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Comment by grecy | Hacker News Reader

I did my part. I just wrapped up installing a 7.3kW system on my roof at 49.5°N.

Yesterday was the highest day of output so far, 50.17 kWh

I'm extremely happy and can't stop checking the app. Our first bill just came in, -$57.

I really like rooftop solar, as an idea. It might not be the cheapest way to generate electricity, but it's good to know you aren't as dependent on the grid. It's like having your own vegetable garden.

Hopefully, with advances in battery technology, homes can become completely independent of the grid.

I wish it was this simple. All energy is still borrowed. Mining and producing and disposing of solar panels is still very energy intensive.

Renewable energy is a piece of what needs to be a much larger effort to fight climate change.

Sure, it's energy intensive, but if that energy comes from the sun, who cares?

I don't understand we keep using "energy intensive" as a euphemism for "emits carbon". The two aren't synonymous. Energy-intensive processes aren't a problem at all, the problem is dirty energy generation processes. Fix your energy generation, and there's no problem.

There's a (diminishing) correlation that shouldn't be ignored. I'm not saying we should abandon solar because of that correlation but it should at least be factored in.

For example, I think it's a dumb idea to turn every road into a "solar road" just because "who cares".

I was replying to a specific argument: That producing solar panels is energy-intensive, and thus bad (this part was implied). My counterargument is that energy-intensive is irrelevant when you've got basically-free, clean energy.

If your energy is dirty, fix your energy. Don't make downstream consumers feel bad instead.

I don't disagree, just taking the conversation a slightly different direction as I think you'll agree that the "it takes energy to make renewables" argument is generally made in bad faith.

I think there is irresponsible consumption of solar panels, particularly when it's done more as a performative action rather than actually producing power to be used.

Yah. I am glad we are deemphasizing residential solar.

Utility-scale solar has better capacity factors and installation economics.

I think it's going to be barely possible to keep our current quality of life and reach a low-CO2 economy. We have limited resources, and even if a residential solar panel "pays back" its energy in 2.5 years, we are better off putting it in a desert where it will pay back that energy in a year.

What about the economies of scale? Does/did residential solar create enough demand to ramp up utility scale production?

> did

I think residential solar was a decent bridge to get things going, and the installed capacity we have is helpful.

Now, though-- at midday we have a glut of power. Residential installations are more expensive per kilowatt hour and don't do as well in reaching into the late afternoon when we need power most. There's no need to add more capacity like this. Better for those panels to go somewhere else.

There are still times that non-utility scale solar make sense-- it's usually when you get some kind of non-normal-generation related benefit that tips it over into worthwhile, e.g.

- getting a shade structure for a parking lot as part of the rollout

- if you want power backup for your house, adding a bunch of storage and solar

etc.

Are there benefits to distributing generation? If I can top up my car on a sunny day the grid doesn’t even have to know.

There were some early benefits to grid stability, but not to the extent we've done it, no.

At this point, there are a lot of residential neighborhoods that need more distribution and even transmission capacity (because their peak power movement is now exporting power at mid-day rather than the previous smaller peak loads used). And operating the grid has become a much more complicated task.

Does a battery system solve this mid day export problem?

Yes, it prevents the house with the battery from being a tax on the grid. However, the capacity factor of both the solar and the battery is less than if they were deployed centrally.

Again: residential solar isn't worthless, but in many places we've reached the point of diminishing returns where any additional capacity is much less useful-- unless there's an ancillary benefit that justifies it (like backup power for your house when deploying storage).

The oil companies all rebranded themselves as energy companies over a decade ago, my presumption is it was a convenient part of a long term promotional plan to mix up the definitions to get the environmental movement to fight itself. Same as how the idea of a "carbon footprint" was sponsored out into the world by the same people.

The trick to good propaganda is to create something that makes you say "well I know it's propaganda, but this doesn't seem so wrong..."

Yes, you have to analyze the embodied energy, but solar panels are energy positive within 1-2 years these days: https://www.quora.com/How-much-more-energy-do-solar-panels-p...

It's really a no-brainer up to a certain amount of your grid mix (and that amount can be quite high).

This is an old trope that's not longer accurate pretty much across the board for renewables/batteries.

Also.. Mining for solar panels has never been the major energy cost. Solar panels are primarily silicon (re: sand). The actual energy expensive part for them is/was melting the sand into glass. Even the next major element, aluminum for the brackets, accounts for far more energy expenditure than the mining of the doping agents.

Even for windmills, the major energy cost isn't mining, it's the smelting the steel for the tower.

