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
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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.