in Minnesota. EV makes no sense to me when it is cold half the year.

My heating system is a heat pump with gas furnace backup. Furnace and control is on generator but het pump compressor is not. For an extended power outage I will have heat but no AC. With 10 ceiling fans in the house I think we can handle a little heat in the summer.

Downside to an EV in very cold climate is reduced range. Batteries don’t like cold temperatures. Our Prius Prime gets 25-30 miles on electric in the summer but only 20-25 in the winter here in Virginia. Still plenty for our in-town trips.

Not much of a buffer for emergencies, unless you have a backup vehicle. But if you’re stuck on the side of the road in the winter in your reduced-range EV, you’re out of luck. Didn’t your part of the country just have a wintery incident of epic proportions if you were caught in it? Try bringing a “gas can of electricity” to refuel your stranded EV the way you can with a combustion vehicle.

Plus, I really don’t like the idea of trading my 5 minute gas station stop for whatever length of time it takes to get a “full tank” in an EV. If you can even find a spot to plug in as they become more popular. After the pandemic lets up, all your recharging sessions won’t be taking place at home overnight. :slightly_smiling_face:

Indeed. And also just for short outages. We have UPSs on just about everything in this house. The power would have to be out for more than 2 hours for me to justify cranking up the generator.

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Believe it or not, many AAA tow trucks are starting to carry battery packs to give EVs a roadside “refill” that will get them to the next charger. I drive my wife’s EV, frequently, from Atlanta to Greenville (SC) and Charlotte (NC) in warm and cold weather. The cold weather does certainly reduce the range but most of the time the car is a delight to travel in. I’ve never had an issue (granted, it’s an all interstate trip) finding space to charge or availability of chargers.

You are correct, however, that time to charge is the thing with which most people will/should take issue. Fast charging doesn’t happen above 80% full either, so your “fill up” is at most giving you back 4/5 of your full range. IMO, EVs are not ready for the masses until they solve this problem. Range, charging availability - these are practically non-issues. 40 minutes to add 200 miles of range while on a trip? That’s going to be a deal-breaker for many or most people.

I’m also wondering what’s going to happen grid-wise if most of the cars move that route. Do we have the excess power generation capacity to power all the cars in the US via electricity? Some places probably wouldn’t have a major issue, but we already have some places that semi-routinely have blackouts and other issues due to the inability to keep up with demand. EVs would obviously make that worse.

Sure we do. We will just use coal and NG to make it! :wink:

I used to be totally off grid (local generation because we were WAY too remote to get any supplied services) and I’m quite happy to not be having to think about that any longer. However, it did teach me that a MacBook Air is better value than a Mac Mini simply because the built in UPS inside the MBA never fails.


The Grid is going to be fine in most places not named Texas.

The biggest issue isn’t necessarily the proliferation of EV but rather the millions of spec homes with bargain basement inefficient applicances.

The two biggest energy consumers in the home are HVAC and Water Heaters. To relieve Grid contention you simply need to incentivize people to upgrade their appliances to Energy Star versions

Let’s put it in simple numbers.

Typical US home uses 30kW a day.
An EV will have a 60kW battery. So fully charging it is equivalent to two days of electricity

My home costs roughly $3 a day in electricity so a fully charged EV is only going to cost me $6 to charge and based on my commute would last me over a week. But lets say it a full chage lasts me exactly a week.

52 x $6 - $312 annually on the crude estimate low side… Granted Arkansas is under 10 cents per kWH and my driving doesn’t account for longer trips but the reality is for many people much of the cost of charging an EV can be offset by replacing their Electric Water Heater with a Heat Pump which typically shaves 300 dollars a year off of heating costs.

If you have the space or roof for solar the cost analysis really begins to tilt in your favor if you electrify properly.

There are definitely some interesting options available, and I’m a big believer in doing whatever makes sense for where one lives.

