shadow effects on pv performance?

Ralph Day

Here in Ontario there is a feed in tariff program about to hit the bricks (real soon we hope!). I'm in the process of getting ready for a 10kw system, with hopefully just a revenue meter. Things are not clear, there's only drafts of the program as of yet.

My site for the pv will require a great deal of brush clearing (about 1 acre at $2500 per day for full clearing, yikes). If the arrays were placed out of this area, not as much clearing needed, but there would be the shadow from my off grid home's 80foot wind turbine tower falling/tracking across the array area. The question is, how much would the performance of the 10kw array (3x3.3) be degraded by a shadow tracking across it? Would it be better to completely avoid any shadows...and spend lots of money in the process?

The price per KWH is 80.2 cents, it would take a lot of lost kwhrs to justify thousands spent on brush clearing. And yes, the price per kwhr is great, but there are NO subsidies for the purchase and installation of the system...the subsidy is essentially in the 20year contract at 80.2 cents/kwhr.

Quick and dirty: spend much money on clearing, or accept some degradation of performance from the shadow of a pole?

Thanks, I know there's probably not enough information here (yet).

Ralph

BB.

Re: shadow effects on pv performance?

I would clear the brush from in front of the array (or mount it off the ground clear of brush)--and you will have to keep up on this for years to come (perhaps elevated mounting with some use underneath--carport, work area, roof of new shed, etc. would make it more interesting.

For the tower--how long will the shadow be there? Sun is still relatively high--layout on the ground a the array's rectangle and time the shadow across the array. I have a tall redwood that is ~100' away--so it only shades may array for 20 minutes or so a day (in the morning)--Not much I can do about it (neighbor's tree)--but more of a problem in the winter than the summer.

I would count on a huge hit on power output while the tower is shading the array (50% is probably not unreasonable estimate just using my keyboard magic :roll:)

-Bill

Ralph Day

Re: shadow effects on pv performance?

Thanks BIll
I've come to the realization that solar power ain't cheap. THe first off grid system (our home) that we put in cost about $65K. But what fun!

The property is 134 acres, so clear cutting the brush and trees out is really silly, I suppose. What I can do is salvage the firewood out of the one acre or so for the 10 kw site, (not much) and have a BIG bulldozer come in and scrape everything else to a spot not visible from the house/driveway or anywhere else except space. This might be the cheapest direction to take.

We do have some shading on our 2.1kw of pv now. It's a morning thing and the trees are lovely in the fall...they aren't going anywhere. What would be the purpose of stripping all the beauty away just for a few more watt hours? Not going to happen for the house site. If we can get the commercial production site cleared to optimum without ruining the view, we shall.

My shading calculations were really just for the lowest sun angle in December 23degrees azimuth. Most of the year there wouldn't be shading at all on the 10kw site.

Ralph

Cariboocoot

Re: shadow effects on pv performance?

I positioned my panels for best 'shadow free' performance in Fall/Winter/Spring. As a result, tree shadows murder my summer production! There's still a couple of bad ones for Winter too, so it looks like some more chainsaw work will be done.

I hate cutting down live trees, especially with a forest full of dead ones. :grr

Ralph Day

Re: shadow effects on pv performance?

Hi Marc
I don't have the luxury of standing deadwood. Of the 5 bush cords I've cut and hauled out of the bush this year perhaps 1/2 cord would be from dead trees. That says a lot for the health of my forest. I get past the guilt by thinking about the growth in a year surpassing my consumption by far. Burn about 4.5cords per year.

I think the chainsaw and 'dozer are in the works for late fall/early winter. I hate cutting in the winter, slippery, you sweat and then chill, September is the best month for wood working.

Once I have the specs for clearances around the proposed arrays it will be easier to lay out the wood work.

Sun good, shade bad, unless you're on the back deck.

Ralph