Hacker News Reader

Rooftop is generally on site. Ground is generally in large arrays owned by power companies. Being on site and owner-operated means not incurring the expenses of lines and various markups (sometimes extreme) from power companies. And it means being completely independent of the power companies who have different incentives.

Conversely, you’re entirely responsible for maintenance and system upgrades/replacement on a per household basis which people won’t budget for

Household? Do business properties not have rooftop arrays?

I'm not sure why that distinction matters, it's the same situation. The CapEx is being decentralized and so also is the burden of ownership

We'll end up in situations where people buy a property (personal or business) then the first year of ownership get hit with a "sorry, needs new solar system" type surprise bill. This is not uncommon for HVAC and sometimes plumbing issues, much more unusual for electric and gas utilities.

To add some other points - rooftop solar being the future is untested. Most of the installations were done in an environment where solar wasn't really commercially viable and people were trying to push water uphill with a shovel. Which can be done, mind you. There are cases like Germany where they seem to have done a lot of damage to their own energy supply.

But now that solar seems to be a viable option it is unclear what the equilibrium point is. For coal, it didn't make sense to give everyone a generator. Even coal-powered fireplaces in homes turned out to be noncompetitive for heating, which is a bit of an unexpected outcome. So since rooftop solar is dangerous to install and comes with a maintenance burden as well as presumably increased risk to consumers, it might still turn out that the best approach is a big centralised solar farm with huge economies of scale. Keep maintaining and using a distribution grid.

Grids are expensive, so it could shake out either way. But I don't think the public knows what will happen yet.

> which is a bit of an unexpected outcome

I don't see it. Coal fireplaces are relying on the same idea as the ICE car, this fuel is so cheap to use that it won't matter if we use it inefficiently. But unlike cars, your house isn't going anywhere.

One thing people tend to get wrong about heating is that because of the laws of thermodynamics it seems as though any method must always be 100% efficient and thus it can't matter. But actually we care what gets heated. Fireplaces heat the air in the chimney well but you don't live there - you live in the rest of the house. As little as 20% of the thermal energy in the coal is converted into a warm living space, and that makes it pretty easy for electrical solutions to compete.

Something like a gas boiler heating water for radiators still can't deliver the same point of use efficiency (as resistive heating) because the burned gas is toxic, so we need to put that warm gas outside (otherwise what you've made is a death trap, not a warm home), yet we'd like to capture as much of the warmth as possible, the result is we're maybe 80% efficient. It's much easier to add radiators than chimneys, so the result is much better, but far from perfect.

We're burning coal - which burns really hot. Nobody has managed to come up with a more economically efficient approach than burning that coal kilometers away from the place that needs to be heated. And not for clever chemical reactions, we're still burning it for heat. So it turns out that the most effective way to heat a space is to burn coal for heat but jam a ridiculous amount of stuff between that and the eventual heated space.

Obviously you've got all the details, but if those details are what turned out to be true for coal then we as the public have no idea at all what the details are going to be for solar. Possibly even the insiders don't know yet. There is a pretty good chance here that centralised solar installations win the economic battle.

> Nobody has managed to come up with a more economically efficient approach than burning that coal kilometers away from the place that needs to be heated.

Have you tried not burning the coal? The coal was fine where it was, leave it there and save on extracting it, then burning it and then cleaning up the tremendous resulting mess.

  - No additional consumption of land
  These benefits are comparatively minuscule

I think that benefit is significantly less minuscule than you make it out to be. For rural installations, sure, but in high density areas the cost of land can be absolutely insane, and those high density areas tend to have high power demands just due to the density of humans that live there.

You can put all the ground mounted panels out in the countryside hundreds of miles away from the density, but high power transmission lines are also expensive and dangerous to maintain. Generating the power right where it's used completely eliminates a problem which has serious negative consequences like wildfires.

At some point, we're going to have to learn to eat the cost of HVDC transmission. You can move GWs of power with conductors of reasonable size and complexity (both underground and undersea), if you can get the right of way, and there are no technical limitations on length besides line loss.

https://www.nationalgrid.com/sites/default/files/documents/1...

https://europacable.eu/wp-content/uploads/2021/01/Introducti...

