Green House in St Michaels – Mid-April Update

Now nine months into our carbon net-neutral experiment, the house is still amazing.  It’s already generated about as much electricity as it’s consumed, and the remaining three months (mid-April through mid-July) typically have easy weather and sunshine.  Info from Choptank Electric Cooperative’s website tells the story so far (see attached chart):
– Starting from July 12, 2018, when our 50 solar PV panels went live, our electricity generation in the summer and early fall far outstripped power demand in the house, which was mostly for cooling and construction equipment.  Having a highly-insulated shell helped too.
– Then, this pattern reversed during peak winter months, when the low sun angle and even some snow cover made solar less effective.  Our 8-well geothermal energy system was seasonally less productive as well, but the house’s 45 SEER ground-source heat pumps still used much less energy than conventional heat pumps while also providing hot water.
– So far in late winter and spring 2019, our solar PV ‘powerplant’ is once again outproducing household demand, on average.
But even though the house is indeed net-negative in terms of energy use (produces more than it uses), we wonder if this means we’re also meeting our goal of carbon net-neutrality?  I suspect it does mean that, but we’ll need to use quarter-hour PJM fuel use data to prove the point, i.e., see exactly what fuels we’re displacing.  On the positive side, we can widen the circle and include carbon avoided by charging electric cars with solar power versus using gasoline cars.  We’ll also try managing our 3 Tesla batteries this spring to minimize carbon production, as discussed in last month’s blog – up to now, we’ve held these for emergency power supply in the winter.  On the negative side, there’s our prodigious lawn that needs to get cut weekly with conventional smelly equipment – we’re looking into an electric mower.  We’ve also got propane distributed through the house to gas fireplaces and the cooktop, but these are basically cosmetic uses, a few gallons per month.
Bottom line is we’ve got a zero-energy house, producing more than it consumes over an annual cycle.  We’re still gathering info to prove the same point for carbon, and we’ll also be able to assess the basic economics of this experiment, including years to pay-back and internal rate of return of our incremental investment.
As always, the devil is in the details!  More to follow.