A long time has passed since my last post, and really any completed project.  With the situation with my dog, Nunya, I have been kept busy and in the limited amount of extra time, I foolishly have allowed myself to jump from project to project.

Solar Panel Controller BoxOne thing that is almost finished (at least finished to the best of my ability), is the solar panel project I have been working on.  It started with Alison building solar panels to charge old UPS batteries for the power wheel tank we are working on and then jumped to real solar panels pieced together by cheap parts that I found on the internet.  The main goal was to have some basic lighting if we have another interesting hurricane season.  I also wanted something I could fit in a box and take with me when going camping or boating – so my idea was built around portability.

The first lesson I learned in the world of solar is it is NOT cheap.  This lesson was quickly followed by another lesson – be prepared to do the reading and make your own mistakes.  The attitude of a lot of the serious message boards echoed the tone of most of the older linux message boards.  They will help you but you have to EARN the knowledge.  Understandably, when asked the same question 10000 times (“I am on a tight budget, say $500, how many solar panels do I need to run an air conditioner, refrigerator and everything else in my house including the pool pump?”), you might grow a little cold.  So at this point in time, you see “lmgtfy.com” as many of the responses.

To help anyone out that might have come to this blog with the question of “how many solar panels do I need”?  First let me tell you that you have to be realistic about price and what you really need to run.  If you are looking for powering your whole house, at this point, forget that idea, buy a bunch of solar panels, get a grid tied inverter (example only – I have no experience), take the tax deduction, and sell the electricity back to the power company.  To my knowledge that is still the fastest way to break even from the costs.

For anyone one else who is wanting to run something when the sun is hiding, you will need to do a few things:

Know Power Usage:

Raspberry Pi 512mb uses 1.9 watts at idleFigure out how much electricity you need by using something like a Kill-o-watt power meter.  If you know the wattage, say 60 watts per hour on 1 light and 30 watts per hour on a small fan (90 total watts per hour), then divide that by the voltage (115-120v) if you are using a normal inverter and you will get the number of amp hours of power you will need to have stored .  With the example above, we would need about .78 amps per hour to run our two items, EXCEPT here is the fun part – inverters are getting more efficient but there is still some power loss to heat so leave at least 10% wiggle room.  In my situation, I bought 12volt lights so I would not have to worry about the inverter, otherwise you will have to find the right type of inverter for your needs.  I would recommend further reading on sine-wave inverters vs. non-sine wave inverters.

Know Solar Power Production:

Panels come in several different wattages.  Most of the ones that you see used in this type of solar application will be 12v or 24v (big boys or panels connected in series).  The wattage they advertise pretty much is based on the best solar conditions possible – no clouds, direct sun, and somehow no heat.  You can calculate the amp hours of power that you can make with the same formula above.  For example, 100 watt panel in full sun, etc, etc divided by 12v gives you 8.33 amp hours (amps per hour).  Realistically, you might hit this yield 4 hours a day in the summer.  This website allows you to track the sun over your exact location.   Try to be realistic in your calculation.  Your panel will still make power when not fully exposed to the sun, but the wattage will be less.  For a hypothetical day with a 100 watt solar panel you might make 4 hrs of 8.33Ah and 2.5 hrs of 5 Ah, giving you a total of 45ish amp hours to store / use.  But again there is loss during the storing / using process so give yourself wiggle room.  Texas is very hot – I assumed 30% loss in my calculations – not sure if this is correct.

Buy Storage for All Your Beautiful Sun Power:

This step is really where the fun stopped for me and I think it is the real glitch in solar panels (and anything relying on energy storage.  There are many battery types but my comments only relate to the little I know about sealed lead acid batteries (SLA).  They are typically the cheapest and the ones you will see for anything other than starting your car will normally have an Amp hour rating.  The pain starts when you realize that you only get to use about half of the number advertised because from my understanding draining them past that point limits the total number of charges in the future.  So the hypothetical 45 amp hour battery you wanted to store all the juice from your hypothetical solar panel becomes a need for a 90 Ah battery (assuming you were only wanting to use 45Ah in a day and there were never more clouds then estimated).  The batteries start getting expensive quickly.  Oh, I should also mention that you need a charge controller for any panel over 5 watts.  They range in price depending on your setup.  Since my system is portable and this solar experience was more about education than function, I found a 35 Ah battery with free shipping and called it a day.

I loved the way they shipped the battery!

I found the battery packaging funny.

As mentioned above, I also found several other small 12v batteries in devices that were not being used (all around the 7-9 Ah range) and I play with those as well.  They make for a great short term portable lighting solution.  From my reading, a lot of people recommend 6v golf cart batteries tied in series to increase the voltage.  The reason/my limited understanding is the thickness of the plates within the batteries and the cost give you a better overall cost per watt.

For now – my system is basically 100watt panel, connected to a charge controller, charging 12 volts batteries – either a bank of small batteries or the 35Ah battery.  I use the energy to run a small pool pump, pump water from rain barrels, or add our door lights.  At my scale, I will never regain the cost but hey I think I learned something.

Solar Panel with a DIY mountI did end up mounting the panel on the roof after watching a youtube video (probably should have watch a few more videos).  The panel is pretty secure and I hopefully did it correctly to prevent leaks.  I can still take it down quickly and hopefully this will prevent me from breaking it when not in use.  I need to run the wires through conduit still to clean it up.  The single panel looks lonely by itself.

One note – in the solar industry they have special connectors – MC4 connectors.  I find them extremely annoying and overpriced.  It is insulting that they ship you a coaster with your purchase of an $8 piece of plastic.  The connectors get cheaper at scale and “you can’t put a price on safety”  but seriously they are impossible to find locally and there are many other cheaper solutions that are just as safe.  Was this standard picked just to be annoying and help prevent water rings on coffee tables?

Warning – Electricity can hurt, please do your own research and take precautions.  I also encourage you to tell me about my mistakes! (quickly please)


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