As a follow-up to my article regarding our water system, I thought I'd do an article on our photovoltaic system. As most of us know in first world countries, electricity is nice to have. The ability to light a home when the sun sets is especially helpful when we have tasks that need to be completed. And of course, electricity assists us in providing entertainment and powering various types of ccommunications equipment.
The modest system that is installed at our homestead provides us with lighting, and it powers our communications station. It can also be used to power laptop computers, Ipads, cell phones, etc. In a pinch, it could power a small fridge and microwave.
Initially, we are using 4 - 100 watt, 12 volt DC panels, which are mounted on a pole mount, approximately 100 feet from our home. The decision as to where to place the panels is probably the most important factor in developing your system. Partial shading of the panels can seriously impact power production. I used an app called Sun Surveyor, which gives you the ability to determine the sun's path throughout the year. The app costs around $10 USD, but it is definitely well worth the minimal investment. The pole mount is sunk into a concrete base, which was dug down until I hit bedrock. The panels are wired in series, putting out a nominal 48 volts. I wired the panels in series because of the potential voltage drop due to the wire gauge (8 gauge) and distance. The cables are rated for direct burial and are UV resistant too. The panels and the rack are grounded, per the National Electric Code. I try to adhere to the electrical code as much as possible. The cables were buried in a trench and then run into our garage.
The cables are then run into a multipurpose box. The Ecoworthy combiner box will combine strings of solar panels. The combiner box also provides lightning protection, and it provides a method of shutting off the panels for maintenance or emergency purposes, which is required by electrical code. The combiner box is then connected to a Maximum Power Point Tracking (MPPT) controller. The MPPT controller is the brains of our photovoltaic system. This controller will take the incoming voltage and convert it to 12 volts DC for our lithium battery system. The controller uses advanced logarithms to extract the maximum amount of power from the solar panels for the batteries. The controller is capable of handling panel voltages up to 95 VDC. It is also capable of charging various types of batteries, such as lead acid, AGM and lithium-ion batteries.
I decided to go with lithium batteries for this particular system. In the past, I've always used deep cycle lead acid batteries. Conventional lead acid batteries are relatively inexpensive and if well maintained they can last 4-8 years. In my previous photovoltaic system I had a set of Trojan T-105 batteries that lasted over 8 years. However, they were religiously maintained, and never overly deep discharged.
Lithium ion batteries are expensive. However, they have remarkable qualities that make them ideally suited for household photovoltaic systems. They require no maintenance, which frees up some of my time. They have an extremely long life of 10-20 years. They can also be discharged to 10% of their capacity without damage to the battery. If a lead-acid battery is discharged to that extent, it's lifetime would be measured in months. Because of the lithium-on battery ability to withstand a true deep discharge state, it's possible to use less batteries for a given situation. In our case, we went from 4 lead-acid deep cycle batteries to 2 lithium-ion batteries. I looked at it from a long term point of view, and if there was a multi-year power outage, I should still have battery capacity, while the lead acid batteries would be long dead. And the nice thing about the MPPT controller, I can charge other types of batteries, if necessary.
The batteries weigh about 28 lbs each, while a comparable lead acid battery would be 75-80 lbs. each. I placed the batteries in an enclosed plastic tote, which is then placed on a furniture dolly. The furniture dolly allows the easy access of the batteries for inspections etc. A 2000 watt Xantrex Prowatt sine wave inverter is mounted to the cover of the plastic tote. We rarely use the inverter, as most of our electrical usage is 12 VDC in nature.
An 8 gauge cable is run approximately 20 feet to our radio room, where DC power is distributed as needed. One unique piece of equipment we use is a multi tap which is manufactured by Hardened Power Systems:
https://www.portableuniversalpower.com/usb-multi-tap/ It's a pass through tap which converts 12VDC to four USB ports, allowing us to charge or power items off of the USB ports. I've managed to locate USB chargers for most of my portable radios. I also use a MFJ-4416C Battery Booster, which maintains the system voltage for the HF radios which prefer 13.8 VDC to operate well.
Our solar system has been designed for easy expansion. We could add more panels, or more batteries. The MPPT controller is large enough to accommodate these possible changes. I advise everyone to purchase a larger controller, so that if some day they wish to increase power production, they can do so without replacing the controller. Then again, it's not a bad idea to have an extra controller on hand, in case of malfunctions, EMP, etc. In my work, I have seen controllers go bad, so it does occur.
We use Anderson Powerpole connectors throughout our system, as they are easy to use, and simple. Heavy gauge wiring is used as much as possible. It's a simple system that meets our simple needs. Thanks for reading!
Photos:
1. Solar Array
2. Combiner with MPPT Controller
3. Battery Box with Xantrex 2000 Prowatt Inverter
4. Powerpole Distribution
5. Basic Communications Station Using Solar Energy
