What a year of solar and batteries saved us in 2025 • Hacker News Board

Re: What a year of solar and batteries saved us in 2025

#291

Post by labcomputer » Tue, Jan 13, 2026, 9:25 PM UTC

mbesto wrote: post #186

pchew wrote: post #163

Earlier quoted context omitted.

This is still not an accurate comparison. I'm not a Tesla fanboy but of all of the major players in the non-diy game (Enphase, Franklin, Tesla, Sol-Ark) they provide the best value for money, and are impressive pieces of equipment. The EG4 18k has 11.5 kw backfeed capability, with a rather pathetic 65ish amp in-rush. Obviously 18kw usable solar capacity(they technically let you land up to 21kw, but only 18 is usable)…

None of those things matter when your solar array is 4.5 kW and you have a standard 150A/200A grid in.... Like I said, they basically are not sold to scale like a normal household uses electricity. EDIT: What the heck is in-rush and backfeed? Are you talking about AC input to charge the batteries? The 18k is 50A @ 240VAC (12kW) fyi. Also, why does the charge rate even matter there? For the AC output its also 12 kW...…

Inrush is surge capacity. Starting a big motor like an air conditioner can require 2x or 3x the continuous running amps, but only for a few seconds.

Re: What a year of solar and batteries saved us in 2025

#292

Post by [deleted] » Tue, Jan 13, 2026, 9:27 PM UTC

Aperocky wrote: post #206

systemtest wrote: post #98

Earlier quoted context omitted.

Is delivering back to the grid economical in California? Where I'm from people disconnect solar panels on sunny days because it costs them money to return to the grid.

Is the disconnect automatic? what happens when you're not connected to the grid but battery is full?

[deleted]

Re: What a year of solar and batteries saved us in 2025

#293

Post by pchew » Tue, Jan 13, 2026, 9:30 PM UTC

mbesto wrote: post #186

pchew wrote: post #163

Earlier quoted context omitted.

This is still not an accurate comparison. I'm not a Tesla fanboy but of all of the major players in the non-diy game (Enphase, Franklin, Tesla, Sol-Ark) they provide the best value for money, and are impressive pieces of equipment. The EG4 18k has 11.5 kw backfeed capability, with a rather pathetic 65ish amp in-rush. Obviously 18kw usable solar capacity(they technically let you land up to 21kw, but only 18 is usable)…

None of those things matter when your solar array is 4.5 kW and you have a standard 150A/200A grid in.... Like I said, they basically are not sold to scale like a normal household uses electricity. EDIT: What the heck is in-rush and backfeed? Are you talking about AC input to charge the batteries? The 18k is 50A @ 240VAC (12kW) fyi. Also, why does the charge rate even matter there? For the AC output its also 12 kW...…

Inrush is exactly what it says it is, it's inrush current. When you have a sudden surge on something, that's inrush. Lots of appliances in your home have a large inrush, much larger than the breaker they're on. Inrush happens faster than a breaker trips, which doesn't matter when you're on the grid and the inrush is lower than your mainbreaker, it matters when you have an inverter in the way with a passthrough limit and an inrush limit. Typical central HVAC units have LRA over 100 amps.

If we're talking about 'doesn't even matter with a 4kw array' well, hell, how the hell you gonna charge ~40kwh of battery with solar array that nominally produces 20kwh a day on its best day, assuming all conditions are perfect?

Backfeed is what the inverter can push out from the battery to the home. It's the size of the tube coming from the gallons of water reservoir. EG4 18k has a tiny tube, no matter how much battery you put on it. Like emptying a 50 gallon drum with a drinking straw(and with the 4kw array, filling it with a 12 oz cup).

Re: What a year of solar and batteries saved us in 2025

#294

Post by vasco » Tue, Jan 13, 2026, 9:31 PM UTC

adgjlsfhk1 wrote: post #193

vasco wrote: post #134

Earlier quoted context omitted.

It could be as simple as a different model. In one of those it was easy to make it feasible if you had no cap on how much to sell back, but it was limited to consumption plus like 10% or something like that. Since the property used very little energy but had a big roof we thought itd be a good thing to produce green energy while making a little money or even just breaking even, but to break even we'd have to use way…

sounds like you were just doing the math for too much capacity. there's no rule that you have to cover your roof

Too little capacity and it takes 50 years to absorb the fixed costs.

Re: What a year of solar and batteries saved us in 2025

#295

Post by MisterTea » Tue, Jan 13, 2026, 9:38 PM UTC

lm28469 wrote: post #29

lostlogin wrote: post #19

Earlier quoted context omitted.

That’s an awful lot of power. I’m waiting on a quote for an hvac that uses its waste heat for the home hot water. Im irritated that I’m cooling the house, pushing out hot air, and heating water at the same time.

