Storage-less Solar PV

One of my favourite personalities is Nate Hagens. He seems to get the mix of problems and solutions (no easy solutions really exist) without going off into woo-woo. Anyways, in a recent presentation that is available https://www.youtube.com/watch?v=2rGyn3EH61c]on[/youtube] Youtube, he mentions solar systems without any kind of base-load. I've been thinking about the same thing for quite some time. (A warning, that presentation is really long and rushed. It isn't his best. This one is better, but doesn't mention the concept of storage-less solar PV.)

So my solar system has batteries which keep everything running at night and for a few cloudy days. (To be clear, I own the solar system, but the house it is going into is still being built.)The batteries are a huge expense and are relatively short-lived. Grid-tie systems use the grid as their storage, which brings a large monthly bill, even if your solar system generates more than you consume. The system I'm imagining would not be grid-tied or have batteries. Perhaps it would have a very small amount of storage, just enough to get the bare minimum load through the night and provide for burst loads (ie. an appliance starting up) during the day. But basically, electricity would only be plentiful when the sun is shining.

If the world were to fall apart, even those of us with an off-grid system would find ourselves with such a system eventually. On the other hand, removing the expense of batteries would make a solar-electric system much more affordable and allow more folk to make the leap.

Does anybody have any experience with such a system? How about just opinions? How painful is it to be without (much) electricity at night?

@Mark F: "How about just opinions? How painful is it to be without (much) electricity at night?"

No direct experience, but some musings. First, I think you are on the right track with trying to reduce your "battery debt", if you get get away from things that are large loads on the system. Don't know how long solar panels are going to stay relatively cheap, but I agree that if their longevity is considered pretty good as an investment, then it may be good to buy into these earlier in the system build and stay lean on the batteries. It was satisfying to see that in the case of some of the solar builds, the idea of combining (in space) the inverter and the panel(s) means you are converting to AC at the panel, the produced power of which will experience less line-loss on its way to its destination.....at least that's my understanding. Second, with LED lighting, I'm not sure you would experience much reduction in lighting at night with a couple of decent-sized batteries driving the power.

Author Edit on 3/5/2016: The information between the dotted lines was in the original entry, but is incorrect. Since it was addressed in responses below, it is being left here for the purposes of linking with those responses. However, please consider the information between the dotted lines to be retracted by the author as it is untenable and confusing to the discussion. My apologies. Thanks. -JW
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It's not a direct apples-to-apples comparison, but I rigged up a string of 150W incandescent flood lamps (8 bulbs) over a remote space for feeding some geese and drove these with a 12V/~30Ah battery running through a 1500W modified sine wave inverter.....would leave the lights on for several hours while they fed and was pretty impressed with the output, duration, and robustness of the system.
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If we embark on a solar change-over similar to what you are describing, we likely will grid-feed for the near future until we felt comfortable pulling the plug....or the price from the grid became exorbitant. But in addition, I hope soon to wade into battery back-up on the well-pump which would introduce our home circuitry to the concept. Would be nice in the future to made judicious decisions on what can be jettisoned from the more high load life.

Thanks for the reply John.

I keep thinking about ways to build the household systems to cope with the loss of electricity over night. One could freeze ice during the day to keep things cool over night. (In our climate, we don't need really need refrigeration for five months of the year as there is plenty of cold air for the taking.) A pressure tank could store enough water/pressure for tooth brushing and hand-washing. Thermal mass could keep the house comfortable over-night.

On the other hand, electric lighting allows one to work pre-dawn and into the evening. That would be a huge productivity boost, and could be the difference between making ends meet or not.

This is the dilemma I face right now - completely offgrid but not willing to spend the exorbitant amount required to build a battery bank that will actually carry us for long. Minimal storage is definitely my choice in the matter thusfar ... greater output than you have bank makes more economic sense.

I'm already very efficient on power usage and have learned to be even more so, but with only two 100AH deep cycle AGMs, I still resort to running a gasoline powered generator to "recharge" after a few days of clouds I truly hate the thing and wish to be rid of it...the noise pollution alone is enough to make me resistant to firing it up!

That said, with two more panels (currently have just two @ 100w), even on cloudy days in December at 45*N latitude, I could bank enough power to keep myself going. It comes down to efficiency of use. During the lowest sun angle, when daily electricity output from the panels is at its lowest, the outside air temps generally are beginning to match up and make for more efficient usage of the stored power since the greatest electricity draw is always going to be for refrigeration (assuming you're wise enough to have moved away from electric heat sources). Through appropriate technologies that is... LED is definitely the ticket for this since the one thing that does increase in demand during lower sun angles and cloudy stretches is that for lighting. More efficient lighting technology, and smarter use of it, matches ideally to the loss of PV output. Still, though, there's need for *some* storage.

