Solar Radiation

[EECmakrin]

I know that in the cloudy UK this question doesn't seem very important but in the southern countries it does. I wonder if Clive and others could suggest 1-2 sensors for solar radiation (W/m^2) and UV Index to be attached to the station in order to have some useful solar data. Thanks.

[clive]

I've not had any direct experience but hopefully someone else here has. Radiation/UV sensors were something we wanted to put on but had to drop due to cost. We'd be interested to hear how you get on.

thanks

[Massi]

I know that in the cloudy UK this question doesn't seem very important but in the southern countries it does. I wonder if Clive and others could suggest 1-2 sensors for solar radiation (W/m^2) and UV Index to be attached to the station in order to have some useful solar data. Thanks.

well, for UV index you can look at a SI1145 sensor. I'd say something around 10$
This also outputs light level (visible and ir), but a TSL2561 would be better for this (+5$)
then you need a place where to put these. I used a light bulb (lol)

solar radiation seems to be something harder to achieve..

Edit to add: for UV consider also a VEML6070 sensor, that does not return a proper UV index, but is cheaper (5$)

[Massi]

Edit to add: for UV consider also a VEML6070 sensor, that does not return a proper UV index, but is cheaper (5$)

sorry for necroing this, but i've just received my VEML6070 sensor and.. i discovered that a brand new VEML6075 is out

6075 will do UVA and UVB (while 6070 only senses UVA)

i do not know any pre built breakout board with veml6075, however

[Massi]

I'm abusing of the RPF Weather Station section (please clive let me know if this is only for "official" weather station, or for "raspberry weather station" in general )

If anyone is going to add a VEML6070 uv sensor to the station, here is a working python code for it. This obviously uses pigpio

Code: Select all

#!/usr/bin/env python3 
#coding=utf-8

'''
A python class to manage VEML6070 UV A sensor
'''

import time
import pigpio 
import bisect

class VEML6070:
	#i2c addresses
	addrLow		=	0x38 # first i2c address of VEML6070 (write -> config, read -> LSB of UV)
	addrHigh	=	0x39 # second i2c address of VEML6070 (read -> MSB of UV)
	
	#constants for the SD part of config register
	sensorEnabled	=	0x00
	sensorDisabled	=	0x01
	
	#constants for the IT part of config register
	intTime_1_2T	=	0x00
	intTime_1T		=	0x01
	intTime_2T		=	0x02
	intTime_4T		=	0x03

	scaleFactor = {
		intTime_1_2T:	0.5,
		intTime_1T:		1,
		intTime_2T:		2,
		intTime_4T:		4
	}

	refreshTime = {		#in ms
		intTime_1_2T:	62.5,
		intTime_1T:		125,
		intTime_2T:		250,
		intTime_4T:		500
	}

	def __init__(self, bus=1):
		self.pi = pigpio.pi()
		self.i2cLow = self.pi.i2c_open(bus, self.addrLow, 0)
		self.i2cHigh = self.pi.i2c_open(bus, self.addrHigh, 0)
		
		#initializing sensor as disabled and with standard integration time
		self.sdnMode = self.sensorDisabled # before set_integration_time()
		self.setIntTime(self.intTime_1_2T)

	def setIntTime(self, intTime):
		self.intTime = intTime
		self.pi.i2c_write_byte(self.i2cLow, self.prepareCmdValue())

	def sensorEnable(self):
		self.sdnMode = self.sensorEnabled
		self.pi.i2c_write_byte(self.i2cLow, self.prepareCmdValue())

	def sensorDisable(self):
		self.sdnMode = self.sensorDisabled
		self.pi.i2c_write_byte(self.i2cLow, self.prepareCmdValue())

	def getUvaRaw(self, integrationTime=intTime_4T):
		self.sensorEnable()
		# wait two times the refresh time to allow completion of a previous cycle with old settings (worst case)
		time.sleep(self.refreshTime[self.intTime]/1000.)
		msb = self.pi.i2c_read_byte(self.i2cHigh)
		lsb = self.pi.i2c_read_byte(self.i2cLow)
		self.sensorDisable()
		return (msb << 8) | lsb

