PCWattVault — User Guide

PCWattVault shows you, live, how much electricity your PC is drawing and what it costs you — and it keeps recording in the background so you always know what your computer added to the power bill: today, this month, this year.

Everything happens on your own machine. There are no accounts, no cloud and no telemetry; your data never leaves your PC.

Installation

From the Microsoft Store — search for “PCWattVault” and install. Done.

From pcwattvault.com — download the installer and run it. During installation you will be asked to approve the PawnIO driver (a Windows UAC prompt): this is a small, digitally signed, open-source kernel driver that lets the app read your CPU’s power and temperature sensors on modern Windows. It is optional — the app works without it — but CPU readings are estimates until it is installed. The Microsoft Store edition does not include the driver; see “Sensor sources” below for the alternative.

First run

PCWattVault starts reading your hardware immediately. Three things worth knowing on day one:

• The window closes into the tray. Closing the window does not stop the app — it keeps recording in the notification area (that is the whole point: the history must not have holes). To really quit, right-click the tray icon → Quit.
• “~” means estimated. Values marked with a tilde are model estimates, not sensor readings — see “Accuracy” below for how to improve them.
• A yellow “Demo data” banner means the app could not reach any real sensor source and is showing synthetic numbers so you can explore the interface. Demo data is never saved to your history.

Sensor sources

The app picks the best available source automatically:

1. Bridge (desktop edition) — the bundled sensor engine, richest data. For real CPU package power it needs the PawnIO driver and administrator rights; the app shows a one-click banner if either is missing.
2. LibreHardwareMonitor web server — if you already run LibreHardwareMonitor, enable Options → Remote Web Server in it and PCWattVault will use it. This is the recommended setup for the Microsoft Store edition. The LibreHardwareMonitor installer also sets up the PawnIO driver it needs, and PCWattVault detects a running web server and switches to it automatically — nothing else to configure.
3. Demo — synthetic fallback so the UI is never dead.

Set up your tariff (2 minutes, worth it)

Out of the box the app uses a default price per kWh. For real money figures open Settings → Electricity tariff:

• Currency — pick from the list, or “Custom…” for any ISO code.
• Default price per kWh — you will find it on your electricity bill, usually stated in cents or your currency per kWh. Include taxes and network charges per kWh if you want all-in figures.
• Night/weekend prices — add a time-of-use rule per window (e.g. 23:00→07:00 at a lower price). Rules can be limited to specific weekdays and months (seasonal tariffs).
• Tiered pricing — if your utility charges by monthly consumption brackets, define the tiers; the household baseline field tells the app how much the rest of your home consumes so your PC lands in the right bracket.
• Solar / net metering — an optional price reduction during your production hours.
• Demand charge — if your contract bills the monthly peak kW.

Reading the dashboard

• Current draw — your PC’s wall-socket power right now. “PSU-measured at the wall” means it comes from a real measurement (digital PSU or smart plug); otherwise it is the sum of the component sensors plus base load, divided by your PSU efficiency.
• Cost rate — what one hour at the current draw costs, at the tariff active right now.
• Today / This month — recorded consumption so far.
• Month-end forecast — where the current calendar month will land: what is already recorded plus the average of your recent days for the days remaining.
• “At current draw — if it ran 24/7” — a live extrapolation of the present wattage. It answers “what if I left it like this?”, not “what will I actually pay?” — that is the forecast’s job.
• Live chart — wall power over time, from 5 minutes to 24 hours. The buffer fills even while the window is hidden.
• Top power consumers — each device with its own power reading (every GPU separately, CPU, drives…), ranked live. Estimated entries carry “~”.

History, predictions and exports

The History & Costs page shows hourly (today), daily (30 days) and monthly (12 months) charts in kWh or money, a per-component breakdown, and lifetime totals.

After ten complete days of recording you also get predictions for next month and next year, shown as ranges (“€24–31”). They come from a regression over your recorded days with day-of-week awareness. They are labelled indicative for a reason — treat them as a compass, not an invoice.

A note on the numbers. Everything PCWattVault shows — costs, forecasts, predictions — is an estimate intended for guidance. The app is not a billing instrument: your actual electricity bill is determined solely by your utility’s certified meter and your contract. Even with a smart plug attached, small deviations from the utility meter are normal. Do not rely on these figures for billing, cost sharing between people, or financial decisions.

Accuracy: making the numbers honest

The software model is good, but two settings make it yours (Settings → Power model):

• PSU efficiency — 88% is a sensible default for a Gold unit at typical load. Check your PSU’s 80 PLUS rating.
• Base load — watts for everything that has no sensor: motherboard, fans, pumps, RGB, USB devices. Default 20 W; well-equipped systems often sit at 40–60 W.

The gold standard is a real wall measurement — a digital PSU (Corsair iLink / NZXT) or a Tapo smart plug (Pro). The next section explains exactly what happens when you connect one.

