Hacker News Reader

I recently installed an Enphase home backup system as a DIY project (crazy, I know). The biggest problem with any home-backup system is moving the loads onto their own sub-panel. When the utility goes down, power needs to flow into the home, but not to the rest of the neighborhood. To do this, a switch needs to physically disconnect the utility meter from the main loads panel. If this isn't possible (such as when the meter is integrated into the panel), all the loads need to move to a sub-panel. This is the hard part.

Once the meter and main panel are separate, the various backup solutions become pretty similar. The disconnect switch installs between the two, with the solar and battery attached. Sometimes the disconnect switch + solar + battery are all in one unit (like the Bluetti EP900), while sometimes the solar inverter, battery, and switch are all separate units (like Tesla or Enphase). The Tesla switch and battery are sleek & glossy, but the inverters are ugly. The Enphase stuff isn't quite as shiny, but at least the boxes look consistent.

Performance-wise, the systems seem pretty similar as well. Most systems are around $10K for 10KWh of capacity, with somewhere around 6-9 KW of peak discharge rate. I imagine these prices will drop a lot over the next decades. If the battery becomes obsolete, just install a different system. Once the home is correctly wired, swapping the storage system should be pretty straightforward.

Why did you choose the Enphase system versus any of the others? How much capacity did you install and is it upgradeable?

I like the distributed architecture. Each solar panel has its own inverter, as well as each battery. If I want more panels or batteries, I just add them in parallel with the existing panels or batteries. If a panel or battery goes down, the remaining ones keep working. Avoiding high-voltage DC also makes the project more DIY-friendly. The downside is that Enphase requires users to take online classes before they grant access to the installer app (easy but time-consuming).

Right now I have 3.8KW of solar and a single 3.3KWh battery. We are producing more than we use most months, so the solar is good but the battery is undersized. If we have an extended grid-down scenario like what happened in Texas, the system will mainly provide daytime backup plus a few evening hours. This is still better than nothing, and we can easily add more batteries as we have the budget.

Thanks for the info. Do you know how much you saved by doing the install yourself? Did you also do the solar install? I was considering using a battery to time shift power as my power provider has free nights.

I installed the solar first, which cost about $10k for parts, plans, and permits. I got quotes between $18k - $26k for the same-sized system professionally installed, so this was a great savings for 3-4 weekends of physical effort.

I don't know how much I saved on the battery, since I didn't get any quotes. The battery was vastly more time and effort, since I had to move my house onto that backup loads panel.

If you just want to shift usage, the backup panel may not be necessary. The Enphase batteries do support a fully grid-tied mode, where they simply connect to your main panel as a branch circuit. I'm sure other brands do too. This would be an easy DIY weekend project, as opposed to a months-long home re-wiring project. The Enphase mandatory training would be the biggest downside for using them here.

Not the person you asked, but Enphase has a reputation of being much more reliable then the Tesla stuff. You can have up to 40kWh of batteries. I think the peak wattage is also higher per kWh than powerwalls.

Also, we tried to get Tesla to install solar on our roof, and will never do business with them (especially that half of the company) again. There's a reason their solar market share is plummeting. Many news stories have been written on this subject. I won't repeat them here.

LG and Generac also make home batteries. From what I can tell, their offerings are also fine.

The main limitation of all the existing systems (vs. the recently-announced Anker) is that they scale amperage linearly with capacity. This is a pain because the batteries produce way more current than you need, but you have to pay for an electrical bus that can handle peak output. This is why the enphase is limited to 40kWh.

I'd strongly recommend against trying to do the installation of the Enphase yourself. It's extremely hands on.

I didn't see much in the way of details on the Anker site regarding their system. It seems none of the companies selling their systems make it as easy as tesla to order one.

It's Germany only at the moment. They intend to expand worldwide in 2024.

You don't move the loads to the sub panel. You make a new main panel, move the feed to that, and turn the old main panel into a sub panel. Much easier.

Sort of a silly question -- how do you know that? Where would you recommend I start reading if I wanted to know things like that?

I'd start with this book: https://www.amazon.com/Wiring-House-Sixth-Rex-Cauldwell-dp-1... (prerelease, but the earlier versions are good)

It'll give you a really good introduction to house electrical systems, things like "any panel that is connected directly to the utility is the main panel, any panel that is connected to a panel with a shutoff is a sub panel".

This is absolutely perfect, thank you!

If you were asking about anything else the answers could come from anywhere, but for this;

https://catalog.nfpa.org/NFPA-70-National-Electrical-Code-NE...

The National Electrical Code contains the rules for this sort of thing, plus whatever extra rules your local jurisdiction adds. I bought a copy of the code itself plus an "Illustrated Guide to the National Electrical Code" to learn this stuff. There are lots of YouTube videos for electricians, by electricians. DIY channels can also be helpful, but they don't always follow code.

