On-grid, not net-metered; how to control RE first, then grid when needed?

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  • BB.BB. Posts: 27,897Super Moderators, Administrators admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bob,

    Sound like you have everything pretty much "wired". My GT Array is about twice yours (3,500 watts STC), and I get a about 18-19kWhrs per day--My system is a bit less than ideal (South-South East facing array on roof)--but the results seem to be about same.

    I think you will find reducing the heat from the fan being placed in the fridge will very noticeable. Using a smaller fan or could also try mounting the motor externally with a stirring blade inside--but connecting the fan to the temp controller will be just about as good (10% duty cycle). The digital controller may take a significant portion of that 20 watts--but it is probably not worth the bucks to reduce its power usage.

    Also, I would suggest that wrapping the fridge in insulation is not going to work very well... Assuming that the refrigeration condenser is not embedded in the walls of the cabinet--Anytime I have seen or heard of that being done--there is a big problem of condensation between the cabinet and insulation. Short of using a liquid spray on closed cell self expanding foam insulation, I am not sure the condensation issue is solvable.

    We had an old freezer (4 decades ago) that had the cabinet rust out and form blocks of ice in the fiberglass insulation just from sitting against a wall and boxes (enough insulation to cause condensation to occur).

    $0.31 per kWhr sounds about what it is here for folks that use a significant amount of power (over ~900 kWhrs per month--~600-900 kWhrs/month is about average around our area w/o AC and with natural gas appliances).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bill

    I sure hope I am making as much use of the PV as I can. I have the arrays oriented due south facing, and tweak the season tilt adjustment actuators often. Having the motorized tilt adjustment sure makes it a lot easier than when I used to have to get up there on a ladder and do it by hand. I hose the arrays down once a week to get rid of pollen and dirt, as I noticed it makes a pretty big difference. Right now I'm getting over 8 hours of direct sun each day, and a few hours of indirect lighting in the early mornings and late afternoons that still generates a fair amount of power.

    The upright freezer that I am using as the milk cooler has injected foam insulation in the cabinet. I noticed this when I drilled the hole through the back for the temperature probe. There are plastic hole plugs on the rear. The only place fiberglass insulation is used is in the door. The condensor coil is offset mounted on the rear of the cabinet, so it'll be easy to unmount, slip in a layer of that radiant barrier, and secure it back. Only 4 screws to remove and replace. I have already lined the compressor compartment surfaces and the underside with radiant barrier. There should be no ice buildup, as the temperature setting is such that there is no freezing inside. The freon lines run through the bottom of the cabinet and are routed up the right rear corner, inside of protective plastic tubing. There are no freon lines within the cabinet walls. Each shelf is made with an evaporator coil tied into the freon tubing at the right rear. There are also two drain holes in the bottom of the cabinet. I poked holes there in the radiant barrier when I covered them. I was getting a lot of compressor heat coming through the cabinet at the compressor compartment, while the top was colder. The temperature probe is at the top rear, where interior temperatures were at their lowest prior to adding the stirrer fan. I checked the digital ETC with the kill-a-watt. Power consumption displays 5 watts when the relay is off, and 6 watts when the relay is on. The fan power consumption by itself displays 14 watts. Both combined, the display toggles between 19 and 20 watts when the relay is off. After starting, which briefly flashes 720 watts, the compressor consumption displays 292 watts, and slowly tapers down to 248 watts right before shutting off.

    The $0.31 per kWhr figure was for the approximately 300 kWhr/mo consumption rate. I had calculated that from the first substantially lowered bill 2 months ago. I need to get off my duff soon and start putting together the solar water heater system. Procrastination doesn't save money in this case ;-)

    Bob
  • BB.BB. Posts: 27,897Super Moderators, Administrators admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bob,

    I don't wash my array very often--I have drag out a ladder for second story access.

    Our E1 (basic residential rate) is $0.1143 for the first 300kWhrs (~$5.00 per month minimum charge). Never thought that anything in California would be "cheap" when compared to area.

    But living in a beautiful rural area has its costs too...

