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"Daylight drive" direct PV solar for equipment

 
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Just wanted to share this with everyone, it's an interesting idea that could reduce the complexity of a solar setup if you can live with the tradeoffs. Their well pump and DC-powered workshop only operate during the day, while lights and such are on a smaller NiFe bank. They even adapted cordless tools to run off the solar DC feed. https://www.notechmagazine.com/2019/07/living-energy-farm.html (Living Energy Farm, via No Tech Magazine)

I don't have solar yet, but I've been looking at systems, and this approach looks pretty attractive. (I am allergic to both unnecessary complexity and expensive maintenance.)

The PDF overview gives a more in-depth look at things.

Any thoughts from people who have or have seen similar setups?
 
steward & bricolagier
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Cool! I haven't seen a setup like that,but it's interesting to me, I'm into low tech/low maintenance/low finances solar and wind generating. Thanks for the links! Welcome to Permies, an interesting first post!
:)
 
Brandon Coburn
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Thanks :) I now see that there are some other posts here about direct PV (like the one right below mine, how did I miss that) but I do think this sort of "hybrid" system where you have some direct PV and some battery-fed PV seems more rare. Of course I am fairly ignorant on solar compared to people who actually know what they are doing. I just like how this system puts extra power to use during the day rather than building a massive (expensive!) battery bank to store everything.
 
gardener
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This is certainly an appealing setup, I've been purchasing my solar system parts and aiming for as small of a system as reasonable, and the inverter power draw is an annoying part. Even in standby there's a phantom load from the inverter itself, and of course you'll lose about 10% of your power in the DC to AC conversion, so a 100w AC load will take 110w of DC. As the inverter capacity goes up (to handle those power hungry devices), so does the cost, and man the charger/inverter model prices are steep! So focusing more power use to DC to limit those AC needs can become cost effective.

Does anyone have experience with DC lighting, such as good sites for buying the lamps/fixtures which use DC bulbs? I have a good supply of AC-powered LED light bulbs I bought when our utility was promoting them, I think they were like $2 each. While I have AC lamps, in a few years I'll be installing fixtures in the cabin and if DC-powered options are affordable, I can do that and run a DC fuse box and skip the inverter.

DC powered fridges are easy enough to find, although pricey compared to the $25 used AC chest freezer I have connected to a $25 thermostat controller which sets the temp to 35F instead of 0F, making it use just 240wh per day from my testing in a very warm garage. With inverter perhaps 300 watts of battery charge per day. Spending $1000+ for a DC fridge for similar power use and I get freezer space and can also power it directly without the inverter, so turning off the inverter when not needed could save that phantom draw.


It all ends up resulting in less batteries needed. While the Edison nickel iron batteries are nice (especially their lifespan), the cost is still really high relative to FLA. Some sample math: 1kwh of estimated power use per day, 5 days of no charging during a winter storm would mean at least 10kwh of storage using 50% DoD for flooded lead acid batteries. NiFe Edison batteries can handle 80% DoD, so total storage needed for that 5 day window would be (5000/.8) 6.25kwh. For a 12v system, that's about 520AH and IronEdison sells 500AH worth of storage for $5468 plus tax/shipping (how much shipping for 800+ pounds of battery?).

It's rated for 11,000 cycles at 80% DoD, but since this will only happen a few days of the year during that winter storm, the cycles are probably much higher, say 15,000-20,000. Being 40-50+ years for that many daily cycles, it's essentially a once-in-a-lifetime purchase for a middle-aged purchaser.

Compared that to say a pair of Rolls Surrette 6 CS 25PS FLA batteries, similar usable capacity and about 5000 cycles for the averaged out DoD, runs $2200 plus tax (bought locally, no shipping) for almost 14 years of use for that many cycles. As a final comparison point, I picked up a pair of 1 year old FLA 225AH 6v batteries, $150 for the pair including tax and no shipping. Probably 1500 cycles left under my calculated typical use. To get the appropriate total watt/hours would cost $600 total for 4 years of use.

So overall the costs are pretty similar per year of use for FLA, if you don't abuse the battery DoD. The NiFe are less toxic and a little less maintenance, but cost the most up front and per year. Here's a point never mentioned about total cost of ownership that will always place the Edison batteries in last place- assuming you invested the *price difference* and earned interest, for example a conservative 4% return long term, the Rolls batteries are about $3400 less up front; that $3400 is worth almost $5900 after 14 years of 4% compounding interest (when you'd buy a new pair of batteries), so all future battery purchases (costing $2200 for another 14 years of batteries) are free using the interest earned, and you still have that initial $3400 of savings which is actually growing. And 4% is considered a conservative long term withdrawal rate to preserve initial capital.