	def getUvaIndex(self, uvRaw):
		#scaling value by integration times
		uvRaw = uvRaw / self.scaleFactor[self.intTime]
		uvIndex = bisect.bisect_left([187,374,560,747,934,1120,1307,1494,1681,1868,2054], uvRaw)
		return uvIndex

	def getUvaPower(self, uvRaw):
		#since it's all linear and every UV index equals a radiation power of 2.5 mW/m2, and every UV index equals to 187 (rounded..) "raw" UV reading, i can calculate the radiation power as uvRaw * 2.5/187 mW/m2
		uvRaw = uvRaw / self.scaleFactor[self.intTime]
		uvPower = uvRaw * 2.5 / 187
		return uvPower
		
	def prepareCmdValue(self):
		cmd = (self.sdnMode) << 0 			# Shutdown mode setting (bit 0)
		cmd = cmd | 0x02					# reserved (bit 1)
		cmd = cmd | (self.intTime << 2) 	# Integration time setting (bits 2 and 3)
		#ack and reserved bits to 0 (bits 4-7)
		return cmd

	def close(self):
		self.pi.i2c_close(self.i2cLow)
		self.pi.i2c_close(self.i2cHigh)
		self.pi.stop()
		
if __name__ == "__main__":
	sensor = VEML6070()
	
	uvaRaw = sensor.getUvaRaw()
	print("UVa Raw:   {:5}".format(uvaRaw))
	print("UVa Index: {:5}".format(sensor.getUvaIndex(uvaRaw)))
	print("UVa Power: {:5.3f} mW/m2".format(sensor.getUvaPower(uvaRaw)))

	sensor.close()

I think the calculation of index and power is "a little" (lol) approssimated.
I based my assumptions on datasheet ( http://www.vishay.com/docs/84310/designingveml6070.pdf page 4) and on definition of UV Index (1 index: 2.5 mW/m2), but i think that in UV Index also UVB enters, information i do not have with this sensor.

First sensor i see with TWO used i2c addresses.. one of them conflicts with the default address of the TSL2561 sensor, that has to be set to another address.

[morphy_richards]

Did you solder directly onto the SMD pads? IS there any chance you can post a picture of how you connected it? Connecting SMD components might put some people off unless they can see how it was done

[Massi]

no way! lol
i bought a breakout board from china of a VEML6070 with a 270k rset resistor
then googling for the datasheet i found the veml6075 sensor, but couldn't find any board with it..

[scruss]

I've not had any direct experience but hopefully someone else here has. Radiation/UV sensors were something we wanted to put on but had to drop due to cost.

Although my experience is in commercial meteorology, cheap and reliable pyranometers aren't really available. The SP Lite2 is over £300, and it's a budget unit. The Davis 6450 is roughly half that price. They also tend to have fearsome power requirements to keep the glass window heated and free of mist.

(Edit) … although a bit more reading dug out some potentially promising results using a phototransistor attenuated behind layers of PTFE tape. Like all weather sensors, making the enclosure would be the tough part.

[Massi]

Well, i installed my veml6070 outdoor.
As you can see..



i used a old light bulb to install veml6070+tsl2561 to get visible, infrared and UVa

Now, the problem: the VML is giving me something like 40% less UV index than what i was expecting. I intended the light bulb to be more or less completely transparent to UV, am i wrong? what am i missing?

[sparkyhall]

Now, the problem: the VML is giving me something like 40% less UV index than what i was expecting. I intended the light bulb to be more or less completely transparent to UV, am i wrong? what am i missing?

I believe pond UV filters use transparent quartz because normal glass blocks too much UV, my guess is that a normal light bulb will do the same. Using a light bulb is a nice idea though.

[Massi]

Now, the problem: the VML is giving me something like 40% less UV index than what i was expecting. I intended the light bulb to be more or less completely transparent to UV, am i wrong? what am i missing?

