DC micro grid solar power philosophy ( as advocated by living energy farms)

mountainmoma's picture

I think this is a robust way to design for power use. My only complaint re living energy farms is their complete lack of aesthetics, but as far as living off only DC power solar power, they are well versed and experienced.

It is very efficient in use of material, cost, reliability and years of service you can expect.

Basically, they look at the homes basic needs and subdivided, they call this using DC micro grids.

For example, there are some high power users on a farm like theirs with a shop, power saws, metal working and cutting, a large grain grinder, a well pump, these all take alot of power, but they can be used in the daytime only, easily, so that no storage of power is needed for those uses. They have found that most shop tools can run on straight DC from the panels, even if they used to be run AC ( if they have a universal motor) and that they do not mind a range of amps/volts.

They took stock of what they need to be able to do at night, and concluded that they only need lights at night, and there are a few other things that people might want at night, a fan for summer cooling, charging a device they forgot to charge during the day. A different household might want to run a laptop or other low power device to watch a movie, etc... So, once that list is thought about, not very much battery storage is needed. Batteries are normally very expensive, but if you only need a very small amount of storage, it becomes affordable. They also advocate, and sell, Edson Nickel-Iron batteries, which last an extremely long time, maybe a lifetime, and take alot of abuse and keep working. A disadvantage of those batteries, for me, was that most I had seen made were so large, but if you do not need much storage, they have small, easy to carry or move ones that living energy farms sells.

For their household, they have a third circuit that has no battery storage, and that powers a DC refrigerator directly, a charging station for phones/laptops, and a fan for their solar thermal air house heating system. They call this and the shop/well circuit "daylight drive solar" things that are only running when the sun is out.

Another nice thing about a distributed system is that it can be added to later if there is money. They just did a volunteer set up in the desert southwest on a couple of reservations of basic solar/battery systems that were to only provide light and phone charging. This is such a life changer for people there who do not have grid electricity or running water, to not have to fire up a generator just to have light or the phone, or not have to go to town and buy kerosene or candles. This type of very small cabin set up they sell for a few hundred dollars, and includes everything, DC LED light bulbs, 10 amp hours edison batteries, a mini flashlight, a table lamp, a cigerette socket for charging a small device. They just installed 47 small lighting systems just last month, here is a bunch of photos of installs/happy reciepients http://livingenergyfarm.org/solar-installations-2020/

"....DC Microgrids are effective because they work with the strengths of renewable energy, rather than trying to use it to replace fossil fuels as a bulk commodity. The emphasis is on designing systems to meet specific energy needs. For this reason we like to describe the DC Microgrid as a permaculture approach to energy systems.

A DC Microgrids looks different for each site, depending on wind and solar resources, local climate and energy needs, etc. But the design principles remain the same everywhere. These principles are:

1. Maximize conservation, efficiency and insulation. Solar energy is only useful when demand is minimized.

2. Minimize battery size by storing energy in forms other than electricity. The bulk of the stored energy in a DC Microgrid takes forms such as a hot or cold thermal mass, pressurized water, or bio-gas.

3. Operate high-demand electrical appliances as daylight drive only. In daylight drive systems, DC (direct current) motors and resistive loads are wired directly to photovoltaic panels with no batteries or other hardware involved. These appliances are used only during the day.

4. Keep electrical hardware as simple and durable as possible. A DC Microgrid side steps inverters and AC (alternating current) electricity, and uses nickel iron batteries, a non-toxic technology that lasts 40 years or more.


I could see something that is a small, new build, like Dave T's office and granny unit, powered inexpensively by this type of thing, leaving the laundry area, maybe freezer, on the main house circuit. So, then the small granny unit and separate office are also a good backup, a place with at least the basics, lights, charging, DC refrigerator maybe, if AC power goes out to the main house circuits.

lathechuck's picture

My after-dark electrical needs include occasional lighting in my shed, and emergency lighting, broadcast radio, and two-way ham radio communication, and phone-charging. For the shed, I have a small PV panel sold as a "car battery maintainer", just a watt or two, but it's enough to maintain a 12V, 7 Ah SLA tucked into the shed. A small strip of 12V LED lights (from IKEA) provides enough lighting to store tools after the sun goes down. For emergency power, I have a single 200W PV panel which was surplus (scrapped) when more efficient units came out. In the same area, you can now get 300W, I think. That feeds a dual-battery charge controller, which has two more 12V, 7 Ah SLA batteries. A DPDT switch selects which of the batteries will feed a RIGRUNNER 4004U DC power distribution strip. It has four independently fused PowerPole outlets (for the radios) and two USB ports (for charging devices that expect USB power). A neighbor threw out a damaged industrial-strength extension cord, so I found a good 50' section of it and put PowerPole connectors on both ends, as well as on the PV panel, so the panel can be out in the sun while the rest is indoors in the shade.

