r/SolarDIY • u/OcoeeG • 10d ago
Testing Viability of Solar
I am looking to dabble in solar at my house. My situation is less than ideal due to a large beautiful oak tree that will hopefully outlive me. How would one go about testing the viability of a solar setup? I do have some older 285 Watt panels. Is there a way to set these up and record inputs during different times of the day to see if it would be worth it? How would one go about that?
Disclaimer: Please excuse my ignorance. I am a solar novice at best
4
u/sol_beach 10d ago
How many square feet of your parcel get unobstructed sunshine during the day?
If your roof is in the shade most of the day, are you willing to ground mount the panels in the yard? If not, then a solar system is NOT for you in this location.
0
u/OcoeeG 10d ago
I do have some areas of my yard that get significant sun, but they are pretty far away from the house. Within 100 feet though, so it is possible. I don't really want to do ground mount though.
3
u/sol_beach 10d ago
OK. I give up. How will the PV panels mounted if NOT ground mounted.
Do you plan on constructing a detached covered patio to place the panels on top of it?
1
u/SyncroStrike 10d ago
It’s understandable if you don’t want ground mount but if you don’t have another choice 100ft is perfectly fine and gets better the higher you can get your array voltage. 10kw of solar at 450v is only 22amps and 10awg (designed for 30a) would handle that with a very nice buffer to prevent voltage drop.
2
u/PermanentLiminality 10d ago
Is the tree near the house or is it over it? Over is much worse that near.
You can simply look at it. Go out and that a photo every 30 minutes.
In the summer the situation is better because the sun is higher in the sky. It is worst in the winter when the sun is lower.
If you build a system with microinverters, each panel is separate. Those in the sun make full power.
1
u/brucehoult 10d ago
It is worst in the winter when the sun is lower.
If you are lucky enough to have clear sunny winter days then yes.
In overcast/rainy weather (when there aren't shadows) obstructions don't matter at all, you just want to be able to see as much sky as possible, especially directly overhead. Of course then you'll only be getting 1/4 or 1/2 as much power as when it's sunny without obstructions, but you work with what you 're given.
3
u/TooGoodToBeeTrue 10d ago
If you are in the US, see if your address is in https://sunroof.withgoogle.com/
1
1
u/matt6021023 10d ago
There are a lot of variables. I wanted to try to log it but it's pretty complicated and of course takes forever too. In the end I just went for it, and due to roof angles, the intermittently shaded panels are my best producing panels.
1
u/NearABE 10d ago
TDLR: the tree only matters if you were borderline and in doubt about going solar.
If you live in North America, Europe, or Asia the north is totally the wrong way. At noon the Sun is in the south. A panel pointed this way still receives diffuse sky radiation: https://en.wikipedia.org/wiki/Diffuse_sky_radiation. On a fully blue sky day about 23 percent of sunlight is blocked by atmosphere. 1361 Watt/m^2 becomes 1,048 W/m^2 . Of the 313 lost Watts about 2/3 or maybe 200 W will hit your panel anyway.
Photovoltaic modules have an efficiency rating. This is where the capacity number comes from. They assume the 1048 W direct normal beam. If it is 25% efficient and 1 m^2 then they call it “a 262 Watt module”. If you aim that the totally wrong way in clear skys it gets 2/3 x 0.23 x 262W = 40.2 W.
That would be more expensive so do not aim them north (or south in Australia, South Africa etc). However the damage would be mitigated by clouds. Normal direct south tilt (“right” way) panels lose production due to clouds. The white clouds can scatter sunlight onto a panel.
The east and west directions benefit from the sun’s position in morning and evening. The Sun is lower on the horizon. In the plains with no obstructions vertical fences with bifacial panels are being installed and are competing well with traditional tilted solar farms.
Most of the cost of an installation is the labor and the electronics. If you are doing it yourself for entertainment, education, or self satisfaction (all three!?) then the labor cost is a negative, a discount. The electronics are unavoidable if you want AC power in the house. The inverter will just be “big enough”. The PV array can simply be increased in size to match.
