What Solar Panel to Use?

Welcome to the forum EhrenB,

This kit is a bit "iffy"... The solar panel output is roughly 10 amps in full sun, and the charge controller is shown as either 8 amp or 12 amps rated current (first picture shows 8 amps, description does list 12 amp controller).

Another issue is that they supply a cigarette lighter socket and alligator clips... That is not a great connection method. Alligator clips are not very reliable. Ideally, you should have "bolted" electrical connections.

Also, watch the shipping costs... Large glass panels are expensive to pack and ship... ~$20 for shipping (at least to my zip code) does not look bad--Just confirm that shipping costs are good for you.

However, if you want to try solar and combine it with a 100 Amp @ 12 volt deep cycle battery... It can work. For a reliable system--Eventually you will want to replace the clips and sockets with solid electrical connections.

Overall system price wise--That is up to you. Assuming the solar panel and charge controller work well, is not a bad price.

If you price out a 180 watt panel, a 100 Watt AC inverter (with power switch), charge controller, and wiring--You can end up with a more reliable system (get a small inverter that is wired directly to the battery bank).

Remember you are dealing with electricity here... A 100 AH 12 volt lead acid deep cycle storage battery can output several hundred amps into a short circuit (or start your car). Using 12 AWG wiring and a 20 amp fuse to the battery bank is a good start for safety.

Solar power systems sit outside for days (to months) without anyone around. You probably are in a "greener" area than I am (Minnesota? vs California for me). But in any case, you don't want to start a tree fire if anything goes wrong.

-Bill

Ehren,

Off grid solar is something like 5-10x the cost of utility power (utility power something like $0.10 to $0.40 per kWH depending on where you live, billing plan, etc.). Solar is something like $1.00 to $2.00+ per kWH (on average) once you roll in the cost of batteries, replacing batteries every 3-5 years (for inexpensive batteries), and electronics every ~10+ years.

If you can run a buried cable from your home to the tree--It can be much easier and much less maintenance (using GFI breaker for outside wiring or GFI receptacle very important to reduce chance of shock in wet locations).

http://www.solarelectricityhandbook.com/solar-irradiance.html

Eden Prairie
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 45° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.39	4.08	4.36	4.76	4.96	5.19
Jul	Aug	Sep	Oct	Nov	Dec
5.40	5.20	4.76	4.01	3.15	2.77

Solar panels need direct sun... Above is an example of how much sun you may get per day (long term average). You never have a lot of sun--But in summer it is decent.

Also, ANY SHADING kills solar electric panel output... Just blocking a single cell with a couple leaves can easily kill 50% to near 100% of a panel's output. Where ever you mount the panel, you want something 9am to 3pm full sun, at least. You can do things like point the panel towards the south east if you have trees blocking westerly sun. And if it is vegetation such as trees creating shade--Remember that trees grow over the years and shading can get worse.

A great way to get started is to measure your power usage. If 120 VAC, a Kill-a-Watt type meter is very nice (and also handy to see what appliances around your home may be wasting energy):

https://www.amazon.com/s?k=kill+a+watt+meter&ref=nb_sb_noss_2

To give you an idea of what energy usage you may be looking at and how to do a paper solar power system design...

• 30 Watt laptop computer * 2 hours per day = 60 Watt*Hours per day
• 3 * 13 Watt LED bulbs * 5 hours per day = 195 WH p_er day
• 60+195=255 WH per day
• Battery sizings... 1-3 days of storage, 50% maximum planned discharge (longer life). 2 days storage is good number
• 255 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 100 AH battery bank @ 12 volts
• Solar panel sizing... 2 calculations, 5%-10%-13%+ ... Suggest 10%+ for full time off grid (and "happier" battery)
• Based on battery bank AH and rate of charge: 100 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 188 Watt panel/array nominal
• Based on hours of sun per day (pick 4 hours as "good weather" time): 255 WH per day * 1/0.52 overall solar system eff * 1/4.0 hours of sunlight average minimum) = 123 Watt array minimum

So, a system with a 12 volt @ 100 AH battery, a solar array of ~123 to 188 Watts minimum would run a weekend/random use during sunny weather power system that would run a good size laptop for 2 hours and 3 LED lights (interior and outdoor floods for example).

My laptops run >2 hours on internal battery anyway--So use outside without solar power, etc...

At least you can see the math for a paper design. Keeping your loads small and efficient is a good start with solar.

Fire is not a huge issue... But doing things right (bolted up wiring of correct AWG for current, keep dry/out of weather, good cooling for charge controller, etc.) is all a big help. Nobody expects a fire--But things happen. We don't do an inspection of our car's electrical system before every drive... Solar is similar--A working system is forgotten (remember to check water levels of deep cycle flooded cell batteries once a month, check system voltage to ensure batteries are being full charged between uses, etc.).

Also remember that current is dependent on voltage and power... For example:

• Power/Voltage=Current: 100 Watts / 120 VAC = 0.833 amps (at 120 VAC)
• P/V=I: 100 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff voltage = 11.2 Amps

So, the AC inverter outputs 0.83 amps to a 100 Watt Load @ 120 VAC, but takes 11.2 amps from a 12 volt battery... So, the DC side needs much heavier wiring (and larger fuse/breaker) to run a 120 VAC load.

The devices (solar panels, charge controllers, inverters, and batteries)--If good quality do not generally cause issues... However, poor quality (aka "cheap") devices can start fires. As can "abused" batteries (boiled dry), overloaded/overheated wiring, and poor/corroded electrical connections.

For example, here is a "gray market" set of panels that caught fire:

https://forum.solar-electric.com/discussion/3375/panel-fire-question/p1

Not saying that will ever happen to you--But you want to be careful that you do things "right".

-Bill