Running storage-less is something that could be done if you wanted to return to the old ways - kerosene lamps and relying on daylight/moon cycles - and a lot can be said in favor of doing so. Without that, however, I think some (minimal) storage is at the very least as important as the panels themselves.

All that said, I am pretty excited about this Tesla Powerwall stuff. It's currently WAY outside my budget, and way above my own needs, but with these things selling like hotcakes now and the "natural" market forces at work, within a handful of years we might be looking at much more affordable, longer lived and lighter weight power storage solutions based around the newer battery tech. When they release a 500AH model rated for 5,000 cycles, under $350, I'll MOST CERTAINLY be making the switch. I just hope that happens before my current bank decides to give up the ghost

Note: I know there's some serious questions about the environmental costs of these newer types of battery technologies. The way I see it, though, is that if we people are going to store electricity, it's far better to make super efficient storage devices that last much longer, are less likely to have potentially catastrophic failures and are completely recyclable, than to continue on with the more dangerous, just as environmentally costly, short lived and much less efficient lead-acid battery tech. Appropriate technologies and all that

Additional questions. We are actually in an "excellent" windpower region, yet due to many trees having been planted have somewhat destroyed this potential unless we wanted to erect a tower to the moon.
Something I've considered more lately is to buy low (but not cheap) on a ~600W wind turbine as a supplement for cloudy/night weather when at least *some* wind power could be obtained. I realize that the cost per watt is not very attractive for larger systems, but perhaps as a supplement for low wattage systems...? In our case, we simply would accept the lost watts for being on a lower pole, cuz there's no way I would want to invest in the pole and guy wires to put a 600W windcatcher 80 - 100 ft high to get the optimal needed height above the trees. An option for either of you two?

I know from looking into this before that it's certainly doable here and, lo and behold, winter, when PV is least effective here, is actually when we have the highest average wind speeds, putting a bit more favor on such a solution, but wind power is difficult to justify financially on a homestead-scale even out in the flatlands/plains where winds are generally strong and steady. Spinning turbines are dangerous, moving parts require maintenance and the infrastructure required for the turbine is usually fairly costly in and of itself. If power needs were high enough, winds were reliable enough, and money was available, it might be an option for some, but would likely still not be economical as compared with simply adding a few extra PV panels to the system.

The only advantage I can see over just adding more panels to the system and having a minimal storage battery bank would be the (typically small amount of) power available during overnight hours for use as a storage-less system.

Micro-hydro, if an option for the given site, makes more sense from this perspective as it's inherently less dangerous. It's also relegated to a second-place, however, as compared to more panels of equal expected wattage output, as it, too, is a fairly low power output solution for the money invested (unless you have some serious flow and head to work with), is subject to longer-term output losses due to drought, damage by flood conditions, and, in northern climes at least, is really only effective on a homestead-scale during the 5-7 "non-frozen" months. It's a far better option on the community scale and when grid-tied, much like wind power is, where output can be averaged out over time and economy of scale comes into play.

I think, in essence, off-grid people are stuck with the need for at least some storage of electricity if we want power at night. Perhaps someday the woo-woo technologies, like mini-cold fusion devices or zero-point tech, become reality and it will be a non-issue. In fact, the cold fusion stuff is getting a little less woo-woo every year

Mark Fox wrote: How painful is it to be without (much) electricity at night?

I've been living at a school that is off-grid solar, for the past 20 years. Even in town, the electricity was very limited until recently and is still unreliable, so nobody depends on electricity completely here. Nobody uses a fridge or freezer for long-term food storage, nor are there any electric plug-in clocks, or clocks on the front of appliances.

At our school, if our batteries don't hold up, we use a generator for backup in the evening until 10:30 so that everybody can be up and around and doing their things in their rooms or all together, but then we turn that off at 11.

So it's not painful to have no power sometimes. I keep a headlamp near my bed in case I need it in the night for going out to the outhouse. Or I'll even read with the headlamp, (which is taking Paul Wheaton's advice to use power only exactly where you need it to ridiculous extremes). Luckily my little skinny laptop holds a charge for several hours, so sometimes I read or work on that. Because this does happen occasionally, I find that I have a mental note of exactly where I've kept things, especially the headlamp, and I can usually stumble into my bedroom in the dark and lay my hand directly on it -- the habit of keeping note develops quickly.

