danielOne of the most common questions folks ask is how much solar do I need. There is not an easy answer to this question because everyone’s needs are different. The default response is generally to perform a power audit. Write down all the things you want to use, how much you want to use them, and how much power they take. I took a bit of a shortcut and used the fact that my hardwired surge protector (Hughes Power Watch Dog) has an energy meter. I was able to monitor my usage over the coarse of a few camping trips to get an idea for the amount of power I was using. Not including A/C I calculated that 200AH of capacity would be my minimum and 300-400 would be awesome. This would be assuming I am using lithium batteries. I would need to double it for lead acid or AGM. The cost of lithium was off-putting but after I found you could build DIY LiFePO batteries for a fraction of the cost the game changed. Below is a quick overview of the major choices I made. I will go into detail of each choice in separate posts.
- ~7,800 watt/hr Lithium Iron Phosphate (LiFePo) battery bank
- 1,660 watts of solar (4x 415w panels)
- 1,450 watt MPPT solar charge controller (when used with a 12v system)
- 2,400 watt hybrid inverter/charger
Battery Bank
Initially I was planning to build two 280ah 12v batteries. When time came to order Eve had released 304ah cells so I ordered eight 3.2v 304ah LiFePO cells to make two 12v 304ah batteries. Wired in parallel these would create a 608ah battery bank. This should be plenty to last through cloudy days and even run the A/C for a little while. The battery management system (BMS) for each battery build will be JBD 150a 4s Smart BMS’s. A Victron Smart Shunt will be used to track the state of charge (SoC) of the battery bank.
Solar Charge Controller
Instead of sizing my solar off my audit I decided to size it around the battery bank. In the summer you get around 5 to 6 hours of productive power generation from your solar panels. If I want to be able to put 500-600ah back into my battery bank I need to push 100amps during those 5 to 6 hours. The solar charge controller I will be using is the Victron Smart Solar MPPT 150/100.
Solar Panels
In order to keep the solar charge controller running at 100amps I would need at least 1450w of solar on the roof. I wanted to error on the side of more solar. This would help with the less then optimal flat roof mounting configuration. This is sometimes called over paneling. Your roof may decide the amount of solar you can mount more then your needs. Mine was thankfully mostly clear. I was able to use just a few large panels vs lots of small panels since I did not have lots of roof mounted objects to work around. I settled on four 415w mono-crystalline panels. They are each just under 40″ x 80″. Total solar power is 1,660w. One more panel would have been even better (2k+ watts) but it would have made access to the roof for maintenance much more difficult.
Inverter & Charger
I chose to use a 12/3000/120 Victron Multiplus Inverter/Charger. The inverter portion is 3000VA or 2400watt. That works out to almost 20amps at 120v. Just enough to run the A/C with a softstart. The existing 30a shore power input has been plenty of power even when using the A/C. The charger side allows for up to 120a of charging. 120a is also about as much as can be expected out of a ~2000w inverter generator. On a series of cloudy days I can run a small generator for a few hours and push 100+amps each hour into the battery bank.
- Just on the inverter ~ 16-20amp of usable power
- Moochdocking with a extension cord (~10-15a) ~ 30a of usable power
- 30a hookup ~ 50a of usable power