In my case, the local utility requires the electrical meter to be accessible (obviously) and to be a certain distance from the gas meter (obviously). Because of the way my house is shaped, there simply isn't room to move the electrical meter, so a sub-panel was the simplest option. Anything else would involve tearing open the driveway, which would be worse. It really depends on the situation.

Solar energy international is a great resource for learning about solar & battery system design:

https://www.solarenergy.org/

These ugly's guides are basically the cliffs notes for the industry:

https://www.amazon.com/Uglys-Electrical-References-Charles-M...

Third option: you get a panel of experts and they tell you what to do with the panel.

You don’t need an isolation switch if you use a sol ark 15k or EG4 18k, you can just tie the grid straight in and they have isolation built in if the grid goes down.

This is the way I'm looking to go once I get a few thousand together. They're really impressive hardware and the software is tolerable and updatable.

"To do this, a switch needs to physically disconnect the utility meter from the main loads panel ... this is the hard part.

It doesn't need to be.

You can just use a physical interlock and toggle between utility breaker and (any input you want) breaker.

You can do this on an integrated meter panel.

This is a dead-simple configuration that you can comprehend - and verify - with your own eyes.

The lock-out switch is NEC compliant, utility approved, etc.:

https://www.amazon.com/Generator-Interlock-Compatible-Homeli...

Yes, you do lose all power for a second or two but ... so much simpler and comprehensible than an ATX solution.

For a generator, yes.

Is it currently possible to do this with a battery setup, for which its normal state is to feed power to the grid with anti-islanding?

Either you'd need two power connections to the panel - one for the every day anti-islanded backfeed, and then a second with the physical lockout to a different inverter output that operates without the grid.

Or the lockout on the main breaker would need to control a logic-level switch that told the inverter to disable anti-islanding, for power flowing through a separate non-locked-out breaker. This would seem like a better solution, but the inverter/battery manufacturer would have to design for it and get NRTL approval.

If you want something crazier, try doing online backup. So that you don't get any power dropouts.

I never stop to be amazed how average consumption figures in the US are often at least 100 per cent bigger than in Europe. At least for water and electricity, let alone fuel.

Just a thought that naturally pops up... :

If you take the reasoning one step back, wouldn't it be easier to optimize the consumption side (low hanging fruit) in favour if optimizing the cost per unit of energy? The latter seems a lot of effort, at least for the devs.

its pretty easy to understand when you spend significant time in both.

european cities: typically built for density. I'm never more than a 10 minuite walk to a grocery store. I can hop on a train or tram to get to work and I can usually stop to get groceries for the day on the way. if you're in a city like athens, you can get fresh fish and meat. was probably dreaming of finding a mate or eating fresh acorns on the other side of the pasture barely a day ago.

USA: Its a hellish landscape of urban sprawl. want to get sone milk or eggs? its illegal in most place for there to exist a grocery store within walking distance. be prepared to walk along the side of a busy road to get to a convenience store which might have what you are looking for. maybe there's a sidewalk if you're lucky. Every damn trip requires a car. your work place is probably 30 min drive minimum. there is no other way to get to work. since getting to the store requires effort, you're going to go get a week's worth of groceries to save time. fresh meat? nah, killed weeks ago in a centralized slaughter house and shipped accross the country after a life of being fed corn farmed with chemical fertilizers and shipped to the animals in temperature controlled facilities. better keep a large fridge to hold it all. wouldn't want it to spoil before you eat it.

you literally can't live in the USA without increasing your consumption. its built into the dna of our infrastructure.

Neither Europe nor the USA are a monolith in this regard.

Live in NYC or even S.F. and you can 100% walk to the store and take transit to work.

Live in rural or suburban Germany and you’re driving everywhere.

SF and NYC are outliers in this regard. the typical US city is more like LA or orlando where sprawl is rampant.

I would imagine in the southern states where it's 40 degrees C+ every day for 3 months-4 months or more on end the heatpump (aka reverse cycle a/c) is basically kept on constantly. Let's say it draws 1kw on average, that's 24kwh right there. They actually draw more than that. There's no way around it if you want to live comfortably. But I think the whole society is designed so much around driving everywhere and living in detached houses that the low hanging fruit is actually to install solar/batteries for these guys.

I suppose Italy, Spain, or Greece may see similar thermal circumstances. It's just harder to afford spending so much electricity there :(

That is the same for europe, N/S cold/hot.

Personally I am convinced by now the difference is mainly cultural, how people live. Some things ~2x size (i might be off a bit but the list is large, I am open to be convinced otherwise) :

Fridge

Clothes dryer

Food plate fullness

Amount of conservatives in food

Car HP and m2 parking space

PC PSU wattage

ml in medium drink

amount of ice cubes in cold drinks

Tap water full flow rate

Breakfast calories (bacon/eggs)

Sugar in bread

Amount of packaging material resp. content

kg of luggage in flights

Number of short flights / person

Cars/ bicycles ratio

Still, it just amazes me. Its not because of wealth or temperature.

Again, I am open to corrections, I am curious about other's thoughts and want to learn.

