Solar Electric
Also called Solar Photovoltaics (Solar PV), these systems generate electricity on roof and ground-mounted arrays. We have Solar PV on our own homes and believe it is good long-term move with regards to economics and generally bigger picture climate related concerns - whether a heat pump pump system is being installed or not.
NOTE: We do not design/sell/install Solar PV. But can refer preferred contractors as needed.
As long as we have your attention let’s go over some basic solar related terms and concepts:
Off-grid Solar
Off-grid solar means it is not tied to the electric grid and utility companies.
Energy produced is stored on-site in a battery bank (lithium or lead-acid)
In northern climates often a generator is required when solar production cannot keep up with the demand (cloudy, mid-winter days)
Off-grid solar homes often require a wood stove or a fossil-fueled propane heat space heating for space heat.
Most heat pumps cannot be used in off-grid locations because they need 240-volt power.
Grid-Tied Solar
Most solar is grid-tied. That means your roof-generated electricity is sent to the grid and its energy production is recorded/managed by the utility.
The homeowner then gets credit on their utility bill (if net metered).
Net Metering
Most grid-tied solar relies on a net metering agreement with your local electrical provider.
The utility sets a one-year calendar preferably starting April 1. The utility tallies the energy produced over 12 months.
In summer the solar usually produces more than is used. This creates a credit or surplus. In the winter things are opposite; solar productions is less than energy used.
Net metering allows excess summer production to offset winter monthly deficits.
Some utilities in Montana do not use net metering (Vigilante and Flathead to name a couple) which means solar is hard to justify economically.
Kilowatt hours (kwh) The measurement unit of electricity. A few examples
<0.5 kwh: One pot of coffee in drip coffee maker
5 kwh: One load cycle for electric drier
8 kwh: 6-minute shower with an electric water heater and low-flow showerhead
10 kwh: Round trip from Bozeman to Bridger Bowl (16 miles) in an EV car (EV pickup/SUV is 30-40% more)
200 kwh: Monthly average electrical usage for small efficient home
300 kwh: Monthly average hot tub energy usage in cold climate location
1,500 kwh: Monthly average electrical usage for large, not so efficient home
4,000 kwh: Annual usage for electric water heater for family of 4
1,000 kwh: Annual usage for electric heat pump water heater for family of 4
Kilowatts (kW)
kW is the “currency” of solar electric arrays: 1,000 kilowatt hours (kWh) = 1 kilowatt ( kW).
A 900 SF home with gas heat and hot water heater may need a 3kW solar array.
A very efficient 1,600 SF all-electric home with heat pump might need 8kW array.
Also a measure of power: the small Arctic heat pump has output of 35,000 BTUs or 10.2 kW.
PV Watts Calculator (pvwatts.nrel.com)
The energy production of a solar array depends on where it is installed, the slope of the panels, and the aspect among other factors.
Using the PV Watts Calculator, a 3kW system in Bozeman that produces 3.8 kW per year would generate 5.3 kW in Tucson, AZ.
Inverter
A solar array produces DC (direct current) electricity. A home, and the grid, use AC current (alternating current). The inverter converts electricity from DC to AC.
Main components
The main components of a solar PV system include: 1) panels, 2) racking and 3) inverter (s)
Sizing solar PV
On existing homes, a solar contractor will look at your existing utility bill to determine how big a solar array will be needed.
It is possible downsize that solar array for example, by upgrading appliances that use less electricity.
Alternatively, if installing a heat pump we recommend upsizing the solar array to match the anticipated energy usage of the heat pump etc.
Electrification
Gas or propane cannot be generated on your roof. But electricity can be. So going all-electric means a solar array can potentially offset all its energy consumption.
Electrical appliances such as electric lawnmowers, heat pump water heaters, heat pumps and electric cars are significantly more clean-burning and efficient than their gas counterparts (3 to 5 times more efficient!)
Load Shift
We use this term when - on a home with solar - a gas fueled range is replaced with an electric induction. Same applies from gas to electric water heater or even a gas to an electric vehicle.