- Slight reduction in transmission and distribution costs, since more electricity is generated directly at the site of consumption

The generation being at the site of consumption has another big benefit: one of the largest roadblocks in the way of utility scale solar in Australia is that it's slow to get approval for the large grid connection you need to actually export that power. That time represents a cost that is sometimes larger than the cost of the actual grid connection itself.

Ground-mount arrays can also use bifacial panels-- solar panels without the opaque backing that can capture light from both sides at once.

> Possibility to use single axis sun tracking mounts for panels, so a unit of capacity generates more electricity each year

I read an HN comment earlier this week that noted that solar panels are so cheap that is is more economical to just install more panels than to pay for the expense and maintenance of moving parts. I.e. you can generate the same amount of extra energy that tracking would give you by adding more fixed untracked panels. And fixed panels with have no moving parts which makes maintenance super cheap.

A quick glance around at internet articles seems to confirm this take.

That may be true in some locations. The most recent information I can find for the United States says that single axis tracking is used by most large solar farms:

The use of single-axis/one-axis tracking in the U.S. utility PV market has grown significantly over the past decade. At the end of 2022, 73% of all U.S. utility-scale PV systems used single-axis tracking. And 86% of U.S. utility-scale PV systems installed in 2022 used single-axis tracking. This growth can be attributed to the reduced cost and increased reliability of trackers, making them the economic choice in a broader distribution of PV systems (e.g., less irradiant climates).

"National Renewable Energy Laboratory: Summer 2023 Solar Industry Update"

https://www.nrel.gov/docs/fy23osti/87189.pdf

Having the ability to generate electricity in the event of a power outage is another benefit of rooftop solar.

Grid connected solar disables itself in this case.

You need a compatible inverter for it to work, and they're quite uncommon.

With my setup I just need to flick a switch to cut power to the main grid, and my inverter will automatically turn back on. In Japan at least this feature is ubiquitous - I looked at systems from several manufacturers, and all had the ability to generate electricity during an outage.

Only if you have battery storage.

My system does not have battery storage. A storage battery would be considerably better in the event of a power outage, but also would have doubled the cost of the system. My plan is to have another look at batteries when it is time to replace the inverter, and hopefully the cost per kWh will have dropped by then to the point where batteries make more financial sense.

That’s mostly true, but not entirely. SMA (inverter) offers Secure Power Supply on some models, which give you a single 120 Vac outlet that can provide up to 2 kW (about 15 A) assuming there is enough sunlight. If the solar panels are producing less, it can still provide lower amounts of power. For things like charging phones, a small TV, laptop, modem, and router, it should give you power during most daylight hours, regardless of cloud cover, if you have a 6 kWdc array.

I’m not sure where you live, but I’ve been privy to thousands of rooftop solar installations deployed in the U.S. (New England mostly) and the common case is to have the inverter wired into the circuit panel with a per-circuit or whole house automatic or manual switch, then also grid tied to realize net metering benefits. Very few installs have battery storage (less than 1%, though this is changing rapidly).

Generally agree, though let's be real that transmission and distribution losses for ground mount solar are not slight, they are in the 30-40% range, like all utility T&D.

That's much too high an estimate, at least for the United States:

How much electricity is lost in electricity transmission and distribution in the United States?

The U.S. Energy Information Administration (EIA) estimates that annual electricity transmission and distribution (T&D) losses averaged about 5% of the electricity transmitted and distributed in the United States in 2018 through 2022.

https://www.eia.gov/tools/faqs/faq.php?id=105&t=3

That's just outright false. Where did you get it from.

I can't find a link so I'll explain it...

Single high voltage transformers approach the 6-8% at full load... Not to mention the wire losses and other transformers in the system minimum 3-5). The number you quoted from the EIA is not accurate. See this Nameplate Z% (impedance aka losses) of an ABB 20MVA transformer: https://images.app.goo.gl/hXNTWAv1xnu83znQ7 It is higher as the transformers get larger.

Correction tho... 30-40% includes the losses from generation, not just T&D. And if you keep searching the EIA quoted that at 34%.

> The number you quoted from the EIA

I didn't quote any numbers.