16 June 2016 - DrSunshine.org - by Dr Jwalk, a friend of Dr Sunshine
This is a story of one experience with solar energy in New England, one of the cloudier regions in the US and with cold, snowy winters. The house, a one-floor residence with typical appliances and lighting, is roughly 1800 sq ft in size, is reasonably well insulated, uses electricity for cooking, and uses fossil fuel for heating.
300 sq ft of south-facing roof area is covered with solar panels. These panels generate about 6000 kWh of electricity per year, which is about 80% of the annual electricity usage - adding another 75 sq ft of panels would result in generating roughly 100% of the current electrical usage. The state has net metering, which allows storage of the excess summertime generation to be stored in the electrical grid for use during winter months when usage exceeds generation. (One February there was zero generation because the panels were covered by snow the entire month.) The state also requires power companies to provide a certain percentage generated by renewable sources, so power companies pay, via SRECs (Solar Renewable Energy Credits), for excess solar generation delivered to the grid. Between the savings in electrical bills and SRECs, the payback on the solar investment is seven years. (After that, it's gravy, as solar panels require no maintenance and should last 30 years.)
To summarize, one sq ft of solar panels for every five sq ft of house floor plan would essentially supply all the non-heating electrical energy needed by a relatively tight house in New England.
What about the heating? Over the past several years annual house heating and domestic hot water have used, on average, (the equivalent of) about 24,000 kWh of fossil fuel. Typical modern air-source heat pumps can realize a Coefficient of Performance (COP) in the neighborhood of 3 at air temperatures of 50°F. Under these conditions, therefore, an air-source heat pump would draw about 8000 kWh of electricity annually and is cost-competitive with fossil-fuel heat. The COP falls off somewhat at colder outside air temperatures, however, so this house would use more than 8000 kWh for heating. The COP of a ground-source heat pump can be up to 5 and does not vary with outside temperature. Thus the annual electricity usage for heating with a ground-source heat pump could be in the neighborhood of 5000 kWh. (Ground-source heat pumps are more expensive to install and maintain, however.) A new home trend in New England is to use air-source heat pumps rather than oil or gas furnaces; in addition to being cost-competitive, heat pumps also provide air conditioning.
Now consider solar panels for supplying the electrical power to the heat pump. A solar array approximately 20% larger than that needed for the non-heating electricity could do that for an air-source heat pump. An array 30% smaller could do the job for a ground-source heat pump. In either case a solar panel installation slightly larger or slightly smaller than double that needed for non-heating electricity would provide all of the clean solar electrical power the house needs, including heating.
In summary, a solar array half the square footage of the house floor plan could easily provide all the annual electrical needs of a well-insulated New England house using a simple air-source heat pump for heat.
Since most heating occurs in the winter, when solar power generation is the least, net metering storage in the grid (or some sort of storage) is critical for this approach to work. With that caveat, this represents a practical way to wean residences from fossil fuel use (including the fossil fuel used by power companies to generate electricity).
The state and federal incentives that make it practical for many homeowners to install non-heating solar generation would also apply to the solar capacity for the heat pump as well. Unfortunately there generally is not the same incentive for converting fossil fuel heating to heat pump heating, making the conversion impractical for most homeowners. However, a "Manhattan Project" type national effort could make it practical for virtually everyone. In the grand scheme of things such a program would be fairly minor, would make the residential segment of society fossil-fuel free, and be very much in the long-term national interest.
(sometimes going against the grain)
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