Heating our home with solar electricity

eheater1editors-blog-entry3So, here I am in my basement office debating whether or not to turn on one of our 400-watt electric wall heaters. It’s a chilly 62 degrees Fahrenheit and we’re sitting on more than 10,000 kWh of extra banked solar electricity that our 5.59 kW solar PV system has cranked out in the past 27 months.

That’s free electricity we’ve generated ourselves just waiting to be used by us.

Yet I’m not only hesitating to turn the heater on, I’ve just decided to not to turn it on at all while I write this entry (I do have two sweatshirts and a warm pair of sweatpants on 😉

What’s going on? Why not turn on the friggin heater, Christof?

Hard-earned electricity
After all, you’ve earned any electricity the heater uses by over-producing with your home solar system to the tune of 200 percent of your home electric use for the past two years.

In fact, during a recent cold-snap we had here on Colorado’s Front Range during which we saw our first snow of the year, I made the final decision to ditch our natural gas furnace and heat our home with six eheat.com high-efficiency wall heaters this winter.

The plan is to continue to heat as much as possible with our eheat.com heaters. This, in an effort to:

a) save some money;

b) burn some of those extra 10,000 kWh — I’m guessing we’ll run through about 2,500 to 3,000 of them if we stick to the plan of using our eheat.com heaters rather than our natural gas forced hot air furnace for the winter;

c) feel good about our comparative energy independence – not many people can say they’re covering close to 100 percent of their home energy use via home solar (we have a natural gas water heater and we can’t say we’re using solar/solar offset to take hot showers).

This should be a really great feel-good moment for us. Yet I can’t quite get myself to feel good.

Here’s why:

    1. I can’t escape the sense of at least partial bogus-ness in terms of solar offset. Solar offset means your solar system generates more electricity than you use across a given period of time, whether it be a day, week, month, a year, years, or, in our case, often all of the above, and that you later “take back” some, or all, of that extra electricity. But, of course, because you’re taking that electricity back at another time (oftentimes at night), it means that electricity is not being generated by solar but by some other means, in our case, by the burning of coal and natural gas at a big power plant.
    2. I’m addicted to energy efficiency and to keeping our daily, monthly, and yearly total household kWh usage low. How low? During mild weather months such as September and May, it’s not uncommon for our family of four to use just five to eight kWh of electricity per day. And, yes, this includes days we are home all day. Our typical daily kWh use average ranges between five and 15 kWh per day.

Six eheat.com heaters
Heating our home with six eheat.com electric wall heaters — I’d rather be paring down our extra 10,000 solar kWh by plugging in an EV, but unfortunately we’re going to have to wait another two years to do that — forces me to confront my discomfort with burning through what, to me, seems like ridiculous numbers of kWh per day, meaning 30, 40, even 50 kWh per day.

To give you an more concrete idea of our radical about-face on electrical usage, here’s our net usage (with TED, we can measure both solar production and our electric use) across the past two weeks — with the days at beginning of the week coming before our first cold snap, and the end of the week coming after the cold-snap and after we turned on our eheat.com electric-wall heaters.








Sat 10/06

47 kWh

$ 5.13


Sat 09/29

-22 kWh

$ -2.41

Fri 10/05

31 kWh

$ 3.40


Fri 09/28

-22 kWh

$ -2.42

Thu 10/04

-5 kWh

$ -0.52


Thu 09/27

-13 kWh

$ -1.41

Wed 10/03

-16 kWh

$ -1.78


Wed 09/26

-8 kWh

$ -0.83

Tue 10/02

-21 kWh

$ -2.32


Tue 09/25

-2 kWh

$ -0.19

Mon 10/01

-18 kWh

$ -1.98


Mon 09/24

-4 kWh

$ -0.38

Sun 09/30

-14 kWh

$ -1.57


Sun 09/23

-18 kWh

$ -2.02

Yikes, 47 kWh net electricity usage on a single day (10/6)! That day, we actually used 52 kWh and generated just five solar kWh (my wife ran three loads of laundry through the dryer that day). That means on a single day we used more than a quarter of our kWh total for the entire month of May 2011, when, with some pretty focused electricity use, we managed to consume fewer than 200 kWh.

