Part I: Start HereChapter 1. Reading Your Site
Why Build Your Own Solar? Costs, Payback, and Satisfaction
A plain accounting of money, time, and the reasons people still build collectors by hand.
- Difficulty
- Beginner
- Cost
- Free
People build a collector for three different products, and they get into trouble when they pretend there is only one. The first product is fuel you do not buy. The second is a room that is pleasant while the sun is out. The third is the skill of having measured something and made it work. A project can be worth doing for the second or the third even when the first is small. It is not worth doing because a stranger's payback, in a different climate, got repeated until it sounded like a fact.
The site survey tells you whether the sun is even available. The first-project flowchart turns this accounting into a choice.
Difficulty
- Level
- Beginner
- Time
- An evening with bills and a notebook
- Skills
- Comparing a fuel bill with a materials list
Cost estimate
Free
The decision is free. The projects it points to are not. A weekend air heater can land under about $110. A permitted photovoltaic system is a construction project, and the module price is not the system price.
Materials
| Item | Qty | Notes |
|---|---|---|
| A year of energy bills | 1 | Kilowatt-hours, therms, gallons. Dollars come second. |
| A materials list for the project you are tempted by | 1 | Include valves, controls, and the permit, not only the glamorous part. |
| An honest hour count | 1 | Your weekends, including the one you will spend fixing the leak. |
What cash payback can and cannot say
Payback is the cost of the job divided by the money it saves in a year. It is simple, and it hides three choices. You have to say which fuel, at which price, and what happens if that price changes. You have to say whether you would have bought that fuel anyway. A solar air heater in a room you were happy to leave cold does not pay back in dollars. It changes the room. Count that as comfort, not as a therm.
Conservation usually beats a collector on payback in a house that still leaks. The air sealing weekend is often tens of dollars. The insulation payback page shows why the first inches of insulation save more than the last. On a house that has not done those steps, a collector is a hobby bolted onto a house that is still losing money.
A handmade water or air heater can be cheap because you are the labor. Price your labor at zero only if you like the work. If you are giving up paid time, put a number on the hours and see whether the project still interests you. Many still do. The number is there so you are not surprised.
Installed solar electricity and installed hot water include racking, electrical gear, plumbing, and someone who will sign the permit. That invoice and the cost of plywood and a sheet of polycarbonate pay for two different products, so setting them side by side tells you little. Use the PV sizing guide when the goal is the electric bill, and expect the interconnection and the electrician to be part of the cost.
A fair way to write the number
- Write the annual fuel the project might touch. Space heat, or hot water, or electricity. Not the whole bill if the project only warms one room.
- Write a modest fraction you believe the project can cover. A window heater covers sunny hours in one room. It does not cover a January night.
- Multiply by the price per therm or per kilowatt-hour. That is the annual dollar guess.
- Divide the full project cost by that guess. If you left out the tempering valve, the damper, or the permit fee, the payback is fiction.
- Do it again with a fuel price one third lower. If the project only makes sense at the high price, say so.
Do not copy a payback from another state. Degree days, electric rates, and sun hours move the answer by more than the precision of the arithmetic. The degree-day guide is how weather gets into a heat estimate.
Satisfaction, stated plainly
A finished collector you can put your hand in front of teaches more than a quote. That is a real outcome. It does not justify a roof you are not safe on, a gas valve you are not qualified to open, or a system that will freeze the first night you are away. Keep the projects small and the satisfaction is more likely to outweigh the regret. The window heater, a shade awning, and a sealed attic hatch are small. A glycol loop and a service-panel interconnection are not first projects.
Separate the bill into pieces
Space heat, hot water, and electricity. A project has to name which piece it touches.
Write the full cost
Materials, the safety parts, and a permit if the work needs one. Add hours if your time is scarce.
Cut the savings claim in half
Then see if you still want to build it. Projects that survive a humble claim are the ones to start.
Prefer a cheap failure
The first build should be one you can abandon without a crane or a plumber on emergency rates.
Further reading
These links go to outside sources. This book cites them by link and does not copy their words or pictures.
- https://www.builditsolar.com/SiteSurvey/site_survey.htm
- https://www.builditsolar.com/SiteSurvey/FindingSouth.htm
- https://www.builditsolar.com/SiteSurvey/MagDecl.htm
- https://www.builditsolar.com/SiteSurvey/StepByStep.htm
- https://www.builditsolar.com/SiteSurvey/challenges.htm
- https://www.builditsolar.com/GettingStarted/GettingStarted.htm
- https://www.builditsolar.com/GettingStarted/ChoosingProjects.htm
- https://www.builditsolar.com/References/SunChartRS.htm
General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.