Hacker News Reader

We have frequent power cuts and follow this same philosophy.

Our first line of defence is the solar system's battery. When power goes out, that will keep things running for some time with the big optional loads switched off - e.g. hot tub, hot water cylinder and pool.

If the sun's shining we can run like this for a long time.

In a solar drought, when the solar battery runs low, the next step is to plug the EV in via V2L and use it as a generator to charge the solar battery. EVs have comparatively huge batteries, so at the cost of losing mobility, which may be important in an emergency, this will keep things going for even longer.

One great feature of using an EV is you can drive to a fast charger, charge up in an hour, and transport all that energy back home.

The final fallback is to plug the 2KW petrol generator in to charge the solar battery. This is enough to keep things going forever assuming a petrol supply. A petrol generator is nicely portable and can be loaned to less prepared neighbours who likely have their own petrol.

The key to it all is the solar battery. That gives you uninterrupted power while mucking around with the alternate sources. It doesn't even have to be all that large if you have an EV.

In the scenario mentioned in the GP post where a giant tropical storm hit resetting the grid for 7+ days, how big is the chance that your solar panels installation has survived? Also, if the grid is gone, won’t the fast chargers also be out of service?

Don’t get me wrong, I think you’re right for most cases but I also think for some more end of the world type of scenarios there is little that beats a generator and stored fuel.

Indeed, that's why I mentioned petrol generator as the last level of backup.

Though the most recent big tropical storm we had a few years ago, the power was out for 3 days, it was dark and cloudy obviously so no solar, the local petrol pumps had no power and the roads were blocked with fallen trees so we couldn't even drive anywhere. In that situation it really is candles and cooking on wood fires once the petrol runs dry.

If you can stay there (no evacuation for building doesn't seal enough to make it habitable), most of the solar should have survived. Moving a broken panel out of the way and swapping one from the end of the array in to make the cables fit, or even having a spare jumper cable to swap in place of a broken panel, is quite easy to do. Mostly just make sure there's no load current at all on the string when you disconnect the MC4 connector with the special tool that keeps uneducated people from unplugging them under load and getting greeted with a persistent low current (not "arc flash", we're in the region of "high powered welder used with just normal welding PPE") DC arc (that may supply several hundred volts for a long drawn out burn). As long as it's around substantially below 500 mA you're not gonna sustain an arc.

> You also do an unfair comparison here

The comparison is unfair for many reasons, actually. A real install would have solar inputs charging the batteries and offsetting loads during the day.

It also wouldn’t run a 5-ton HVAC system 24/7 for 7 straight days, which is how the post got to the extremely high number.

It’s about as bad faith as the argument can get.

Add wind and I think you are onto something. Where I live it can rain for weeks on end so having another source of renewable is great.

I managed to go a week off the grid a couple years ago after a cyclone on a 27k~ AUD system that includes a septic system, home servers, starlink and the rest.

The servers obviously had to come down a few nights, but never had to bring down the fridge or anything critical. Didn't even have proper 4/5g service for a few days.

Main issue was the hot water tank which could have in theory been hooked up to my gas via an instant hot water heater for such occasions.

> You can install a solar+battery system because it makes economic sense and pays for itself

Would take longer than 20yr at current power rates in many US locales.

It's nice to do this for more than just the direct economic costs. The generator doesn't have to run 24/7 since the batteries absorb the excess power produced by the generator. This means less fuel wasted as well as less noise produced. I used to have two small generators that I could run (and team, if needed) but adding a battery component meant being able to sleep at night without a combustion engine burning fuel all night long.

Yup, even better if you power a separate battery charger with the generator, but let loads be handled by the battery+inverter. You don’t need to provision the generator for peak loads (which can be quite high), or even worry about high harmonic distortion from a cheap generator screwing with your electronics. It basically turns your system into a fully ‘online’ UPS.

Also, really handy for diesel gens which will ‘wet stack’ if you only run them for short periods or with light loads.

Provision a generator size which you expect to run say 6-10 hours at a time (at say 70-80% rated load) to fully charge your batteries, and a battery bank sized for 3-4 days of load.

Keeps your total gen hours much lower, much more efficient fuel wise (you can set the ideal load using your charger, and it will keep it that way regardless of increasing/decreasing loads), doesn’t require as big a generator if you have things like AC compressors, heat pumps, etc. with high start loads, and gives you a lot of redundancy and flexibility. It even gives you time to fix your gen or find/beg/borrow another if yours breaks, and you won’t need to keep the gen running overnight if you plan appropriately, so your neighbors will like you more.

Best of all worlds. Especially if you have natural gas, or get a tri-fuel generator and keep propane handy. Propane doesn’t go bad like gas or diesel can.

And in some, like ours, it takes 5.

Will you not own your home for more than 20yr?

I think for most people it would be if they can they afford a 20 year advance on electricity costs all at once. That is a lot of money if you have more pressing needs, but if you got that money sitting around then yea of course it is a good investment.

If you have free night charging plan you can recoup quite faster. My system paid off for itself in 3 years - although I designed and set it up myself, so it was about 3x cheaper than through contractors (and yes I'm in US and I pulled permits to do this).

Highly dependent on where you are, what your electricity costs, and what your backfeeding compensation scheme is (eg net metering). In California solar alone is no longer economically viable with NEM 3.0 but solar+batteries to maximize self consumption is still in that sticky ~7 year layback range - and those calculations tend to assume today’s power prices, that are in reality going up quite quickly.