Main household power is a 4 kW grid-tied rooftop system, which runs the kitchen (hot and cold), a/c, and a dehumidifier. In my humid mid-Atlantic location, a dehumidifier is essential to protect books and furniture in the basement from mildew. That's an appliance that could be restricted to sunny-day-only operation, if I didn't have grid backup.

add photo: 
mountainmoma's picture

it is nice idea to have a backup system for the minimum needed. Someday, if/when I get time, I intend to have a small panel and set up I can use to take in the travel trailer -- I want enough for ham radio, the one dc light in the trailer, maybe even the trailer fridge, unless that is too much storage/panel to be practical. When I am at home, I have battery back up power, almost 7KWh, which runs the neccesities for many days

mountainmoma's picture

How did you find a scrapped 200 w panel ? That is some find !

lathechuck's picture

Solar City had a marketing arrangement with Home Depot which involved a booth for a Solar City employee or two in Home Depot stores. The 200W panel was mounted on a wooden frame with a few shingles around it, to attract attention and show people what it would look like installed. When the 200W panels became obsolete, and "business conditions" changed, the panel display got rolled out into the breezeway and apparently abandoned. After a couple of months of seeing it there, I asked someone at Home Depot if they needed "help" disposing of it. They referred me to a Solar City manager, who said that I could take it. So, armed with a few tools and a confident attitude, I disassembled the display and packed it off in the back of my station wagon. Nobody asked me what I was doing. After acquiring the first panel, I asked other local stores if they had any more Solar City debris, but none did. Fortune favors the prepared mind.

lathechuck's picture

They may last a long time, but they require regular maintenance, and they are not as power-efficient as more modern chemistries. The difference between the charging voltage and discharge voltage, for a given amount of charge stored and drawn, indicates wasted energy. They're not necessarily a bad choice, but one should be aware of their limitations.

mountainmoma's picture

The benefit is that they never have to be replaced, which is a very big plus for our assumption of needing to live thru " interesting times" I used to have to check and add fluid in my old lead acid batteries too, but I had to open the caps to do so, while these at least have semi-transparent housing so it is easy to see when to add

As for wasted energy, there is an awful out of energy wasted when we replace batteries, first. Second, as said above, we need to plan on not being able to aquire replacements easily

But, the main takeaway though from their philosophy is to minimize the need to have much storage at all

Sweet Tatorman's picture

Very interesting read. I followed most of the links wherever they led. Kudos to these folks for their pro bono installations with the Navajo and Hopi. While I personally have a rather high capacity storage of ~30 kWh I have long recognized that very modest systems provide the most utility for the buck. The difference in quality of life of no electricity at all vs a few low power lights, electronics, and fan ventilation is huge. Regarding the statement >They have found that most shop tools can run on straight DC from the panels, even if they used to be run AC ( if they have a universal motor)<, Immediately post WW2 a lot of motor driven items were still equipped with universal AC/DC motors but that largely went away over 40 years ago. Looking at the photos of their various shop equipment items it is apparent that they changed out the original motors for DC capable motors.

mountainmoma's picture

This link gives more details of their system and a bit of a primer for those thinking of trying it themselves.


".... What kind of device have universal motors? Universal motors are high-powered, lightweight motors. Portable appliances often have them. All corded power saws, drills, angle grinders, and similar shop tools have universal motors. Other tools that use high-powered motors, shop as shop vacs and blenders also have universal motors. If you can look into the motor while it is running and see blue sparks inside, then it is almost certainly a universal motor and can run DC. ..."

" .... Some kitchen appliances, like ordinary blenders, have universal motors as well. We have run those, but you will need to put an external, heavy switch on them. Larger, heavier appliances (like
washing machines, dishwashers, refrigerators) do NOT have universal motors.."

Sweet Tatorman's picture

Yes, most corded electric hand tools do have universal motors. In my original comment I was thinking of stationary shop equipment as pictured in their image galley which can be found here:
The more expansive definition of "shop equipment" is of course valid. I did get a chuckle about this very expansive interpretation of shop equipment in your quoted text "as shop vacs and blenders also have universal motors" but I certainly am not one to begrudge them a margarita while they work ;-) .
From page 6 of your linked pdf they correctly understand that even though most corded portable tools like drills, circular saws, etc., have universal motors they do not come with trigger switches capable of switching DC. Their solution of adding a suitably rated switch back at the outlet or alternately taped to the tool is certainly a clunky solution which they at least acknowledge makes the tool less safe. It would also make a tool such as a drill or circular saw much less convenient to use. A much better solution is to retain the use of the tools' trigger switch as the control signal to a suitably rated relay either mechanical or solid state.

Below is a photo from their image galley showing their DC capable air compressor. I've owned plenty of Sears Craftsman stuff over the years and clearly that is not the motor that compressor came with. Similar examples of motors they have added can be found in their image gallery.

add photo: 
Sweet Tatorman's picture

I've added this one not so much for the DC capable motor they have added but because it is a gorgeous antique drill press.

add photo: 
mountainmoma's picture

Yes, not all can run as is, some they changed motors. But, most of us regular people, like me, in our garages use regular partable corded or battery portable which switch easier, not that I am going to switch right now. But, it is good to know when the world changes and I need to only use DC ( lack of inverter) how it can be done

mountainmoma's picture

I have solar and run my place on it, grid intertie with battery bank.
Well Pump

I already intend to run my well off of direct DC, at some point, almost switched last Sept. when my pump stopped working, but it turned out to be a wire short. But, I am putting research into how I would do it here and preparing. This is my first, best way to add to solar capacity here, I am no longer evening out in power useage, but very close, so instead of adding to main array, I woul take things off of it, like this.


This would also be very easy, but I woul get one of the more typical looking DC ones with a footprint that fits my kitchen layout and has a small freezer, but close to 500kWhr/day would be very nice. When this used AC refrigerator that I am using that gets around 1kWhr/day dies, I can switch.

My solar panels and inverter are 22 years old, it is good to plan for next stages in our powering down world, I am big on collapse now and beat the ruch, it has been serving me well, and I will continue as my needs come up to follow along ahead of the curve