A caccia di efficienza domestica da sun-news-336

The response from homeowners with newly installed solar panels is to excitedly watch the utility meter run backwards–“Look, I’m making electricity!” But for me, it’s been two years and I’m still checking the meter because I’m so close to that magic number–zero.

With grid-tied solar photovoltaic panels, you get what’s called a net meter (unrelated to a smart meter). It means your meter can run in reverse when panels produce more than a house consumes, with the excess electricity piped back onto the grid for the neighbors to use. So when nobody’s home and the sun is shining, you’re subtracting from your monthly electricity bill.

What’s your net?

(Credit:Martin LaMonica/china-heatpump)

Cutting my monthly bills was one of the reasons I had the panels installed in the first place. But what’s happened is that the bills are so low, it’s become kind of game to see if my household can get to or below zero every month. In other words, investing in solar has pushed me to be more efficient, which is not at all what I expected.

But as people start talking about “net zero energy homes,” this is precisely the game that designers and homeowners need to play. Because making energy on site is expensive and space is limited, the key is to lower the energy “load” of homes in the first place. So before you hire to a solar contractor or install a geothermal heat pump, talk to an insulation guy and learn how to use a caulk gun.

In my case, we’ve always had very low electricity bills. For a house that’s about 1,200 square feet, the monthly bills used to max out around $85 in the summer in Massachusetts, where the rates are relatively high. When I first had an energy audit through my utility, the auditor said that many people paid many times what we did.

To lower the load, I did the standard power-saving steps like installing compact florescent bulbs and upgrading to energy-efficient appliances (replacing the old fridge and ditching a freezer made a big difference). Then I got power strips, which I turn off to cut the stand-by, or vampire, draw from electronics. I had a second audit and plugged up air leaks and added insulation (I heat mainly with a pellet stove which uses electricity). I even use a small solar panel and battery to charge up my phone and other gadgets.

In all, my household electricity consumption before the panels was roughly 3,000 kilowatt-hours (the U.S. average U.S. was 11,000 kilowatt-hours in 2008). What I realized is that my solar panels–rated at 2,300 watt capacity–can put out about 3,000 kilowatt-hours a year, too. So it’s a race, sort of like hypermiling but I’m maxing out my home’s “mileage” instead of my car’s.

Sign of things to come?
Unfortunately, houses don’t have the equivalent of a miles per gallon rating or even a dashboard that tells you how you’re doing on mileage. Many people believe that the lack of information and automation is a barrier to raising the bar in building efficiency in general, never mind edging toward net-zero energy status. I check the solar panel production once a month on the inverter and report it for a state monitoring program. But I’m in the dark when it comes to energy consumption; I just get a monthly statement with net usage and the bill.

This is where a whole house monitor or energy management system could be a real help. If done right, a monitor can track what consumes what in your house–is it your refrigerator, your stereo, or the fact that your kid leaves theXbox 360 on all day?

There are dozens of companies working on in-home energy monitoring systems, some of which are being tested with utility smart-grid programs. My guess is that energy information will show up in different places, or screens, within the home. You could use your PC to look at historical information. But to quickly check the status right now (Are we consuming more than usual right now? What caused that spike yesterday?), I could imagine glancing at my smart phone oriPod Touch once in a while to make adjustments.

The more sophisticated tools can let people dial down electricity during peak times in places where there is time-of-use pricing or compare themselves to others, which has proven to be a great motivator to conserve.

Nowadays, I just walk outside and look at the meter on the side of my house. When I checked on Tuesday morning, my net meter read 46 kilowatt-hours with just a few more days before I hit the two-year anniversary of the solar panels. To put that in perspective, a full day’s production on a long, sunny summer day is about 15 kilowatt-hours, so we’re really close. (The meter dropped four more kilowatt-hours while I was writing this article–woo-hoo!)

I bought the panels because I saw it as an environmentally-friendly thing to do with a long payback of 14 years. But if I use less electricity, my financial incentive increases: in addition to lowering my bills, the utility now has to pay me the full retail rate for the surplus electricity we generate. That’s a result of changes to Massachusetts regulations designed to promote clean-energy business development.

So in the end, the solar panels have made me far more aware of my energy usage than I was before, and having a shot at net-zero electricity (we still use natural gas) has been a fun side show. I’m sure there are few other home energy-efficiency techniques I could still do (got any tips?). But in the meantime, here’s hoping for a sunny spring.

Similiar as heat pumps, solar system is also new technology, but solar need a bit longer timer to improve its transfer efficiency from solar to heat or electricity.