Sun hrs vs actual sun

mountainman · February 2019

For 3 months of summer may June and July pv watts gives me 5.97 6.46 5.97. But with trees and mountains blocking I only get 4 in may and july and 4.5 in june of full sun on the panels how does that figure?

Estragon · February 2019

I have similar summer insolation, but if I hadn't taken out ~1/2 dozen big conifers, my pv production wouldn't have been much better than zero.

If your 4hrs are around noon, you probably aren't losing all that much potential production.

BB. · February 2019

Any shading basically "zeros" out the solar harvest (shading kills solar panel's electrical output).

If the shading is after 4pm, you may not have much harvest anyway... VS a power pole that blocks an hour of harvest at noon.

You can use PV Watts to better estimate your output.. They have an "hour by hour" estimated harvest output (24 hours * 365 days) in a spread sheet:

https://pvwatts.nrel.gov/

I know that some folks have used a Google drafting program that lets them "build" a house/array and put in other items that can block the sun, then run a simulation of how shadows fall...

There should be other "professional" software packages that can predict actual harvest--But I am not in the business, so I cannot help there.

And if the shading results from Trees/other fast growing greenery, it only gets worse over time if you cannot trim them back.

-Bill

mountainman · February 2019

Yes where I placed the panels roughly 10:45 to 3:15. so just figure the time the panels are in sun or a little more for diffuse light.

mountainman · February 2019

Thanks @bb and @estragon. Now I have to start all over sizing with different sun hrs. 1000 w/hrs daily 5 days 5000 With a 416 amp/hr @12 volts my 400 watt array is producing 22 amps. I'm adding a separate cc and 520 watts. An additional 28~29amps.50~51 amps total 12% c rate. 920 watts in 4 hrs might produce 2800. Im thinking That's not enough for a 50% deficit b bank and 500 w/hrs day time loads. Guess after a long stretch of clouds I could run the generator early in the morning and let solar finish. thoughts?

Estragon · February 2019

IMO, you don't necessarily have to get back to 100% on the first sunny day after a run of cloud. If you can get back to 75-80% or so and catch up to full in a couple days, that's ok. If the forecast is more gloom though, probably time to spark up the genny.

BB. · February 2019

A well match genset and charger will do a very fuel&time efficient job of charging up to ~80% state of charge, as the battery SoC gets higher, then the charging current falls (especially for FLA batteries).

Most gasoline gensets are more efficient at 50% or greater of rated loads. And as the loads fall below 50%, the fuel flow only marginally reduces.

Diesels are more fuel efficient at lower loaded outputs, but they also usually run better with 40% or greater loads on the engine (keep combustion temperatures and pressures higher).

Running the genset in the early AM and letting the solar panels charge from mid-morning through evening is a pretty common suggestion.

If you are not expecting much sun, adding water pumping, household chores, and such as the battery bank is charging is good.

In theory, as long as your batteries are "cycling" (like 50% to 80%) daily, as I understand, they will not be sulfating quickly/badly. Just get >~90% state of charge once a week (genset, conservation, etc.) and FLA batteries should be pretty happy.

FLA batteries sitting for days uncycled (and below ~75% state of charge)--They do not like that.

-Bill

Sun hrs vs actual sun

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