Guides
Longer explanations of the numbers behind the tools on this site: where a solar production estimate comes from, how roof direction and climate change it, when homes use electricity, which clock solar data runs on, which stadium seats end up in the sun, and how NOAA predicts the tide.
How much energy will my solar panels actually make?Where the kWh number on your solar quote comes from — sun position, irradiance, roof orientation, shade, panel temperature, and inverter clipping — and how to tell whether it’s real.Read the guide →Is solar a good investment? What it costs and what the power is worthWhat home solar costs at $3.36 a watt, what its power is worth under each state’s export rules, and how long it takes to pay back in ten states.Read the guide →Should you get a battery for your solar installation?A home battery saves money when evening power costs far more than midday exports earn. Modeled savings for 40 Bay Area homes under four export rules.Read the guide →Why west-facing solar panels fall further behind east-facing ones in north Florida than near PhoenixIn north Florida a west-facing roof plane gets about 5% less sunlight a year than an east-facing one and 11% less in summer; near Phoenix the gap is about 1%.Read the guide →When homes use electricity: hourly load by heating fuel and climateHow heating fuel, floor area and climate shape a home’s hourly electricity use, and why solar sized to a year’s use supplies only 33% to 50% of it directly.Read the guide →Why solar noon is rarely at 12:00, and which clock your solar data usesSolar noon in Boston, Detroit and Amarillo falls between 11:28 a.m. and 1:58 p.m. on the clock, and solar, load and rate data each follow their own clock.Read the guide →How tide predictions workA NOAA tide prediction is a sum of up to 37 cosine waves timed by the moon and sun and fitted to years of gauge data; five of them carry most of the tide.Read the guide →Which stadium seats get sun and which get shadeSeats go into shade when the sun is at their backs, so the direction a field points and the sun’s position at game time decide who sits in sun.Read the guide →