Last week we did the (sorta) solar equivalent of 200,000 mile rollover on the odometer, and surpassed 2 Megawatt-Hours of production on our 2.53kW rooftop solar PV array. (Watt-hours are a measure of energy; it’s what you get billed for by your utility.  One watt-hour is production or use of 1 watt for 1 hour.  Burning a 100W bulb for 10 hours gives you 1000 watt-hours, or 1kWh, which is the normal unit of sale.)

The array has been up for 9 months, since July 2010; how have we done so far?

For the big production picture, you can look at the Enlighten Monitoring Site for the array.  We’re finally coming out of the short, overcast winter days, and production is picking up again (though today is another 1″ of snow…)

How does this output compare to the projected production from, say, the pvwatts.org calculator?  It’s roughly on par; the estimate is 2112kWh, so we’re just slightly under that – I am fairly sure that pvwatts takes into account sky conditions, but not lingering snow cover; despite my best efforts, the huge amount of snow this winter has definitely hurt production.

Ok, that’s all well and good, and 2 MWh sounds like a lot, but what does that really mean?  Well as the Enphase site says, that’s roughly the carbon equivalent of planting 42 trees, or not-burning 182 gallons of gas, or running 6,242 light bulbs for 1 day (using standard EPA formulas for such things).

What is that in Cold Hard Cash?  At around $0.10/kWh, about $200 of avoided bills.  Clearly not a money-making proposition yet, but especially as rate go up, there is (distant) payback in sight, and there is some cash flow advantage.

What does it mean for our house and our usage?

As of today, the numbers on the meters are:

• 2023 kWh produced
• 2602 kWh imported from the grid (use > production)
• 1230 kWh exported to the grid (production < use)

So our home consumed (2023-1230)+2602 = 3395 kWh since installation, and we produced 2023kWh, or about 60% of our use during that time.  To put it in average monthly perspective, we produced about 224kWh out of our 337kWh usage each month.  I was hoping to cover closer to 75% of our usage, but that’s not too bad for our small array.  We may still get there for annual production; we’ve had the array through almost an entire winter, but only half of a summer.

I’ll do another post at the 1-year mark, of course!