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Inverter failure is real, but the industry standard has risen to 12 years for string inverters, and 20-25 for micros. Even for string inverters, most of the residential/small commercial market has moved to using optimizers for voltage regulation, which means the inverter itself is a lot lighter weight/cheaper.

Backup batteries are still relatively rare, as they should be - they are fairly expensive as backup power. Most systems remain grid tied. Smaller systems don't require retail net metering for a solid payback, since almost all of the energy is used as it is produced.

Roof repair is again, real, but not as likely as you might think. Asphalt shingles under an array are protected from wind, and even more importantly, heat. They degrade at half the rate of the rest of the roof. Assuming 12-15 years for roof replacement, you will hit the module warrantied life of ~25 years before you need to replace the roof underneath the array.

Cleaning the panels really only comes into play when the pitch of the roof is relatively shallow (3 on 12 or shallower). Otherwise rain will clean them fairly well. A lot of people won't have any trouble walking such a shallow pitched roof, and will simply hose the panels off once in a while.

Also, in general, the price of modules per watt is about half of what it was 5 years ago. Peripherals are a major component of the improved economics, but module prices themselves have mattered just as much.

   > On another note, calculating the payback of 
   > residential solar panels is tricky because many
   > online calculators don't consider (stuff...)

Sometimes they do, we installed Solar in 2003, we replaced a failed inverter in 2016. At the time we installed the system we got a new roof with asphalt shingles (50 year roof) which both helped the roof load (they were lighter than the previous wood shake) and was a time period longer than the payback period for our panels.

Stick with a grid-tie system for the time being, especially if you can get the right feed-in tariffs. I don't really see the case for domestic storage systems yet.

I suppose you mean the 'economic case'. Some people is doing it for other reasons, as is frequently the case for early adopters of any technology.

The biggest market for domestic storage is people who would want an emergency generator anyway. You get most of the same benefit for a lower cost with a Powerwall (if the expectation is temporary outage tolerance).

IMO that's the best comparison for domestic storage though.

A Powerwall doesn't store enough energy to be worth much in a real emergency. It's going to be nice to keep your refrigerator running during a short power outage, but it won't provide days or weeks of power the way an inexpensive generator can (for example http://www.homedepot.com/p/Generac-11-000-Watt-Air-Cooled-Au... ).

Sure, you have to either trust that nat gas is available or deal with fuel, but a propane tank isn't obscenely expensive considering that it bumps your backup from hours to days/weeks.

I don't understand your argument. A Powerwall, if it can get you through the trough, means in an emergency you have the same amount of power you'd have in a non-emergency.

The comment I replied to reads as if people without solar are going to install a Powerwall instead of a generator. Maybe I misread it.

That was what I meant. In my area at least, the longest power outage in the last 15 years was about 18 hours.

Clearly, the emergency he's planning for is the sun going out.

....or a winter storm that lasts a few days.

Any long storm really.

A few years ago in Vancouver a storm caused quite a number of major but localized power outages, some of which took a few days to fix. During that month or so there were a few weeks where the sun was blocked for almost the entire day - not even like overcastt.

That being said, I'd you're in a more inland area, with more sun and less clouds it might make sense.

In that case put your groceries on the back porch.

That might work for food in the freezer, as long as you don't live in an area with wildlife like bears and raccoons. It seems like a huge market for this would be off-grid people, who are going to live in the country where such animals will live. It seems like raccoons are in most American cities anyway.

You are still going to have a problem with refrigerated food - lots of vegetables spoil when frozen and frozen milk isn't much fun. Plus the house is going to be consuming lots of power from lighting and TVs as days go by.

I have family that live in very rural areas. Most of them have diesel generators or tractor PTO generators to cope with power outages that last many days. Such a situation is certainly is something that is survivable without a generator, but not very pleasant. Going through the experience once, many people realize that generators aren't that expensive and buy one to be prepared next time.

You might also wonder about running out of diesel fuel, but most farmers have 500 gallon tanks of (untaxed) diesel for equipment. Hundreds of gallons of diesel lasts a long time.

And if you have something like a dairy farm, a generator is a necessity for such a situation with a milking machine.

Storm-damage-related power outages are the killer, particularly if you rely on air conditioning. The last major storm in my area that impacted me knocked out power anywhere from a few days to several weeks, depending on the area.

It is decidedly unpleasant to be in 70+ degree heat with 80% humidity at night and hotter during the day.

> You get most of the same benefit for a lower cost with a Powerwall (if the expectation is temporary outage tolerance).

Ehh? A Powerwall costs $3500 alone, WITHOUT the inverter or transfer switch. A Powerwall supplies 3.3 kW, which isn't enough to run a 3-ton air conditioning unit (30 amps x 240 Volts == 7.2 kW).

If you run 15kW (air conditioner plus a few other stuff), you'll need FIVE Power walls for a minimum price of $17500. (Plus the inverter, plus... etc. etc.)

