Hi....new to this game....have had a quote for 6.48kw panels and 10.4 kw battery system.I have an unvented hot water system powered by gas boiler and/or immersion. We are at home all day and the plan is to use as much of the power as we can and hopefully charge the battery towards the end of the day.My question is can we heat the hot water tank via panels and battery (when there is sufficient capacity)without any other fittings or gizmos. TIA.
PV and Battery system
- Thread starter Ixeo
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via battery, yes, but better off with a gizmo so that it heats water first before charging battery, it's more efficient. Solic 200 is my fave, and the cheapest.
BorisJ
Well-known member
Exporting to the grid earns around 5p per kWh. Diverting to immersion heater saves around 5p per kWh if you normally heat water with a gas boiler.
Yes use an iboost or whatever. With that size of system you will be able to heat the hot water pretty much for free for 8 months of the year. This is likely, if it is a 240litre cylinder, to use between 6 and 12kwh of energy a day - depending on how much you are using or doing the washing up etc. Bearing in mind that the system you have there is capable of generating 35 kwh of power in a good summer's day, it seems to me that it will also charge your battery and cover the house's needs handsomely. Bravo. You can then ask it to charge on a night time tariff in the darker months perhaps. If you get an EV, there is an argument for charging that from a night time tarrif in order not to upset the excellent balance you have with the diverter and battery. Having said that, 35kwh in one day would charge an EV largely for free using a Zappi on full Eco mode.
johnb2713
Well-known member
Interested why heating the water first is more efficient?
Yes, there's energy lost in converting to DC for battery charging and same again when discharging, immersion gadgets must have some small losses but you aren't converting AC to DC and back again, so I would say the losses are smaller.
johnb2713
Well-known member
But it's already in DC form from the panels so no conversion necessary. If you heat the water first there's thermal losses going on longer and therefore greater losses over time?
I know it's splitting hairs and probably would be about the same.
J
But you are running BMS and there's losses in the battery cells, don't ask me how much. As you say it's probably fairly negligible difference, but running the immersion indirectly from the battery adds an extra step in the energy management, ergo incurrs an extra stage of losses. Or at least I suspect it does.
This all depends on whether it is a dc side or ac side battery. Ac side involves more conversion dc side would only go through the inverter once. However dc side batteries are more expensive and only some inverters can do this. So it all depends on which inverter you're getting.
not seen a retrofit DC battery for quite a while, they used to fit to one PV string and charge up during the day, then release energy from when the inverter shut down/ got to a low level of output.