Get a basic heat recovery unit, it basically has no moving parts (just a few fans) and good ones recover 90%+ of the heat going out of your house. It's almost useless if you don't have an airtight envelope though. All in one systems with water heating are way too complex and _will_ fail relatively quickly, mini heat pumps won't last 10 years, and by the time it dies you won't be able to find a replacement for your sp…

> All in one systems with water heating are way too complex and _will_ fail relatively quickly, ...

Can you offer some evidence of this? I don't see how adding a refrigerant to water heat exchanger after the compressor, before the reversing valve, could possibly hurt the longevity of a system.

> ... mini heat pumps won't last 10 years, and by the time it dies you won't be able to find a replacement for your specific model

Thing with mini-splits is you replace the entire unit so it doesn't matter.

Re: What a year of solar and batteries saved us in 2025

#296

Post by Scott_Helme_ » Tue, Jan 13, 2026, 9:40 PM UTC

pixl97 wrote: post #81

lm28469 wrote: post #16

Earlier quoted context omitted.

The average household doesn't have two electric cars though

Yea, averages don't work well when talking about single units without any further details. How many sq/ft is the house? Is it filled with windows facing south? Are they firing a continuous laser beam at the moon? 2-3x usage is actually pretty typical when looking at a single house when comparing to average. It's when you start getting close to an order of mag difference that you're an outlier.

How did you know about my laser?!

Re: What a year of solar and batteries saved us in 2025

#297

Post by Scott_Helme_ » Tue, Jan 13, 2026, 9:41 PM UTC

lostlogin wrote: post #9

kccqzy wrote: post #2

Good analysis. And kudos to the author for saving money. But still 21.6MWh per year excluding solar production seems too high for a household. I use electric heating and drive an electric vehicle, and my household annual energy consumption is about one fifth of that.

I can’t see any mention of hot water or cooking in the article, which may be relevant. I was stoked at the power saving from turning off an espresso machine a bit sooner, a swapping out a nuc to a Mac mini. Maybe there is a bit coin mining operation in his basement?

Nah, there's no Bitcoin mining, honest!

Re: What a year of solar and batteries saved us in 2025

#298

Post by phantom784 » Tue, Jan 13, 2026, 9:42 PM UTC

labcomputer wrote: post #271

1980phipsi wrote: post #146

Earlier quoted context omitted.

Any idea why swapping didn't pan out for Tesla? My understanding is they are doing that in China.

> Any idea why swapping didn't pan out for Tesla? ~~Two~~ Three things: 1. California changed the rules shortly after Tesla demonstrated their swap station, which practically eliminated the tax credit for battery swap (at the behest of lobbyists for Toyota, who were backing Hydrogen Fuel Cell technology). Specifically, the credit would be prorated by the percent of “fast refueling” sessions a car did, so EVs primaril…

I could potentially see value in a car with a smaller built-in battery for use around town, and an empty space for a larger battery, that you rent from swap stations for longer road trips. Of course, that doesn't work with anything on the road today.

Re: What a year of solar and batteries saved us in 2025

#299

Post by scarecrowbob » Tue, Jan 13, 2026, 9:48 PM UTC

thechao wrote: post #136

scarecrowbob wrote: post #107

Earlier quoted context omitted.

Well, the math still maths, right? I am writing this off grid, using about 15kwh of batteries and a $1200 (6kw) inverter. My entire system puls panels and racking those panels, plus wiring some un-powered shacks was about $10k, though I did the work myself (which would probably hae been another 3-5k if I could have found someone to do it.

> which would probably hae been another 3-5k if I could have found someone to do it. Yo. If you can find an electrician to stop by my house and turn a light switch off for less than 1000$, please inform me. I got a quote for 25k$ to install a system that size, and that price. City code has me by the balls: I can't modify my main panel without inspection, the inspector won't show up without a licensed electrician, and…

Hoss I am sorry to hear that- I have literally no idea what electrical costs, as I've been doing it myself. If you're living close enough to other humans that the can observe and complain, then we're not really in the same situation.

But that doesn't really change my point, does it? Like, if they are installing $6k worth of equipment and materials, then that's what the up-thread points was about paying 10K more for tesla-branded equipment, right? I get that at a certain point the labor makes the cost of materials less of a deal, but my point was that my battery+inverter+panels+material is still less than the equipment they are describing.

Re: What a year of solar and batteries saved us in 2025

#300

Post by Scott_Helme_ » Tue, Jan 13, 2026, 9:48 PM UTC

domh wrote: post #91

> The batteries can fill up on the off-peak rate overnight at £0.07/kWh, and then export it during the peak rate for £0.15/kWh, meaning any excess solar production or battery capacity can be exported for a reasonable amount. Honestly I didn't know this was allowed. I recently got a heat pump and am on a time-of-use tariff ( https://octopus.energy/smart/cosy-octopus/ ) and have been thinking about pulling the plug on…

The only restriction placed on you is the export rate, which is provided to you by the DNO here in the UK. We had a limit of 3.8kW placed, which is programmed in to the batteries by the installer.

Octopus also have more flexible battery export tariffs if you want to explore those: https://octopus.energy/smart/flux/