We needed to make a winter trip to Barcroft to service the inverter/battery system and check on winter conditions. This is the first winter that the Sunny Boy inverter system has been left running unattended, and periodic checkups are needed to get the right battery voltage settings for our unusual configuration. The light snow conditions made the snowcat trip relatively straight-forward, and Josh Zierten and Jonathon Crass (two of the UC Santa Barbara astrophysics team) also needed to work on their equipment, repairing a computer and installing a web cam. This trip served as a test run for making multiple-day winter trips to this remote high-altitude facility.
We left OVL at 8:20 am, and met Gary Milender and Ryan Kitts up at Westgard Pass with the snowcat. They drove us up to Barcroft, dropping us off at 12:30 pm. We three passengers were squeezed in the tiny back seat of the cat like sardines in a can. We brought up about 20 gallons of water for cooking and operating the toilet, and food for a day or two. We also brought up 20 gallons of distilled water for the station electrical storage batteries.
At Barcroft all looked fine except for some damage to the rooftop solar panels, which we will deal with next June when we open the station. After checking the battery voltage (which looked good) I started the boilers to heat the building. It took a few tries to get the boilers to ignite, but boiler#1 came on soon and started providing heat. It took 10 minutes or so to get boiler #2 to ignite, and it never functioned properly (it is supposed to work in tandem with boiler #1), staying in standby mode the whole 2 days. After getting the heating going, I opened the batteries and put 4 gallons of distilled water in. This was from only 2 weeks of use (I last filled them on January 8) which meant that the sunny boy inverters were over-charging the system. I therefore re-set the load diversion threshold to a much lower voltage (56.4V instead of 58 volts). This threshold determines when the bank of electric heaters turns on and drains power from the system, protecting it from high voltages which electrolyze water out of the batteries. The batteries were fully charged, as they should be with the light load and the Sunny Boy solar inverter system operating. I also turned on the gas to the kitchen stove and Josh and Jonathon cooked up some lunch.
The weather turned bad in the afternoon and started snowing and getting windy. Without large snow drifts surrounding the building, the wind kept the building fairly cool. Nevertheless, by 8pm the inside temps were up to about 50 degrees F, and we were fairly comfortable wearing warm clothes. Josh and Jonathon had trouble adapting to the elevation and cold, perhaps because they were so tired from getting up a 1 am that morning for the drive from Santa Barbara. However, they slept well and the next morning they woke up fine and got a lot of work done. By morning the temp in the building was up to 57 degrees, and our overnight use had drained the batteries down to 88% of full capacity according to the meter.
The next day after completing our work projects it was time to shut down the station in preparation for our departure. I first turned off the boilers (boiler #2 never came on fully but was still in standby mode). I then added antifreeze to the boiler condensation reservoirs (only #1 needed any, as indicated by the lack of blue color in the reservoir). We then washed up in the kitchen using water heated on the stove, and added antifreeze to the sink drains after the last use. We added antifreeze to the toilet bowl also. We used less than 10 gallons of water total. I put the unused distilled water inside the battery compartment, and replaced the lid, making sure the batteries were full of distilled water. I then went around shutting off all the circuit breakers except those marked for winter use with a red dot or square. I checked the power draw after shutdown: it was 280W for the AC draw and 3.4A (x48 = 160W) for the DC heaters and devices. This is nearly within our original target of 400W, and well under our new adjusted target of 650W. The new target is based on the observation that the electrical system generates about 6 KWh even on the darkest winter days, adding that amount to the daily budget.
We found that the kitchen track lights provided excellent illumination and suggest that similar track lights be placed around the building. This would eliminate the need for the fluorescent overhead lighting which is very energy intensive. For example, the kitchen overhead lights draw 450W to operate, while the four tracklight compact fluorescent bulbs draw only 92W.
We locked the building and left during a partial whiteout. As we drove over Sheep Mountain the whiteout became severe and it was a good thing Gary and Ryan had the gps unit to find the route. It took about 2h to make it back down to Sierra View, where we loaded up in the truck and headed down to Bishop.
The insulated battery box keeps the batteries above freezing temperatures.
A view of the battery-inverter system. click on photo to enlarge.
DC power switches connecting battery bank to inverters. Note that in the winter configuration switches 2 and 4 are shut off, corresponding to inverters 2 and 4. We use the convention that switches marked with red stay on all winter and all others are shut off.
AC power output switches to inverters 2 and 4 are also shut off, cutting off power from the sunny boy inverters. The input switches don't matter as no power is coming from the grid or generator in the winter shutdown mode.