7 Months In: Mike Tabone Shares Data on Heating and Cooling with Heat Pumps
Solar Power | December 11, 2013 | Posted by Fred Greenhalgh
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We had a chance to catch up with Mike Tabone, whose solar-powered home uses air source heat pumps for heating and cooling, and a heat pump water heater for domestic hot water.
As of December 4, 2013, his 12kw solar electric array had produced over 9,550kWh of electricity. Much of that electricity went into Mike and his wife Louise’s ‘bank’ of credits with CMP, and, according to Mike’s estimates, he will heating his home most of this winter from those credits.
“We haven’t burned a drop of oil since the day we installed the solar,” Mike says, “It was a cold November and we had the heat pumps keeping our house comfortable even at 8 degrees outside. It looks like we’ll make it all the way to January without having spent a nickel on energy.”
Mike keeps his solar array honest by using a robust whole-house data monitoring solution called the eMonitor. While nearly all solar electric arrays come with some form of monitoring of the solar output, the eMonitor goes a step farther and tracks on a breaker-by-breaker basis how electricity is being consumed in the home.
For example, the eMonitor will show him in real-time his home’s consumption vs. production:
Another view will show you, on a circuit by circuit basis, which parts of the home are consuming the most electricity:
Or view historical overall consumption in the home (Green) and compare solar production (blue) to whether you were feeding to or from the grid (yellow):
For the deeply data-hungry, you can drill down to the performance of each circuit – on a minute-by-minute basis if you’d like! – and analyze performance over time.
So for instance, say you were trying to really understand the kilowatt-hour usage of electric heating vs. cooling with one of the Tabone’s Fujitsu heat pumps. You can drill down to this individual circuit, and then look at the performance over time:
What’s impressive about the above graph is how small a dent the heat pumps make in the summer months – when they are used as primary cooling for the Tabones. Heat pumps double as cooling units because they have a feature whereby the refrigerant can move in the opposite direction from heating mode. This allows the unit to absorb heat from inside the home and release it to the outdoors. Mini split heat pumps typically use roughly half as much electricity in cooling mode when compared to a conventional window air conditioner. While heat pumps use more electricity in heating mode, the costs to operate them pale in comparison to oil heat.
To Mike, a clear return-on-investment was critical to justify the project, and so far the solar is meeting those expectations. “By this time last year we had spent over $3,900 on energy,” he says, “In addition to electricity savings we have nearly eliminated our propane and oil consumption. We even added an electric car (Chevy Volt) to further reduce our dependence on fossil fuel.”
Mike tells us he is disciplined about putting solar energy savings into a separate investment account. Freed from the burden of energy bills in their retirement, the Tabones look forward to putting their money to better uses than filling their fuel tank.