Need practical advice on solar system

By z on Wed, Sep 12, 2012 - 3:37am


I am about to plunge for the first time into the solar world... I am going to buy a 100W (12V) panel, 20A charge controller, battery and 12V/220V converter. The idea is to "wet my feet" with this small off-grid system, and I would appreciate some sage advice from the experts here!

1. Is 20A charge controller too much for a 100W panel? Should I go for 10A instead?

2. Which battery should I use? Lead-acid, car battery, etc... how many Ah would be appropriate for this small system?

3. Are there any special considerations for electrical cables, plugs, sockets, etc.?

I'd love to benefit from your experience!




Oliveoilguy's picture
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How some personal experience. Send me a PM and I'll respond

Wendy S. Delmater's picture
Wendy S. Delmater
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Posts: 1988
We have a few solar paels on

We have a few solar paels on the roof and run a charging station off of it. We use batteries from Uninteruptable Poower Pupplies (UPS) used to keep computers running util they can be shut down. They are "deep cycle" batteries, which is the kind you need.

When we bought oout solar kit, the batteries were not included. They cost as much as the rest of the system. Good places to buy them are the chain Batteries Plus and Interstate Battery.

silvervarg's picture
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Posts: 57
A few answers

I know this is a really late answer on your post, but as there are few posts in this section and you didn't get answers to your questions so far I will give it a try.

IIf you are sure that you will never increase your solar array you could do with a 10A controller. The 20A will give you a lot more headroom and also a possibility to expand, so if the price difference is not too big I would go for the 20A controller.

As for batteries the best is batteries that are meant for deep cycle, those are typically labled something like recreational use. Typical uses are in golf-carts, trailers, boats, ...
Usually they are only slightly more expensive that a normal car battery.

The amp-hours of your battery bank depends on your intended usage.
A few general assumptions: Aim to never drain your batteries lower than 50% (it will save battery life and give you some room for margin).
Most people consider worst case is complete cloud cover for 2-3 days (no electricity from solar panels).
What battery bank capacity will you need to cover your needs?
Personally I use a single 100Ah battery (about the biggest that is reasonable to carry alone) and I only have 60W panel.
Do note that the way I think the capacity of the battery bank does not depend on the watts of solar panels.

For low power appliencies I use normal car cigarett lighter output and USB output.
For more demanding output, like an inverter I connect it straight to the battery.

For cabling etc I choosed a switch panel intended for boats where each output has a lighted switch and a fuse with reset button. It is always good to have some kind of fused connections on the output when dealing with electricity. 

As far as the cabel diameters goes I will let an American answer as you incist on measuring cables in a strange fashion.

My advice is to keep it simple to start with, so the hurdle of starting does not become a major issue.'s picture
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inexpensive batteries government surplus

I am a frugal person who likes to get bargains. Several years ago I bought 2 banks of iron nickel batteries. Each battery bank was 128 volts dc. The cells were 145 and 180 ampere hours per cell with a short circuit current of 1400 amperes. Each cell was connected with 2 1inch wide bus bars per pole for a total of 4 bus bars per cell. These cells were about 400$ each on the open market. I bought all 124 cells for $390 which was just slightly more than the scrap value of the metal from the General Services administration surplus sales. These cells were the emergency standby power supply for the montrose colorado  area power plant and according to the person I talked to had been cycled less than 20 times in the lifetime of the batteries. The cells were about 15 years old but had filler caps for electrolite and were in perfict condition. Every power plant and nuke plant has these emergency standby power supplies so at least a couple of them show up at the surplus sales every year. I bought 36,000 dollars worth of batteries for less than the new cost of a single cell. The secret to buying government surplus is doing the research to contact the person responsible for scrapping the batteries so that the condition of the batteries can be determined before bidding on them. Mine were all in great condition but needed electrolite.


Best Regards



timothy smith's picture
timothy smith
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Joined: Mar 22 2011
Posts: 6
practical advice

Wondering if you made any progress on your project. I am similarly looking at

how to get started with "back-up" system for basics (frig, freezer, computer charger)  that has solar/battery combination.

If you are open to exchange would welcome learning more.






Denny Johnson's picture
Denny Johnson
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Joined: Aug 13 2008
Posts: 348
Home Power Magazine

I recently got an online subscription to home power magazine, a 3 Year Digital Subscription (18 issues) is $11.95 and includes free download access to our complete back issue archive.

The best $12 I've spent in a long time, a great education re things solar.

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