Episode-987- Jeffery Yago of DTI Solar — 28 Comments

  1. What Jeffery said about the large power transformers not being built in the US is not entirely true.
    I am a large power transformer designer and our factory is here in the US. We are in south GA. It is a Portuguese company but we design, build and ship from here. This factory has been in service and producing since 2010. Specifically built in the US because of the demand for large transformers.
    Mitsubishi is currently building a factory in Memphis, TN right now as well.
    Both companies have opened US facilities to meet the overwhelming demand for transformers to replace the aging ones in our national grid.

    • Good to know that transformers are being built here now. Here’s hoping a massive hurricane doesnt take out south Georgia now… Well, I hoped it wouldnt happen before, just more so now.

  2. Jack,

    We’re trying to figure out how to use solar to keep water from freezing in a portable chicken coop. Like you and Jeffery, we think that if we can stick with 12v whenever possible, we’ll get a lot more out of a lot less energy. Powering a light with 12v is cake, but we haven’t found a 12v option for keeping water thawed. Any suggestions? Seems like all the heating options involve 110v and that’s a pain in the butt with a portable coop.

    Thanks guys! Good show!

    • 12v lights produce heat also. Just put a light under the water bowl. It might take some expirimentation to figure out how many are needed to fight certain temps. You may also be able to find 12v heating elements.

      • On Jeff’s comment about the energy capacity of a single golf cart battery: he is very close to exactly right. See calculations below if you care.

        Suppose you could buy an off-the-shelf inverter with 6V input instead of 12V (they’re not widely available, but stick with me for the comparison). Suppose further that your inverter had an efficiency of 80%, which is reasonable.

        Looking at the specs of a standard golf cart battery, the Trojan T-35:

        If you discharge this battery over a 20-hour period, the manufacturer says there are 6 Volts x 245 Amp-Hours = 1.47 kW-Hours available at DC. For that 20-hour period, you can pull a maximum of 245/20 = 12.25 Amps from the battery.

        To convert this energy to 120Volts AC, we have to go through our inverter, which is only 80% efficient. So, we have 12.25 Amps x 6V x 80% / 120V = 0.49 Amps we can supply to a 120VAC load.

        You can’t run a lot on that. Maybe a lightbulb or a fan, or a laptop charger.

        That is 0.49 Amps x 120 Volts x 20 Hours = 1.176 kW-Hours of energy available. That figure is very close to Jeff’s 1kWH per golf cart battery.

        This just goes to show how much battery capacity is required to run even small loads through an inverter.

        • I would add to it that is also a huge case for using DC directly anywhere you can with solar and wind. The conversion to AC looses a great deal of the baseline of efficiency.

        • Backwoods engineer, I’d guess you could actually get about half that energy from the battery because you would never really use 100% of the energy stored. Isn’t 50% depth of discharge more realistic? Also to be considered in the dramatic loss of capacity with low temperatures. Those energy ratings are usually at 25C (room temp), and we have seen graphs showing a 50% derate at 0 C (freezing.) So unless the batteries are kept in conditioned space, it may be safest to assume that in the winter (here in the north at least) you can ACTUALLY use about 25% of the battery’s rated capacity.
          Also to Jack’s point, the 80% efficiency is realistic to assume with battery-based inverters, and the use of DC can help greatly on off-grid systems, esp with the larger loads, people should know that battery-less grid-tied inverters are converting DC to AC at 95-96% efficiency.

    • I look into earth tube technology to keep the water from freezing. if you dug a real deep hole and centered your water bucket in that hole, cold air should drop in fetus place warmer air on the bottom to come back up. it might be possible to use the weight of the chicken to lift the lid which would be insulated. just some ideas

    • Electrical resistance = heat. Your oven elements heat up and glow because of the potential across them and their resistance to current flow. I suspect you could build something similar, sized for 12V and the correct power output.

      I’m no electrical engineer, but some trial, error, thick gloves, and lexan could get you there pretty quickly 🙂 For example, I once used a 9V battery and a paper clip to start a fire. Just required some leather gloves to protect my fingers… a few seconds later, it was as if I had used a Bic.

