We had a 3.8 KW photovoltaic system installed on our roof about 2 years ago. It was sized to produce about as much electricity as we use. We signed up for a buy all/ sell all system so we get two statements from Progress Energy on what we produced and what we consume. One of the side effects that I had not expected is how attuned we became to our electricity usage. We had always been pretty conservative with our electricity, buying Energy star appliances, CFL light bulbs and turning off lights as much as we could remember. So as our statements started coming in and we were running pretty close to even, we started to look for where our biggest energy loads were that we could do something about to get our consumption lower and be more comfortably zero or even positive in our use and production balance.
We put in several switched outlets for the famous vampire loads on the TV and computer and phone chargers. Then I went around the house plugging everything I could into a Kill-A-Watt Meter to try and find the biggest culprits. I knew the hardest load to lighten would be the dehumidifier. We have to run it in our daylight basement from mid June through August and it is hard to find an affordable replacement. I suspected our 11-year-old refrigerator and our small chest freezer. The freezer actually wasn’t that bad . The Fridge was significant, at over 500 kwh a year, compared to some of the new ones that are rated at under 380 kwh for a year. That is on the replacement list.
What I hadn’t suspected was our pump for our goldfish pond that has become home to several frogs and a constant display of water Lilly’s. It was sad to see the meter reading showing it as worse than our fridge and not far off of our dehumidifier. In hindsight it makes sense. Water is heavy so it is going to take some work to move it around even just lifting it 5 feet to the top of the waterfall. We put that on a timer and turn it off in the winter now and are looking at other ways to clean the water while growing plants through aquaponics to at least make the energy use more productive.
That made me realize our well pump must also be a culprit as it is 200-foot deep with a 2 horsepower pump and we have a lot of gardens that need irrigation at times. We added two 300-gallon cisterns that gravity feed down to the gardens and expect that will make some difference though the math for that gets tricky. Basically you get 620 gallons of water off of 1000 square feet of roof area for every inch of rain. A plant growing in a square foot of soil needs about a gallon of water a week or a 1000 square feet of garden needs the 620 gallons a week. So if it doesn’t rain for a week I will use all of my cistern water for about a fourth of my garden. It will save some pumping energy but if I want to make a significant dent in my irrigation energy use I am going to need a lot more water storage. If you are on city water it is a similar energy situation. The Asheville water department has about 1625 miles of pipe and 35 pumping stations and uses approximately 11 million kilowatt hours a year and produces 7,830 metric tons of CO2. (Asheville Sustainability Management Plan, 2009)
When we added the production of renewable electricity to our house we knew it would be a good thing to do but we didn’t realize the impact it would have on our consumption. Our Summer electric use has been higher than our production and all most all of the extra load is in dealing with water, both pulling the water out of the air in the form of humidity and pulling the water up from our well to irrigate our gardens.