I believe pond UV filters use transparent quartz because normal glass blocks too much UV, my guess is that a normal light bulb will do the same. Using a light bulb is a nice idea though.

i was so proud of my light bulb (i did miracles to set up both sensors LOL)
i couldn't find any "official" data about glass filtering, i'll make a deeper search tomorrow.. i expect something aroud 40%, as said, in case i'll offset my code..

[mohog]

Standard glass does block some uv radiation. In working with screen printing I found out there is a sheet plastic that is used in tanning equipment that allows most uv and ir to pass. Ask at a sheet goods supplier for some thing that passes uv. Bonus is that it is resistant to breaking.

[nrich]

I have a number (over 30) of used Kipp & Zonen pyranometers similar to the SP Lite2. These are an older model (2004 or so), without the bubble level and leveling screws but are weather sealed. They were removed from stations that were used to monitor the solar radiation on PV panels and have been exposed to a few years of radiation. As is typical for this type of units, they can be expected to have lower sensitivity than when new ( ~ 2%/year). While there are services that will re-calibrate them, one can come up with a fairly good calibration by using the Apogee clear sky calculator (http://www.apogeeinstruments.com/when-t ... alculator/ ). These are analog out, approx 90 micro-volts/Watt/m^2.

I would be happy to spread them out to the community for packing and shipping costs, I have no use for them. I am in Massachusetts, USA.

Ned

P.S. I also have a similar number of NRG #40 anemometers, removed from the same systems.

[julespiman]

I can't help with the circuit, but there are a few pre-wired uv sensor modules available. These contain a gallium nitride photo diode to measure uv in the approx range 200-300nm, plus opamp and a few other components. The circuit outputs a linear regulated voltage 0-1V, corresponding to a uv range of 0-10.
The 3 pinouts are for voltage in, ground, voltage out.
Adafruit (UK) list the ML8511 @ £10.40 incl VAT
Adafruit (USA) list the GUVA-S12SD, no price shown
These could be the basis for a uv sensor for the weather station.
Hope this helps.

[Gavinmc42]

Acrylic plastic is mostly transparent at UV range, just get as thin as possible, 3mm is too thick, I tried.
I just got some microscope cover slips, very thin glass, still to try.
But I am only using an i2c Lux sensor not a UV one.

[yv1hx]

I can't help with the circuit, but there are a few pre-wired uv sensor modules available. These contain a gallium nitride photo diode to measure uv in the approx range 200-300nm, plus opamp and a few other components. The circuit outputs a linear regulated voltage 0-1V, corresponding to a uv range of 0-10.
[...snip...]

Although an UVI range from 0-10 can be useful for most high latitude regions, in most cases the UVI ranges can exceed the 12+ figure.

Other possible(?) disadvantage is the need of implementing an ADC for converting the analog magnitude to digital values that can understand the RasPi.

I live in a coastal region, near 10°25" degrees North, and our UVI proms are usually 13~14 most day a year.

[yv1hx]

Acrylic plastic is mostly transparent at UV range, just get as thin as possible, 3mm is too thick, I tried.
I just got some microscope cover slips, very thin glass, still to try.
But I am only using an i2c Lux sensor not a UV one.

BTW, Good Idea the use of microscope glasses, I will give a try.

The glass (or plastic) window is a very critical component of the device, so the designer must choose the window material wisely.

As far as I know, most plastics and glasses are opaques to the UV light, the App note "Designing the VEML6075 into an Application" from Vishay, recommends the following:

http://www.berghof.com/en/products/ptfe ... ical-ptfe/
http://www.aetnaplastics.com/site_media ... _Sheet.pdf

Quote from the same App note:

MECHANICAL CONSIDERATIONS AND WINDOW CALCULATIONS FOR THE VEML6075

As already mentioned, this UVA / UVB sensor will need a well-selected cover that is not only completely transmissive to visible
light (400 nm to 700 nm), but also to UVA and UVB wavelengths (280 nm to 400 nm).
Teflon or polytetrafluoroethylene (PTFE) is a known optical material that allows transmission of UV up to near infrared signals.
A teflon diffusor (PTFE sheet) radiates like Lambert’s cosine law. Thus PTFE enables a cosine angular response for a detector
measuring the optical radiation power at a surface.
Using a 0.4 mm teflon diffusor placed on top of the VEML6075 sensor generates a very close to cosine view angle response.
Compared with the ideal cosine response, the measured view angle response error of a 0.4 mm teflon diffusor is less than 10 %. [...snip...]

