Category Archives: Uncategorized

Rethinking the Smart Home Part 1 – Offsetting power usage

Like myself, many people have grid-tied solar power generation and also like me, I suppose that many people are doing it wrong.

“Nobody uses your power better than you do” -Milton Electron Friedman

With a typical grid-tied solar system, the solar inverter converts DC power into 240V AC which feeds directly into the grid.  Using a net meter, the power company will credit you something for any power that you don’t immediately use.  After those electrons leave your house, your ability to understand how that power is being used disappears.  Your generated power may be used by one of  your neighbors to power an inefficient incandescent light bulb where 95% of that power will be wasted.  For ethical reasons, it may be best for you to use the power you generate yourself.  In the very least you’ll be able to control how the power is used towards more personally valuable objectives.

There’s also economic reasons.  Many electric companies will only credit you for the energy you generate per kilowatt-hour.  Only part of your bill is energy consumption.  The other part of your bill is transportation fees per kilowatt-hour.  The electric company may not credit you for these fees when you gift the grid your power.

How do I use more of the power I generate?

The simplest, but most expensive, is to couple your solar system with a battery system like the Tesla Powerwall.  A battery system can allow you to offset when your generated power is used.  You charge the battery when you would normally be gifting the grid and you use the power later when you need it.  A large battery system can cost tens of thousands of dollars, however, and the payoff length is long.  Some estimate 30-38 years.  My goal was to start smaller, work up, and see if we can not only build savings over time.

I started with the goal of charging my phones from battery.  This is pretty simple.  I purchased a large 3.7V lithium-ion battery for $90.  This battery is a pack of (21) 18650 cells in parallel.  The total capacity is 40 Ah or so.  To charge it, I picked up a pack of 10 TC4056A charging chips for $10.  Putting two in parallel allows me to charge at 2A via USB.  Many USB chargers won’t go over 2A, so that’s slow, but fine for now.  These also offer over-current and under-voltage protection.  Bonus.  I need to boost the 3.7 volts up to 5V to charge USB devices so I bought some 3V to 5V USB boost converters that can charge up to 2A each.

DZS Elec 2pcs Mini DC 3V to 5V 2A USB Output Step-up Charging Module Battery Converter for Mobile Mp3 Phone Charging DIY Power Supply Charger

Using this $110 battery setup, I can charge almost all the phones in my house.  I also use it to charge our fitness watches, and anything else that charges over USB.  Using it to charge my two kid’s phones, I save about $0.06 per month.  That’s not very much.  If I can utilize the entire 40Ah of the battery, I can save around $0.53 per month.  There’s only so many USB (type A) devices in my home, however.  My phone and my wife’s phone are USB type C.  These devices can charge at 5V 3A.  Furthermore, I have a laptop that also charges via USB type C.  This time, it’s at 20V 2-3A.  How do I charge those off a battery?

USB Type C charging from battery

There are already aftermarket batteries that charge both USB type A and type C devices.  Each of these however comes with unique flaws that make it unusable for my purposes.  I have a 10Ah battery and a 20Ah.  The 10Ah battery made by Anker can power up to two USB type A devices at 2A but will only do so after you hit the power button on the battery.  It’s not automatic.  The 20Ah battery, which has one USB type C port, is similar.  It won’t charge until you hit the button, but worse, it will not charge devices and allow itself to be charged at the same time.  The 20Ah battery also only charges type C devices at 5V.  This won’t work for my laptop (which alone could save at least $0.16/month if powered off-grid).

We need a type C charger that can be powered off a battery, and charge up to 20V.  I’ve searched for years trying to find one that can charge 20V.  There are many DC-DC Type C chargers made for vehicle charging of phones.  These typically come with both a type C and type A charging port.  Some can even charge at voltages as low as 2.6V (Tronsmart).  This one will work perfect for phones from my 3.7V battery.  After much searching, I finally found one that charges my laptop made by Gearmo.

It claims to support up to 60W on the type C port.  I’ve tested it with my laptop and seen it do 40W.  The point is, it works.  I have to supply 12-24V to this adapter, however.  My 3.7V battery won’t cut it.  I had about (16) 18650 laying around that I made into a 16V battery.  I configured it with four in parallel, and four in series (4S).  Each cell is 2000mAh so in total it’s about 8Ah or 118Wh (8Ah * 14.8V).  This is almost three times that capacity of my laptop.  To charge this, I spent $30 on a 700W+ Drok power supply.  I charge this battery at 5A.  I’m also using a Drok 4S battery protection board so I don’t kill the battery with under-voltage or over-current.

So now all my phones, most of my USB devices, and my laptop are all off-grid now.  How much do I save?  About $4.34/year.  Ouch.  That’s nothing.

What else can I save (future plans)?

