Totally agree. Indeed, some of those old threads are fascinating. Such asadam2 wrote:There is nothing wrong in adding to long dormant threads, indeed this can be preferable to starting a new discussion on the same subject.

**this one**from just about 11 years ago.

These are still relevant, useful data and will continue to be.Pauls Mobbs wrote:Your central heating pump is rated at around 500 to 1000 watts (in practice it might draw only 200W to 600W of continuous power, depending on the size of the system). A square metre of PV might, and an average bright day, produce 40 to 80 watts per square meter (amorphous cells produce about half the power of monocrystalline/polycrystalline silicon, but for the sake of the maths let's call it 50). In terms of instantaneous power you're going to need 10 to 20 square metres, plus about 20% for the inverter efficiency losses = 12 to 24 sq.m of PV to run the central heating pump directly!

The alternative is to charge a large battery bank for a long period of time and then use the power directly for the short periods it's needed. Let's aim at 480 watts of continuous power as our target figure. Producing 240W from 12 volts will require (240/12) 20 amps. Add the inverter losses on top (say 20%) we multiply by 1.2 = 29 Amps. Running your pump for 1 hour (which more than is enough to defrost the house to stop the pipes freezing -- which is my major concern) will therefore take 29Amp-hours. However, the charge/discharge cycled on the batteries will be between 20% and 40% efficient (depending on their age) and so you'd actually have to scale the PV array by this factor to get that amount of power outr of the storage again.