[SteHo]

I have a number (over 30) of used Kipp & Zonen pyranometers similar to the SP Lite2. These are an older model (2004 or so), without the bubble level and leveling screws but are weather sealed. They were removed from stations that were used to monitor the solar radiation on PV panels and have been exposed to a few years of radiation. As is typical for this type of units, they can be expected to have lower sensitivity than when new ( ~ 2%/year). While there are services that will re-calibrate them, one can come up with a fairly good calibration by using the Apogee clear sky calculator (http://www.apogeeinstruments.com/when-t ... alculator/ ). These are analog out, approx 90 micro-volts/Watt/m^2.

I would be happy to spread them out to the community for packing and shipping costs, I have no use for them. I am in Massachusetts, USA.

Ned

P.S. I also have a similar number of NRG #40 anemometers, removed from the same systems.

Hi Ned,

I am currently building my own weather station with a Raspberry Pi 3, which I am planning to take on fieldwork with me to Greenland next summer. Do you still have your old Kipp&Zonen pyranometers? It would be easy for me to recalibrate them, as I have a lot of weather station data, from Europe and Greenland. I would love to see how close I can get to a 10000 $+ weather station with my 400£ budget set for this project. I would also be interested in some of the anemometers if you still have them?

Cheers,
Stefan.

[yv1hx]

I have a number (over 30) of used Kipp & Zonen pyranometers similar to ...snip....

Ned, I just drop you a PM a few days ago..

[Skahan]

I have a number (over 30) of used Kipp & Zonen pyranometers similar to the SP Lite2. These are an older model (2004 or so), without the bubble level and leveling screws but are weather sealed. They were removed from stations that were used to monitor the solar radiation on PV panels and have been exposed to a few years of radiation. As is typical for this type of units, they can be expected to have lower sensitivity than when new ( ~ 2%/year). While there are services that will re-calibrate them, one can come up with a fairly good calibration by using the Apogee clear sky calculator (http://www.apogeeinstruments.com/when-t ... alculator/ ). These are analog out, approx 90 micro-volts/Watt/m^2.

I would be happy to spread them out to the community for packing and shipping costs, I have no use for them. I am in Massachusetts, USA.


P.S. I also have a similar number of NRG #40 anemometers, removed from the same systems.

Ned,

Do you still have any more of the pyranometers? I am working on a project for school and need to measure solar radiation.

Sam

[janie66]

I've not had any direct Solar Panel Cleaning services but hopefully someone else here has. Radiation/UV sensors were something we wanted to put on but had to drop due to cost. We'd be interested to hear how you get on.

thanks

Hello clive.

About half of the radiation is in the visible short-wave part of the electromagnetic spectrum.
The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum.
The portion of this ultraviolet radiation that is not absorbed by the atmosphere produces a suntan or a sunburn on people who have been in sunlight for extended periods of time.

[jgveill]

Nrich,

I may be much too late but if you have a pyranometer / anemometer, let me know. I'm in Quebec, not too far ... I found you post as I'm looking for measuring UV and transfering my WS from arduino to Pi3.

J Guy

[piotreeek]

I have a number (over 30) of used Kipp & Zonen pyranometers similar to the SP Lite2.
I would be happy to spread them out to the community for packing and shipping costs, I have no use for them. I am in Massachusetts, USA.
P.S. I also have a similar number of NRG #40 anemometers, removed from the same systems.

Hi, do you happen to still have them, and wish to send?