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Wednesday, November 8, 2017

Making every watt count



In the bad old days of terribly expensive solar electric power, there were some tricks to keep power usage down. Now that solar electric is a fraction of the cost, most of those don't make much sense anymore. There is one trick that still has merit in a number of specific instances.

Here's the thing about solar electric systems. The panels generate DC power. Everything in your house runs on AC power. An inverter is used to convert that DC power, stored in batteries, into AC power that all your electrical stuff uses. Good sized quality inverters used to be terribly expensive. Even today, while there are cheap ones on the market, the better ones will cost some real coin. For most people, they are necessary.

Another disadvantage of inverters is that they are not 100% efficient. At best they run around 90%, but under some load conditions they can be much lower, around 50%. When you are counting every expensive solar watt, throwing half of them away was a terrible deal.

Most small solar panels run at the proper voltage to charge 12 volt batteries. That's pretty handy, as there are lots of things that run at 12 volts. When panels and inverters were expensive, many people set up their places to run totally on 12 volt. There are lots of things built to run on 12 volt, everything from radios to coffee makers. People even went to the trouble of buying 12 volt deep well submersible water pumps.

People who have small solar systems might want to consider taking a page out of the early days of solar. For example, my small sailboat doesn't have a lot of room to mount solar panels and store batteries. My van has only a 105 watts of power. The longer I can stretch those watts, the longer I can stay out.

You probably already have things like 12 volt adapters to charge your cell phone and tablets. My marine radio has a 12 volt charging option. I use 12 volt fans to keep cool. My small computer has a 12 volt charging option. Recently I even ordered a DC adapter for my C-pap machine. Not having to run the inverter saves energy. In fact, I can use a cheap 400 watt inverter for the remaining things rather than a more expensive larger inverter. Running directly on 12 volt, there is one less piece of machinery that can fail. An added bonus is not having to listen to the buzz of an inverter working.

Sometimes the old tricks find life in new applications.

-Sixbears



12 comments:

  1. Interesting. I've been trying to figure out a way to make a small workshop 12 volt. I'm not sure I've found it yet, but I'm still thinking.

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    1. That's an interesting idea. I've seen high voltage DC workshops. Most power tools will run just fine on 110 DC, except the switches burn out. Those have to be changed to something more robust.

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  2. Our house is 100% off-grid. 1800AH of batteries @ 24VDC. We have a good 4.5kW+ inverter but it was not cheap. Standard AC wiring throughout but I ran a separate DC buss straight from the batteries for all of the lighting (24V LED strips). Also have DC at fridge and freezer locations (add cheap 1.5KW inverter and foods stay fresh) and a couple of 24VDC outlets (IP rated motorbike plugs!) throughout. I got paranoid about the inverter failing, so we'd at least have lights and refrig. That said, it hasn't skipped a beat in ~4 years now...

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    1. You have quite the system. Good mix of DC and AC. My old Trace 2024 inverter has lasted over 20 years, but I've friends who replace them almost every year. One guy I know just across the border in Maine gets hit by lightning all the time. Bad location and he must be doing something wrong.

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  3. Wish I could convert to solar but $$ I don't have.

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    1. You can start small -and stay small. It's nice to have a light and a charged phone.

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  4. Sounds like you've got it figured out, Sixbears. Good for you ~

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    1. Just sharing in case it could help someone.

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  5. Have you seen this? http://www.businessinsider.com/hydra-light-lantern-uses-salt-and-water-to-charge-2016-3

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    1. I have my doubts, but I'm going to wait and see. I don't doubt that it works, but I wonder exactly how it works and if it's any sort of a breakthrough or not. The salt water could be an electrolite and other parts would need to be replaced when reused.

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  6. https://www.youtube.com/watch?v=fLuNycSIiSo
    Bob Wells @ CheapRVLiving has lots of solar info and ideas, as well as interviews with people that put together small solar systems.. Good info.

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