Solar System Facts & Commonly Asked Questions
1. What should I do with my batteries over the winter with my cabin and solar system left unattended?
- Should the electrolyte in flooded batteries stratify, your batteries may freeze and crack the walls of the containers
- Discharged batteries are at the greatest risk of freezing
- If practical, batteries should be removed and moved to a warm location and charged regularly through the winter
- In most cases that is not practical though. Regardless of battery type, you will want to shut down the inverter, and ensure all DC loads are removed that might discharge the batteries, but keep the solar controller on, and applying charge to the batteries throughout the winter. This will help warm the batteries during the charge cycles and will assist in circulation of electrolyte (flooded batteries).
- Removing snow from your PV modules when practical at intervals over the winter is recommended to ensure that at least periodically through the dark/cold months that your batteries will see some charge current to keep up their state of charge.
- Equalizing lead acid batteries is a process designed to de-sulphate the battery plates by carrying out a controlled overcharge. Sulfation of the plates leads to an early failure or lack of capacity for your batteries
- This process will cause gassing, so ensure the electrolyte is topped up before and after the process
- The time between equalizations varies greatly by OEM, and greatly depends on the type of cycling your batteries have seen. Battery OEMs recommend that you equalize your batteries anywhere from 2 x per year to monthly, however the best approach is to check the specific gravity of each cell, so understand the variance from cell to cell. After equalization the specific gravity should be 1.265 ± 0.005.
- Ensure you monitor State of Charge closely. Having a functioning battery monitor is key. These vary greatly in price and level of sophistication, but even the most rudimentary models like a BM2 (Bluetooth mobile device that sells for $60), or Midnight BCM do the job just fine. Moving up to a Magnum BMK or Victron BMV series provide additional functionality and accuracy under load conditions, but what is important is to know what the state of charge of your system is at all times and to take action if you are driving regular discharge cycles that are beyond 50%.
- If you are finding that at the end of a solar production day, the system has not returned the batteries to a 100% state of charge on a regular basis you would be wise to apply top up charge with a generator, and look for reasons that your system has seen production that is not exceeding your loads and take action as required.
- Short answer is yes. Fuses / breakers provide circuit overload protection that will ensure that shorts or overloads do not result in fires, or damage to your components caused by a short circuit in the system
- This is the easiest math of all the solar circuits. The fuse/breaker size would equal the amp rating of the controller. Ie a 40A controller would take a 40A fuse.
- This one is bit more math. After calculating the total amps your solar array puts out (based on the spec sheet of the specific PV module), multiply the array amps x 1.25% then round up to the next available fuse or breaker rating. ie if you have 4 x 100W panels in series (voltage would be additive) and each puts out 6A, the fuse would be 6A x 1.25 = 7.25A so round up to a 10A fuse is practical. If you have 4 of the same PV module in parallel, the current would be additive, so in this case the fuse size would be calculated as 6A x 4 x 1.25 = 30A.
- While most inverters have their own built in circuit breakers, this circuit is the one carrying the most risk due to the high levels of current the battery bank contains. Protecting this circuit and the associated wiring from overload, or a short is critical. While most inverter manuals will specifically define the required fuse, this is often calculated by taking the continuous wattage of the inverter and multiplying that by a 25% safety factor. Ie a 1000W inverter running off a 12V battery array would draw 83A x 1.25 = 105A so you would size this fuse at the next available size which is a 125A , or 150A fuse.
- The sky is the limit….if your budget matches need for power hungry electrical loads. For those who have budget constraints (as most of us do), always start by defining your “must-haves”, then move on to convenience items. While solar off-grid solar has become increasingly economical, it is wise to invest first in spec’ing out the most energy efficient appliances / energy consuming devices as the first step. A good rule of thumb is that off-grid solar will cost you between $5000 and $10000 for 3 kwh/day of daily energy consumption.
- Tip 1 – if possible use an alternate approach for all electrical loads that create heat (coffee makers, space heaters, electric stoves/oven etc) These appliances will quickly double / triple the cost of doing off-grid solar.
- Tip 2 – Consider using a backup generator as a key component of your system. With manual intervention and planning, this enables specific high load appliances to be run using a generator on demand, and also top up your battery array at the same time. Using this approach, high energy consumption appliances can be used without upsizing the solar array, or battery bank.