Developers won't make homes below a certain square footage because it's not profitable for them. That means that there will always be an amount of square footage that will need to be cooled and warmed, despite the space being largely unused.

Most people, like the couple in this article, aren't buying green 1350sqft homes, they're buying 2500 sqft McMansions because those are what are available in the market.

I believe that US households on average get a higher percent of their energy from electricity than do European households. For a proper comparison we need to compare energy use, not electricity use.

The average US household used 77 million BTU of energy in 2015 [1]. That's 1.94 TOE (tons of oil equivalent).

The EU average in 2014 was 1.3 TOE. It ranged from a little under 0.5 (Malta) to around 2.7 (Luxembourg) [2]. UK and Germany were around 1.4, France around 1.7, Italy around 1.9. Belgium was just under 2.

[1] https://rpsc.energy.gov/energy-data-facts

[2] https://www.enerdata.net/publications/executive-briefing/hou...

> If you take the reasoning one step back, wouldn't it be easier to optimize the consumption side (low hanging fruit) in favour if optimizing the cost per unit of energy?

Yes, absolutely.

In general, if you talk to a good solar sales rep, they'll first ask if you have done energy efficiency projects. If you have good quality windows, insulation, appliances, etc, not only are you going to be more efficient up front but you'll need a smaller array+battery overall.

There are also tax benefits for doing some of those projects together so you get some upside there too.

> Probably not worth it and I'd expect 3 days to be overkill. But a community that was double our size will have a cost of about 25k per unit for 1.5 days of power - which doesn't sound too bad to me.

If you're not looking to go completely off-grid, I think you want to double it again. At basic level, battery pack is there to soak solar power during a day and give it off when the solar is down.

16 hours is enough to cover most or all of that..

I think the model could work if the local community basically "sold" the battery storage capacity to the users.

Pay few cents for kWh to store it for 24 hours, anything in excess can be sold back to residents at slightly lower than market price, producing some money for maintenance and upgrades.

Realistically you could get that number 6x smaller, because people could voluntarily cut their usage from 30kwh to 15 when the power is out, and 1.5 days of power is probably overkill when 12 hours would get you through 99% of power out scenarios in America.

On top of that, when the grid is functioning normally, you could use the batteries to get cheaper electric rates with time of use pricing.

Pair the storage with some solar, and you could probably reduce the storage size or increase the survival duration (or both).

Here's a fun tool that lets you play around with the balance of these things and see the expected cost: https://reopt.nrel.gov/tool

You probably should divide all those number of days estimates by at least 2 or 3, because in many (most?) places the times when power failures are most likely are also the times when households need the most electricity.

For example here in western Washington outages are most likely during winter, which is also when we are using the most electricity. My daily winter use is 3.5-4 times my daily summer use, perhaps even more on those years when we get a week of near record cold.

Some of the Bluetti home power stuff looks nice to me as an individual and not requiring any community cooperation. It’s not as sleek as a power wall but I have space for it

https://www.bluettipower.com/collections/home-battery-backup

Things like that are incredibly overpriced, you're paying almost $1000 per KWH of capacity.

It'd become much more sustainable to do what you're talking about if it was accompanied by energy saving measures. Do it well and you could easily aim for 5kWh per day per house by minimising heating and cooling choices.

25k per unit, assuming the battery lasts 5 years, is uneconomically high at $5k/year per home.

A 100kw generator can produce enough power for 100 homes, costs ~$50k all in, and ~$1k per day in fuel costs to run during an outage. Assuming the generator also lasts 5 years, that's only $100/year per home, 50x less than the battery solution.

Batteries are for the foreseeable future way too expensive.

Surely doubling the households would only half the cost or the duration available, not both?

I don’t think so? Household Cost = Total Cost / Households, Household Duration = Capacity / (Household Usage * Households), Houshold*2 would half both.

Oh duh, right. Thanks.

The price of 50k per house will probably be 25-30k in 5 years.

>"random Pacific islands aside"

kind of dismissive..

Islands tend to have good sun exposure, minimal cloud cover, and little in the way of alternatives. Of course they do solar there.

Doing solar in places that perhaps aren't as sunny, and which could easily connect to a grid, is newsworthy.

anker, being a Chinese manufacturer, doesn't have much chance to penetrate the western markets. even assuming they can develop a dependable product. but I wouldn't trust more than a headphone, or a wall charger from them.

Anker knows batteries and their LiFePO4 batteries are solid stuff (as are their traditional lithium cells).

Even if you prefer a US maker, competition will help lower prices.

I agree on being careful with China goods in general, but Anker is one of the very few very trustworthy brands out there. IIRC, the only fuck-up regarding batteries they did was with the 535 power banks, and they handled that one very solidly [1].

[1] https://www.cnet.com/tech/computing/anker-recalls-some-535-p...

Unfortunately, no they're not. Anker owns Eufy and they had some massive issues.

https://www.digitaltrends.com/home/anker-admit-eufy-security...

Pretty strange view, when you consider that China still is the workbench of the world.

lol