And then I fall asleep, and the sun comes up, and the solar batteries recharge. Even on a cloudy day there's enough power coming in to charge up my phone and computer.

A 2W LED bulb right over the head of the bed or the desk is very bright for reading, sometimes seems even too bright. If the power is low, I only keep the one bulb on, right over where I'm reading.

So just list what you would still need when the power goes out. Can you get by just fine with batteries and candles like I can? Or will you have a cubic meter of meat thawing....?

Capacitors are an alternative power storage mechanism. They could easily hold enough electricity for LED lighting into the evening, and can power surge-loads during the day.

I charge AA or AAA batteries during the day, and use LED headlamps or flashlights at night. A little bit of power produces a lot of LED light when it's only two feet from the light source on my head to a book. Stand alone batteries in laptops, tools, phones, etc could be charged during times when power is plentiful. My family thinks I'm weird when I visit. Because even though they have grid-electricity, I prefer to wear a headlamp at night...

I highly recommend doing without refrigeration in any off-grid setting. My family mostly stores sauces and leftovers in their fridges. The way to get around that is to use sauces/spices that don't need refrigeration, and to cook only the amount that you intend to eat. Also, many westerners are germ-a-phobes. My experience is that food spoils much more slowly than I was lead to believe in school.

Skylights are amazing lighting devices. They can completely eliminate the need for lighting during the day and on moonlit nights.

I lived in a place one time where a trickle of water was lifted to the roof, and was then gravity fed to the faucets. That would be a great use of excess power during the day.

My freezer will go for 24 hours without electric power at least so why would I need a battery just got it ?
What I really want is a black box that would let me micromanage my electric supply .

David

As D. Livingston suggests, a well-filled chest freezer can last a while, even in the summer, with no power for at least a day. Our freezers are inappropriately placed and in an un-insulated garage....stay cold in winter, but the building is pretty warm in the summer. The latter problem could be somewhat ameliorated by having them placed in some sort of earth-bermed shelter that would buffer the temperature swings more. I agree with Joe L. about refrigeration and how, between earth-buffered chambers (root cellar idea) and just learning about what goes bad fast and how best to avoid that, one can reduce the need for refrigeration in the home. Just a FWIW, it's probably been mentioned before, but there are those small thermoelectric "six-pack" coolers that draw ~50 - 60W that may be of use for some small refrigerator-storage applications. Many of these are transitional solutions with an eye ever towards "What did the natives of this region do?".....and that points to a lot of food drying for preservation, eating fresh when and where possible, and minimizing night-time lighting and power consumption. As Rebecca N. noted, what started out as "sacrifice" really does not seem so terrible after getting used to practiced alternatives.

One more concept question in the small-scale solar/wind grid-intertie department.

The transfer switch at our power pole allows me to disconnect the mains from the utility and use my generator for times when the power is out. Assuming enough solar panels (+/- complementing wind turbine) were installed and were producing enough AC power (via inverter) to feed into the house, one might simply disconnect from the utility in the morning and use the panels by day to run low-load appliances and re-power a few batteries. High-load appliances would be turned off during this period. Does anyone know of any rural cooperative utility law (USA) that would prohibit one from doing this on a routine basis? Does anyone's rural coop have a clause(s) about minimum KWh usage or frequent disconnect that I'm not aware of? Thoughts about an automatic transfer switch that might do this?....Clearly, this would be different than a "true" grid intertie set-up.

I can't imagine spending the money on solar and having no battery at all, since I consider lighting to be greatest utility for the least watts of all possible applications of electricity!

Mark, as you describe, there are workarounds for many things. As Joseph and Rebecca have pointed out, flashlights/headlamps go a long ways, and you don't necessarily need a lot of watts for decent lighting. I recharge my 8650s(lithium-ion flashlight batteries) in a USb-powered charger that can run off a car adapter, or a laptop, or any 12V system with a cig-lighter plug for my USB adapter. It is truly amazing how far a flashlight or two worth of watts can go, in a room with a nice reflective white ceiling.


However, I am fond of the ability to run power tools after dark, especially when 'dark' is 4PM for part of the winter here... It's a good time for this sort of work since the garden is put to sleep, and it may be unpleasant outside... enough power to work in the evenings is a big help IMO.


Couple things to consider about minimizing or eliminating the battery bank...

1) A properly maintained battery's lifespan in cycles will be vary based on depth of discharge... so a 100AH battery discharged daily down to 50% will wear out notably faster than a 200AH discharged daily to 75%, and then on rare occasions discharged to 50%. Of course, since batteries also degrade with time, there's bound to be a sweet-spot...

