Methodology: How We Research and Verify
Which sources we use, how a guide is checked before publication, what the dates on each page mean, and how often we re-verify.
A guide to plug-in solar is worth only as much as its sources and its date. This page describes how a guide comes about at Voltgeber, what the labels Published, Updated and Last verified mean, and when we mark a guide as in review.
Source hierarchy
We distinguish three tiers of sources and cite the highest tier we can find for every claim:
- Primary sources. Statutes and enrolled bills from state legislatures and the federal government, agency publications such as those of the IRS, public utility commissions, state energy offices and the German Federal Network Agency, standards from UL, the NFPA (publisher of the National Electrical Code) and the VDE, utility tariffs, and the rules of rebate programs.
- Expert secondary sources. National laboratories such as NREL, universities such as HTW Berlin, consumer organizations such as the German Verbraucherzentrale, and bill trackers maintained by nonprofits such as Bright Saver.
- Press and manufacturer claims. Only for context, never as the sole basis for a legal claim or a figure.
Every guide lists its sources at the end with the date of access. Prices and market figures carry, in the text, the month in which we observed them.
Four steps to publication
- Research and draft. We identify the question behind a search, collect the primary sources and write the draft.
- Source verification. In a separate pass, every figure, deadline and legal statement is checked against the listed sources. What cannot be verified is removed or marked as uncertain in the text.
- Language pass. Terminology, tone and readability are checked; technical terms are explained on first use, and for Germany-related guides the German term is given alongside the English one.
- Automated checks. Before every publication, our software checks that sources are present, internal links resolve and the language versions are linked correctly.
We use software for research, drafting and checking, including AI-assisted tools. The editorial team is responsible for every publication, and no guide goes live without the source verification.
What the dates mean
- Published: the day of first publication.
- Updated: the day of the last change to the content.
- Last verified: the day on which every claim was last checked against the sources, even if nothing changed.
A guide marked as in review is published but has not yet completed the source verification. We show that label rather than hide it.
How often we re-verify
| Type of guide | Verification interval |
|---|---|
| Rules, laws and registration | every six months, or when a law changes |
| Rebates and subsidies | every three months |
| Cost and payback | every six months |
| Technology and mounting | every twelve months |
When a law changes, the affected guides are moved to the front of the queue. The year in a guide’s title describes the state of the rules, not the year of publication; the address of the guide stays the same.
Corrections
We correct errors in the guide and update the date. For corrections that change the substance, we add a note in the text. Reports go to kontakt@voltgeber.com.