The Texas TDU Audit: How Solar Buyers Find $400+/year in Hidden Delivery Charges

Texas TDU charges are 30–40% of your electric bill. Solar does not touch most of them. Here is how to audit your bill, calculate what solar actually saves, and avoid signing for math that does not exist.

Every Texas solar installer's proposal includes a "monthly savings" or "bill elimination" number. Almost none of those numbers correctly account for the part of your bill that solar does not touch: TDU delivery charges. Understanding the TDU portion of your bill is the single highest-leverage thing you can do before signing a Texas solar contract.

How Texas electric bills are actually structured

In Texas (outside Austin Energy and a few municipal utilities), your electric service has TWO separate companies billing you on one bill:

  • REP (Retail Electric Provider): The company you chose — Reliant, TXU, Cirro, Gexa, etc. They bill you the "energy charge" — what you pay per kWh of electricity consumed. Solar offsets this directly.
  • TDU (Transmission & Distribution Utility): CenterPoint, Oncor, AEP, or TNMP depending on your area. They bill you the "delivery charge" — what you pay for the physical infrastructure that brings electricity to your meter. Solar offsets almost none of this.

The REP charge is what most solar proposals model. The TDU charge is what most solar proposals ignore.

What TDU charges look like on your bill

Pull out a recent CenterPoint or Oncor bill (or whichever TDU serves your area). Look for these line items:

  • Customer service charge (flat, ~$5–$10/month)
  • Distribution charge ($/kWh consumed, ~$0.02–$0.04)
  • Transmission charge ($/kWh consumed, ~$0.01–$0.02)
  • Metering / various fixed charges (~$2–$5/month)
  • Various pass-through fees and riders

For an average Texas household consuming 1,200 kWh/month, TDU charges run $50–$75/month — about $600–$900/year. Solar offsets the consumption-based portion (because lower import volume = lower delivery charge) but cannot offset the fixed monthly portion AT ALL.

The audit: do this before signing any solar contract

Pull 12 months of past electric bills. For each month, separate:

  1. Total bill amount
  2. kWh consumed
  3. REP energy charges (what solar offsets)
  4. TDU consumption-based charges (solar offsets proportionally)
  5. TDU fixed monthly charges (solar offsets ZERO)

Sum line 5 across 12 months. That is your annual unavoidable cost — the bill you will still have after even a perfectly-sized solar system covering 100% of your consumption. For most Texas households, this is $300–$600/year that no installer's "bill elimination" claim acknowledges.

How this changes the payback math

An installer who quotes you a 7-year payback assuming 100% bill elimination on a $25k system is implicitly claiming $3,571/year in savings. If your real savings (after TDU floors) is $2,800/year, your actual payback is 8.9 years. That is a 25% error.

Multiply across the 25-year system life and the difference is $19,000+ in overstated savings.

What to ask Texas installers

Demand the proposal show three lines:

  1. Year-1 actual bill (after solar, with TDU charges remaining)
  2. Year-1 actual savings (today's bill minus the above)
  3. Annual savings escalation assumption (this is where installers often pad with aggressive utility-rate-increase assumptions)

If the installer can't break this out clearly, they are either using marketing math or genuinely don't understand TDU charges. Either way, get a second opinion.

Honest broker take: The TDU audit is the single most expensive question most Texas solar buyers fail to ask. reviewingsolar.com runs the audit for free.