    I would be interested if you can quickly see the effect of reducing that 14 watt fan to 1.4 watts via cycling with the compressor... I would bet that your compressor cycling will also drop quite a bit too. Although, it would seem, at best, you will be reducing the power used by 14-28 watts or (save motor running + cost to remove motor heat from fridge 24 hours per day) 336 to 669 Watt*Hours per day... Or about 10-20 kWhrs per month

    I forgot who here (Jim?) has a converted chest freezer and his only runs once an hour and is something like 0.5 kWhrs per day (possibly even less--don't recall exactly). He has the advantage of not having the cold air dump out of the chest fridge when opening... Although, I went through the numbers here once and don't think that this would account for more than ~1/10 of the energy used (dumping cold air from an upright freezer--forgot the exact numbers--not worth the trouble to lookup).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bill, I finished the RB wrap and set it back up, this time with the fan switched. I let it cool down and stabalize, then started watching the kill-a-watt and temperatures. Without the stirring fan running, it took 18 to 20 minutes to cycle, but when running, it took 3 minutes to shut back off. Right before the compressor/fan restarted, the upper shelf was 4 F warmer than the lower shelf. After the compressor/fan started, the lower shelf temperature climbed 3 F before it started cooling back down. Looks like I'm getting some stratification of air due to the lack of continuous stirring. I'm going to let it run for a few more hours and see if it stabalizes any better. There is no milk in the cooler right now, as our next dairy run will be thursday. So these tests are being done with just a gallon of water with a remote temperature probe in it, and a couple of air temp probes - one at the top shelf and one at the bottom. We only open this to load it, and then once every day or two to remove gallons, so the upright design should not be much of a problem for us. We had to go this route because with family in the house, the regular fridge was opened and closed so much that the milk would spoil after 2 weeks if stored in there.

    I agree, would rather have high electric costs than live in the city. I had enough of city life ;-)

    Bob
  • BB.BB. Posts: 27,897Super Moderators, Administrators admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bob,

    In the end, the overall costs (power + loss of food + driving more often to get food + etc.). A few bucks on fan power vs $50 in milk/driving costs. Hands down where the best decision is here.

    I keep making noises of moving out of CA--if nothing else, because of taxes and laws. Wife is a city girl--so not sure that will ever happen.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Posts: 1,832Registered Users, Solar Expert ✭✭✭✭
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bob,

    Another option for the stirrer fan would be to look for a smaller model (10 W?) or, maybe even two much smaller units (5 W each?)... my gut feel is that a 20 W model may be overkill... All things considered, I'd agree that the extra energy is a small price to pay compared to the value of the milk.

    Best of luck,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    I let it run for a few days while logging temperature, run times, and power consumption. So far, as of yesterday, with the fan off except when the compressor is on, overall power consumption had actually increased to 1.4678 kWhr/24 hrs! Weird I know, until you know what is happening.

    Without the fan running all the time, the temperature swing went wild. Thick ice formed on the evaporator coils, thicker on the upper shelves, apparently insulating them from the air. The fan/compressor cycled on at the same preset temperature, 34 F, but as the fan began to circulate the air, the air temperature reading at the ETC climbed to 39 F. It took 3 minutes of run time for the air temperature reading at the ETC to drop to 33 F and shut off power to the fan/compressor. The air temperature then overshot and dropped to 29 F. About 10 minutes later the cycle repeated. The water jug on the bottom shelf (no evaporator coils in the bottom shelf) with the temperature probe never dropped below 37.8 F the entire time, according to the recorded lows on that thermometer. That jug of water used to hold at a steady 33.3 in that location. So only the initial cool-down period seemed to extend the off cycles, but that was only due to the even wider temperature swing variations that occured until they settled down more.

    The conclusion appears to be that the added RB insulation had little to no effect at this point, and that cycling the fan allowed a layer of ice to build up on the coils that negatively impacted efficiency. Yesterday I thawed the ice, reverted back to continuous fan operation, and loaded the cooler with milk. I will allow the temperatures to stabalize with a full load and begin a new log. This way I will be able to get a better comparison of before and after readings to compare.

    Should I bring this up in the energy conservation section? I have not begun to read that section yet as I am still trying to finish catching up on reading older posts in this section.

