Solar panels and batteries - How clever are systems that top up batteries at overnight rates?

Yes @Bosscat0110 it depends on your current plan so there’s no ‘forcing’ a different rate for charging batteries. 
It would be helpful if there was though!

@Bosscat0110 without the benefit of an EV for cheaper off-peak rates your best fixed rate option may well be Economy 7, especially if you can pick a supplier with a very low night rate at the expense of a high day rate.

The agile tariff you talk about is a bit unreliable price wise lately. Generally even the overnight prices are high, often above 30p/kWh, although there have been one or two plunges recently. You'd have to work out how much you'd be importing and at what time/rates to see if a time of use or good old Economy 7 would work out better.

There may be other options coming soon so keep an eye on any announcements.

Hi all

After some more advice, I am looking at a 5.0kw Lux hybrid inverter with 20x405w Longi solar panels and 3 x 3.2 Greenlink batteries. I have been told that i will require a G99 certificate for the 5.0kw inverter but the company will install the system on a G98 certificate and cap the inverter at 3.6kws until the G99 certificate is approved (likely to by 8-12 weeks) Does that make sense to people. I have my L plates on when it comes to solar but looking to reduce my massive electricity costs.

One more question please, how long will it take to fully charge my batteries from the grid overnight, looking at either economy 7 or Octopus Agile to take advance of the cheaper rate during the winter to use during the day when the panels are are not as productive.

@Bosscat0110 the approvals are all about local grid and DNO notification. The difference between G98 and G99 is mostly about system size
This might help

https://www.deegesolar.co.uk/dno_for_solar_panels/

Hi BPLightfog

Thanks for your response. My concern is to do with capping the inverter until the G99 has been approved. I am not sure if this is possible/legal or just a sales pitch to commission the sale. What would be the impact of generating 8.1kw PV array during solar production hours with an inverter capped at 3.6kw? 

I am no expert on the approval process @Bosscat0110 but from my electrical knowledge, if power is being generated, it has to go somewhere. The DNO approval seems to be connected with their systems ability to cope with the potential feed back into the grid.

The only way that I can see a system being capped is not to connect all the string - which seems strange to me, unless the inverter is capable of being controlled to this level of output.

National Grid have their own advice for connections here https://connections.nationalgrid.co.uk/g99-connection-procedures

Some DNOs appear to be taking a more relaxed approach with export limitation. They used to require a G99 even if you were limiting to 3.68kW. Now I've heard to at least one DNO who is happy for an export limited inverter to be fitted under a G98. It's probably worth checking with your DNO.

Battery charging rates depend on your inverter and batteries. They will each have a maximum rate but you'll get the lower of the two.

Your inverter can charge at 3.6kW but the batteries charge at 2kW. I think the system might be able to charge all the batteries at once so your limit would be the 3.6kW of the inverter. That means it would take 2 hours 40 mins to charge them (in practice it's probably closer to 3 hours).

Hello everyone,

I have had solar panels and several additional updated storage heaters fitted with a Government grant. I have an Economy 7 system and previously the hot water was heated at night, as was my one old storage heater, however the charges are going up every month, much more than under the old system. Is it because the solar panels are only contributing to day time electricity use ( although with it being Winter they probably don’t do much anyway?) 

would it make sense to alter the timer for the hot water to be heated during the day? Your thoughts would be appreciated

Hi @Rubberducky , you should still be getting a cheaper off peak rate overnight for your storage heaters and hot water. The only bit to think about is if you also have to add heat to either the storage heating or hot water during the day. 
Solar PV will help but without batteries it can only give what it is producing towards whatever you’re using at that time. So at the moment, it will be on lower generation during winter but will help more during the rest of the year. 
There are devices which can use excess solar to heat your water but again this will only work when it is producing more than the home requires.