50 kWh used in one day
We do have some precedent for near 50 kWh days. After seven years of pretty miserly central AC usage, including two during which we had our 5.59 kW system, for the record hot summer of 2012 – it was the hottest summer ever recorded in Colorado and Wyoming – we used our AC fairly often. As a result, we saw some days on which we sucked down about 40 kWh of electricity.

But that’s a little bit different than our upcoming winter time scenario where we have a choice of heating mostly with natural gas (our gas furnace does have an electric 750-watt fan that blows the hot air around our house) or nearly 100 percent with electricity using our eheat.com heaters while tapping into our 10,000 kWh of banked solar-generated electricity.

It’s clear we’ll save money by ditching our natural gas furnace as much as possible this winter (we already had four of our six eheat.com heaters, though I did just shell out about $220 for an additional two to push us to six).

We could be looking at winter monthly total utility bills of about $25. It’s fair to say that’s a number 99 percent of people with a four-person, 2,000-square foot home similar to ours are going to be jealous of.

In fact, we could be looking at monthly total utility bills of about $25 for November, December, January, February, and March – the biggest five heating months of the year in Colorado, and in much of the Northern Hemisphere. It’s fair to say that’s a number 99 percent of people with a four-person, 2,000-square foot home similar to ours are going to be jealous of.

Environmental impact
But the big question here is the difference in environmental impact in terms of heating our home mostly with natural gas as opposed to electricity.

solar-panels-snow1Yes, the electricity we use to power our six eheat.com heaters will be solar offset electricity, meaning at one point we put extra solar electricity into the grid that was sucked down by our neighbors. But it will also ultimately be generated by burning coal and natural gas. According to the EPA’s Clean Energy Calculator, 68 percent of that electricity will be produced by burning coal (that’s considerably higher than the national average of 45 percent), and 22 percent by burning natural gas.

There’s also the basic efficiency question: Is it more efficient to burn natural gas at the source, meaning in our basement furnace or use solar-offset electricity produced by burning coal and natural gas offsite?

The common sense answer would be it would be more efficient to burn gas in our home than to have gas, and coal, burned elsewhere to produce electricity that is then sent onto the grid and which we then – again, we’re tapping into our massive 10,000 kWh of solar offset here – use to power our six electric wall heaters.

Therms to kWh conversion
Finally, there’s the therms to kWh conversion: How many therms worth of natural gas do we need to burn to keep our house warm this winter as opposed to how many kWh of electricity do we need to burn in order to accomplish the same thing?

Here it’s instructive to look at our total therms consumption of natural gas last winter.


We burned through 364 therms of natural gas from Nov. 2011 – March 2012, though, of course, not all of that was to heat our home: some went to heating our water. A quick look at our gas usage during non-heating months shows that on average we burn about 10 therms of natural gas a month to heat our water. So, let’s take 50 therms off that 364 therm total for Nov. 2011-March 2012. That brings us down to 314 therms.

Various therms to kWh online calculators [http://www.unitconversion.org/energy/therms-to-kilowatt-hours-conversion.html etc.] show that 314 therms = about 9,200 kWh.

We won’t come close to burning 9,200 kWh to power our six eheat.com electric wall heaters this winter. A rough estimate – probably on the high side – is that we’ll use about 4,500 kWh to heat our home using these six eheat wall heaters from Nov. 2012 – March 2013, though it’s possible we could use as many as 5,500 kWh, or as few as 3,000 kWh, depending on a number of different factors.

Whew! That makes me feel a bit better about tapping into our 10,000 solar-offset kWh to heat our home with electric wall heaters this winter. Of course – even though I’m not a big fan of natural gas thanks to fracking – I have to admit I’d feel quite a bit better about our whole plan to heat with electric wall heaters while tapping maybe 2,500 of our 10,000 solar-offset kWh banked with Xcel Energy (we’ll be generating more solar kWh as we go along this winter, which is why I cite 2,500 kWh rather than 4,500 kWh) if most, or all, of the actual generation of the 2,500 solar-offset kWh we’ll be using was being done by natural gas rather than coal.


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