Heat pumps aren’t particularly feasible up here in Wisconsin, although ground loop is an option - but the numbers make it at best cost-neutral over the lifespan of the system, unless one is building a new house and can get the excavation handled as part of the landscaping. I’m of the impression that’s true for the northern half or so of the US.

The most interesting option I’ve seen for heating water is actually to use solar energy, but not as electricity. I saw something pretty cool where they’d run the water up through the roof area and basically use the “dark surfaces absorb heat from the sun” principle to warm water in pipes.

That all said, I think the areas that are hardest-hit are going to have some of the biggest problems. California is averaging over $0.24/kWh in energy costs, so theoretically there would be incentive to make things more efficient or add solar panels or whatever if possible - but I wonder how much of the low-hanging fruit has been picked already?

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The cost for the energy itself (and perhaps for the environment), yes. But you’re leaving out the cost of the infrastructure to make it happen. Today, you don’t make back the premium you paid on an electric car in fuel savings (I have one and track diligently). It’s hard for me to believe we are anywhere close to neutral or positive investments in energizing our homes this way. The “stuff” is just too expensive compared to power plants.

Yeah the Solar Water heaters are something my company (A green builder- Solar Company) have done for decades. I had no idea they even existed. My wife who has traveled for work extensively told me “oh year i’ve been to countries where they all had the tanks on the roof”.

I haven’t been to Wisconsin but the wife told me about pretty cold winters in Waukesha growing up. I guess the latest Heat Pump can generate heat down to -20 but the reality is a gas furnace is simply cheaper to purchase and NG isn’t expensive.

Took the kids to Disneyland last Oct. I forgot how expensive gas and electric is on the West Coast (I’m from Seattle). Even right now big three electric companies are trying to gut Net Metering. Good luck CA residents

For solar to take off we simply need the avg cost to drop to $1.5 per watt installed. I’d say we’re pretty firmly above $2 a watt for all but your must cut rate stuff. Australia has incentivized to point where they are at $1 per watt. That’s impressive and for a lot of people a no brainer. If someone can put up a 10kW system for anywhere near 10 grand i’m ALL over that. I couldn’t hit that even with DIY here.

I agree.

We as solar providers are in this weird position. We hear the Government saying “We want to be carbon free by 2050” or whatever target date they’ve circled on the calendar. We’ve done the numbers and essentially ever solar company would have to double their installs YoY for the next decade or so to have a chance. Meanwhile Cali, Florida and other states with huge PV potential are all facing legislation that curtails the net metering benefits of solar.

Net Metering is our biggest selling point. Batteries are too expensive right now. So if net metering is gutted the chances of doubling solar installs YoY isn’t happening.

I’d hazard a guess that electric co-op are less worried about the impact to the Grid from EV and more worried about paying for infrastructure that will have bad ROI as people generate their own energy.

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For this to have a chance of working in Minnesota, you have to have a practically airtight super-insulated house (R-40 walls; R-50 ceilings; triple pane, argon-filled, windows with 3 low-e coatings; mechanical ventilation; and de-humidifier) according to claims made in this article which did not give costs of the retro-fit Can a Heat Pump Work in Minnesota? - Energy Vanguard

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And this sounds like a lot more work along with questionable reliability than my current natural gas furnace.

Heat Pump Troubleshooting: 10 Common Heat Pump Issues & Their Fixes

And at least a little ways back, to even get rebates and incentives for some of the “green” stuff Wisconsin was requiring that the person have a conventional furnace. It’s basically conceded that it’s necessary as a backup in Wisconsin.

I’ve heard that they’re working on some new panels that could almost double solar efficiency. If that’s true, that would make a big difference.

Although don’t PV systems have decreasing performance over time, and require periodic replacement?

The biggest costs, from what I’ve heard, are the costs of installing the ground-loop for the heat pump. That typically requires a backhoe and a fair bit of work, and last I heard it was in the tens of thousands of dollars. If one was already re-doing their whole yard it could probably be tacked on pretty reasonably, but I don’t think most people ever rip up their entire yard. :slight_smile: