home battery

My off-grid buddy has ~10kW(?) in PV panels, and uses resistive heaters to slide off the snow. Has to, otherwise he goes 'dark.'

Even with that, and a prime location, he stills runs a generator ~1,000hrs a year, maintains two generators, and yes, they fail. The oil-change interval on at least one of them is 100hrs, about twice a month.

Cheers, James Arthur

A guy was installing panels next door, and tried to sell me, too. He said that power output was down about 50% on cloudy days.

Like a Chevy Volt? ;-)

But it's (more than) 100% efficient! ;-)

Yes, we use electricity for heat (heat pump) and HW. It's the cheapest TCO heat available. So in terms of BTU/$, it's the most "efficient".

We sorta need both, making the heat pump the obvious choice.

The only thing wrong with the Chevy Volt is everything. I'm not sure exactly what went wrong. Certainly the fires and politics didn't help: It seems to me that GM threw everything they had, starting in 2006, at the project and still didn't produce anything worth buying. I would guess(tm) that the basic problems are that it costs too much and does not distinguish itself in any way. The latter is important because early adopters will willingly overpay for making a statement, but want something in return that will distinguish them from "ordinary" automobile owners. You can easily spot a Prius or Tesla, but the others are rather ordinary and boring. If one is expected to pay $35,000 and up for a Volt, they would want everyone to know that they had overpaid: Nice try, but not quite what I had in mind.

"Peak oil."

trillion barrels of oil. Another trillion barrels are also said to be trapped in rocks in Colorado, Utah, and Wyoming,[185] but are in the form of oil shale."

I just spoke to my off-grid pal. I was mistaken about having him having embedded heaters. He has to scrape his panels with an ice-scraper on an extension pole. Once they're partly clear, they heat up on their own. (I must've been thinking of someone else regarding the heaters.)

He's on a mountain top in the dry southwest--perfect solar country. He quoted some actual output numbers from the past week--his thin-film panels make 10% on cloudy days, not 50%. (That's real-life data.)

Cheers, James Arthur

That depends on what you consider to be cloudy. Offhand clouds seem to drop the output to somewhere between 15% and 70% depending on cloud density and the position of the sun.

Here's about 9 months of numbers from an installation in California. We haven't had much in the way of storms and clouds, but when present, the effects on solar output is noticeable. All the big drops in output are from clouds (or PG&E outages). The big plunge around the beginning of Feb 2015 is from a 3 days storm. Even so, this 5.6 kw (21*270w) array still managed to produce about 2.0 kw-hrs (about 15% of Feb normal) during the storm. The lowest was 0.8 kw-hrs on Feb 6 which was caused by a 6 hr PG&E power outage. Grid tied solar systems without auxiliary power sources are shut down when utility power is absent.

There are lots of ways to sell residential grid tied solar. In my never humble opinion, the best is that it helps prevent your power bill from climbing into the next higher billing tier. Since PG&E lowered the tier thresholds in Jan 2015(?), that's more difficult than before, but still possible. Much depends on your total consumption. Notice the big jump in price between tier 2 and 3: I don't have my numbers handy, so I can't produce typical savings right now. Most residential users end up somewhere in the middle of Tier 3. If you're into Tier 4, think about investigating where the electricity is going and looking into appliance efficiency.

Grinding the numbers: You're in Territory T with a baseline rate of 8.5 kw-hr during the winter and 7.0 kw-hr during the summer. That produces tiers of:

Per Day Tier 1 Tier 2 Tier 3 Tier 4 (kw-hr) winter

Ok, let's see if that works. The weight of a 42 gallon barrel of oil is about 300 lbs. 1 trillion barrels of (crude) oil would weigh 300 trillion lbs or 300*10^12 / 2000 lbs/ton = 150*10^9 = 150 gigatons Yep, there are gigatons of oil in the ground in Canada.

Averaging the conflicting predictions of daily petroleum consumption, I'll pontificate that the world is burning about 90 million barrels of oil per day. That should last: 1*10^12 barrels / 90*10^6 barrels/day = 11,000 days 11,000 days / 365 = 30.4 years Not exactly hundreds of years, even if we squeeze the Canadian oil sponge dry.

Sadly, the side effects of burning fossil carbon and and adding even more CO2 to our atmosphere means that we ought to leave most of those gigatons in the ground, ready to be used by the next species that evolves symbol-manipulating intelligence.

It's to be hoped that they are better at it than John Larkin.

There's no need to create the perception. Burning fossil carbon is evil and destructive,and the stocks - while not depleted to the point where there i sn't any more to be had - are depleted enough that it's becoming progressiv ely more expensive to dig them up.

The economic reality is that that the capital cost of renewable electricity is about twice as much per installed kilowatt as that of fossil-carbon fue led generating plant. If we were to get the bulk of our power from renewabl e sources, we'd have to manufacture at about ten times the scale, which wou ld roughly halve the unit cost per kilowatt of generating capacity.

It's cheaper already per mile - just less convenient, with shorter range, s lower refueling and few recharging points and lower production volume, when ce a higher capital cost for each vehicle.

High capital cost and short battery life trump lower cost per kilowatt hour . You don't recover 100% of the stored energy either. The utility-scale num bers are equally unattractive.

Thermal solar does have a uniquely useful capacity to store energy - in hot molten salt - for some hours before it gets converted into electricity. Hu ge insulated tanks for the hot molten salt are relatively cheap.

With bated breath. The vanadium redox battery is just one of number of half

-baked possibilities floating around the literature, waiting for somebody t o find a few million dollars on finding out why it won't work. Eventually o ne will work ... but one has to suspect that it's going to need one of the genuinely rare rare-earth elements, and China will own the only mine that p roduces it.

That's just two oil fields, and it's a big world.

Of course. So build your PV solar farm well inland, where the air moving above the panels hasn't got much water vapour and rarely generates clouds.

That's exactly what First Solar is doing in Australia.

And your comment about photon energy - wavelength - still reflects an imperfect grasp of the physics involved.

Oh, he was lying, of course.

It depends on the density of the clouds. The First Solar lecture showed time series of a small cloud crossing a solar farm, and it knocked back the output to perhaps 70% of cloudless for a few minutes.

Thick "black" cloud could knock it back to 10% or less - but that's rare in places where you'd build a solar farm.

The solar farm is going to be delivering power for most of the sunlit hours - not just at noon. You have enough panels so that you can deliver a more or less constant power output - which is what the grid wants - for most of the day.

Excess maximum generating capacity does raise the capital cost, but not dramatically. It's certainly cheaper than power storage.

How much light gets through two feet of snow? Putting solar farms that far north is a pretty stupid idea to start with.

Fill up Arizona with solar farms and build a heavy duty high-voltage transmission system to get the power up to the people who are freezing to death.

The Germans are talking about building their solar farms in the Sahara and shipping the power up through Italy or Spain.

Build wind farms in the far north instead. They love blizzards (though they do have to be designed to cope with the maximum wind speeds).

So the grid had to provide the remaining 85%. It doesn't matter that this was only for three days out of nine months. During those three days, the backup was required, and therefore had to exist.

Sylvia.

Yes - there's always someone who thinks the rules don't apply to them.

Sylvia.

Everyone lies, but that's ok because nobody listens. Does your neighbor keep or download production statistics? If not, my guess(tm) is that his guess is as bad or worse than mine.

Look at the graph I produced for your benefit and notice the drops on cloudy daze. It's difficult to put a number on these drops, but you can sorta guess by dividing the lowest output, by the highest output that would have been produced using a smoothed curve of the expected peak power. For example, in December, the minimums were around 2 Kw-hrs/day while the typical peak output would have been around 9 Kw-hr/day had there been no overcast or clouds. Daily output was therefore 2/9 = 22% of "normal" which is much lower output than your neighbors 50% output loss. If I expand the data, the output varies radically as storm cells float over, as holes in the clouds appear, as the angle the light has to pass through the clouds, whether it was raining, and other weather effects. 78% loss is probably a decent average for the left coast.

Incidentally, if you want to see what others are doing, go thee unto: These are all Enphase microinverter users and does not include all solar installations. The system I graphed is one of my customers and is NOT publicly accessible. However, there are plenty of others that are available for inspection. Never mind the guesswork, just grind the numbers and see if it can be made to work for your house.