Two Investments That Work Better Together

Solar panels and energy-efficient windows address different parts of your home's energy picture — but they're connected. How your windows perform affects how much energy your home needs. And how much energy your home needs affects the solar system size required to cover it.

For the right homes, tackling windows and solar together — or windows first, then solar — produces better outcomes than either project done in isolation.

The Logic of Sequencing

Here's the core principle: every kilowatt-hour your windows let escape in winter or let in as heat in summer is a kilowatt-hour your solar system eventually needs to replace.

If you install solar first, based on your current usage, and then replace old single-pane windows, you've reduced your load — but you already have a solar system sized for the higher load. You paid for panels you no longer need.

If you replace the windows first, then size solar around the lower post-window usage, you get a smaller, cheaper solar system that accurately matches your actual need.

Who Benefits Most From Solar + Windows Together

This combination delivers the clearest benefit for:

  • Homes with original windows — If your home still has its original windows from construction (common in Illinois homes built before the 1990s), those windows are likely single-pane or early double-pane without low-e coating. The efficiency gap between your current windows and modern replacements is large — and the load reduction is meaningful.
  • High heating bill homes — If your heating bills are higher than seems reasonable for your home's size, inefficient windows may be a significant contributor. Replacing them reduces your load before solar is sized.
  • Homes where windows are already due for replacement — If your windows are failing — fogging, difficulty operating, visible gaps, water intrusion — they're going to be replaced anyway. Doing it before solar sizing is the right sequence.
  • Homeowners planning both projects in the next 1–3 years — If you're planning to do both within a couple of years, doing windows first and solar second is the more economical approach.

When Solar-First Makes Sense

Solar-first (with windows to come later) is more reasonable when:

  • Your windows are already modern, double-pane with low-e — there's not much efficiency gain left to capture
  • You want to capture solar incentives now and windows are a lower priority
  • Your utility bills are moderate, suggesting windows aren't a major loss point
  • You plan to replace windows in 5+ years — the sequence is still right, but the timing of the solar project doesn't need to wait

The Financial Picture

Both windows and solar generate returns through reduced utility bills. Windows pay back through lower heating and cooling costs. Solar pays back through reduced or eliminated electricity bills.

When the projects are sequenced correctly — windows before solar sizing — the combined return is better than either project done in isolation because:

  • The solar system is smaller and less expensive
  • The window savings stack on top of the solar savings (rather than partially canceling the value of an oversized solar system)
  • The total project cost can be lower while delivering more comprehensive results

SPM Handles Both

Because SPM installs both energy windows and solar, we can coordinate the sequencing for you — no need to manage two separate contractors or time two separate projects. We evaluate your windows and solar potential together and build a plan that makes economic sense for your home.

Practical Steps

  1. Get a home energy assessment that covers your windows, insulation, HVAC, and solar potential together
  2. Review the window efficiency assessment: are your current windows a significant loss point?
  3. If window replacement is warranted, get a combined proposal that sizes solar around post-window usage
  4. Review incentives for both: ComEd has historically offered rebates on qualifying windows; Illinois Shines credits apply to solar. Verify current availability for both before finalizing plans.

Frequently Asked Questions

How much smaller could my solar system be if I replace windows first?

It depends on how inefficient your current windows are. Replacing single-pane windows with high-performance double-pane low-e windows in an older Illinois home can reduce heating load meaningfully — and when combined with air sealing and other efficiency work, the total load reduction can be significant enough to change the solar system size by a panel or more. SPM will estimate the impact specifically for your home before recommending a project sequence.

Can I finance windows and solar together?

Financing options vary. SPM works with financing partners for both solar and home efficiency upgrades — contact us for current financing options. Some utility programs also offer low-interest loans or on-bill financing for qualifying efficiency upgrades including windows.

How do I know if my windows need replacement?

Signs your windows may be due for replacement: visible fogging or condensation between the panes (indicating a failed seal), single-pane glass, difficulty operating or locking, visible gaps between the frame and the wall, drafts you can feel near the window on a cold day, or frames that are rotting or cracking. Any of these warrant an assessment.

Learn about SPM's energy windows or get a free assessment that covers both windows and solar together.