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Or, you can get a 16kW generator AND switch for $3300.

http://www.electricgeneratorsdirect.com/Generac-Guardian-646...

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Powerwall is actually a lot more expensive than standard generators. Something like 5x more expensive.

Erhm, do you honestly expect to keep your A/C running during a power outage? First world problems indeed..

Insulating your property to keep heat out/in is a hell of a lot cheaper than buying enough backup power to keep your A/C running...

> Erhm, do you honestly expect to keep your A/C running during a power outage? First world problems indeed..

Yeah. Lets pay $18,000 for a backup solution instead of $3000 one.

The real "first world problems" are the guys who have so much money they can afford to purchase based on ethics, as opposed to practicality.

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My power-outage plan is btw: walk to the mall / library and use their AC. If I were to get a backup unit for my house, it'd be sized for my AC unit for sure however.

It depends on where you live. About 15 years ago, the geniuses of our power company decided that they could save on tree trimming near power lines. a few years later, they were bragging about the savings... and then, in the middle of winter, with about 3 feet of snow on the ground, we had an ice storm that took out power for well over half the city. My house was without power for 4 days, with highs in the 20F. There's enough population density our lives were not in danger, but the house was only habitable because we had a generator.

And guess what? 5 months later, the summer comes, the tree trimming still wasn't done, and half the city lost power again due to a summer storm. Out for 6 days in our house. Every day we reached the 90s. Good luck insulating yourself from that heat for almost a week! Having A/C was pretty nice. The power company now inspects and trims around lines every couple of years, just to avoid power outages so wide they can't bring power back at an acceptable timeframe.

That said, the situation is rather regional: I'd not care about AC or heating in a power outage if I lived in Northern California. Around here, where we can hit the 100s in the summer and go under zero in the winter, you have to care a bit. My friend in Alaska cares even more.

So first world problems? Depends on where you live.

Relying on electricity for heating should be on the list of questionable decisions, though. That changes the parameters of emergency planning significantly.

We also had temperatures in the nineties for the last five days here, yet nobody has AC in their home. It's not a big problem with insulation. Of course we also don't have non-redundant overland power lines. Power outages we super rare.

Proper passive house design in the future should ameliorate temperature issues, both in terms of heating and cooling.

From what I've heard, houses in certain humid and warm regions (like Florida) quickly succumb to mold without air conditioning. In some cases of abandoned properties, the house quickly becomes a total loss.

Ventilation != aircon. Believe it or not, people lived in Florida before a/c was a thing... And maybe use some damp proofing while you're at it.

You're assuming that the capacity of the Powerwall is all the power available. With a solar-tied backup system, there is power coming in from the modules as well which is additive to the discharge rate of the Powerwall if wired correctly.

So even your massive A/C should be useable for a while during daylight hours if your solar system is large enough. Most people here in humid hurricane country opt to have a 15 amp 120v window unit available instead, and limit themselves to a single comfortable room.

> You're assuming that the capacity of the Powerwall is all the power available. With a solar-tied backup system, there is power coming in from the modules as well which is additive to the discharge rate of the Powerwall if wired correctly.

That still begs the question: why use Solar + Powerwall when Solar + Gas Generator has higher capacity and is cheaper?

> 15 amp 120v window unit

1800 W, which is more than half the capacity of your Powerwall. Not enough electricity left over to run a single-room AC and a dishwasher at night.

Got an electric oven or stovetop? 4000W or so? Yeah, Powerwall just ain't gonna cut it. 3.3kW capacity is just way too small for the typical house.

The answer to backup is frankly Solar + Generator. Battery backup just doesn't have the specs or the price to be practical yet.

> why use Solar + Powerwall when Solar + Gas Generator has higher capacity and is cheaper?

Because Elon Musk! Senpai notice me!

Y'all have thoroughly convinced me to disregard Powerwalls :)

Or, solar+battery+generator for uninterruped power while still keeping costs low compared to a large battery?

What does the battery accomplish? I mean, maybe an UPS for your computer if you're running something mission critical? Something that can last for 20 minutes while the generator boots up?

But I don't think most people are running mission-critical programs at home.

In my home, a single Powerwall battery could cover 90+ percent (or perhaps 95+ percent?) of nights even in an off-grid arrangement. Covering the rare extremes with a $150 generator would be more cost-efficient than using a larger battery, and likewise, covering the usual case with a battery would be more cost-efficient than running all nights inefficiently using our $5/USgal gasoline.

Why go off-grid when Net-Metering exists?

"which isn't enough to run a 3-ton air conditioning unit (30 amps x 240 Volts == 7.2 kW)."

Wow, it always surprises me how much Americans waste and consider it totally normal(I bet you are American, in the rest of the world it would be difficult to emit that expression with a straight face).

Have you considered alternatives? My house in sunny Spain spends less than 1Kwatt in August pumping water in a pipeline in the soil that has a big thermal inertia, and small air conditioning units for the air.

