Solar & energy

Solar output is driven by three things: peak sun hours, orientation, and shading. Peak sun hours (PSH) is a normalized number — how many hours per day your location averages 1,000 W/m² of sunlight. Phoenix runs about 6.5 PSH; Seattle about 3.5; a US average is roughly 4.5. NREL's PVWatts calculator gives your exact number by ZIP.

Orientation and tilt: in the northern hemisphere, panels face true south (not magnetic south — declination matters), tilted roughly equal to your latitude. Off by 15° in either direction costs about 3% annual output. Off by 30° costs about 10%.

Shading is the killer. A single leaf across one cell can drop a whole panel's output by 30–70% because cells wire in series. Map shadows across the seasons — a bare tree in December casts a very different shadow than one in leaf in July. Use a $30 sun-hours meter or the free Sun Seeker app.

Every off-grid solar system has four parts. Panels convert sunlight into DC electricity. A charge controller (MPPT is the modern standard — 20–30% better than PWM in cold and cloudy weather) regulates that current into the battery bank safely. The battery bank stores it. An inverter converts DC to 120V AC when you need to run standard household appliances.

Batteries are where budgets die. Lead-acid AGM (Group 27 or Group 31) is cheapest to buy but only cycles ~500 times to 50% depth and hates freezing. LiFePO4 (lithium iron phosphate) costs 2–3× more but cycles 3,000–6,000 times to 80% depth, weighs a third as much, and handles cold. Over 10 years LiFePO4 is cheaper per kWh cycled.

For a garden system, 12V is the sweet spot up to about 1,500W of loads (pumps, LEDs, fans, laptops). Above that, step up to 24V or 48V to keep wire gauge sane and losses low. Match your inverter's voltage to your battery bank.

Sizing is arithmetic, not intuition. Step 1 (load audit): list every device, its wattage, and hours of run time per day. Multiply for each; sum for total daily watt-hours (Wh). A 20W LED coop light × 12 hrs = 240 Wh; a 60W water pump × 2 hrs = 120 Wh; a 30W laptop × 4 hrs = 120 Wh. That's 480 Wh/day.

Step 2 (array + battery sizing). Array: total Wh/day ÷ peak sun hours ÷ 0.75 system efficiency = watts of panel. Battery bank: total Wh/day × days of autonomy (2–3 for critical, 1 for luxury) ÷ depth of discharge (0.5 AGM / 0.8 LiFePO4) = battery bank Wh.

Example: 480 Wh/day, 4.5 PSH, LiFePO4 bank, 2 days autonomy. Array: 480 / 4.5 / 0.75 = ~142W. Round to a 200W panel. Battery: 480 × 2 / 0.8 = 1,200 Wh. That's a 12V × 100Ah LiFePO4 battery. Total budget for the electrical guts: ~$800.

The simplest garden solar setup skips the batteries entirely: a solar panel wired directly to a DC diaphragm or centrifugal pump that runs when the sun is shining. Cost: $150–$300 for a 100–200W panel and a matching pump. Perfect for filling a stock tank, transferring rainwater to a drip system, or slow-circulating a small pond.

For pressurized drip irrigation, use a 12V RV-style diaphragm pump (Shurflo 4008 or equivalent). It pushes 45 psi at 3 gpm — plenty for a home garden's drip zones. Wire it through a pressure switch so it cycles on demand. Add a small battery + charge controller if you want to run it after sunset.

For deeper wells (>25 ft), solar submersible pumps (Grundfos SQFlex, Sun Pumps SDS) run $1,200–$3,000 and pump 5–20 gpm from wells up to 400 ft. Combined with an elevated 500-gallon storage tank, you get gravity-fed irrigation with zero grid dependence.

The two loads that transform a backyard coop: a low-wattage LED on a timer to keep hens laying through short winter days (they need ~14 hrs of light for consistent egg production), and a summer ventilation fan. Both run on 12V, both are trivial to solarize.

A 20W LED bar × 4 hrs supplemental winter light = 80 Wh/day. A 5W 4-inch DC fan × 8 hrs of summer runtime = 40 Wh/day. Combined: 120 Wh/day. A 100W panel + 30Ah LiFePO4 + $30 charge controller handles both with margin. Total budget: ~$200–$250.

Mount the panel to the coop roof (south face, matching the roof pitch or tilted separately if the pitch is wrong). Run 10 AWG DC wire to the controller inside. Use an automotive-style fuse block and inline fuses on every circuit — a mouse chewing a wire in a coop is when-not-if.

Passive solar isn't panels — it's design. A well-oriented cold frame, hoop tunnel, or greenhouse uses the sun as a direct heater, storing daytime warmth in thermal mass (water, stone, concrete) to release it overnight. On a bright winter day, a south-facing cold frame can hit 80°F while it's 30°F outside.

Three moves make or break a passive-solar structure. Orient the glazing (glass, twin-wall polycarbonate, greenhouse film) to face true south, tilted 60–75° for winter sun capture. Insulate the north wall — a solid, insulated back reflects light forward and holds heat. Add thermal mass: 55-gallon barrels painted flat black and filled with water, stacked against the north wall, moderate overnight temperature swings by 15–20°F.

For serious season extension, layer strategies. A greenhouse + row cover inside a hoop bed + heavy mulch = zone 5 winter production of spinach, kale, arugula, and mâche. Eliot Coleman's four-season farm in Maine runs on exactly this stack, no supplemental heat.

Low-voltage DC solar systems under about 100W and stand-alone from the house (a coop kit, a pump kit, a portable panel + battery) generally need no permit in most US jurisdictions. Follow common sense: fuse every circuit, ground metal frames, use exterior-rated wire, keep batteries in a ventilated enclosure.

Once you're tying to the house electrical panel — batteries powering an inverter that feeds AC breakers, or grid-tied panels selling back to the utility — you're in NEC (National Electrical Code) territory. Requires permits, licensed electrician sign-off, utility interconnection agreements, and inspection. Do not DIY this even if you're capable; a bad connection can back-feed the grid and kill a lineman.

Batteries deserve extra respect. Lithium batteries in fire or thermal runaway release toxic gases and burn hot enough to melt aluminum. Locate battery banks outside living space when possible, in a vented enclosure, on a non-combustible surface, with a Class C fire extinguisher within reach. Never store gasoline near batteries.