There are actually many things that use voltages in the 5V to 12V range.  My stair lights are 5V.  My garage and front door lights are too.  Those use APA102 LED strip lights.  Those lights can consume up to 40W, but typically are around 10W.  If I can power those off of battery, that’ll save me about $20/year.  Now we are getting there.

I have several 12V devices as well.  I have two wireless access points.  Those can consume up to 46W each and are on 24/7.  These end up being the biggest pigs so far.  Almost $100 in savings.  These, however, have a maximum power usage of 1.1kWh.  Our little 16V battery is only 0.12kWh.  We need more batteries.  We only have to power these from battery during non-solar hours.  So the battery bank that powers them should be at least 500Wh.

Nissan Leaf Powerwall

Batteries made for electric vehicles can be purchased at pretty good prices.  There are dozens of videos on youtube of people using Chevy Volt batteries, Tesla, and even Nissan Leaf batteries for off-grid projects.  The Nissan Leaf battery is in a 7.4V configuration and is about 33Ah.  Two in series gives me 14.8V and about 0.49 kWh of storage.  That’s almost enough.  I picked up two of these a while back on ebay for around $100 each.  I plan on getting a few more later.

In the end, how much will I save?

With just two, plus my other two battery banks, I estimate I can save almost $115 per year.  My total cost is close to $500 but may be close to $800 when I’m all done (two more batteries, wiring, DC converters).  That’s a 5-8 year payoff.  Not bad.  Much better than the 30 years of a much more expensive unit.

This setup really only works if we have the available solar power to charge our batteries.  Since not everything in the house is going to be powered from the batteries (like the HVAC system), we need to take those devices into consideration and be smart about when we charge the batteries.  I figure that in total, these 5-12V DC devices amount to about 2.7kWh usage.  In the dead of winter, my solar system does about 4.4kWh a day average.  We have power to spare, but if we really want to save, we need to only charge the batteries when there is excess available power on top of the devices already being powered.  More on that in part 2 of this series.

RedHouse – System Test 2

The RedHouse is online!

We’ve got plants, we’ve got greenhouse and we are connected.  Using the particle photon and some very simple code, I can monitor the status of the redhouse from anywhere with internet connection.  I’ve been testing it for the past week and it’s been working well.  The biggest problem is unreliable wifi in the greenhouse, but that isn’t a killer problem.  I was still able to turn on the watering system while I was on vacation for a couple days.

There is still a lot of work to do, but we are far enough along to grow some serious plants.


Update (Sept 23): Wifi problem solved in software.  Connection is great now.  I added a huge external antenna, but it’s completely unnecessary.

Redhouse (previously “geohouse”) – Construction

Over the past few weeks a lot of progress has been made on the redhouse.  First, the name of the project changed.  As we got the frame built, my son who is 8 started calling it the “redhouse” instead of greenhouse because of the red burgundy paint we used.  I liked the name.


After painting we built the arches that will act as the equivalent to a Mittleider t-frame.  The reason there is no “t” in the frame is because we are maximizing wood usage.  The outer bed will also act as the support wall for the greenhouse film.  The benefit is, I can fit two beds in the redhouse.  The drawback is, the plants will be very close to the wall.  After building each arch, we put the arches in the ground from 12-15″.  The ground we are working with has a slope.  To make the arch level, one side is more shallow in the ground than the other.


Oregon is rainy, so instead of using dirt or worse: cement to secure the posts, we used 1/4″ and 3/4″ crushed rock to allow for more drainage.


Once both arches were up, we painted and laid the 2×10 boards that will become the garden bed.


We also painted and installed some 2×4″ boards at the top to support the pvc hoops.

Once that was done, I created a base for the inner-bed tubing.  I used a 36″ x 2.5″ 12 guage aluminum sheet as the base and used zip ties to secure the tubing to the base.  Over the tubes in strategic location I put thin sheets of aluminum that are typically used with pex for radiant heating applications.



Under the aluminum and tubes I put a sheet of reflective insulation.  I probably could have gone thicker, but this is okay for now.


I put two holes in the board and attached braided tube for the inlet and outlet.  PEX tubing is not UV protected.  So I don’t want it exposed to the sun.  It’s also not very flexible.  So the braided tubing is great for in between the pex, the pump and the earth.


Now that the inner tubes are installed and in place, time for the soil.  Following the Mittleider pattern, I’m using bark dust.  Normally the Mittleider system calls for traditional sawdust.  This fine dark hemlock dust, however, looks great and looks could help with heat absorption because of the dark color.  I mixed with about 30% sand and dumped it in the bed.


For this 12 ft x 18″ bed, I used 400lbs of dust and close to half a cubic yard of hemlock dust.

Irrigation plumbing time.  Nearly following the Mittleider system by the book, I got thin wall 3/4″ pvc and drilled tiny boles in it for water to come out.  I also installed some ball valves so I can adjust the pressure and also close off the second bed if needed.  A bit about the second bed.  I’m assuming for the moment that I will not be able to heat/cool the second bed.  I’m being conservative.  If the first bed’s temperature is easy to maintain, I will add the second bed to the system next season.



