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Old 12-10-20, 08:31 AM   #1
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Default Running a heatpump on solar power

Has anyone run a heatpump on solar power?

To date I've run mine on the grid but I also have a solar electric installation (and solar hot water/heating but that's another subject).

I was using gel batteries but they were pretty old so I've just replaced them with lithium ion. I now see that the batteries charge up pretty quickly so I end up with power that I'm not storing.

My idea is to add a small heatpump (around 1.2K power consumption) that comes on when my batteries are full and stop charging.

Has anyone considered/done this? Any experience?

I can get a MODBUS TCP data feed from my charge controller (Midnight Classic) so I know when the batteries switch from absorb (bulk) to float (I'm hoping to get hold of the api for the batteries so I can get a feed from them too).

Anyone done anything like this?

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Old 12-12-20, 06:17 PM   #2
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You can definitely look into thermal storage using "IBC totes". Basically, you'll add copper tubing inside the tanks to act as the heat exchanger and then fill the tanks with water to use as the thermal storage medium. On the control side, easiest would be to use a VFD driving a 3 phase compressor and program the controller to try to hold the battery charge level at 90% or whatever.
To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
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Old 12-14-20, 06:03 PM   #3
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Yes we ran a geo-thermal heat-pump most of the summer on solar. Actually we where off-grid most of the summer.

Our system is sizeable 14.5 kW of solar 34kwhs of battery (lithium) and 20+ kw of inverter

The scenario was like this: As the sun rose in the morning the batteries began to charge and as the sun became more intense the air-conditioning would cycle more and longer By 10:00am the batteries where near full and the heat pump was beginning to flex its muscles to keep our home most comfortable.

The inverter supplied a clean uninterruptible 240 volt to supply the house. Not even breaking a sweat!!

As well the car is charging and clothes and dishes are washed and the list goes on.

Yes solar and air-conditioning fit well

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Old 12-19-20, 11:30 AM   #4
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Wow, a BIG solar system, my solar isn't quite as big, I have 2K of panels, 10K lithium batteries (Pylontech) and a 4.4K Studer inverter that's now about 14 years old so not much chance of getting much data from that. I'm planning to build a DC current monitor (using a hall effect sensor, not a shunt as I gather Lithium batteries don't work well with shunts) so I will have an idea of the DC current being taken by the inverter as the battery data only tells me the charge/discharge of the batteries, not the whole system. I can calculate this from the charge controller power - the battery charge power but it will be interesting to know.

I've now managed to get a data feed from the batteries so I can monitor the state of charge, charge/discharge current, battery voltage etc. that will let me better control the switching in of loads to take up the excess generated power. I also have the feed from the Midnight charge controller so I know what's coming in from the panels.

Have you automated your system to optimize usage in any way or is it just that it's big so you can load it up? What about cloudy days, even with 34K of batteries there is only so much you can use and if there is no control then it could get used up pretty quickly.

I'm fortunate in having both grid power and the solar, my idea being to optimize the use of the solar running the heatpump when I know I have the batteries fully charged. For times when I don't have excess solar I can fall back to the grid.


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