2) Rate of discharge impacts how much you can draw from a battery; a '100AH' Trojan 27-AGM is rated thusly:
5-Hr Rate 77AH
10-Hr Rate 82AH
20-Hr Rate 89AH
100-Hr Rate 99AH

So the higher the draw relative to the bank capacity, the smaller the percentage of AH you can actually draw...


3) Solar charge controllers are really designed to charge batteries, and don't necessarily operate correctly without them in the loop. The cheapo on my folding panel won't work at all without a battery; it will provide 12V power to 12V devices connected to it, it NEEDS a battery connected as the controller determines what to put out based on the battery voltage. I think this is fairly common behavior...

If you're going to skip the charge controller, then you better make sure whatever you connect to your panels has a broad input range that can handle the the varied input it will receive... And even then you may get some interesting behavior when clouds pass over the sun and you suddenly have a power deficit with nowhere to draw from...

John Weiland wrote:The latter problem could be somewhat ameliorated by having them placed in some sort of earth-bermed shelter that would buffer the temperature swings more.

Yup, this would be a really good thing for efficiency. I found one example that observed the consumption of a chest freezer decline from 3.04KWh/day to 2.14KWh/day on lowering the ambient temp from 99f to 75f... and a room kept at roughly earth ambient would be even cooler than that that. Plus, the room would be a great place to store lots of food that doesn't need refrigeration but would benefit from the cool temps.

John Weiland wrote:

The transfer switch at our power pole allows me to disconnect the mains from the utility and use my generator for times when the power is out. Assuming enough solar panels (+/- complementing wind turbine) were installed and were producing enough AC power (via inverter) to feed into the house, one might simply disconnect from the utility in the morning and use the panels by day to run low-load appliances and re-power a few batteries. High-load appliances would be turned off during this period. Does anyone know of any rural cooperative utility law (USA) that would prohibit one from doing this on a routine basis? Does anyone's rural coop have a clause(s) about minimum KWh usage or frequent disconnect that I'm not aware of? Thoughts about an automatic transfer switch that might do this?....Clearly, this would be different than a "true" grid intertie set-up.

I might hit this problem from another angle; practicality would really depend on the house/property/usage though. Maybe it would be possible to move lighting and low-draw stuff over to the solar/wind system, with separate wiring? Then use a transfer switch(much smaller and cheaper than the one on the pole since it wouldn't need nearly as much capacity) at the house to switch this stuff back to grid in the evening if/when needed. The high load appliances run on grid whenever desired...

John Weiland wrote:Just a FWIW, it's probably been mentioned before, but there are those small thermoelectric "six-pack" coolers that draw ~50 - 60W that may be of use for some small refrigerator-storage applications.

The efficiency of a peltier-based cooler is absolutely *terrible* compared to any phase change refrigeration system I've ever heard of, even the ammonia-filled absorption cycle sort that RVs tend to get since it can run directly on propane. IIRC they're about 1/4 as efficient as a compressor based fridge. Plus they will not be able to hold a useful temperature in a hot environment.

There are DC powered compact compressor based fridges and freezers available, including compact/portable units used in boats and 4x4s(ie National Luna, Arb, Engel, at the low-end Waeco), and these are generally very efficient, but not cheap. There's also the chest-fridge option of converting a chest freezer to operate as a fridge, which is quite efficient due to the orientation and better insulation.

John Weiland wrote:
I rigged up a string of 150W incandescent flood lamps (8 bulbs) over a remote space for feeding some geese and drove these with a 12V/~30Ah battery running through a 1500W modified sine wave inverter.....would leave the lights on for several hours while they fed and was pretty impressed with the output, duration, and robustness of the system.

I think I'm misunderstanding something here! 8x150W bulbs? AKA 1200 watts... for several hours? A 30Ah 12V battery has 360 Watt-hours in it till flat dead... So something is interesting about this setup!

Joseph Lofthouse wrote:Capacitors are an alternative power storage mechanism. They could easily hold enough electricity for LED lighting into the evening, and can power surge-loads during the day.

I think some beefy capacitors would probably be a very good idea for a system trying to economize on batteries, and would certainly help with startup surges especially for larger loads. However, my understanding is not so practical for storage... let's see...

Per engineering toolbox, energy stored = 1/2 C V^2

where C=capacitance in Farads, V=voltage

So, a cheapo (16V rated, run at nominal 12V) 83F ultracapacitor bank off ebay for $115 would give: 0.5*83F*13.8*13.82=7903 Joules

So, that's 2.2 watt-hours for $115. Enough to run a decent LED for an hour...

