I moved to Martha's Vineyard on June 1st, 2010, with my sweetie Jill and a dog. I'm passionate personally and professionally about living well with less throughput of materials and resources (OK, bicycles excepted here...) The focus here will be how I'm thinking about our house, transportation, food, waste, etc. Opinions expressed may be well thought out or not - no warranty express or implied. Please let me know what you think, and feel free to take issue.
Girl and dog
Sometimes you gotta just have some fun, and when you get a 50F and sunny New Year's Day, riding up to Gay Head is one way to do it. Bring out the skinny-tire bike!
Here's the view to the south coast from Middle Road:
And Quitsa Pond and Stonewall Pond across State Road from one another:
I rode out past the Lobsterville Beach to the West Basin, looking across at Menemsha:
Then rode back out and up Lighthouse Road to the Gay Head Cliffs and Gay Head Light.
Happy 2012!
Here's two graphs for July through December, showing our usage vs. PV production, and where the energy is going. In the first graph, one can see the usage increasing as we begin to use the heat pump at the end of October, and the solar electricity is dropping off as the days get shorter and cloudier. In December we go from being a net energy exporter to a net energy importer. Only by installing the woodstove will we be able to be energy exporters each month, which is my goal. Our shortfall of 183 kWh in December is caused by the 238 kWh the heat pump consumed.
In the graph below the energy usage is broken down by end use. Other includes the composter exhaust fan, lights, wireless router and modem, computers, and small kitchen appliances, as well as any power tool usage. I'm a bit confused why there are peaks in Other in August and October. Oh wait, in August we had an influx of guests, which also shows in the DHW energy usage. Maybe on MV that month should be AuGuest :-) October, that's still a mystery... One can also see the increase in cooking energy in November and December. Less fresh food straight from the garden, plus holiday cooking and baking, are the reasons. R/F are the refrigerator and the chest freezer, and the change in their energy consumption is addressed in this post.
I think we have a strong chance to achieve net zero for our first year. The utility meter read 100,137 kWh when the PVs came on line in early June, and it read 98,448 this morning. Since June 9th the PV system has generated 1,689 kWh more than we've consumed. I can imagine our January and February usage cutting that surplus in half, yet sometime in March I expect we'll get back to net exporting. Stay tuned...
We all know that residential heating load is highest in the winter and cooling load is highest in the summer. What's a bit more subtle is how the seasons, and how we respond to them, change the loads on other household energy uses.
For example - this summer our basement temperature climbed above 70F, and the incoming water temperature from the water pressure tank was in the mid to upper 60Fs. Here at year's end, the basement temperature is in the mid-50Fs, and cold water temperature has dropped to as low as 48F. Both of these changes since summer add load to the water heater, as it must provide more energy to get the lower temperature water up to 120F, and the tank loses more heat to the colder basement. Here's a graph of our DHW usage in gallons/day (GPD) and the corresponding kWh/day:
August through December DHW usage has been very constant at about 14 GPD, yet kWh/day has gone from just over 2 to just over 3.
Similarly, the 15 ft3 chest freezer is in the basement, and the refrigerator is on the main floor, both of which areas are cooler than they were in the summer. Here's the kWh/month usage combined for both devices:
The load on the freezer and fridge drops because the spaces they are located in are cooler, so the temperature difference driving their heat gain is lower. In addition, the heat rejection components work more efficiently to reject heat to the surroundings when the air is cooler, so it takes less energy to meet the load. Just as with the water heater, the two effects combine to change the energy usage, but in the case of the freezer and fridge, the energy usage goes down. That reduction isn't as large as the increase in energy used by the heat pump water heater, unfortunately! Again I find myself wishing for a fridge/freezer that rejects heat to a DHW preheat tank, just as it's done in commercial refrigeration. But energy will need to get more costly before that device appears.
When we yanked the oil boiler we replaced it with a wall-mounted minisplit heat pump in the main level open area that includes kitchen, dining, living and our little office area. We closed off the first floor bedroom and bathroom so those rooms are only heated by conduction and air leakage through the walls, and so they get cold - in the high 40Fs at the lowest last winter. The second floor bedrooms and bathroom are only heated by warm air from the main floor rising up as cooler air from upstairs drops. This is a natural convection cycle, and it works pretty good and for free! Doncha love physics?
I'm datalogging temperatures in the basement, main level, upstairs, and outdoors with Hobo dataloggers. Here's data from the past week:
Outdoor temp dropped as low as about 16F and climbed as high as 57F. The upstairs ran 2-4F cooler than the main level, except when it was good and sunny and it heated up with more unshaded south glazing per sf of floor area than the main level. Dec 26th was the only good sunny day in the six days shown in the graph and you can see where the upstairs temp climbs above the main floor temp briefly. We set the heat pump thermostat to 70F when we're here and to 66f when we are asleep or gone. This being christmas week we've been here a good bit more than usual, since both of us have been off of work since the end of day on the 23rd, which is the first full day of this series shown above.
If one of us were to be working at home upstairs, we'd need some supplemental heat, probably an electric radiant panel, like the ones we put into the Eliakim's Way homes I wrote about here. A panel like this heats up quickly and can be located so that it heats a person in a fixed location, like a desk, directly. It's a good supplement in a point source heat pump house.
Of course, we could also install more heat pump cassettes. In the most extensive case, there would be four, the one we have and one in each of the three bedrooms. I think if we ever use the first floor bedroom we might install another Fujitsu single zone unit for that room, albeit the 9,000 BTU/hour model rather than the 12,000 BTU/hour unit we have now, because it's a smaller space. Then we'd add the radiant panels in the upstairs bedrooms as well, which we may do at some point as I have two of them laying around in the basement! But for our present use of the house, the point source system works well, and was inexpensive way to get off of fossil fuels and let the PV system supply the energy we use for heating (albeit on an annual basis...)
When I put the solar electric array in, I knew that there would be some shading from an oak on my neighbor's property that I could have had removed, but didn't want to spend the additional money. Now that we're in winter solstice season, and because today is clear and sunny, I took some shading photos and looked at the output of the array. Here's a shot at about 10 am, when the tree is beginning to appear on the array:
At this point, the 4.76 kW array is putting out 2915W. The tree covers both strings of ten.
Here's a shot an hour later, around 11 am, and the output is 2844W:
Half an hour later, only the lower east edge has any shade, and the output is 3495W:
At 11:50 am, 18 minutes later, the array is unshaded and the output jumps to 3900W, which is 82% of the rated output, and typical of peak output. I have some data I took at 10:30 am on Dec 11th and with the tree smack dab in the middle of the array the output was 1 kW lower than what it was at 11:50 am eighty minutes later. So I conclude that during the roughly 1-1/2 hours that the tree crosses the array, I'm losing about 1 kW, or about 25% of the peak output.
My house faces about 11 degrees east of south, so 11 am this time of year is when the sun is perpendicular to the array. From here on out the output will drop. At 12:30 pm it's down to 3650W. At some point, the smaller trees to the west will start to shade the array and output will drop off quickly.