Renewable energy is a piece of the puzzle and not everything. It's a major and important piece. Switching the grid away from fossil fuels accounts for a huge portion of emissions and renewables are some of the fastest and cheapest to deploy solutions currently.

It is that simple. "Energy intensive" is irrelevant. On average, a solar panel will capture more energy in its lifetime than the amount used to create and eventually recycle it.

So please stop repeating that useless whine.

This is easy to refute. Take the commercial price of power for the location of manufacture and divide your retail price by that amount. The result will be the upper bound in MWh that could have possibly gone into the creation of that panel.

Chinese solar panels cost less than 15 cents a watt. In the NW with residential prices at 10 cents per KWh, it takes 1500 hrs to break even. With 4hrs of "full sun" per day on average at PNW latitudes, about a year. This is just the panel not the system. The BS that panels take more energy to produce than they generate is disproven.

https://www.alibaba.com/product-detail/In-Stock-TRINA-Vertex...

The tariffs on solar are stupider than the Iraq war. If China can produce panels at 10 cents a watt wholesale, we should give them billions of dollars to make as many as they can. Train everyone in the military to install them.

Energy-intensive is fine, as long as the energy is renewable.

Smelting aluminum and silicon or mining aluminum and iron ores with electricity produced by solar and wind is ideal: else that energy of light and air motion would be wasted.

Steel and concrete are harder to produce in an emission-free ways, but steel smelting in arc furnaces is very much a thing, and can be powered by renewables, at least partly.

A lot of misunderstanding about this comment. I think adding solar energy capacity to the energy supply mix is helpful. What I want to clarify is this, adding all energy supply has costs. Rare earth metals and other mining and habitat destruction that goes into increasing renewable supply needs to be considered. Like I said all additional energy supply has a cost.

The real problem is we need to reduce consumption. We also need to rework our energy supply chains with renewables when appropriate as well as nuclear that isn't vulnerable to meltdowns.

It’s interesting seeing the difference in how solar is usually talked about versus backup generators.

Whole-home generators are expensive and get used rarely but are often justified as a “just in case”. Solar doesn’t enjoy this kind of leniency, unfortunately.

Being less dependent on the grid has many benefits that get ignored over a perceived return on value.

At least around here, backup generators are for outages that happen when solar would be mostly useless: heavy storms or during Winter.

Cheap and safe batteries paired with solar will help, but the capacity will likely still be an issue for extended outages.

An islanding solar system with storage is not useless during storms or the winter, it still generates during the day. Not sure where your "around here" is, though.

Do solar panels ever get trapped under large amounts of snow the day after a strong snow storm?

Sure, but with a couple inches of snow on them, mine still generate power. And in areas which regularly receive snow, roof pitches are generally steep enough to encourage it to slide off else the building would suffer overloading. Worst case a push broom or squeegee with a very long handle works wonders.

Also fairly trivial to rig up a resistive heating system for melting the snow in cases where the above isn't possible. Even possible to automate it based on time of day and expected power input.

> Also fairly trivial to rig up a resistive heating system for melting the snow

Couldn't you just run power through the solar cells as if they were giant LEDs? Or don't they like that?

It is possible to back-feed power through a solar cell such that it emits photons (or maybe just heat - I'm not entirely clear on that). But all solar panels include diodes to prevent this and provide protection from hooking them up in reverse.

Ah, makes sense. As you mentioned though, easy enough to fit some thermal heating foil on the backside unless you're using bifacials.

It does happen occasionally, but it's rare that my panels are covered for more than a day or so. Heavy snows almost always slide off within 36 hours - sometimes a light snow (~3" or so) can cover it for a while because it's not heavy enough to slide off from gravity. The panels are very low friction compared to a normal roof.

Yeah - When covered in even a moderate amount of snow, output drops almost all the way off. I had thought that being black, they would melt off quickly, but that doesn't appear to be the case. As an aside, my daughter's neighbor has solar and after a big snowstorm, a foot of snow slid off his panels, right into the side of her house destroying a basement window and blowing shattered glass 5 foot into the basement.

Sadly at least where I live the backup generators are well-used, winter and summer alike. There was a period of about a year where we went no more than a week or two between power outages. Absolutely a lifesaver, when you have a freezer full of frozen goods.

In this context I'm saving my pennies for a solar and battery set up - it both makes financial sense when connected to the grid, and obviates the annoying side effect and high cost of running the backup generator during outages, unless they're extremely lengthy.

How costly is it to run a backup generator?

