Solar PV + Aga cookers (part 3)

Read part 2 (and part 1!) of my solar series - click here. Read on below!

More questions answered, what a clever lot our readers are! I am getting closer to a firm plan and also feel like I have quite a good understanding now of solar power in general and especially how it will interact with my Blake & Bull electric Aga cooker!

So what questions and issues have been raised and what are the answers or solutions?

"Batteries often cannot send enough power out to all that might be demanded by a home, especially with an electric Aga cooker." This is absolutely true as it turns out, but not an issue! The Powervault P5 battery I have on my quote has a max power output of 4.8kWh. Some of our Aga cookers, whether running on Electrickit or eControl, can demand more power than that in theory. In practice though they would only do so if the whole cooker was cold and the whole cooker (all ovens and hobs) were turned on simultaneously. Every element would be in action then and the demand for power, especially when combined with the rest of the house usage, might exceed 4.8kWh. This would almost never happen but in this case the grid seamlessly tops up the battery supply and this is fine! Getting solar and battery is not about getting off grid, its about lowering costs efficiently. My system should save me about half of my electric bill at a cost of £11k. Saving the other half would probably cost £22k more as you have to build in so much extra generating power and battery storage to cover the dark days of winter. Most of the summer this is then wasted. Not an efficient use of resources!
"Batteries don't respond fast enough to demands for power from appliances that switch on/off all the time."The Powervault P5 battery has a response time of <3s, very few appliances are calling for power at durations of under 3s - I can't think of any in fact! Its another example of how solar+battery works with the grid, not to entirely replace it. Its there, use it!
"What happens to all the excess power generated in the summer?" I won't get much for electricity sold back to the grid, its more efficient to use it at home. If the Aga is hot though and the sun is shining where might it go? The answer is hot water! The Powervault controller can divert 20amps to a third destination for storage if the demands on solar PV are low and the battery is full. In practice this means we'll use a hot water tank, heated by those 20amps, as a kind of electricity store. It should mean zero gas bills in the summer as our hot water will be provided by the excess power from the solar array. If only I could heat a big enough tank to get through the winter!

Now to the sceptic, a very interesting email received from David on the Isle of Man. I have not even replied to you yet David which is very rude but I will do so in a moment when I have published this!

The gist of Davids email?

"Is it not possible that after your seven years [when I have saved in bills what the system cost] has expired that, for one reason or another, the equipment is virtually scrap? In this scenario one would be faced with starting over……another £10,000 + inflation."

I admit this made me think. It IS possible yes, but I think unlikely. The panels, connectors and wiring for a solar array are ridiculously common. They are simple and reliable and predictable, also cheap to replace if the worst was to happen. My parents have a 15 year old solar array that has needed precisely no maintenance and operates flawlessly. The panels in my quote have a 12 year product warranty and a 25 year performance warranty. I'm fairly sure they'll perform adequately even beyond that. They are made by a vast Chinese manufacturing company, I have no reason to assume they will disappear, solar PV is a tough business but an ever expanding one!

I guess the main worry is the battery and 'fancy' AI tech. This is where the proprietary tech is and I don't think there is any avoiding that kind of risk with battery systems - someone somewhere is making and maintaining this clever stuff and fundamentally I'd rather deal with a UK company than overseas in this case!

As an alternative David wondered...

"How difficult would it be for you or one of the B&B engineers to install the panels? If you have, say a garden shed, a collection of lead-acid car batteries may be used for a small fraction of the price."

Again this made me think! An hour of Googling later though and I'd changed my mind. It would take even me, with my clever engineers and electricians at Blake & Bull, a long time to DIY my own system. I don't think it would save a huge amount (£4k maybe on a £11k quote) and would not be eligible for any feed in tariffs as not installed by an approved installer. In case you are wondering lead acid batteries hate solar unless you have a HUGE storage capacity so most of it stays charged all the time. Very inefficient, very heavy and not that cheap! The Powervault batteries are designed to almost completely discharge and recharge every day. Lead acid batteries would decay rapidly if used like this, a measurable percentage per cycle, so are quickly useless!