I'm looking for a way to partially power an applicance (a fridge freezer for argument's sake) using solar/renewable energy.

I don't expect the couple of hundred watts of solar power to be sufficient to fully power what I have in mind, but wondered if such a device as the following exists or is easily made so as to reduce energy bills but not have to interfere with the incoming mains power supply or investing in a bank of batteries.

What I'm imagining is a solar inverter which plugs into the mains (230V AC) and also takes 12V DC as input (from the panels), and only uses mains power to "top up" any requirements not met by solar, with a 3 pin UK plug socket as output to plug the appliance into?

Does such a device exist, and if it doesn't is there good reason for it not to exist?

[edit] I've found this http://www.amazon.co.uk/dp/B00C0D8C3W but it's unclear whether it will flow back into the grid?


closed as off-topic by Keelan, placeholder, Daniel Grillo, Chetan Bhargava, tcrosley Oct 4 '14 at 19:08

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  • \$\begingroup\$ What you are talking about is a solar system that delivers energy to the power grid, that is no need to think of a specific device you want to "support". You can read about that in detail on Wikipedia: en.wikipedia.org/wiki/Grid-connected_photovoltaic_power_system and elsewhere. \$\endgroup\$ – Andreas Wallner Sep 22 '14 at 18:48
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    \$\begingroup\$ @AndreasWallner That is something different. OP wants something that does not allow energy to flow out of the house (because that would mean additional paperwork and approvals). \$\endgroup\$ – venny Sep 22 '14 at 18:57
  • \$\begingroup\$ @venny I don't read anything that would explicitly rule out such a solution, but you might be right. We'll have to wait for the OP to clarify. But at least it's a starting point. \$\endgroup\$ – Andreas Wallner Sep 22 '14 at 18:59
  • \$\begingroup\$ Correct, I'd like if possible to avoid messing about with feed in approvals and the electricity board \$\endgroup\$ – Rich Sep 22 '14 at 20:59

If you have a solar powered inverter that works some of the time (because the sun don't shine all the time) AND your inverter works from 12V (from some kind of solar regulator and battery?) then why complicate things by trying to get your fridge/freezer dual powered from the inverter output and mains AC.

Simplest way (to me) is take your AC mains, step it down with a transformer, convert to DC (bridge rectifier), regulate to +13.4 volts and feed onto the 12V your inverter is using. Call it a "power supply".

If the solar stuff aint producing the goods (energy wise), the 12 volts will be topped-up from the power supply. If the solar panels are producing the energy then, by careful control of the "power-supply", it'll barely consume any energy.

I think this overcomes several headaches of trying to ensure your solar inverter AC output doesan' "clash" with the real AC mains.

  • \$\begingroup\$ Sounds reasonable, how much would I lose in inefficiencies from going from 230V-12V and back again? \$\endgroup\$ – Rich Sep 22 '14 at 20:59
  • \$\begingroup\$ @Rich - it won't be perfect for sure but it could be better than 70% efficiency if you used an AC switcher. On the other hand, if you are looking for an efficient solution then maybe consider replacing the motor in the fridge with a DC type that runs from 12V. Fridge lighting might still need AC though. Just a thought. \$\endgroup\$ – Andy aka Sep 22 '14 at 21:04
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    \$\begingroup\$ How would you actually do the wiring of the converted main DC power to the inverter, with the solar panel in the mix? \$\endgroup\$ – Josh Diehl May 15 '16 at 20:36

To add to Andy's post. So, you have your solar array and your power supply, feeding and building up the batteries. but as others mentioned, it's a very inefficient system. So there are units available to handle it another way.

The AC into the house goes through a relay which is normally selected to feed city AC to the appliance(s)

The solar panels feed a battery "pack" which feeds an inverter after the charge is full. This triggers the relay to switch over to the inverter output. When the charge goes too low to feed proper AC current out of the inverter, the relay switches back to city AC.

Now you are providing some of your own power while still having enough to power everything.


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