Author Topic: Wacky PV stuff  (Read 2260 times)

PonoBill

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Wacky PV stuff
« on: March 04, 2024, 09:59:00 AM »
It seems like everything I know needs to get upgraded every few years. For decades the gold standard for PV was installation on a slanted roof facing south, or if you had a flat roof, then racks, carefully angled to catch midday sun at a perpendicular angle. Then east/west roofs became popular. If you look at the output curve of a properly angled south-facing panel it's a single hump, with a maximum at midday tailing off to not much at all in the morning and evening. Here's what the panels at Ponohouse produce. I've never washed those buggers, I need to:

The sun angle at anything past noon is not optimal, so you don't get continuous generation. Your wiring, controllers, battery charger, inverters, etc. need to be sized for the peak, which lasts less than an hour. Conversely, panels on an east-west orientation have humps at morning and evening, depending on which side they are mounted. When panels cost bazillions, they were the expensive part of the system. Now they cost less per watt than an English muffin, so flattening out the curve makes sense. They benefit from being mounted more steeply to catch the low-angle sun, but it works like gangbusters and you don't need to upgrade the rest of the system.

Cool. But now we have Bifacial panels that are dirt cheap. They benefit from being mounted freestanding in a vertical position east/west so one panel does the work of two. They generate almost nothing at midday but do well for the rest of the day. Shading is tricky, but then it always is. They work best in a mixed installation where there are a more or less equal number of south-facing panels, depending on latitude. Shortly there will be panels optimized for vertical east/west installation that also take advantage of lower reflection, but current bifacial panels work fine. Current panels peak out at about 22% of the theoretical solar energy available regardless of installation because most of the sunlight gets reflected.

There's more. Current solar plus battery tech has crept up from 6V to 12V to 48V, driven mostly by the wire size necessary to deliver significant wattage and power expectations. Now it makes sense to use something like 400 V (the voltage of most EV batteries) because it's easy to get with ten or so PV panels in series and the wire size required is modest (current determines wire size, 1000 watts at 12 volts is 83 amps, meaning you need wire thicker than the battery cable in your car, at 400 V it's 2.5 amps). So basically, everything I learned from fiddling with Solar over the last few decades is now wrong. ....very weak Yay!
« Last Edit: March 04, 2024, 10:58:14 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

sflinux

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Re: Wacky PV stuff
« Reply #1 on: March 04, 2024, 05:50:00 PM »
Interesting.
I am curious if cleaning will have any affect on performance.  My work had a traditional panel array cleaned, after a decade of use. and saw no change in performance.
They did see a big improvment in performance during the summer compared to winter months.
I monitored the logs over a decade and saw no drop off in performance over respective months.
Quiver Shaped by: Joe Blair, Blane Chambers, Jimmy Lewis, Kirk McGinty, and Bob Pearson.
Me: 200#, 6'2"

PonoBill

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Re: Wacky PV stuff
« Reply #2 on: March 04, 2024, 08:41:10 PM »
I doubt it's going to make a huge difference though we live at the end of a dirt road and every morning our cars have a nice layer of dust and pollen. It's winter, so I expect variation even this close to the equator. Depending on what Maui Electric Company has up its sleeve I might add another row of PV and some batteries. I no longer have to worry about outages since I bought a little portable power EcoFlow thingy. In my experience, the day you add backup power of any sort is the last time you ever have an outage. But I'll add to the system and do a whole-house battery if it pencils out. This system paid for itself even though I had some prolonged outages due to microinverter problems. The lifetime generation for the system is 95.43MWh. At 43.31 cents per KWh that's $40,080, which is about what the system cost unadjusted for inflation. As a guesstimate, if I'd fixed the microinverter issue promptly it would be roughly double that. 40K for being a lazy buggah.
« Last Edit: March 04, 2024, 08:42:53 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Beasho

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Re: Wacky PV stuff
« Reply #3 on: March 05, 2024, 12:14:02 PM »
This is interesting.  Can you provide any links to:

1) Sources for buying these cheap PV panels
2) How to rig these systems up
3) What type of batteries you would recommend

I realize this is a complete 'Start-Up' list but that is where I am / would be.

PonoBill

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Re: Wacky PV stuff
« Reply #4 on: March 05, 2024, 05:59:06 PM »
Actually even premium PV panels are pretty cheap now, but the ultra bargains are from Santan Solar. They're cheaper than plywood and they have frequent BOGO sales.

I'm going to be using a Tesla model 3 battery, you can buy the long range (75KW) batteries on ebay for about $7500, the standard-range batteries(62KWH) are less--about $5K. The big trick for using these panels safely is a good battery management system. Unfortunately the best one (from EVTV is expensive, 7500 bucks, or $20K installed and testing on a long-range battery.

EVTV is a company started by Jack Rickard, a legend in the DIY EV car world. He unfortunately passed away about a year ago and the company is now being run by (I think) his daughter and son-in-law. The daughter seems very smart and capable, but Jack was a wizard, though old and irascible. The easiest way to understand what I'm up to is to watch this video, though you have to sit through Jack's musings, some of which are interesting, some brilliant, some wacky: https://youtu.be/7zO11Q237nA?si=uR15xktHA6hhGxhl

This might not be the right video. He made a lot of them.
« Last Edit: March 05, 2024, 06:25:38 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

jondrums

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Re: Wacky PV stuff
« Reply #5 on: March 05, 2024, 10:34:15 PM »
as far as batteries go, if you aren't wanting to hack into a electric vehicle battery, I think the best bet are putting together a pack from Lithium Ion Iron Phosphate primatic cells.

I have a bunch of these and they are excellent, good life, low cost.
https://www.evlithium.com/hot-lithium-battery/eve-lf230-230ah-lifepo4-cell.html

You'll need a Battery Management System.  I have experience with Daly, which are pretty easy to wire up and configure
https://www.dalybms.com/smart-lifepo4-bms/

Decide how much energy you want to store, and how much peak power you want to be able to source to your home.  You'll need an inverter/charger rated appropriately for the panel voltage.  And that will steer you in the right direction of number of cells in series/parallel for the battery.

Here is one example for a small system 1400W solar, 48V battery, 5kW AC inverter.  I don't have direct experience on this one.
https://www.amazon.com/Inverter-Charger-Controller-Lithium-Batteries/dp/B096B7JQVH?th=1

Go down the youtube rabbit hole on this stuff and there is a ton to learn about putting together a battery pack, inverters, mppt solar charger, etc.

 


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