Daytime-only operation of pond equipment

[kb58]

We have a koi pond which consumes roughly 500 watts continuously. At first I was considering the "nuclear option" of a grid-connected setup, but between reading more and also having SDGE implementing TOU costs, I've been considering alternatives.

Number one is going to be looking into a more efficient way to move water in the pond. Regardless how that works out, the next step is looking into putting together a small (~500W) off-grid setup dedicated to running the pond. When the sun goes down or it's cloudy, there'll be a relay which switches over to grid power. Once the proposed system is drawn up, it'll be analyzed to see if it's an economic go or no-go.

So the reason for the post is: what's a reasonable way to generate ~500W (lets aim for 600W due to inefficiencies)? I don't need a full-blown inverter, so I was thinking of maybe something intended for a motorhome. That said, I know most (all?) of those are intended to work with batteries, which I do NOT plan to use. So I'm asking the hive, what type of inverter should I be considering? I know automotive inverters are really cheap due to the numbers made, but they won't work well if I want to use several largish panels that generate 30V or so.

What say you!

[littleharbor]

You should look into a DC pump option. You can potentially have a direct from panel to pump setup, needing no batteries, charge controller or inverter. A linear current booster would optimize a setup like this but may not necessarily be needed with the right solar type pump.

[kb58]

Understood, but when the sun goes down, a grid-powered power supply would have to step in. There are other loads besides just the pump, there's a second smaller pump, two air blowers and a UV light. Since I already have the 115VAC equipment in place and running the pond, I rather not start over. That said, I appreciate the input, as options are always a good thing.

[SunEagle]

Understood, but when the sun goes down, a grid-powered power supply would have to step in. There are other loads besides just the pump, there's a second smaller pump, two air blowers and a UV light. Since I already have the 115VAC equipment in place and running the pond, I rather not start over. That said, I appreciate the input, as options are always a good thing.

DC to AC inverters require a constant voltage source which you will not get directly from a solar panel.

A battery is the easiest way to create that voltage source but it will end up costing a lot more then finding a way to get grid power to your AC pond loads.

[kb58]

DC to AC inverters require a constant voltage source which you will not get directly from a solar panel.

A battery is the easiest way to create that voltage source but it will end up costing a lot more then finding a way to get grid power to your AC pond loads.

Getting grid power to the pond is was done 20+ years ago. The purpose of this exercise is to see what it takes to minimize grid power usage. A buck/boost DC/DC converter can deal with input voltage variations, so the dire warnings are noted but can be addressed.

[ButchDeal]

Getting grid power to the pond is was done 20+ years ago. The purpose of this exercise is to see what it takes to minimize grid power usage. A buck/boost DC/DC converter can deal with input voltage variations, so the dire warnings are noted but can be addressed.

if you have grid power there then the cheapest and most effective solar solution for minimizing grid power usage is .......... Net metering, not off grid

[PNPmacnab]

There are numerous youtube videos on this, most poorly executed. Grid tie panels are cheap and technically this isn't that hard to do, but switching between sources requires a bit of logic. I do elements of this now with highly modified equipment. Given that you feel you have to ask, I doubt that this possible for you to do. The big cost advantage is not running the grid wires initially. I do question the need to run these pumps all the time. What do I know about fish.

[bcroe]

The advice above is spot on, suggest you carefully consider it. Other methods can be made to work if you throw
enough money at them, but that violates the original idea.

It would be more accurate to say that while the MPPT operating voltage of panels varies little, the available
current current varies MORE than an order of magnitude over the seasons, time of day, and with clouds or
lack of them. That means the available POWER varies in a similar way, and your buck/boost converter can
do nothing about the power available. Trying to pull any more power from the panels
will result in the voltage (and power) collapsing to practically nothing.

An AC induction motor pump wants a nice solid source of power to run and a much larger surge to get started.
The PoCo provides this, but PV panels do not. With just enough panels to get running under best sun, the
system will be cutting out at any variation of conditions, such as a small cloud drifting by. With lots more panels
to run it much of the time, extra output available under best sun will be thrown away.
And daytime shutdowns will still occur.

A couple ways around these problems, are a variable speed DC system, and a net metering setup with the
PoCo. good luck, Bruce Roe

[SunEagle]

Getting grid power to the pond is was done 20+ years ago. The purpose of this exercise is to see what it takes to minimize grid power usage. A buck/boost DC/DC converter can deal with input voltage variations, so the dire warnings are noted but can be addressed.

If you are trying to save money then stay with the grid. If you are trying to experiment with solar technology then open your wallet and pay the man.The only solar equipment that will eventually pay for itself would be a grid tie system.


I am sure there are ways to power AC equipment from solar panels without using a battery but you will need the proper electronics to eliminate voltage fluctuations. I

MO most DC to AC inverters won't work that way. But if you want to try it then have at it. It's your money.