A gallon of gasoline produces about 36 kWh, and costs about $3.6. Assuming that the motor + generator + inverter chain has efficiency is 25%, it's 9 kWh of electricity per gallon, or about 40 ¢ per kWh. Likely twice as expensive as the grid, but fine for a few days.

Well, mine is propane, and propane is substantially less energetic than gasoline, and is also subject to delivery fees.

The issue you really run into is that, even at idle, the generator burns a fixed amount of propane. The minimum is about 2 gallons per hour. Which is roughly $6

So you can imagine that, for 3 days of usage, $500 provides a strong incentive to seek out alternative sources of power.

We run about $1200 a year in propane costs for the generator, estimated.

> The issue you really run into is that, even at idle, the generator burns a fixed amount of propane. The minimum is about 2 gallons per hour. Which is roughly $6

All the loads that I might consider a generator for are intermittent (well pump, fridge, microwave, space heater).

I've wondered if it would make sense to get inverters for the fridge, microwave, and heater and get a pool of batteries, and just use the generator for charging batteries and powering the well pump.

With a sufficient number of batteries in the battery pool it should be possible to only need to run the generator when there are sufficient batteries to charge that the generator can run at its most efficient output.

Yes this is roughly what I'm looking to do, but if you have an inverter and a battery charger, it seems silly not to also hook up some solar panels!

At that point the generator will only run if the batteries dip below e.g. 20% charge, making it extremely affordable.

Whole home generators are miles cheaper than a solar-battery setup. I can get 10kw of backup power tied into my house for 5k with an automatic switch, but that barely covers the labor costs for a solar system, and you still have to buy the rest of it.

Sure you can DIY it and get close, but most people are not going to do that.

You can also DIY a generator. Mine is tied into my 500 gallon propane tank, and would probably run the house for a month or more. And it cost less than $2k. No automatic transfer switch, but I actually prefer that because if the power goes out for a short time I don't start it up, and I turn it off at night as well.

Depends on your local grid reliability.

It would have been foolish to have a whole house generator where (and when) I lived before I moved where I am. Where I live now, utility power is less than three nines, and some years doesn't quite make it to two.

Solar without storage usually is grid tied, but even if it runs isolated, it doesn't help overnight. Batteries for a multiday outage are still quite expensive compared to a generator.

A whole house battery would be nice though, at least some of the systems can switch power quick enough that I wouldn't need UPSes at all my computers, and the battery maintenance that requires (of course, the large system would probanly require maintenance)

Once you add in the costs of additional transmission needed for utility scale solar, rooftop solar is extremely competitive.

Especially as transmission capital costs start to skyrocket, and solar capital costs plummet.

I have yet to see an economic argument in favor of utility scale solar over residential solar that takes into account the T&D upgrades necessary from utility scale solar.

We will need both, or at least something else, since not every building has a rooftop that can generate sufficient solar.

Agreed. I think we will also start to see lots of industrial sites that have their own utility scale installs that don't even feed back into the grid, and are used directly, and coupled with thermal or chemical storage.

It's a testament to how inefficient "the system" is that rooftop solar is economical for a lot of people.

Why? Sunlight falls everywhere. It’s not obvious to me that there should be efficiencies in capturing solar power centrally and then moving the energy over transmission lines.

If you want one rooftop’s worth of electricity, you can either pay someone else for a rooftop’s worth of real estate and have them run solar panels on it, and transmit the power to you over wires, or you can put solar panels on the rooftop-sized area you already own at zero marginal land cost, and have the electricity already right where you want it.

That that works out economically doesn’t seem like a surprise.

> It's a testament to how inefficient "the system" is that rooftop solar is economical for a lot of people.

Solar panels are rapidly falling in price, and now I'm generating the power right where I'm using it - so no transmissions losses, no power transmission infrastructure, no transformers, no poles to replace when they get old, no lines to replace when trees fall on them, no trees to trim. No accounts to maintain, no billing, no credit card fees, no taxes. In fact, to get power to my house for the next ~30+ years requires absolutely zero labor from anybody.

Of course it's economical, it would be baffling if it wasn't.

I'm surprised more conservatives in the West don't like it. It's the ultimate individual independence from the government and corporations. Individual sovereignty over your energy needs. Instead they want to rely on a foreign dictator and government-funded transmission lines. Bizarre.

This isn’t an interesting line of thinking because it depends entirely on your definition of conservative. There’s nothing surprising (or interesting) about a straw man.

Same with EVs. You can generate your own electricity a hell of a lot easier than making your own gasoline.

There are two attitudes that you skipped over: "dependability" and if it works, then don't fix it.

