View Full Version : PV water heating and grid-tie description

05-31-2018, 05:33 PM
I have tried various renewable energy sources, this is my PV system presently rated at 1Kwp.
Originally it consisted of only the Booster and hot water system, the GTI was added later to use energy surplus to water heating.

The reason for water heating is to save running the oil boiler that normally heats it at all in the summer, the energy input from solar also saves a small amount of oil in winter.

The booster is designed to allow a normal 3Kw/240V immersion heater to be used to heat the water, a major obgective of the system is to re-use existing wherever possible to save costs.

The Booster is a mixed mode SMPS that runs the MPPT algorithmn to maximise PV production. This means sometimes it must increase the effective resistance of the heater (naturally ~20 Ohms) to reduce the load on the panels and allow there voltage to rise to MPPT. At other times the panel voltage is to low for the heater to fully absorb there output so the panel voltage must be boosted before delivery to the heater. Finnaly a thermostat is included to avoid over-heating the hot water, this is an electronic function as mechanical switches like the one included within the heater do not like breaking high voltage DC.

When not required for heating the Booster output is diverted to a Fronious IG15 grid tie inverter and the boost function of the booster used to reach it's minimium PV input voltage as the presently installed panels are lower than this, MPPT control remains with the DIY Booster and the IG15 simply thinks it has a constant voltage source that reduces to regulate how much power it delivers.

Finally the grid entering the house is measured and direction determined, should export begin the IG15 power is reduced to eliminate it, in other words the grid tie power is maintained at whatever is the consumption of the house, delivering none to the grid.

I hope this overview makes sense and interests other people in DIY PV systems :) I will try to follow it up with more detail if people are interested.