Q1 2013 summary: 20% more cold, 22% more usage and 15% less sun.
Now that we are starting to collect our second year of performance data, I’ll be comparing our new data to the same period last year. Year-over-year comparisons should be more illustrative than comparing to previous months. I’m also switching to a quarterly reporting period to look for larger trends, but I will continue to post data monthly at netplusdesign.com
**See April 7 Update at end of post.
In Q1 last year our net usage was 228 kWh. This year is was 953 kWh, a 300% increase! In March 2012 we actually generated a surplus, but not this year.
Overall, here’s how the first quarter compares to 2012.
|2013||Usage||Solar PV||Net usage
|2012||Usage||Solar PV||Net usage
Seeing all the increases, I wanted to understand if our 22% increased usage (445 kWh) was due mainly to the 20% increase in colder weather (HDD), or if other factors were leading to our increased electricity usage.
Broadly speaking, hot water, heat and all other circuits (mainly plugs loads and lighting) each accounted for about 30% of the total energy for the 1st quarter. Out of the three, hot water is the only one we can accurately compare because we still lack circuit-level data for Q1 2012.
For the last three months we’ve averaged 74.8 gallons of water per day, up 46% from first quarter 2012. That’s an extra 600 to 800 gallons of water per month, or nearly 24 extra gallons per day. This includes a 25% increase in hot water usage. Although we don’t have circuit-level data on the hot water heater, we do have monthly hot water usage data. We can use this to estimate the energy required to make hot water in Q1 2012.
Our hot water heater used an average of 275.8 watts to heat one gallon of water in Q1 2013 (water heaters have to work harder in the winter). We used an extra 533 gallons of hot water in Q1 2013. 533 * 275.8 = 147 kWh. That’s 33% of the overall usage increase right there.
As for the cause of the increase? To remain happily married I will only say two words, goats and mother-in-law. I don’t think I should say anything more on that topic.
Now let’s look at heating.
Determining the increase in heat energy is not easy to answer because we only have estimated usage values for heat in Q1 2012. Estimated values for heating have a much higher degree of uncertainty. Using this quarter’s values to check the accuracy of my 2012 estimate shows that my estimate may have been off quite a bit. It’s hard to know how much it may be off because I don’t know an easy way to factor in heat gain directly from the sun shining through the windows. Below are the heat pump electric usage values for Q1 2012 and 2013.
Based on the values in this table, we used an additional 422 kWh or a 128% increase in energy use for heating in 2013. This would almost completely use up the 445 kWh overall usage increase! So I know this can’t be correct. For example, if I use the HDD formula, 0.2261 x 1900 HDD(base 50) + 0.756, I get 430 kWh, which is far below the actual recorded 746 kWh. Which means my estimated heat values for 2012 are off. But we know that heating has increased some amount due to the colder temperatures and cloudier skies. We just can’t determine how much it increased.
So let’s look at all other circuits. Again we can’t really compare apples-to-apples yet, but there are a number of changes that have occurred this year. As I mentioned, we now have a barn full of goats, chickens and other critters. On the coldest days we used heated water buckets to keep the water from freezing. In March we had an egg incubator running for 23 days and and we’re using grow lamps to start our garden seedlings. As of March 30 we’re also now using a 250W heat lamp in the chic brooder. This will last for a few weeks before we switch to a smaller wattage, pushing our energy usage up 4 to 5 times it’s usual base load for about 5-6 weeks. Soon the incubator will be in use again. We’re going to try hatching and raising some turkeys this year.
In summary, Q1 usage is up compared to last year. Some of the reasons for this are fairly obvious, others remain difficult to tease out of the data. Hopefully next quarter will offer better comparisons and we’ll finally be able to compare apples-to-apples with circuit-level data. It should be easier to see where usage has changed and why. If we understand why, then we have a better chance of improving performance over time.
April 7 Update: Using a different method I estimated that heat energy most likely did increase 20%. That means out of the 445 kWh increase in 2013, 65% of that increase was due to heat energy, 33% was water heating and everything else was 2%. That sounds a little more realistic.
You can see heat maps and detailed charts of temperature and electrical usage at netplusdesign.com. View hourly, daily and monthly values for solar, usage, net usage, temperatures and HDD.