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

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

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

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

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