One problem is that this is to discharge to 0V; the amount of power actually available would be less, because at some point the voltage will be too low to be useful. If you're direct-driving LEDs, maybe this is 6V? In practice, you'd probably have a LED driver of some sort to manage the brightness. This is probably going to want at least 2.5V, though I do see one rather expensive option good down to 1V. So, some power will be lost from the voltage dropping to an unusable level, however you set things up.

(There's a list of drivers here: http://www.videofoundry.co.nz/ianman/laboratory/research/driverlist.php)

However, the real problem is a single 18650 lithium-ion rechargable battery is good for at least 8 watt-hours, and will cost less than $15 each even for high amperage capable protected cells...

(I don't much like the idea of series capacitor arrays, especially not the cheap and chinese sort; I would at a minimum greatly underrate such caps before using them... but it's just an example. Quality caps would make it even worse value.)

@Me : "It's not a direct apples-to-apples comparison, but I rigged up a string of 150W incandescent flood lamps (8 bulbs) over a remote space for feeding some geese and drove these with a 12V/~30Ah battery running through a 1500W modified sine wave inverter.....would leave the lights on for several hours while they fed and was pretty impressed with the output, duration, and robustness of the system. "

Absolute rubbish! Looks like I was not able to edit nor delete my original post. If the moderators can somehow let me do that, I wish to correct such a bald-faced lie that I posted in my 3/3/2016, 11:19:09 AM entry above.
After checking my notes and equipment, I must have been mixing up projects and wish to retract the quoted material so as to not confuse others. Thanks to Dillon Nichols for calling me out on that end-of-the-week brain-cramp math---I'm eating some serious Teriyaki Crow this evening for dinner Thanks also, Dillon, for the excellent additional information in the response. Important factors to consider for true functionality.

[Note: The moderators have allowed me to edit the original post and the modified version will hopefully appear upon completion of their review and approval.]

As can be divined here, I would have needed a much larger battery, or smaller load, for that system to be functioning for the time period originally noted:

Mark Fox wrote:

Does anybody have any experience with such a system? How about just opinions? How painful is it to be without (much) electricity at night?

I don't have a lot of experience with storage-less solar but I do have insufficient storage, meaning that our power goes out often and we intentionally shut it off every night before bed.
We have LIons with built-in underchrge and overcharge protection (that we got relatively cheap and will last us 10 years before needing replaced) so using the battery down to shutoff doesn't damage them.

We do have a pressure tank for water but we drain it at night in the winter because we had the pipes freeze once and we don't want that to happen again. We keep a pitcher of water for night time drinks and we don't flush or shower till morning. During warm weather our pressure tank supplies our water needs during the night, which are few.
Hot water is an issue for us--we have to turn on our generator when our insulated Hot water tank runs out whether there is sun or not. I'm planning a DIY solar hot water heater to fix that problem (done it before--it's super cheap and easy) and a bigger insulated tank to keep it hot at night.

Our fridge runs off propane but if you convert a small electric chest freezer to a fridge (I can tell you how--it's super-simple) you can have no power at night and all your food will still be good in the morning because chest freezers are much better insulated than fridges and the cold air doesn't fall out when you open them, maintaining safe temps all night.

For lights we bought bright solar hanging yard lights. I take them out and hang them in the sun in the daytime and bring them in at night. They are bright enough to work by. We also have an old center-draft kerosene lamp which is hella bright and also warm so that's good for winter. I recently learned about a screw-in LED bulb that operates like normal but has an internal battery and sensor that turns the bulb on when the power goes out. I intend to find out more about that.

We don't have wifi once the power goes out but we use our mobile data if we really need it.

We have learned to take care of biz during daylight hours, mostly, and then do things that don't require electrifying the entire house at night.
We've adjusted so well that I've had a few instances where the power has gone out and I haven't even noticed for over an hour. Sometimes we get up at 6 in the morning, make tea, chat, start the chores, etc and then realize about 10:30am that we haven't turned on the power yet.

For us, it's simply not much of an issue to have limited access to electrical power. It's amazing what humans can adapt to and eventually find normal.

These nifty Delta inverters work with no battery. Up to 6000 watts during the day. My friend bought 2 of them but has not tried them yet. Not a bad price too.
https://www.ebay.com/itm/Delta-H6-6000W-Grid-Tied-Inverter-NEW-Battery-less-Backup-UL1741-Rule-21-2MPPT/233314195391?hash=item36529c17bf:g:6pEAAOSwyJFfEflo