This is the first entry in my solar power blog. The subject will be solar power in a residential setting. My house, specifically.
The people who will benefit most will have a post secondary education. Solar energy is a science intensive subject. Math is important but not a critical need.
The station is composed of :
1.) solar panels
2.) the hardware which holds them, frame included. Referred to as the 'array'.
3.) the the array is connected to the indoor electronics by PV cable using MC4 connectors.
4.) the cable enters a charge controller. The controller regulates the energy going into the batteries. The most efficient controller, and worth the extra expense, is a MPPT (maximum power point tracking) controller.
5.) The controller feeds four batteries for a total of 2,952W, or about three kilowatts of stored energy.
6.) the batteries feed an inverter. The inverter converts battery/panel D.C. voltage into standard household power, 120V.A.C.. The best model is a pure sine wave inverter. The pure sine model most closely approximates the utility electricity in the house. Other inverters use PWM (pulse width modulation) which can run many, if not most electrical equipment. Some rely on the VAC as a timing reference. Some digital clocks use the 60 hertz power signal to measure the seconds in the clock. A PWM inverter will create chaos in the timing. Some elctrical equipment simply requires the clean power provided by a pure sine inverter.
Equipment brand, model list:
solar panels: Solar Fennel/Renogy/Ramsond/HQST
framing : Unistrut, Superstrut
cabling, connectors: generic
charge controller: Epever 3210A MPPT charge controller
batteries: generic 12V, 18aHr sealed gel/ Duracell Ultra Marine 12V,108aHr
inverter: Cotek 1.5KW pure sine inverter
Each of the items in the lists presents its own set of problems in implementation.
Solar panels come in several different chemistries (compositions) and different sizes and power ratings.
The panels I have are, but for one, monocrystaline in composition. The remaining one is polycrystaline. The performance for the two is similar enough that the price differences are worth looking at. Panels for large sites usually range in the 250-300 watt area. Mine are 100 watts and serve in smaller systems, e.g. RV's, trailers, boats, small residential systems. My system is rated at six hundred watts. The panels can be wired up in many different configurations. Series, parallel, and a mix of both, series-parallel.
My charge controller is most efficient when wired for a 36 volt panel array and a 24 volt battery bank.
I wired the panels in two groups of three. The three were wired in series, then the two groups of three were wired in parallel. Panels usually come with small utility boxes on the back with connecting cables in place.
The charge controller is an Epever 3210A 30A controller with UART communications with Modbus protocol in an RTU format. I've written a programming script in the PHP language that reads registers in the controller and prints the data to a text file in spreadsheet (CSV) format. The software is installed on a Raspberry Pi 3B computer board. The Raspberry Pi (RPi) is a small, but powerful and versatile computer the size of a shirt pocket. The RPi is connected to the controller with a USB to RJ45 cable. There is also wi-fi on the computer that allows me to access the board from my laptop, phone, or the internet.
The webpage to access the data over the web will be a PHP script or HTML page that uses D3 charting tools, or similar, to present the data in a way I consider most easily digested and making all the data I think relevant available.
Major difficulties have been encountered in the mounting framework. My installation is ground mounted and one, or hopefully, two axis tracking. The tracking of the sun's position is another way to improve the efficiency of the system. A linear actuator will control axis movement in one direction, typical elevation/altitude. Another will control movement in the second axis, typical azimuth.
Most systems are mounted on rooftops and are fixed. Many are fixed but mounted on the ground.
Remember, we're discussing residential and smaller systems here.
Tracking systems involve more sophisticated, and therefore, expensive hardware. Unfortunately, the technology in this area lags extremely far behind the rest of the residential solar power station.
There are several approaches to designing and building the hardware for a tracking array. I took a slightly different approach. Mind, I am prepared to change my approach at the drop of a hat if new technology becomes available, and I'm not committed by way of previous purchases or agreements.
I have a steel pipe leaning at about forty-five degrees and facing South, This is about optimum for my latitude. The panels are mounted on some steel struts. The struts are mounted on the pipe using pipe clamps. The top of the pipe has a tee fitting and the bottom has a cap. There is enough freedom in rotation that the extra rotational movement takes the place of bearings. Reminds me of the Archimedes screw pump. The bottom cap will be fixed in position as will the tee fitting at the top. The pipe will rotate to move the array in a way that follows the sun's path. Tee fittings at the top and bottom would allow adjustment of elevation. Both ends will be anchored to four inch posts of treated lumber embedded in or attached to the tops of, concrete bases or pylons. This will also raise the array into the air and increase sun exposure time.
. Trees and brush on my and surrounding lots need to be removed. This will take dealing or a visit to a court.
I have prepared scripts written in the Python language that will calculate the sun's position mathematically. I have also constructed a small device composed of four small solar cells. The cells are mounted on a sheet of metal in the shape of a cross of the kind associated with medicine. The cells, square in shape are glued, one on each arm of the cross, with silicon caulk. The arms of the cross are bent back so that when the center square of the cross is aimed toward the sky, the voltages of the cells, taken as a group, will indicate the direction in which to move the array. One method acts as a backup for the other.
30Ax36V=1KW, the rated power of the controller as set up. I may use a 48V setup and increase the rated output but lose some efficiency. The rating would be 30Ax48V=1.44KW. Moving to a larger controller would be in order above one klowatt.
