Electricity bills are rising across most of the developed world. Residential electricity prices in the EU increased by over 40% between 2019 and 2024. In many countries, the combination of solar panel cost reductions (prices dropped ~90% over the last decade), falling battery storage costs, and rising grid tariffs has crossed a threshold: generating and storing your own electricity is now economically rational for a large fraction of households.
Yet most guides to home solar and storage are either superficially optimistic (“pay back in 5 years!”) or technically overwhelming. This book occupies the middle ground: it treats you as an intelligent adult who wants to understand the numbers, do the math, and make an informed decision.
The approach throughout is quantitative. Every chapter leads with data tables and follows with worked examples. By the end, you will have a complete toolkit for sizing a system, estimating its output, and projecting the economics for your specific household.
Before any numbers make sense, you need command of the units. This section is short but essential.
Power (W, kW) is the rate of energy use at a given instant. Energy (Wh, kWh) is power integrated over time — the actual quantity consumed or produced.
A 2 kW electric kettle running for 5 minutes consumes 2000 W × (5/60) h = 167 Wh ≈ 0.17 kWh.
The distinction matters because:
| Unit | Equals | Typical use |
|---|---|---|
| 1 W | — | Small appliances, LED bulbs |
| 1 kW | 1,000 W | Household appliances, panel ratings |
| 1 MW | 1,000 kW | Small commercial, grid scale starts here |
| 1 Wh | 1 W for 1 hour | Very small amounts |
| 1 kWh | 1,000 Wh = 1 kW for 1 hour | Standard billing unit |
| 1 MWh | 1,000 kWh | Annual consumption of a small household |
Your utility connection is often rated in kVA (kilovolt-amperes, apparent power). The relationship to real power (kW) involves the power factor:
kW = kVA × power factor
For resistive loads (heating, incandescent bulbs): power factor ≈ 1. For motors and electronics: power factor is typically 0.8–0.95.
A typical residential connection in Europe is 9 kVA (France: 6, 9, or 12 kVA subscription levels). This limits the peak simultaneous draw of all appliances.
A peak sun hour is one hour of sunlight at an irradiance of 1,000 W/m² (the standard test condition for solar panels). Real irradiance varies throughout the day and year, but PSH is a convenient normalization:
Daily energy yield (kWh) = Panel rated power (kWp) × PSH × system efficiency factor
A location receiving 4.5 PSH/day on average means a 1 kWp system produces roughly 4.5 × 0.8 = 3.6 kWh/day (applying an 80% system efficiency factor for realistic losses).
For batteries:
Most lithium batteries should not be discharged below 10–20% SoC. A 10 kWh battery with 90% max DoD has 9 kWh usable capacity.
If you want to understand your bill first, read Chapters 1–3 before anything else. Chapter 2 alone — the appliance reference table — answers most “where does the electricity go?” questions.
If you are sizing a solar system, Chapters 4–5 are your core reference. You need Chapter 3’s consumption profile as an input.
If you are evaluating battery storage, Chapter 6 is self-contained once you have a consumption profile (Chapter 3) and optionally a solar production profile (Chapter 4).
If you are optimizing an existing system, Chapters 7–8 cover tariff strategy and dispatch logic.
If you are deciding on hot water technology, Chapter 9 can be read independently.
If you want the full picture for a specific household type, jump to Chapter 10 for pre-worked scenarios, then Chapter 11 for the economics.
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