The coming together nicely.  Once I test the irrigation system and install the controller, I’ll transplant some bathroom tomatoes that are getting too big for the bathtub.  The only thing left after that is to attach the greenhouse film.




Geohouse – Heat pump and irrigation system explained

Here’s an explanation on how the pumping system will handle both the irrigation and the heat exchanging through the geo exchange.  It involves two relay-controlled valves: one normally open for the geo exchanger and one normally closed.  They will be hooked up to the same relay so that when the open one is closed, the closed valve will open and water will immediately be pumped into the irrigation pipes to water the plants.

This allows me to use the same water, water which is being temperature regulated, and the same pump for both irrigation and regulating the soil and air temperature.



Geohouse – Risks

I feel like the geohouse project is something unique that carries lots of risks.  What I’m doing has been done, but not quite the way I’m doing it.  What if my assumptions are wrong?  What are the costs?  This post hopes to answer those questions.  First, what components will this geohouse have?

  • Solar Power System – $2,000 (5 panels, 4 batteries, charger)
  • Pump and tubing system – $140
  • Greenhouse plastic – $170
  • Wood – $250
  • PVC pipes – $120
  • LED grow lighting – $120

The worst case scenario is that I cannot keep plants alive during the coldest months (Nov – Feb).  This system gives me at least 3 months extra growing and production in the absolute worst case.  Best case is that I get 12 months of production.  Here’s a short list of other things that can go wrong:

  • Not enough sun to power solar array (North West sun hides for substantial parts of the year)
  • Too much heat loss
  • Not enough sun to add energy to system
  • Not enough heat storage (geo-battieries)
  • Components break (power supplies, pump, etc).

Geohouse – The geo-exchange heated smart green house

Once my first raised bed garden is happy producing food I started planning the next raised bed.  It was to be an 18 inch wide and up to 16 feet long bed in the Mittleider tradition.  However, while watching youtube videos about people using the Mittleider method, I became inspired to try and extend my growing season -perhaps even year round by using the earth as an energy storage system (aka, a battery).

Each gram of wet soil can hold 0.35 calories of heat energy.  At depths from 4ft to 6ft, the soil is far enough down to be insulated from the air above and maintains a year-round temperature from 55 to 60 degrees F.  Many residential and commercial buildings utilize this almost free energy and feed it into heating and cooling systems that would normally be pulling from less optimal sources such as trying to cool air from outside during the summer time or trying to heat cold air during the winter.

I started researching methods of accessing this geo energy.  After digging around on youtube some more, I found several systems that blow air through the ground via tubes and back into the greenhouse.  The air would be heated by the sun and then some of that energy would be transferred into the ground where it can be used during the night.  Air, however, is a poor conductor of energy at about 1/4th the specific energy as water and less than the soil itself.  So I wondered if there was a better way.

Water has one of the highest specific heat properties of any medium.  At first I thought about pumping water through a radiator and warming or cooling air via that method.  However, it occured to me that the system could be much simpler.  During warm days, a common method of cooling the plants is to water them.  The plants, via the roots then become cool.  The same principle should be possible with heat as well.  If the soil temperature is maintained, we may be able to keep the plants happy.  Can water be used to heat/cool the soil directly?  Yes!

An efficient way of heating businesses and homes has been in-floor radiant heating.  The method pumps hot or cold water through PEX tubing in the flooring system.  The warm/cool floor then heats or cools the ambient air in the room.

To make a long discovery process short, I decided to combine these methods.  I will pump water into the earth and cool a 12 ft by 18 inch bed directly at the root level.  To insulate the bed, I’ll put a double layer 6mm green house film around it.  The hope is that I can keep the temperature around 50-60 degrees all year (+20 degrees in the winter).  Can it be done?  Let’s find out.

Auto-irrigation for raised garden – Part II: The raised garden

Quick update on the raised garden project.  The first garden bed is built!  This is a 6 x 3 ft bed with 5 x 3 ft of growing space.  I used cedar outdoor wood and I think it looks pretty nice.


Shortly after building, I did a bit of research on the Mitleider gardening method.  In order to do vertical gardening, I need taller posts which I initially thought I would just use for grapes or other vine plants.  I may end up redoing the post system or at least modifying it so I can vertically grow my tomatoes and melons in order to maximize space.


This bed is also equipped with an equipment box.  This is where most of the auto-irrigation system will go (valves, Edison module, panel charger, energy storage, etc).


Finally I’ve mounted my 10 watt solar panel.  After observing, I don’t like this position.  It should go on the back pillar to avoid casting shadow on my other solar panels: the plants below.

Next Part: Rainwater gathering