Between those two and people who have tried an electric or hybrid vehicle and had it turn out poorly (totaled because the battery went bad in the heat and it isn't worth replacing). There is a degree of wisdom to the advice "chemical energy storage is more convenient, dependable, and cheap for intermittent to constant daily use". I look forward to on site residential solar powered propane production and liquification for this reason.

How will onsite propane work?

Do you mean carbon capture?

That would be great but isn’t it similar to flying cars where it’s not feasible around humans because you have to move a LOT of air?

1) it takes co2 from the air and water to produce propane hydrocarbons (mostly theory with some promising lab results)

2) not quite. Well, it is a form of carbon capture, but with the intent of releasing again soon.

3) 4% co2 is everywhere (open a window and turn on a fan and you have almost infinite). Water is everywhere humans are. I think it is a lot more an engineering problem than a feasibility problem

As you said the benefit of combustion fuels is the energy density. Air isn’t dense. 4% of not much is… not much.

So how much air do you have to move to put a day worth of propane into a car?

It just doesn’t seem feasible to me at a home but I’m not a chemist or physicist. At industrial scale it works but involves a lot of fans and energy.

Good questions. From a quick Google search, direct air capture of carbon will supply 50kg a month from a residential site.

https://climeworks.com/subscriptions

Those supply you with up to 50kg of carbon a month from DAC (direct air capture). If I were to drive a sedan 120 miles (entire day commute) then I would probably burn 250kg of propane and only 80% of the weight of propane is carbon.Therefore, you are exactly correct that it is not feasible. However it may become feasible if I get creative: hybrid work and different fuel sources.

So for me to be perfectly carbon neutral I would need an average total daily commute of 30 miles to be able to have 100% of my fuel usage from solar powered propane.

I think this is some tech in infancy. I think I would be willing to install a o2 tank and a c3h8 tank on my car to have better efficiency if I had to produce all my own fuel.

Fun line of thinking.

That link appears to reference industrial carbon capture. I don't see a residential unit there or any claim of 50kg per month. A half acre facility isn't feasible in a residential setting. The site seems to sell carbon offsets (credits) for sequestration, which is nice but isn't residential carbon capture and fuel synthesis.

I just don't see how this is feasible at a residential scale. Certainly not with the convenience of solar plus battery storage.

Carbon capture and fuel synthesis is very exciting technology, especially when combined with solar for load shifting. Generate "clean" fuel from excess sunlight. But even then it doesn't scale as well as direct transmission. Combustion fuels will have to be reserved for those cases that really need the energy density, like aviation. Battery electric is far more practical for self-sufficient personal transportation.

It's 0.04% not 4%.

Replace "conservatives" with "libertarians" maybe.

Independence from the government was the revolutionary idea of the American colonies, eventually culminated at founding the USA (with checks and balances to limit the government). Calling this idea "conservative" is weird, but I understand why some may see it like so.

i think - when the grid goes down, your rooftop solar will go down too. Without grid generation there is nothing that can keep your inverters synchronized…

There are inverters with a power outlet that can be used in case of a grid outage. Supplying your whole home with power when the grid goes down is possible too with the right hardware.

It is probably cheaper or at least equivalent to utility scale, if we consider the cost of transmission and distribution, neither of which are needed with rooftop. Of course, it is grid tied, but it uses existing power lines to the home without requiring any new lines to be installed.

And the indestructible resiliency of distributed power production from tens of millions of rooftops is unparalleled.

A 50KW battery is <$10,000.

Sounds like he is allowed to sell excess back to the grid and payback period would be <20 years. They are warranted for longer. If financing is available it is basically free. ;)

Big if that but more realistically the real kicker here is that all of that is about x3 larger than what most households need.

I get that not everybody has $10k laying around to plop down on panels/batteries all in one go but if you do you can get off the grid now.

That is awesome. I live in the PNW (Oregon,45°N) and the summers here are fantastic for solar power. I have a 20.2kW system on my roof and crank out 100-120 kWh a day in the summer months. I can store 42kWh, and push the rest back to the grid at full cost return.

Thank you for saving our water!

20kw on the roof is awesome! Do you have anything high load in your house or property or is it more just to sell back the excess to grid?

Well.... yea.... I do sort of have some high load... but not too much! https://www.youtube.com/watch?v=-b3t37SIyBs

How expensive is the electricity in your area? I think here it is so cheap that might not be worth the installation cost (though that did drop a whole lot lately).

That's the trick. On one of the longest days of the year, OP got ~$5 worth of electricity where I live.

