DIY Reliable Low-Power Home Solar Backup Solution

Here is a highly reliable low-cost low-power home solar backup solution. You can use this as a renewable energy power source too. Since as long as you got abundant sunlight beyond what can be charged into the batteries you can use this power to charge your gadgets. It is so small and lightweight you can build something inside your camping or RV Vehicles, cars/van/trucks and of course at home.

What is my use-case:

1. I want a renewable energy source for low-power devices which is "HIGHLY RELIABLE"

2. I want to charge or run my gadgets entirely from this power source

3. For powering/charging my Tab, Mobile phones (whole family), 3G rechargeable wifi router, DSLR camera, Video camcorder, my TrafficSqueezer prototype thinclient PCs, a backup CFL/LED Lamp if there is a power-cut.

4. I need to use this everyday when there is sunshine to power my gadgets and at night if there is an emergency.

I tried earlier lots of combinations from which I learnt several lessons what to do and what not to do. End of the day the reliability matters when you need this backup power. And also cost of overall solution matters.

Step 1: Parts Needed

Here are the parts which are needed:

Solar Panels: You need solar panels or a huge single panel. I got these panels long ago. I got a 70Watt 14Volt and two 12Watt 14Volt panels. So combined power output I get is: 70+(14x2) = 98Watts. Which means in a perfect full sunlight I get around 90+Watts, when the sky is bit cloudy I get around 50% output i.e 50Watts. During mornings and evenings or during when there are more clouds I get around 10-20Watts or even less. I purchased these panels around 5+years back. Back then Solar Panels are too expensive. I spent around: $280

Inverter/UPS: Cheap yet reliable low-power Inverter/UPS. In my case I purchased a CFL 45W UPS popularly sold these days in India. The advantage of buying exact type of UPS/Inverter is that amount of power it consumes when there is no load should not be too significant. Assume you have a Tab to charge which may be around just 10 Watts. I checked my Samsung Tab2 charger specs. It is rated 5V 2Amp output, that translates to 5x2=10Watts power. So never use those car Inverters for this need. I got earlier 1000w, 500w car inverters long ago attempting this. But later I realized it is such a waste of money. These inverters with no load in it, will itself consume lots of power by itself. So get a low-power UPS. This CFL UPS is just 45W is more than enough to power all your low-power gadgets. It will not get hot. It will not contain any heavy transformers inside and so they are highly reliable and light-weight. I paid around: $22. Along with it as promotional offer from Frontech guys two 5w LED Lamps. Which is cool ;)

Battery for UPS: The UPS I got is without battery included. So I got a Deep Cycle SMF (Sealed Maintenance Free), 12V 7.6Ah Lead-acid battery. For which I paid: $12.5

Solar Battery Charger or Charge Controller: I ruined couple of batteries without using one. So if your UPS does not have Solar charging option, I highly recommend to buy a separate Solar Battery Charge Controller. I got a charge controller which can support upto 300Watts of Solar panels and can charge battery upto 20Amp. So it is essentially a 20Amp 12V charger. I paid around: $10

Optional a Car Audio 1.5Farad Capacitor: I got this Cap long ago during my US trip for my jeep. But I never used it so far since the jeep is sold. I finally got a purpose to use this Cap for this project. I got this online via Sonic Electronix. It is Power Acoustik PC1.5F: 1 @ $39.99(copy paste from its bill)

So I spent around overall: $365/-

I believe you can get far more cheaper depending on your area.

Step 2: Putting Together

As shown in the picture connect the things together.

Solar Panels: If you got multiple panels connect them all in parallel as shown. Please make sure your polarity of connections are correct. If you are little scared about its power output you can do this job in morning or evening when there is not much sunlight or else cover a piece of cloth on the panels and work so that there is no high current involved and accidental short circuit.

Solar Charge Controller: The charge controllers will have typically 3 sets of terminals. One for solar panel(s), one for Battery, One for Load. We do not use the Load terminals, since we do not have any 12volt lamps or units to be directly connected to the load. Instead we connect the output cable of Solar panels to the Charger Solar Panel terminal set and connect the Battery connection output terminal to the UPS battery or in this case to the Capacitor (if you got one).

