Using a Smartmeter display unit I have monitored my use of energy from the 6 pv panels lodged on my roof while heating water in a fast-heating kettle and discovered that there is not enough instant energy to make a significant contribution to heating the water. Because of the high power demand most of the energy was provided from the National Grid supply while heating up the water.
The Smart meter tells me the cost of energy usage at any time and it remained the same for boiling kettle water during sunlight and darkness hours. When energy is derived in real time from the pv panels, it by-passes the meter to supply energy directly to try and match the demands. High energy consumption exceeds the available rate of supply from the pv panels.
From the above observation I would infer that the pv panels are not suited for providing high rates of energy usage as required for heating unless, of course, a large bank of them is installed.
If you have in mind thermal solar panels then there is a modest contribution to the heat required, for example, to provide hot-shower water. In fact, during the winter months the infeed water to the boiler (domestic) tank comes from water warmed by sunlight and simply makes a very modest contribution for storing heated water from your boiler.
Typically in Winter in the UK (Epsom) on a clear day the solar cylinder has its water warmed to between 20 and 30 C. As an infeed to the domestic tank cylinder it beats feeding in mains water at 5 to 8 C.
The problem with thermal panels is the imbalance between heat generated on a clear, hot summer’s day as opposed to the demands in Winter. The collector temperature can rise to 160 – 180 C in Summer and, unless you use the hot solar-heated water, you risk boiling the glycol-water mixture, notwithstanding the pressurised heating circuit.
Installing a large bank of thermal solar panels creates excess heat problems during the Summer months. On hot, clear days I manually unfurl banner-shading over some or all of the thermal solar panels and limit the collector temperature to ca 100 C: this provides a cylinder water-tank temperature of ca 80 C.
As for relying on batteries charged up with solar energy, the resistive heating demands on the stored energy for heating would rapidly drain the batteries. I have 6 pv panels that on a very hot day in Summer generate 7 kwh of energy. In winter on a heavily overcast day, the daily solar gain is ca 100 watt-hr, enough to keep a light bulb on for an hour!