    Thank you.
    Bob
  • System2System2 Posts: 6,290 admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Jim, I looked around for lower powered fans, and all I could find in the stores around here were fans with higher power consumption. The fan I'm using has one of those little phonograph style induction motors spinning a long double-sided squirrel cage blower. This blows a wide rectangular coloum of air right up the front/rear centerline of the shelves. I orient the milk jugs so that the air blows up between the front and rear rows. The air splits at the top, half flows down in the back and the other half flows down the front. If I were to use 4 of those 12 VDC brushless DC muffin fans from PCs, it would require more power than the fan I used to get less amount of air stirred. In side by side testing, this squirrel cage fan circulated 3 times the volume of air, so I felt that this squirrel cage blower design would be a more efficient use of power than the bladed fans. For comparison, a poultry incubator I made from an old RV/Dorm sized mini-fridge. In this incubabor, I used 4 of those 12 VDC PC muffin fans and a small 100 watt heating element. When the incubator is on, the fans run all the time and the heating element cycles on and off. A digital temperature control with 0.1 F resolution maintains internal temperature regulation to within 0.5 F overall. The fans are powered by a small computer power supply mounted  in the old compressor compartment. Power consumption of the power supply and fans of that incubator is about 35 watts continuous with the temperature control and heating element turned off. That old mini-fridge is less than half the cubic foot capacity of the milk cooler unit. It was my past experience of building poultry incubators out of converted fridges and freezers that drove me to try converting this old freezer into a milk cooler.

    I checked the milk cooler today and the ice is not forming now that the fan is back on continuous, In 30.5 hours of run time since I reset the kill-a-watt, total power consumed was 1.75 Kwhr, which works out to 1.377 kWhr per 24 hrs. So it does look like the radiant barrier may have helped a little. I will track it longer to see what the long term results are. Temperature stability has greatly improved. The compressor kicks on as soon as the ETC ticks to 34, cuts off as soon as it hits 33, and overshoot is to 32 for a few minutes. Run time is back down to about a minute, but I have not yet had the time to sit out there and log the on/off cycles precisely.

    We've had a LOT of cloudy/rainy weather lately, so daily incoming PV power has been pretty nearly halved. This does happen a lot during the warmer months here, we'll get many days of this. I guess I need to start searching the govt surplus for more PV panels again ;-)

    Bob
  • crewzercrewzer Posts: 1,832Registered Users, Solar Expert ✭✭✭✭
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Bob,

    Interesting experiment and results! Thanks for the time and effort to collect and post the data.
    I forgot who here (Jim?) has a converted chest freezer and his only runs once an hour and is something like 0.5 kWhrs per day (possibly even less--don't recall exactly).

    I think this may the the discussion topic: http://www.wind-sun.com/smf/index.php?topic=1073.0

    HTH,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Wow Jim, great topic! Thanks for the link. Hopefully I'll get caught up with the older General Solar Topics in a few weeks, and can start reading the Energy Use & Conservation topics.

    I can see now that using an old freezer that we bought new in 1986 was my first mistake. I guess I should have bought a new freezer, or at least a newer used freezer, to convert. And here I thought I was doing real good to drop power consumption down to less than half of the original 3 kWhr+/day power consumption as a freezer ;-)

    Bob
  • rickeolisrickeolis Posts: 110Solar Expert ✭✭✭✭
    Re: On-grid, not net-metered; how to control RE first, then grid when needed?

    Finally posting again on this thread-  8-)
      I have been on a mixture of RE and Grid at my place for about 5 months now, and the built in charger in the Xantrex 4024 I have is answering my initial question about how to force the use of RE first, then Grid power.
    I have run a line into the house from the Xantrex and have placed several items on that circuit: Bose system, computers, Wii console, lights, dishwasher, garbage disposal, and charger packs for the phones.
    Based on this usage, I monitor daily how much voltage (24v) my battery bank (a dozen Trojan T-105's) is staying at.
    Then, I have placed my KillaWatt meter on the grid based line that goes into the Xantrex that feeds the charger, which cycles throughout the day to maintain the float voltage.
    This way, at least for the items placed on that circuit, I can read many KW's I use to offset my RE system from the grid daily and monthly.
    So far I seem to average about 3.7 KW daily to feed the charger. The recent transition from the cold months to warm has kept me from seeing how this all affects my power bills, but I know I am charging my RE system via my small solar panels and the new wind generator I have. I am slowly but surely buying more solar panels, and when the wind is up, I do see positive results on the 24-volt meters.
    The key to giving me control over how much I use my RE over the grid is based on how much I use the grid to recharge the batteries. My Xantrex allows me many options in this realm, which is great. I can tell it to only charge based on certain times, such as at night only, (we currently have no TOU option) but it also allows me to choose the item that supplies the charge, such as an external gas powered generator if I later decide to go completely off-grid.
    Right now, I just let it cycle as needed throughout the day, and keep my eyes on the usage and voltage, but when I get more solar panels, I will try to convert the remaining items in the house to all run off of the RE project, and see how it works out.
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