Capacitor: Make sure you know some basics about Electricals/Electronics. Capacitors are very dangerous. If you accidentally short-circuit it may damage the entire cables and may cause fire and damage your UPS and may damage your battery too. For a brief moment if the capacitor is not charged, it acts as a short-circuit for the battery charger. It may damage the charger. Since capacitor can take FULL power whatever is put out by charger and may charge. But this sudden pull of current will damage almost similar to short-circuit. Refer the next step in which I explained in detail how to install a cap. So know what you are dealing with and be aware what you are doing !

Disconnect/Remove voltmeter in car capacitor: Optionally you can remove the capacitor LED volt-meter. This alone will consume around 2-3 watts. Solar energy is precious, so lets not waste it. You can anyway use a multi-meter to check the voltage on demand. I visually noticed without attaching the battery by connecting solar power to the capacitor via charge controller. The charge controller charge LED often blinks which means it is charging capacitor since capacitor is wasting power powering its LED fancy voltmeter. After it is removed, I tested once again, the capacitor seems to be now holding charge for longer time. Now the charge controller LED stops blinking often once it is charged. Which means capacitor is holding the charge and not wasting it or neither self discharging.

UPS/Inverter: The UPS A/C input is of no use, since we are going to use 100% solar power. This UPS is intended to be used as regular A/C powered backup UPS. When it is connected to the mains, it charges the batteries, as well you can consume via its output. When the A/C supply is cut, it gives the backup power. But if A/C powercord is connected then what is the purpose of this project? So do not connect or use the A/C power source. The UPS came with no battery inside. So I got a 12V 7.6AH Deep-Cycle UPS SMF (sealed maintenance free) battery and installed inside. I soldered 2 cables near the battery terminal and extended outside of the UPS so that it can be connected to the capacitor and to the solar charge controller. The output of the UPS is connected to the powerstrip as shown in the picture. The other lamp output of this UPS is connected to a Lamp extension cord which I got already and connected the 5W LED Lamp to it which I got free with this UPS.

Including the pictures of my full setup.

Step 3: Installing Capacitor

You can use any high capacity capacitor. Even you can use a super-capacitor if you got one with appropriate specs. I.e which can support 12v (i.e) a safe max voltage upto 20volts.

Here are the detailed steps which shows you how you can install safely a cap along with a battery in parallel.

Step 4: Results

I am more than happy to find that it charges well all the gadgets. You never need any DC to DC converters. These off-market devices are highly unreliable sometimes and may fail or even damage your devices. Instead you can use the same manufacturer AC-DC chargers/adaptors to charge/power your devices. There will be some significant conversion power-loss, but we can compromise with reliability and simplicity w.r.t using these gadgets via power supply or via renewable energy sources.

Here is a picture of my Samsung Tab2 getting charged. It is getting charged at the same rate as with conventional grid power supply. I am posting this Intructable after 4-5 days of use. I want to see the real results and benefits before posting here.

Let me analyze my overall power consumption of various adaptors I got. And analyze the battery backup time during night:

Samsung Tab2 charger -> 5v 2Amp = 10Watts

Samsung Phone charger (also I use it for my rechargeable 3G wifi router) -> 5v 500mA = 2.5Watts

Nokia Phone charger -> 5v 450mA = 2.25Watts

Sony DSLR -> 8.4v 750mA = 6.3W

LED Lamp -> 5w

Assume all these are being used simultaneously at night (absence of solar power), so total consumption is: 26.05Watts

Battery per hour watt output: 12v x 7.6Ah = 91.2Watts

So 91.2/26.05 = 3.5 Hours battery backup I get for this amount of consumption in the night. This is a case for exact 7.6Ah output from battery. But in real scenario even if the current from the battery reduces a bit (after first 1 hour of usage) it should still continue to deliver the power output easily upto 4-5 Hours. Which is not bad, when you need for emergency at night. Especially when you use this for any outdoor portable use.

And this is the exact reason why you need a low-power reliable UPS/Inverter unit. A high power output UPS will heat-up too much and consumes significant amount of energy by itself (losses in the form of heat during conversion).

I am very impressed with the overall outcome so sharing this DIY with you guys :)

I hope you enjoyed this Instructable and might have inspired you. Please feel free to post your comments and suggestions. English is not my first language so kindly excuse me for errors in grammar.

Thank you.

Kiran Kankipati

Founder: TOFFEE http://www.the-toffee-project.org - Linux Open-Source WAN Optimization

My Youtube channel: THE LINUX CHANNEL https://www.youtube.com/c/thelinuxchannel/videos