Solar immersion rods – 380v AC od 48v DC
Hi to everyone in Canada. I live in Austria, which has a similar climate to you guys, and need to reduce our heating bills a LOT.
I need to heat 2x 1000ltr water storage units for heating/hotwater as quickly as possible every day – even in Winter with snow 🙂
My intention is to add 30x 455W solar panels in a 2 string array.
My question to you guys who are doing this daily – is it better to feed 4x 48v/2000W immersion rods via DC directly from the panels, OR install 4x 380V 9KW rods and install an inverter?
Of course we have a 30KW oil/wood furnace to use when the panels dont supply enough …
Thanks for any advice i can get.
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I think the rods are just electric resistance with a COP 1.
Where in Austria are you? In Vienna the weather is similar to NYC where I live. In this case a cold climate heat pump will fit the bill much better, with avg cop at least 3, will use 1/3rd the total electricity.
These are likely quite standard across Europe more so than Canada or USA.
You generally don't want to feed DC directly to the heaters without an MPPT. Directly connecting the panles is possible but you loose a lot of efficiency (~50%) from temperature and sun variation.
So either way you are buying electronics. To me, inverters are more useful as they create power you can use elsewhere in the house as well. It also means you can use standard AC heating elements and controls.
Heat pump option is definately better for efficiency but does add extra cost. Depending on the cost of the solar install and how much extra area you have, the heat pump option could be wroth it.
Heat pump can provide enough low temperature heat for space heating, but you would still need a separate tank to give you the temperature lift for hot water. This could be a standard electric water tank.
+1 for using inverters here. You may lose a little overall energy in the conversion process, but the inverters ability to help optimize the load on the panels and also to provide power to things other than just the water heaters is a big plus.
"Better" will be clearer are you price the options. A heat pump is likely to be added complexity at about the same price.
Caution: never apply DC to a temperature controller designed for AC - the contacts will arc.