Is anyone else interested in micro generation and self-use?

We have 4kWp of SSE-facing solar PV with an immerSUN energy management system configured to enable the charger for my electric car when I have sufficient surplus and/or divert a variable amount of power to the immersion heater. In winter, if there has been insufficient diversion of power to the immersion heater during daylight hours, the gas boiler is set to raise the water temperature to a minimum acceptable value at the end of the day if necessary. A combination of different temperature settings for the immersion heater and gas water heating, and use of the timer on the gas heating controls to delay heating until early evening, ensures maximum use of free electricity while ensuring that there’s always hot water after even the dullest day. In summer the combination provides most of the electricity to run my car and almost all our hot water needs at zero marginal cost with no gas use as the hot water tank is large enough to provide more than a day’s typical hot water use.

Hi @nick_seplin, your set-up is really interesting. Are you charging your car during the day, or do you have battery storage?

I’ve been thinking of getting a similar set-up, but I’ve been assuming that I’ll continue to charge by car off the grid at night, and use solar either principally to heat our hot water tank, or have battery storage to cover our evening electricity use.

I do charge the car during the day directly from solar at weekends, or when I work from home, or commute into London on the train; although on most days the car is at my work car park during the day. The solar charger steps between 0, 6, 10 and about 14 Amps depending on power availability. Water heating is second priority based on cost (my night rate electricity for car charging is more costly per kWh than gas for water heating); although depending on vehicle use the panels can provide both vehicle charging and hot water. The way my system works the car charging responds relatively slowly and with quite large steps to changes in power availability (steps of several Amps at a time and every few minutes) while the heating is very responsive both with much smaller power increments and faster response (continuously variable and many times per minute).

I’ve been looking at storage batteries but so for can’t make an economic case. The systems seem too expensive to recover their costs during their lifetime. Also some cannot release storage energy during the day, so can’t help with daytime peaks beyond the PV output or evening cooking (except in winter when there’s potentially little storage energy anyway). Either the price needs to come down or there needs to be some financial incentive to help out the grid at times of peak demand.

Thanks Nick, this is incredibly helpful. I think I have some research to do!

Nice one @nick_seplin

One really interesting thing that was brought up in a talk we recently had was that battery technology and their prices are improving at a rate similar to that of solar panels. I.e. really fast! The work at Elon Musk is doing with his gigafactory, as well as other people with the global push on battery tech is really encouraging. Hopefully we’ll see battery tech becominga lot more attractive soon.

Here’s a quick blog we wrote up after the talk -


I’ve just signed up with bulb for a new property which is a bit more rural than my Bristol central location. I’m looking at 1.5kWh of plugin solar panels myself. We have room for more but unfortunately there’s quite a few trees around, so am going to experiment to begin with.

Hi @coles and @nick_seplin,

I am attending to this conference
I will make sure to share with you all the latest news about energy storage techs. If you guys can don’t miss it!

Since my original post I’ve joined a battery storage trial, so now have a 4kWh battery as well as solar car charging and water heating. Usage of surplus solar is prioritised as: (i) battery charging, (ii) car charging, and (iii) water heating on the basis on cost i.e. replacing day time electricity, night time electricity, and gas respectively. All we need now is some decent weather!

@gugahenker - thanks! I’d love to hear about it.
@nick_seplin, who’s battery storage solution do you have?

My battery storage is a 4kWh Powervault. Powervaults are AC-coupled systems that can be configured both to store surplus from solar panels (or indeed any other micro generation) and to store cheap night-time electricity to replace costlier day-time consumption. However I’m expecting that as we move out of winter and PV output naturally rises then I’ll be scaling-back overnight charging to allow maximum use of the generation surplus.

How is the power vault battery going? Can it power different appliances like fridges or computers?
How much did it cost?


A PowerVault has a 1.2 kW output so that’s easily enough to run low power items like computers, lighting, the fridge/freezer, microwave etc. It’s also enough to cover things like the dishwasher or machine through most of their cycles. What it can’t do is sustain heating, so things like the kettle, hob, or oven draw too much power; and the likes of the dishwasher and washing machine use too much power while heating but are OK the rest of the time. I paid £2K, but that was a special offer price.