Tesla Batteries, late winter solar energy, and more…

Our attempted-carbon-neutral home in St Michaels, Maryland, is now finished and we’ve moved into this most beautiful house! Energy bills are incredibly low – just paid our January bill to Choptank Electric Cooperative, $22.,,,and that’s the highest monthly electric bill since July, when the solar PV panels went live.  Awesomely low compared to other houses this size in the mid-Atlantic region, e.g., just paid $660 for gas and electricity in a comparably-sized, and well-insulated Bethesda house.  As we’ve pointed out before, this amazing savings owes to 50 SunPower PV panels, 8 geothermal wells with 45 SEER ground-source indoor heat pumps, and highly insulated walls.

On January 9, Tesla delivered our 3 PowerWall batteries and installed them on the garage wall.  Here’s the trio – Manny, Moe and Jack if you like – and Joyce’s Model 3 Tesla. .

Given the severe winter weather that’s ensued, we’ve kept the batteries topped off, relying on them mainly for emergency back-up.  Sure enough, they powered the house seamlessly during one brief outage in February.

PowerWalls charge preferentially on solar power, so it’s green storage, but also a green challenge. The question is how best to use them to maximize carbon avoidance. We’ll start next month by experimenting with different modes to time-shift loads. Initially, we’ll use them to abate steep evening ramp-ups in energy demand that follow sunny days, much as major Li-Ion battery installations are used in Southern California. The idea is that PJM uses its most polluting generators to meet this need, so we target the batteries to avoid that. Another pattern will be to use them to meet our mid-evening demand using stored solar power. Yet another will be to preferentially charge the EVs with solar power. Only with a more complete understanding of PJM’s marginal fuel at each 15-minute interval will we be able to maximize the effectiveness of our batteries in avoiding carbon emissions.

Meanwhile, the “power plant on the roof,” combined with a low-energy-demand house, is amazing. As the days grew longer, we’ve found that by late February we’re now steadily putting more energy into the grid than withdrawing on sunny days. Snow cover has been less of a problem than we thought – despite their nearly zero-degree angle (flat) mounting, it’s been taking only a day for the snow to melt away and for solar energy production to be restored.

More to follow!