So the take away is that if you have the money up front to buy the Edison batteries, and total cost is a primary driver, they are not worth buying. You can instead purchase flooded lead acid batteries, invest the rest of the money, and effectively never pay for the replacement FLA batteries again because they will all be purchased using just the interest on that 4% investment return. You essentially have "lost" that same chunk of money in that you don't get to spend it on other stuff, but at any point you can take that cash out and use it for something else, like a totally new energy storage technology, versus the Edison battery purchase is a sunk cost unless you resell the batteries. Sort of a moot point to me, I'm not trying to bash them or say it's a bad choice. But when I see sellers always pushing how the long-term cost is always less, that seems deceptive. It's the same with lithium claims of costly less long-term, it's not true when you include the opportunity cost of investing the money. Of course we could argue the chance that society collapses and those investments are lost, anything's possible. The reality is, unless you abuse FLA or hit 50% DoD on a regular basis, they are still the most cost effective option over the long term.
 
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What I found intriguing in that article was the fact that they took a conventional stick framed home, leaned strawbales against it, and then cobbed over that. I would have moisture concerns about that arrangement. It looks like they lost a bit of overhang from their roof. But they lost no interior floorspace. Anyone know if anyone else has given this a try?
 
steward
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I have an electric assist bicycle. It uses 200 Watts. Hmm. That's the same as the output of a typical solar panel. Therefore, I'm imagining a solar panel resting on a bike trailer for those times when I just have to take a hundred mile bike ride.

 
pollinator
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Mark Brunnr wrote:This is certainly an appealing setup, I've been purchasing my solar system parts and aiming for as small of a system as reasonable, and the inverter power draw is an annoying part. Even in standby there's a phantom load from the inverter itself, and of course you'll lose about 10% of your power in the DC to AC conversion, so a 100w AC load will take 110w of DC. As the inverter capacity goes up (to handle those power hungry devices), so does the cost, and man the charger/inverter model prices are steep! So focusing more power use to DC to limit those AC needs can become cost effective.

Does anyone have experience with DC lighting, such as good sites for buying the lamps/fixtures which use DC bulbs? I have a good supply of AC-powered LED light bulbs I bought when our utility was promoting them, I think they were like $2 each. While I have AC lamps, in a few years I'll be installing fixtures in the cabin and if DC-powered options are affordable, I can do that and run a DC fuse box and skip the inverter.

DC powered fridges are easy enough to find, although pricey compared to the $25 used AC chest freezer I have connected to a $25 thermostat controller which sets the temp to 35F instead of 0F, making it use just 240wh per day from my testing in a very warm garage. With inverter perhaps 300 watts of battery charge per day. Spending $1000+ for a DC fridge for similar power use and I get freezer space and can also power it directly without the inverter, so turning off the inverter when not needed could save that phantom draw.


It all ends up resulting in less batteries needed. While the Edison nickel iron batteries are nice (especially their lifespan), the cost is still really high relative to FLA. Some sample math: 1kwh of estimated power use per day, 5 days of no charging during a winter storm would mean at least 10kwh of storage using 50% DoD for flooded lead acid batteries. NiFe Edison batteries can handle 80% DoD, so total storage needed for that 5 day window would be (5000/.8) 6.25kwh. For a 12v system, that's about 520AH and IronEdison sells 500AH worth of storage for $5468 plus tax/shipping (how much shipping for 800+ pounds of battery?).

It's rated for 11,000 cycles at 80% DoD, but since this will only happen a few days of the year during that winter storm, the cycles are probably much higher, say 15,000-20,000. Being 40-50+ years for that many daily cycles, it's essentially a once-in-a-lifetime purchase for a middle-aged purchaser.

Compared that to say a pair of Rolls Surrette 6 CS 25PS FLA batteries, similar usable capacity and about 5000 cycles for the averaged out DoD, runs $2200 plus tax (bought locally, no shipping) for almost 14 years of use for that many cycles. As a final comparison point, I picked up a pair of 1 year old FLA 225AH 6v batteries, $150 for the pair including tax and no shipping. Probably 1500 cycles left under my calculated typical use. To get the appropriate total watt/hours would cost $600 total for 4 years of use.