You don't need more if you have good insulation.

"Geothermal" (as they call it here) of that sort can be had in the US, but it's very expensive to install unless you have a large yard (otherwise you have to dig even deeper) and it's difficult to impossible to recover the cost of the system at sale if you move before saving enough to justify the cost—which itself may be difficult if you consider the opportunity cost of the money, and especially if you take out a loan to do it. The buried hoses/pipes also have a limited lifespan, and will need to be replaced in a couple decades, again at great expense.

In short, we don't do stuff like that in the US (at least, not much) because it's often a good way to lose money.

Also, I don't know about Spain, but large parts of the US suffer very high humidity through much of the year. Unless you're on an exposed hilltop with a breeze, it's miserable without good air conditioning. Houses aren't build with cooling-via-open-window in mind anymore, either, having fewer and smaller windows than older houses and being built with no thought to positioning the windows and the house itself such that prevailing winds can blow through it. Many interior materials aren't intended to tolerate even moderate temperature and/or humidity swings anymore, and will deteriorate much more quickly under those conditions. So there aren't many days in a year when it's possible to get by with no heating or cooling and just open your windows, either.

Spain is pretty darn temperate. Average daily highs don't even rise above the 90s in the hottest months. There are a lot of areas in the US that are far hotter, and if you're thinking about taking advantage of solar energy, chances are you're in one of them.

> Have you considered alternatives? My house in sunny Spain spends less than 1Kwatt in August pumping water in a pipeline in the soil that has a big thermal inertia, and small air conditioning units for the air.

Lol, Geothermal costs more than the electricity prices. Geothermal costs $25,000ish. It'd be cheaper to install the Powerwall!

In my state, a kWhr costs $0.08. Large air conditioning units are more efficient. I have a programmable thermostat that keeps the air conditioner off the vast majority of the time.

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The name of the game is to buy big, efficient units. They draw a lot of power while they're on but then they shutoff once your house reaches 76 degrees (or ~24.5 Celsius).

Again, you buy big to be more efficient. We've run the math already. A big efficient whole-house 3-ton AC unit for $1500 is much much cheaper than a Geothermal unit of $25,000.

Then get a programmable thermostat to keep it on only when you need it.

I suspect that one reason for a domestic storage system would be having solar in one of the states where the power companies have imposed punitively high charges for tying to the grid.

You have a good point re roof penetrations. There are too many cowboy solar installers casually drilling holes thinking a blob of silicon is enough to seal out the rain. Also, when you eventually want to replace the roof handling and reinstalling the panel probably doubles the labour costs.

My thought is that you would install the solar panels when you're replacing the roof. Put 30 year panels on a 30 year roof. 30 years later you get to do it all over again, but at least you're not removing and reinstalling the panels when you replace the roof.

Even without solar, few last 30 years without major repairs where I am (pacific northwest). There are lots of things to consider. Some/most solar installs don't take debris into account, creating dams that can send water places it shouldn't be, like up and under shingles. Not an issue in the desert but in rain forest it is a big deal. And the number of penetrations ... I've seen people put dozens of screws through what used to be a good roof. They cannot all be perfect.

Around here (midwest) hail or wind usually knocks out composite roofing in 10-15 years—much less if you're unlucky. There's little point in springing for the "50 year" composites and similar.

I guess the solar panels would protect the roof a bit, but I'd expect a bad hail storm to be bad news for those, too.

This was a reason I put solar in after installing a standing seam metal roof. The roof will last 50+ years, and the solar just clamps onto the seams. Only penetration is for the cables to the inverter.

Not only that, but it's not uncommon for panels to crack. Kids throwing stones or balls, weather-related, etc. Replacing the glass is often difficult or expensive. Alternatively, you can fix it but that will often reduce the clarity and thus the generated electricity.

Panels are sturdy enough to withstand 4 inch hail and hurricane winds if properly mounted to a roof or concrete ground support.

>The article emphasizes that the declining price is due mostly to peripherals & installation rather than any efficiency breakthroughs of the solar panels themselves.

Over the last few years racks, mounts, wiring, inverters and labor have made up ~60% of the cost.

Plus, Obama started slapping ~30% tariffs on the cheapest imported solar panels.

Not sure why you're being downvoted, I assume the ~20℅ anti-subsidy rates plus the individual anti-dumping rate referenced in the below article are what you're referring to?

http://www.bloomberg.com/news/articles/2015-07-09/u-s-impose...

Yep that's the one.

I read the state department report too. The 'disguised subsidies' they called China out on included 'advertising' the solar companies' existence on local government websites.

Clearly they didn't expect anybody to actually read that.

In the US, I'd image tariffs on panels having a much lower influence then elsewhere in the world. Even if panels were completely free in the US, a US-based residential solar system is going to be more expensive to install than even European ones (including European panel costs).