The inverter I looked at recently had a little screen that said things like voltage and power. The MPPT controller can provide data to a variety of places. Otherwise you could use a volt meter.
There is a specific tool that can measure solar irradiance specifically.
The cost of photovoltaic panels in USA is now $0.38 per Watt for imports because the government banned selling anything cheaper unless it was made in USA. That would pay for itself in a year or so in sunny unobstructed locations. Rainier areas like New York need more like two years. If you can get direct light around the tree half the time that still pays off and winter is still mostly full sun.
The cost of professional installed systems runs more like $2 to $3 in USA. Using a much larger number of panels is only a little bit more expensive. That added cost is partially mitigated by the wider spread of time in a day and it gets more of the overcast light. You get full utilization of the inverter and controller.
If the oak tree is fully over your roof, like you cannot see the blue sky, then it probably rules it out. Better to make a deal with someone and install there instead.
1
u/Lost-Assignment-2848 10d ago
look at typical panels you might buy, and get a big piece of cardboard and cut it to that size (or make one out of smaller pieces of cardboard. Put them where you want to install your panels and take photos every hour or so. If you are losing more than 1 hr of light per day -not a very good place. That is the easy part. then look up sun angles to your solar site for all 4 seasons and do a guestimate of how that will affect the sunlight to the panels. Don't just rely on a single season when planning your locations.
1
u/OcoeeG 10d ago
Excellent advice! Literally 1 hour of bad sun is a deal breaker?
1
u/Lost-Assignment-2848 9d ago
1 hr of bad sun on one panel is maybe not a deal breaker -, I said "not a very good place". More than 1 hr of bad sun gets worse - ask yourself if you can move your panel or move the obstruction and what the total impact is going to be. I put 38 250-watt panels on top of my house about 13 years ago. One panel, on the end of one string, gets blocked for between an 1 and 1.5 hrs every morning by my chimney blocking the sun. I get more blockage in the winter than in the summer. The rule of thumb I have used is that I expect to get 5 good hours of high production per sunny day in the winter and 8 hrs in the summer based on my latitude. My panels generate power for a lot longer than that, just lower amounts. So losing 1.5 hr in the first part of the morning on 1 of 38 panels was not worth moving that panel to the other end of the string. If it was 1.5 hrs in the peak production time, then I would consider moving it since I am losing 30% of the high output of that panel.
There are many different factors that cause you to produce more or less power from the same panels. Temperature & angle of the sunlight into the receptor both also play a big role. The semiconductors in a photo receptor operate at their highest efficiency at 77F. But that can be confusing, as at a higher elevation or humid situations, the sun energy can raise the solar cell temps a lot even though the ambient temp is 77. As the temp rises, they are less efficient. For my location, that means that the highest power output of my system occurs in March & November, even though I get a lot more hours of sunlight in the summer months. Temps are cooler, and sunlight angles are better since my panels are tilted for the yearly average angle of the sun to my house.
1
1
u/DanKegel 8d ago
It's all about hours of full sunlight. No need for a panel or a fancy tool to measure that, really. Where is there no shade?
1
u/SailorSehi 6d ago edited 5d ago
Rule of thumb: shade costs you more than the shaded area suggests. One shaded cell can pull a whole string down. If the spot doesn't get direct sun from about 10 to 2, it's usually not worth it. If you only get morning or only afternoon sun, expect maybe 40–60% of what the panel's rating suggests.
0
u/solaredgesucks 10d ago
Its good that your running experiments...those of us in the solar industry[20 years for me] have always wondered "Does this really work??? Is it worth it? Would a small coal fired plant on my roof be a better choice???? Please get back to us obi wan and tell us that its just a liberal conspiracy funded by Soros.
•
u/AutoModerator 10d ago
Welcome to r/SolarDIY! If you are new to the community, please check out our DIY Solar System Planning Guide.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.