What “Offset” Really Means in Solar — and Why Partial Offset Still Matters

When homeowners start researching solar, one of the first terms or numbers they see is “offset.”

You’ll hear things like:

• “This system offsets 85% of your usage”

• “We can get you to 100% offset”

• “Anything under 100% isn’t worth it”
  
  

That framing sounds simple — but it’s incomplete.

Offset is an important concept in solar, but misunderstanding it often leads homeowners to overpay, oversize systems, or delay going solar entirely.

Let’s break down what offset actually means, why systems aren’t always designed for 100%, and why partial offset is almost always better than doing nothing.

What Is Solar Offset?

Solar offset refers to the percentage of your home’s electricity usage that your solar system is expected to cover over a year.

Example:

• Your home uses 12,000 kWh per year

• Your solar system is designed to produce 9,000 kWh per year
  
  

That system has a 75% offset.

It does not mean:

• your bill goes to zero

• you stop using the grid

• solar “doesn’t work” unless it’s 100%
  
  

It simply means solar is replacing a portion of the electricity you would otherwise buy from the utility.

Why Solar Systems Aren’t Always Sized for 100% Offset

A 100% offset sounds ideal — and in some cases, it makes sense. But there are very real reasons many systems are intentionally designed below that threshold.

1. Roof Constraints Are Real

Not all roofs can physically support enough panels to offset 100% of usage.

• setbacks reduce usable space

• shading limits productive areas

• roof orientation affects output
  
  

Designing around these realities often leads to a smaller, more efficient system instead of forcing panels into poor locations.

2. Diminishing Returns at the Margins

The first panels installed usually go on the best-performing roof planes.

As you try to push toward 100% offset:

• panels move to less productive areas

• cost per kWh often increases

• overall efficiency can drop
  
  

That last 10–20% of offset is frequently the most expensive electricity your system produces.

3. Usage Changes Over Time

Solar systems are designed using historical usage, but life isn’t static.

• families grow or shrink

• work-from-home changes load

• efficiency upgrades reduce usage

• EVs and heat pumps increase usage
  
  

Designing for a flexible, realistic offset often makes more sense than chasing a perfect number based on today’s snapshot.

Why Partial Offset Is Still a Big Win

This is the most important part.

If your solar system offsets any portion of your usage, it means:

• fewer kWh purchased from the utility

• less exposure to future rate increases

• more predictable long-term energy costs
  
  

A 60–80% offset can still:

• significantly reduce your bill

• stabilize your energy costs

• deliver meaningful savings over time
  
  

Waiting for a “perfect” 100% solution often results in years of paying full utility rates instead.

Offset vs. Cost per kWh (The Better Comparison)

Offset is helpful — but it’s not the only metric that matters.

What actually determines value is:

What do you pay per kWh for solar electricity vs. what you pay per kWh from the utility?

A smaller, efficient system with a strong cost-per-kWh comparison can outperform a larger system that:

• relies on poor roof planes

• costs more per unit of energy

• stretches beyond practical design limits
  
  

This is why many modern solar designs — especially lease-based systems — focus on efficient offset, not maximum offset.

Why Offset Looks Different With Solar Leases

With leased solar systems, the goal is not asset ownership — it’s energy replacement.

Leases are typically designed to:

• offset the most expensive or most predictable portion of usage

• deliver immediate monthly savings

• minimize long-term maintenance responsibility
  
  

Because of recent changes to residential incentives and tax credit availability, many homeowners are now prioritizing:

• immediate savings

• price stability

• simplicity over ownership
  
  

In that context, a system that offsets 70–85% of usage at a strong solar cost per kWh can be more attractive than a larger ownership-focused system built around long-term incentives.

Why “Doing Nothing” Is the Worst Offset of All

It’s worth saying plainly:

• 0% offset means 100% exposure to utility rates

• every future rate increase affects all of your usage

• there’s no hedge against long-term cost growth
  
  

Even a modest solar system reduces that exposure immediately.

Solar doesn’t have to be all-or-nothing to be worthwhile.

The Right Question to Ask

Instead of asking:

“Why isn’t this system 100% offset?”

A better question is:

“Does this system efficiently replace the most expensive and predictable portion of my electricity usage?”

That’s where real value lives.

The Bottom Line

Solar offset is a tool — not a scorecard.

A well-designed system balances:

• roof constraints

• production efficiency

• cost per kWh

• long-term flexibility
  
  

Partial offset is not a compromise — it’s often the smartest path forward.

If you’re reviewing a proposal and want help understanding whether the offset makes sense for your home, VirginiaSolar.org can help translate the numbers and assumptions before you decide what comes next.