Comment by mikestew | Hacker News Reader

Comment by mikestew | Hacker News Reader

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Picking a daily perfect value and assuming that value scales to all days is not a good estimate.

What I'm seeing on this topic is a lot of folks that I can only assume have never spec'ed out and actually used a solar installation. Go throw some panels on the roof of your house and RV, and then we can talk about how "all we have to do" is put panels on a passenger car. Not one of the "all ya have to do" crowd has mentioned how efficient their solar installation is, how the math works. Nope, it assumes a spherical cow, yada, yada, yada, and the sun is always pointing at a direct 90 degree angle to the panel.

The 410W on our RV, for example, is good for recharging the house battery after running the microwave to make breakfast. If it's cloudy, you won't get to run the microwave for supper, but at least the lights can stay on. The most I've ever seen come out of that installation was 390W. I've not looked that hard at the charts, but I'd assume on average maybe 200W. A cloudy Seattle day? That's when we're glad we bought the bigger house battery.

Curious how many kwh per day, roughly, you're seeing on that 410w solar?

I can't get you really good numbers without some work, but what I did do was look back when I knew it was not covered, and when we were actively using it regularly, and when the Seattle sun was at it's best: June and July. In other words, give the most charitable number possible. For reference, the panels sit flat on the roof and I do not adjust them during the day.

With some quick-and-dirty visual estimates from the charts, I'm coming up with about .85kWh/day. Yeah, I know, but I looked at it twice. I went back and looked at some other time periods as a sanity check. And <1kWh/day is what we get. In the summer. Right now the RV is sitting in the drive with the panels uncovered, and the driveway is sloped and slightly angling the panels to that sad little January-in-Seattle sun. Yesterday the panels cranked out a massive 0.1kWh. That's right: enough to run a 100W light bulb for an hour.

Despite all that, it's enough to run the microwave a couple of times a day (which is really the only large draw the RV has), watch some TV, run the lights at night. And if the panels can't keep up, that's what the giant-ass 300ah lithium house battery is for.

Sorry, what does RV stand for? Thanks

“Recreational vehicle”. Large camper, caravan, motor home.

Generally speaking that 100w light bulb was probably replaced with an LED 20 years ago and now consumes 10w and runs for 10 hours.

Well, yeah, it's just a "Library of Congress" measurement that is probably long past its expiration date. The entire vehicle's interior lighting is LED; on the monster house battery it has, you could probably keep it well-lit for weeks.

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