      You could build a resistive circuit and waterproof it so you could submerge it in the water. But there might be a commercial solution that is sufficiently cheap that it isn’t worth the time, effort, and safety hazard to chase a DIY solution. Missouri Wind & Solar pops up in Google with some 12V heating elements for $50. Here is a link to their 100W element –

      • Oops… meant to throw in the whole reason behind directly heating a submerged element.

        A light bulb would not only heat the water source, but also all of that nice cold air around it. So you would lose a lot of energy to the ambient environment. For efficiency’s sake, you want to maximize contact between the water and whatever resistive/heat-generating load you use.

    • Another thought may be the use of a fish tank bubble stone with small 3-6 volt DC air pump. On a larger scale we used it w/ a horse trough(also was 110v back then). I don’t know if the volume would be deep enough to work. Good luck
      PS. It worked down to around ~22-25 degrees, then we used an axe 🙂

    • This company spent about $120 million dollars initially and assumed they would take a loss for the first 5 years in order to gain market share.

  3. Question for Jeffery (or other expert):

    When building/designing a home from scratch.. Does it make sense to wire a home for ‘mostly’ DC? (With the exception of power for major appliances)

    Besides the usual argument I hear (resale issues).. is it worth it from an efficiency standpoint? (transmission loss of wires vs. conversion loss DC->AC)

    The assumption is that your PRIMARY energy source is DC (solar) not AC (grid).

    • I’m asking because I’ve installed DC lighting transformers all over the house, and of course most LED lights you’re buying have built in transformers of questionable efficiency (because they’re ‘disposable’).

      • Insidious, I built our off-grid house with dual wiring, 12v dc and 120v ac. We use the 120 ac for normal lights, receptacles, and small appliances. The 12v wiring supplies power to our fridge (Sunfrost), booster pump, LED task lights and cigarette lighter style receptacles for charging stuff. Many off-grid homes don’t have 12v wiring but I prefer the redundancy in the event the inverter fails. Another benefit of using 12v is so your inverter can shut down instead of using 24 watts to run 3 watts of LEDs. I wouldn’t wire a house completely 12v because of the limitations, no standard (cheap) appliances or tools

  4. once again a great show. I’ve seen small chest freezers used as refrigerators. the used about a fifth of a kilowatt a day to keep food cool. and that’s without beating up the insulation.

  5. Another expert question, is there any issue with storing storage batteries for long periods of time without using them (years)?

    If not, is a particular technology better for storage? (such as an ’empty’ flooded battery vs. a gel type)

    • Check out the steven harris episodes. There is one in particular where he covers batteries and rechargeable batteries at length. Just download and listen to all his episodes cuz he probably has answeres to other questions you havent even thought of yet.

  6. Hey Jack and Jeff,

    We have a low draw solar pump that pumps water constantly at a low flow up a very steep hill to a high volume cistern. Gravity has given us a powerful enough flow to shower under when the power has gone out.

    When we had a number of very cloudy days in a row and a bunch of teenage girls for a camp program, I ended up having to fill the cistern by powering the pump with our backup generator. The gurls were takin so many showers that they drained the cistern in just a couple days. I had to tie in a set of lines for the generator to attach to in the well housing to do this.

    It’s very important to make sure the solar panel pump controller system have a circuit breaker switch and that it is OFF when you tie in otherwise you could fry the system when u run the generator. This isn’t the same as simply turning the pump controller off.

    Also, a nasty shock occurs when you try to tie in backup wires with ur leatherman to lines still live from the panels…..

    But I wouldn’t know anything about that…ahem.

    Anyway, what im saying is there are relatively inexpensive solar systems that provide redundancy and continued power for critical infrastructure regardless of grid productivity.

    I’ll try to find the name of the system for anyone interested.

    • I would be interested in the details, the pump, the height and capacity of the cistern and the solar/battery specs.

  7. Re; battery storage. You can order deep cycle batteries without the electrolyte (acid) in them. The acid is supplied separately and you add it to the batteries when you plan to use them.

    • That looks really awesome! Except they don’t have anything for sale AND they link to a MLM company. RED FLAG!