The Best Solar System Is One Sized Around a Lower Bill
Before you size a solar system, lower the bill it needs to cover. Every kilowatt-hour you stop consuming is a kilowatt-hour your solar panels don't need to generate — which means fewer panels, lower upfront cost, and a better return on the solar investment.
This guide walks through every step of load reduction, from no-cost behavior changes to major efficiency investments. The right stopping point depends on your home's specific situation — not every step is right for every home.
No-Cost Steps (Do These First)
Thermostat adjustments
Heating and cooling typically account for the largest portion of a home's energy use. Small changes to your thermostat settings — lowering the heat setpoint by a few degrees at night, raising the cooling setpoint when no one's home — can reduce HVAC energy use with no equipment cost.
LED lighting
If you still have incandescent or halogen bulbs anywhere in your home, replacing them with LEDs is a cost-effective change with a payback typically measured in months. LEDs use 70–90% less energy for the same light output.
Eliminate vampire loads
Electronics and appliances draw power even when "off." Televisions, game consoles, cable boxes, and desktop computers are the biggest offenders. Smart power strips or manual unplugging can reduce standby consumption. The impact is small per device but adds up across a modern household.
Low-Cost Investments ($50–$500)
Smart or programmable thermostat
A programmable thermostat lets you automate the setback schedules that manual adjustment requires discipline to maintain. A smart thermostat can learn your patterns and optimize automatically. These typically pay back within a single heating season for most Illinois homes.
DIY air sealing
Weatherstripping around exterior doors, caulk around window frames, foam sealant around utility penetrations — these are inexpensive materials and can be installed by most homeowners. They address the most accessible air leaks without needing a contractor.
HVAC filter and maintenance
A dirty filter forces your HVAC system to work harder. Replacing filters regularly and scheduling annual maintenance keeps the system running at its rated efficiency. A professional tune-up typically costs $100–$200 and is worth doing on any system over 5 years old that hasn't been recently serviced.
Mid-Range Investments ($500–$5,000)
Attic insulation top-up
Most building professionals consider attic insulation one of the highest-ROI efficiency investments available. Heat rises — in winter, poorly insulated attics are where a significant amount of heat escapes. Blowing additional insulation into the attic to meet modern R-value recommendations for Illinois (R-49 to R-60 is commonly cited) is typically a one-day project.
Professional air sealing
A building performance contractor with a blower door can find and seal the leaks that DIY work misses — penetrations into the attic, gaps in the wall-ceiling juncture, bypass paths in mechanical chases. Professional air sealing combined with attic insulation is one of the most impactful efficiency investments for older Illinois homes.
Duct sealing
If your home has forced-air heating and cooling, leaky ductwork can be a significant source of energy loss — conditioned air that escapes into unconditioned spaces (attics, crawlspaces, garages) before it reaches the rooms you want to heat or cool. Duct sealing (professionally done with Aeroseal or mastic sealant) typically costs $1,000–$3,000 and can improve system efficiency meaningfully.
Major Investments ($5,000+)
High-efficiency HVAC replacement
If your heating and cooling system is more than 15–20 years old, a modern high-efficiency replacement will use significantly less energy to produce the same comfort. HVAC replacement is disruptive and expensive but has a long service life over which the efficiency gain pays back.
Heat pump replacement for gas heating
Replacing a gas furnace with a cold-climate heat pump shifts your heating from gas to electricity — and does it at 2–4 times the efficiency of electric resistance heating. If you're also planning solar, the heat pump adds electrical load that the solar system can offset. The combined economics of eliminating gas while solar offsets the electrical cost can be compelling. See our guide on heat pumps and solar.
Window replacement
For homes with old single-pane or early double-pane windows, replacing them with high-performance modern windows reduces your heating load. See our guide on windows and energy load.
Insulated siding and wall insulation
For homes with poorly insulated walls, insulated siding provides continuous exterior insulation. See our guide on siding and solar sizing.
Geothermal heating and cooling
The most efficient heating and cooling system available, using the stable temperature of the ground as a heat source and sink. Higher upfront cost than air-source heat pumps, but highest long-term efficiency. See SPM's geothermal service.
Then: Solar
After you've addressed the efficiency opportunities that make sense for your home, the solar proposal is built around your actual, post-efficiency usage. The system is smaller, less expensive, and accurately sized for the home as it will perform for the next 25 years.
This isn't about delaying solar unnecessarily. It's about making sure the solar investment is the right size. For some homes, the efficiency work is quick and the solar project follows immediately. For others, the efficiency work represents a year or two of phased projects before solar goes in. SPM will help you sequence it correctly for your situation.
Frequently Asked Questions
Do I need to do all of these steps before going solar?
No. The goal is to address the efficiency opportunities that are realistic for your home and timeline — not to complete every possible upgrade before touching solar. Some homes are already efficient and can proceed directly to solar. Others have meaningful opportunities that should come first. SPM evaluates your specific situation and recommends a sequence that makes sense.
How do I know which efficiency upgrades are worth doing?
A home energy assessment can prioritize them by impact and cost. SPM conducts this assessment as part of the solar consultation process so you have the information to make smart decisions about sequencing before any project begins.