Smart plug: real measurements and auto-calibration (Pro)

Connecting a Tapo P110/P115

1. Plug your PC into the Tapo. Whatever is on the plug is what gets measured — for PC-only accuracy, put only the PC on it. If your monitor and speakers share the plug, their watts will be counted (and calibrated) into the PC's figures — fine if that is what you want to track, just know it is a choice.
2. In the Tapo app, open your plug → ⚙ → Third-Party Compatibility and enable it. TP-Link requires this one-time step before any third-party app (PCWattVault, Home Assistant, …) may talk to the plug on your own network — without it, the connection test below fails.
3. Open Settings → Smart plug: enter the plug's IP address (Tapo app → your plug → Device Info) and your TP-Link account email and password, then press Save credentials & test. You should see a reply like “✓ P110 — 312.4 W right now”. The credentials are needed because that is how Tapo authenticates apps on your own network; they are stored encrypted on your PC and never sent to the internet.
4. Tick Use the plug's wall reading and save.

What changes when the plug is connected

• Live watts become a measurement. The dashboard badge switches to “PSU-measured at the wall”, and your history and costs are recorded from the real wall reading instead of the model. Note that the prices never change — cost is always wall watts × your tariff; the plug makes the watts (and therefore the money) accurate.
• The software model keeps running silently in the background as a fallback and for the calibration comparison below.
• If the plug drops off (Wi-Fi hiccup, unplugged…), the app waits a few seconds and hands back to the model automatically — history never gets a hole, and no stale number is frozen on screen. When the plug returns, the measurement takes over again by itself.

The calibration bar

While a wall measurement is active, the dashboard shows a small bar: measured (the plug) vs model (what the software would have said) and their average gap over the last few minutes.

If the average gap is meaningful, a one-click button appears — “Tune base load by +36 W” — which folds the observed difference into your base-load setting. That is the point of the whole exercise: after one click, the model itself becomes honest, so your numbers stay realistic even when the plug is offline, and even if you later remove it entirely.

Tips for a good calibration:

• Do it during typical, steady use (a few minutes on the dashboard at your normal desktop load — not mid-benchmark, not during a spike).
• The gap naturally varies a little with load, because PSU efficiency is a curve, not a constant. Calibrating at your everyday load gives the best overall fit; you can repeat it whenever the button reappears.
• A large gap is not a bug — it usually means your base load (fans, pumps, RGB, USB gear) was underestimated, which is exactly what the button corrects.

Transparency note

PCWattVault is an independent application: it is not affiliated with, endorsed by, or in any commercial relationship with TP-Link. TP-Link and Tapo are trademarks of TP-Link Corporation. The integration talks to the plug through its local device interface — the same community-established approach used by Home Assistant, openHAB and similar projects. TP-Link officially permits third-party local access (that is what the Third-Party Compatibility switch is for) but does not publish this protocol, so treat the feature as best-effort: if a future TP-Link firmware change breaks it, PCWattVault's software model takes over automatically until an update adapts.

Pro features (optional)

The free app is complete — tariffs, history, forecasts, predictions, themes, languages. On top of that, PCWattVault Pro adds:

• Alerts — Windows notifications when temperature, wall power or daily cost cross your thresholds. Anti-spam built in.
• Sessions — “what did this gaming night / render / training run cost?” Start from the dashboard or the tray; every session records kWh, cost, peak and average watts.
• Reports & export — Excel-friendly CSV, and a monthly PDF report with charts, tariff summary, predictions and a CO₂ line.
• Smart plug — connect a TP-Link Tapo P110/P115 and your history is recorded from real wall measurements. Your TP-Link credentials are stored encrypted on your PC and are used only to talk to the plug on your own network — never sent to the internet.

Right now, all Pro features are free. While PCWattVault is young, every user automatically receives a Founder / Early-Adopter license. And this is a promise, not a trial: if Pro ever becomes a paid upgrade for new users, founder licenses stay free — forever. Nothing to do on your side; you can see yours under Settings → PCWattVault Pro.

Your data

Everything lives in plain JSON files under your user profile (About → Open data folder): hourly energy and cost aggregates per component category — no raw per-second samples, so nobody can reconstruct your minute-by-minute activity. Copy the folder to back it up; delete it to start fresh. There is no telemetry of any kind.

FAQ & troubleshooting

CPU shows “~” or 0 W. The CPU power sensor needs the PawnIO driver and administrator rights (desktop edition — the banner sets both up), or the LibreHardwareMonitor web-server source. Until then the app estimates CPU power from load — that is the “~”.

The app “doesn’t close”. It minimises to the tray by design so history has no holes. Right-click the tray icon → Quit, or disable Settings → Behaviour → Keep recording in the tray.

My NVMe temperature looks different from the vendor tool. PCWattVault shows the official composite sensor — the same one Samsung Magician & co. display. Some tools show the controller hotspot instead, which legitimately runs 20–30 °C hotter.

Two GPUs? Each appears separately, with its own power draw, in Top consumers and Components.

Sleep and hibernation are never billed — gaps in time are detected and excluded from the energy integration.

Uninstalling (desktop edition) keeps your history unless you delete the data folder yourself; the Store edition’s data is removed by Windows on uninstall.

Privacy

The full inventory of what is stored (and what is not) lives at pcwattvault.com/privacy. The short version: everything stays on your machine.