In this article I will explain how to set up a solar grid. I will also explain the basics of electricity, wiring, batteries, and power. I did this on my boat. If you are doing it for a house you wouldn’t need a battery bank for a starting battery (used to start an engine).
Dual Battery Charge Controller
100 Watt Solar Panel
Battery Selector Switch
I used WindyNation’s 100W Flexible Solar Panel on my set up because I installed them on my sailboat’s fabric bimini. I would recommend using the rigid ones because they are cheaper and more durable. However if you are putting them on a bimini or want them to be flush with the roof of your RV I would recommend the ones I have here.
Low power systems are better suited to a PWM controller because:
- A PWM controller operates at a relatively constant harvesting efficiency regardless of the size of the array
- A PWM controller is less expensive that a MPPT, so is a more economical choice for a small system
- A MPPT controller is much less efficient in low power applications. Systems 170W or higher tickle the MPPT’s sweet spot
Watt, Amps, What!?
Watts are basically just a measure of how much power a device uses when turned on, or can supply. A watt is a watt – there is no such thing as “watts per hour”, or “watts per day”. If a something uses 100 watts, that is simply the voltage times the amps.
Watt-hours: A watt-hour is simply how many watts times how many hours that is used for. If a light uses 100 watts, and it is on for 9 hours, that is 900 watt-hours.
Amps: An amp is a measure of electrical current at the moment. Amps are important because it determines what wire size you need. All wire has resistance, and amps flowing through a wire makes heat. If your wire is too small for the amps, you get hot wires. You can also get voltage drops in the wire if it is too small.
Amp-Hours: Amp-hours (usually abbreviated as AH) are what most people mean when they say “amps per hour” etc. Amps x time = AH. AH are very important, as it is the main measure of battery capacity. Since most inverters run from batteries, the AH capacity determines how long you can run.
When shopping for your batteries there is one main requirement. They need to be deep-cycle NOT standard or starting. There are a lot of battery types that fall under that including flooded, gelled and AGM. I have learned that the batteries from Walmart do the job fine and are a lot cheaper than the fancy AGM ones. I have two EverStart Marine Battery, Group Size 29DC. It has 845 cold cranking amps and 65 amps reserve capacity. I have a refrigerator on board that uses 0.7- 2.5 amps an hour. It charges from my solar panels daily so it runs the refrigerator perfectly. Monitoring your batteries is very important, I use this cheap battery monitor to make sure the batteries are in good condition. It is so important I even included it in my Top 10 Essentials. I have heard great things about using 6 volt golf cart batteries in this setup as well.
Battery Type Categories
Flooded (Wet Cell) (Non-sealed)
- Contains a liquid in an unsealed container
- Better availability of types and sizes
- Requires adequate ventilation for the batteries.
- Requires an area where maintenance can be performed
Sealed (Dry Cell) (Maintenance Free)
- Do not need to be kept upright
- Reduce the electrolyte evaporation and spillage that is common with wet-cell battery
- Greater resistance to extreme temperatures, shock, and vibration
- Same flooded batteries except that the antimony in the lead plates is replaced by calcium
AGM (Absorbed Glass Matte)
- No spilling of acid
- Low maintenance (no top up needed)
- Temperature tolerant (operate at -20°C)
- Vibration resistant
- Discharge much deeper
- Charge much faster
VRLA ( Valve Regulated Lead Acid battery)
The valve regulating mechanism allows for a safe escape of hydrogen and oxygen gasses during charging.
Overall (in comparison to lead acid) these batteries are lighter, have a deeper life cycle (they can discharge 100%), charge faster, have a greater lifecycle and have a higher output. Really the only downside is the price. Currently they are around 8x or more expensive than a lead acid battery.
Lithium Cobalt Oxide
- High capacity
- Common in cellphones, laptops and electronic cameras
- Shorter lifespan and limited specific power
Lithium Manganese Oxide
- High thermal stability
- Common in medical equipment
Lithium Iron Phosphate
- Long cycle life
- Common in electric vehicles
Lithium Nickel Manganese Cobalt Oxide
- Either has a high specific energy or high specific power (not both)
- Common in power tools and electric vehicles
Lithium Nickel Cobalt Aluminum Oxide
- Long lifespan
- Common in electric powertrains and in grid storage
- High energy
- Not as safe
- Very fast charge time
- Lower voltage
- Common in storing renewable energy