So overall the costs are pretty similar per year of use for FLA, if you don't abuse the battery DoD. The NiFe are less toxic and a little less maintenance, but cost the most up front and per year. Here's a point never mentioned about total cost of ownership that will always place the Edison batteries in last place- assuming you invested the *price difference* and earned interest, for example a conservative 4% return long term, the Rolls batteries are about $3400 less up front; that $3400 is worth almost $5900 after 14 years of 4% compounding interest (when you'd buy a new pair of batteries), so all future battery purchases (costing $2200 for another 14 years of batteries) are free using the interest earned, and you still have that initial $3400 of savings which is actually growing. And 4% is considered a conservative long term withdrawal rate to preserve initial capital.

So the take away is that if you have the money up front to buy the Edison batteries, and total cost is a primary driver, they are not worth buying. You can instead purchase flooded lead acid batteries, invest the rest of the money, and effectively never pay for the replacement FLA batteries again because they will all be purchased using just the interest on that 4% investment return. You essentially have "lost" that same chunk of money in that you don't get to spend it on other stuff, but at any point you can take that cash out and use it for something else, like a totally new energy storage technology, versus the Edison battery purchase is a sunk cost unless you resell the batteries. Sort of a moot point to me, I'm not trying to bash them or say it's a bad choice. But when I see sellers always pushing how the long-term cost is always less, that seems deceptive. It's the same with lithium claims of costly less long-term, it's not true when you include the opportunity cost of investing the money. Of course we could argue the chance that society collapses and those investments are lost, anything's possible. The reality is, unless you abuse FLA or hit 50% DoD on a regular basis, they are still the most cost effective option over the long term.



Outside the US the math may change. Everything is more expensive in Canada, especially shipping... those Rolls would be a pretty penny here. OTOH, lack of tariffs meant my chinese LiFePO4 cells were noticeably cheaper here than in the states.

Being in a tinyhouse, some of the other upsides are nice: sealed cells that require no venting and do not offgas, and occupy less space. Keeping lead acid cells outside is not practical with extended periods of freezing weather..

Of course given that they are chinese made, the long term value of my cells is something that only time will tell..
 
Jeremy VanGelder
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It turns out that my reading comprehension was off. They built a conventionally framed house and then put strawbales on the inside. They believe that this is cheaper than either post and beam with strawbales or structural strawbales. Anyway, they have put their thoughts about green building in thisPDF

We can talk about our preferred battery chemistry. But I think that misses the point. Because probably 95% of the solar energy they use is not stored in a battery at all. They store a lot of their solar energy as heat in their floor, and then some in their oversized water tanks.
 
Brandon Coburn
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Jeremy VanGelder wrote:We can talk about our preferred battery chemistry. But I think that misses the point. Because probably 95% of the solar energy they use is not stored in a battery at all. They store a lot of their solar energy as heat in their floor, and then some in their oversized water tanks.



This is what I liked best about the "direct drive" aspect. With a larger system, if you use the power immediately during the day, the rest of the system can be simpler and smaller. It would also make the winter easier since you have an oversized array. Of course this won't work for everyone, it is only a useful approach if you have a productive purpose for the extra energy.
 
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Recently I been traveling with my friend in his van on fishing. I was impressed when he showed me his device on solar energy. He said that crock pot 3.2 amps used in the slow cooker versus 9.665 amps drawn from the oven I you want to compare the figures to my electricity bill the slow cooker used .768 kWs in 8 hours and my oven used 2.320 kWs in the time taken to cook those dear potatoes his slow cooker draws .4 amps on the low setting (He use this setting for most of  slow cooked meals).  .4 amps by 8 hours is a total of 3.2 amps (.768 kWs) used for the duration of our cooking time. I read something same in this article https://websolarguide.com/solar-crock-pot/ What you thing?
 
pollinator
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While my system is fairly large, my well pump is on a timer to operate only between 10:00 and 4:00. The solar guy I had out said, if needed, we could link it to something more precise like the incoming voltage or the battery level.

The well pumps up to storage tanks that gravity feed the houses, so it doesn't limit our usage.

And while my system runs regardless, I do wait until we are in float to recharge tool batteries, do laundry, etc.

