Solar Electric

Solar Photovoltaic (Solar PV) systems generate electricity on roof or ground-mounted arrays.  We have Solar PV on our own homes and believe it is a solid long-term move with regards to both economics and bigger picture climate-related concerns - whether a heat 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, here are some basic solar-related terms and concepts:

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 may be harder to justify on an economic basis.

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.

Main components

  • The main components of a solar PV system include: 1) panels/modules; 2) racking; and 3) inverter(s)

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.

Sizing a solar PV system

  • 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 to downsize that solar array for example, by upgrading to 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. We can help you estimate annual usage of a heat pump for space heating.

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 of a home’s energy consumption.

  • Electrical appliances such as electric lawnmowers, heat pump water heaters, heat pumps and electric vehicles are significantly more clean-burning and efficient than their gas counterparts (3x to 5x times more efficient!)

Load Shift

  • We use this term when - on a home with solar  -  perhaps a gas-fueled range is replaced with an electric induction range. Same applies from switch fro gas to electric water heater, or from a gas (ICE or internal combustion) to an electric vehicle (EV).

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 woodstove or a fossil-fueled propane space heater.

  • Most (not all!) heat pumps cannot be used in off-grid locations because they need 240-volt power.