Solar panel to DC heater

Mon, 16 May 2022 00:00:00 +0000

In Norway electricity is the most popular form of heating for households at 96% (source). Pure 230V AC is a very high-level energy, and we don’t really need that precision for heating.

This is a project to see if easy, not-perfect, locally generated energy can be used to lower the heating bill.

Disclamer: this is mostly for fun. A more economic aproach would be insulation, heat pump, put on a sweater, etc.

# The plan

             ┌──────────────────┐
             │                  │
             │                  │
   ┌─────┐   │  ┌──────────┐    │
   │     │   │  │          │    │
   │ PV  ├───┼──┤ Heater   │    │
   │     │   │  │          │    │
   └─────┘   │  └──────────┘    │
             └──────────────────┘
                  House

A solar panel, with no controller or inverter, and a heater. Dumping heat in a basement that needs heating all year round.

# The problem

Solar panels have an optimal voltage, where they produce most power, and this changes based on light conditions. A proper controller (MPPT) is expensive, so I want to see if I can do without.

# Hardware

Specs of my first setup:

180 Watt panel (the most power I could get in a normal 12 Volt range)
100 Watt heater with fan (I’ve ordered a 180 W model too)
ESP8266 for statistics (with dht22, ads1115, acs712)

# Setup

The panel, wall mounted in a very sub-optimal location (shadows from people, walls).

Panel connections in
Current sensor
Relay to switch off
Connections out to load

The heater with fan. It’s tiny. The heater is a PTC, so I don’t think it will pose a threat if the fan dies. In front of it is a white temperature sensor, to see that we actually produce heat.

A micro controller, with an external ADC. The micro controller generates graphs and control the relay. The resistors by the ADC are a voltage divider, to scale down the ~23 Volts the panel can deliver to a safe 5 Volts the ADC can measure.

Unloaded the panel will be at ~22 V. With this load one can see that the output is only good when the potential keeps between 12-14 V. I have no way of controlling the voltage, except for changing to a smaller load (less effective heater).

Graph of power output. Totally this gave around 600 Wh on a mostly sunny day.

Green line is the temperature sensor next to the heater. Measuring right next to the fan, I’ve seen it at ~60 °C, but this one is placed a bit away. The orange line is a temperature sensor elsewhere in the room. The room seems to rise about 2 °C during a day. The gray field is cloudyness in percent.

# Conclution

So far this seems to generate heat as it should, but it will have to run for a pretty long time to earn back the ~1700 NOK I paid for the panel. I will test with different heaters to see if I find something that works better. A posibility is also to have several heater that can be switched on with relays based on the power available. A kind of very crude MPPT.

# Thermal

The panel seems to have some significant hotspots. Normal? Cheap panel?

The relay is producing heat, but waste heat isn’t a problem in this case. =)

The relay is pulling more current than a GPIO from the ESP is rated for, so it’s voltage regulator is getting very hot. Should probably fix that.