My cooking has changed since moving to off-grid solar. The summers here are brutal, but we have excess power, so small electric appliances that don't exude heat are preferred. We will see what we will prefer in winter.
 
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I was excited to see a thread about "Daylight Drive solar," and that some other folks may be exploring or experimenting with this kind of Zone 1 energy design.

I've been an intern at Living Energy Farm (http://livingenergyfarm.org) for nine months now, experiencing the daylight-drive systems through the seasons, and am constantly amazed at the ever expanding list of things we are able to accomplish with the direct current from a 2,000 watt array of PV panels: today for instance, when the sun hardly broke out of the clouds the entire day, we were able to run the well pump for a few hours to water our seed beds and refill our water tanks, run our (direct drive Sundanzer) fridge, and grind cornmeal at the same time. On a sunnier day, we could also simultaneously run machinery in the shop, run blowers to warm the house or dry our food and seed crops, wash our laundry, cut firewood, winnow... we also just discovered this summer that in addition to passive solar cookers (our outdoor parabolic and "sun box"), we can also power a hot plate, blender, and mini-oven with solar electricity. Using solar electricity for cooking or to generate heat is generally out of the question unless you have an enormous system, but it turns out that when you're taking all that energy right off the solar panels, without going through an inverter and battery first, it totally works! And to think all this came from a PV array that was originally sized and intended just to power the well pump. Yay for stacking functions (and yields), and the flexibility and willingness of direct current to share loads.

Since almost all of our usage (and all the motors and heavier loads) are powered with direct current wired straight from the PV panels, we only need a small NiFe battery set (100 amp hours), for lights and charging electronics. The much smaller battery capacity required because of the direct-drive systems helps offset the higher initial cost of the nickle iron batteries -- not to mention the fact that they aren't toxic like lead-acid, and their durability (we have an original Edison battery from the 1950s that still works, and our current battery set is still at 110% capacity after 10 years of up to a dozen people using it daily).

But it isn't that the NiFe batteries are a miracle technology. The magic is really all in the larger design: tying the specific energy needs of your site and activities to the appropriate source(s) -- which may well not be electricity, but rather gravity-fed, thermal mass, wood-fire, etc. And when you do need electricity, connect each motors right to the PV source and use them while the sun is shining. Simple, multi-linear, powerful permaculture approach, rather than channeling everything through a complicated, "weak-link" centralized battery bank and inverter.

Stacy, it's cool to hear you are doing something like this also with your well pump and cooking... hope it's continuing to go well for you through the winter! Would love to hear more about your systems/experience. Curious if anyone else is also working with direct-drive solar?
 
Joseph Lofthouse
steward
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I ride an electric bicycle. At maximum output, it draws about 250 watts. Hmm. That matches the output of commonly available solar panels. So I've been daydreaming about putting a solar panel on a trailer behind the bike and getting a direct-drive solar bike with unlimited sunny day range.


 
Rachel Brylawski
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A direct drive electric bike is an intriguing idea! To be honest, I'm more involved in the farming than the tech side of the project, not an expert by any means. With that disclaimer, I would be concerned with how the solar panel would hold up to the ride over time. Scratching of the panel, debris on it, etc. would lower its output, and it would be quite vulnerable if the trailer bumped against something, etc. Also, depending on your route/time of day you are traveling, it might or might not be easy to angle it towards the sun and I wonder how much of your path is shaded by trees, buildings, etc? However, assuming your route is mostly sunny, at least the parts where you most want the electrical assist, you are able to cushion/protect the panel from the jarring bumps of the road, and you clean the surface frequently, it might well be worth a try? I'll see if I can ask our resident expert here and get back to you.
 
Rachel Brylawski
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If anyone is interested in learning more about "daylight drive," we recently made a video walk-through of the Living Energy Farm energy systems: https://www.youtube.com/watch?v=N5Wk7inoIxI

Also, we have just launched Living Energy Lights (http://livingenergylights.com) to start offering some DC and nickle iron (NiFe) products -- a lot of elements of these energy systems are by their very nature site specific and must be built into the design of a house or homestead, but there are a few things, like the Sundanzer refrigerator and "Iron Sun" NiFe kits for lighting and charging, and a few other small DC appliances, like lights and fans (in the works) that we can offer as a first step for people to begin to break their dependence on the grid or toxic and short-lived lead acid batteries.
 
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