Smart Solar Powered Hot Tub

One of the things I had planned as part of our smart home solar installation project was a hot tub that was powered by solar energy and controlled by my contextual smart home.

Research

My research so far has concluded the following:

1. The key thing to reducing running costs is to buy a quality model with really good insulation and a well insulated cover.
2. A model that uses a heat pump will use a lot less power, typically about a third less for heating the water.
3. The filtration pumps use a significant amount of energy but, these can be run using solar energy, off-peak energy or stored energy.
4. It is best to leave a hot tub on whilst it is in use, so that it is only being topped up with heat. Heating it up from from cold uses a huge amount of power and takes a long time.

Heat Pump

An air source heat pump has a Coefficient of Performance (CoP) that varies throughout the year. In the winter months it will be relatively low at around 2.5, in the summer months the CoP may be 4 or more. This means that for every 1kWh of energy put in to the a heat pump with a CoP of 2.5 will produce 2.5kWh of energy, so you gain 1.5kWh or 150% more energy. Whilst there is a

Monitoring

A key element in understanding how much energy our hot tub is using will be having the right sensors installed to monitor, temperatures, usage, energy usage, etc. I plan to have this all connected to my contextual smart home, as it will also be doing my smart energy management.

Design

My plan is that we would only ever use solar power and battery storage to get our hot tub up to temperature and to then maintain the normal operating temperature (typically around 37.0°C to 38.0°C). I will consider importing energy at off-peak rates though.

I am looking at one that is between 2.0m × 2.0m and 2.4m × 2.4m. Some hot tubs use a 13A power feed but I've already installed 25mm ducting underground for a 32A cable.