The payoff can be long, and people often forget to account for the added cost to home insurance to cover the panels in that.

OTOH, if where you live electricity is more expensive or labor is cheaper, it can be a really nice addition without too long a wait to make it back. The company I talked to said I get too much shade to be worth installing (150 foot tall trees near my house) so I'll be waiting awhile before I get mine even if electricity prices go up, sadly.

The ROI calculation can be a little tricky because solar can be a low risk leveraged investment with tax free returns. Remember money you don’t need to spend isn’t taxable.

So for most home owners it’s easily worth it. While from a worker safety, economic, and even environmental standpoint rooftop solar is terrible compared to grid solar as an individual homeowner you can often get subsidies.

>So for most home owners it’s easily worth it.

Can you elaborate on how you arrived at that conclusion? At least where I live, the math didn’t work out. It seemed like smarter conservation was a much better alternative. A couple portable/window A/C units that pay for themselves within a year or two made a heck of a lot more sense than $30k of solar on a roof already at half it’s life. Maybe when it’s time to replace my roof I’ll reconsider, but the payback didn’t seem there. (FWIW, I probably average < $100/mo in electricity.) I know conservation can go against human nature, but it sure seems like the better option for me.

I got there by just looking at how far north people go before it becomes questionable and then realizing most of the world’s population is closer to the equator. The other approach is to look country by country and solar generally works in China, India, US etc.

For your specific situation, you can reuse panels, inverters, and most wiring etc between roofs or depending on things like a HOA install them elsewhere for less. A solar gazebo or car port for example can directly use the panels as a roofing material. Some people are even using them as fences.

The actual calculations get involved including things like permits and your weather etc. But don’t assume your only option is spending 15+k for some contractor to show up and slap a bunch of panels on your roof.

PS: 30k is overkill for your usage, and you don’t need a battery unless you are particularly worried about power outages.

I am waiting more for the longevity of the roof than the panels. I’m not too keen on putting a lot of penetrations on an aging roof. The $30k number was based on a 10kW system (we’re limited based on a multiple of actual usage). But what you said makes sense and I should ask around for other quotes. But even at half that cost, I’m still looking at a 12-15 year simple payback. On a 20-25 year system, that puts the IRR at ~5%. My thinking is I’d rather have the liquidity of putting that money in the stock market.

Good luck. Also, at least in the US you’re looking at 30% federal and possibly state incentives plus again savings being tax free.

And don’t forget about inflation when doing your ROI and invest returns calculation. US electricity prices averaged 16.04c/kWh March 2023 to March 2024, but 15.50c/kWh March 2022 to March 2023. https://www.eia.gov/electricity/monthly/epm_table_grapher.ph...

As to liquidity, the stock market may be a better long term investment but it’s quite risky even over surprisingly long periods.

In my place (NZ) finance is only available for 3 years, power is cheap and install is expensive. No subsidies either. I’m looking at anywhere from 15-25 year payback (assuming same power prices and interest rates I pay for house (7.5% atm)).

I’m still keen to at least DIY a shed, but even then it’s like 5 years to pay back.

To compare with my parents place in LT (or even Australia) - power is 3x more, install 2x less and subsidies are available. You are basically looking at 6x quicker payback.

Ooh that's pretty good at 49.5°

49.7kWh in San Diego yesterday.

We take a hit from the from the prevailing temperatures in the Summer. Peak this year so far was 53kWh back in May.

Very exciting and satisfying! What’s the current break even date?

I'll need to see a whole 12 months of output before I can be sure. I suspect winter production will be well down, especially on heavy snow weeks (we get a lot here).

Roughly, it looks like it will make about $1000 worth of power per year, and the price of power here is already locked in to go up between 5% and 12% per year, basically forever.

I'm right on $8k out of pocket, which is on a 10 year interest free loan. So if I just put the savings from my old electricity bill into the loan, in 10 years it will be gone, and I'll just free power for 20 or so years after that.

One day I'll build a garage, cover that in solar too, then get an EV so I don't have to ever buy gas again.

That’s a phenomenal ROI if you’re in it for the long haul. Thanks for sharing the details.

And I'm in the rocky mountains in Canada, where basically everyone says "Solar will never work here".

In my experience, solar works everywhere. TONS of friends in Alaska and Yukon have been off grid since ~2010.

My MSc research at UWaterloo involved mapping photovoltaic viability in Canada. The data was somewhat uninteresting because the conclusion was: pretty much everywhere.

Where do you get a 10 year interest-free loan for solar?

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