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Making the best of a bad solar PV installation

ticktockhouse

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Jul 14, 2020
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I'm after some practical, expert advice on changing a solar PV system.

I've got a 4 kW system which I probably paid too much for in 2016-ish when FiTs were still a thing and which is annoyingly inefficient, mainly due to the Growatt SP2000 battery which only kicks in after dark, when the panels are no longer producing.

Our usage pattern tends to be 3-4 kWh in the evening. In the summer, the battery, which has grabbed the power during the day, holds onto it through that usage peak in the evening and only starts discharging about 9pm, when the house is only drawing around 300-500 W. We've also got Economy 7, so it's doubly useless at that time.

I haven't had much luck getting in touch with Growatt, so I would like to try and sell this to someone who might get a bit more use out of it, and try and knock the price off a new, more useful one. Something with a bigger capacity and that could be used to "top-up" the solar when needed during the day or be used at night etc. Basically, it should knock a bigger chunk of our electricity bill. Any advice on ebaying, etc.? I don't think I'd miss it much if I got rid of it before this winter - it doesn't help much then...

We're also looking at a Sunamp heat battery to replace our gas boiler and I'm planning to try and use Octopus Agile to charge that when the electricity price goes negative (as well as obviously off the panels and/or Economy 7). This should be happening a bit sooner, with any luck..
 
Not familiar with growatt or whatever an FiT is. But..

Ditch the all in one solution. Get a separate charge controller, battery bank and inverter. I have a similar sized system and you can see the details in my sig. As to "knocking a bigger chunk" off your electricity bill, solar generally has a pretty long return on investment, although it is dropping all the time.
 
Thanks for the quick reply :)

FiT = Feed-in Tariff - a payment made ultimately by the government to net exporters of electricity. I believe this has since been phased out in the case of residential solar, but because of when we got our system installed we're getting around 4p per kWh, I believe.

I'm all in favour of ditching the next-to-useless battery system, but would be interested to know if there's any kind of market for second-hand stuff to knock down the price of a replacement.

A few questions:
- What does the charge controller do? It seems obvious, but I might be missing something :) I might try to put something in at a later date when I plan to be on a flexible tariff that will allow negative pricing, so being able to programatically charge the battery e.g. from the mains would be great...
- Any recommendations for an inverter? According to my emonpi monitoring, we can end up using up to 7kW for short periods when various kitchen appliances are going(!)
- Would I be able to re-use my current battery pack? It's separate from the inverter and the other unit (BMS?). Are there common plugs?
- As I'm planning to have a heat battery installed, how would I manage directing PV to this and the Li-ion battery?
- Is there functionality to charge the battery at a time when electricity price is cheaper and use it during the day? This would be useful in the winter, when we get hardly any kWh of solar, but can still use cheap electricity...

Just trying to use this all a bit more smartly
 
Ah, thanks for the definition of FiT. I guess I tend to think of things from the off grid perspective, as that is where I live. I don't think there is much of a market for a "next to useless" piece of equipment. Besides, do you want to push of a piece of crap on someone else?

The charge controller takes the power from the solar panels and charges the battery with it. But, since you are grid tied and in another country from me, I think someone who knows your local regs should chime in for recommendations as to equipment. Here you need to have a grid tied inverter that is OK by your local power company and then have it installed by a licensed electrician.
 
. Besides, do you want to push of a piece of crap on someone else?

The thought did occur to me, but I guess I figured someone with a bit more knowledge might be able to get some use out of it, I assume the battery pack will be of some use to someone, if nothing else. I'd hate to just have to send it to be disposed of..
 
Do you know what all of your current gear is? What are the panels? Is it wired as all one string or more? What are the battery specs? Is it FLA or LiIon? What voltage (how many cells)? Total Kilo watt hours?

I found this on the web

Is that your inverter? Maybe the battery usage can be programmed to fit with your "Time of Use" billing to use battery power at the highest rate and charge only from your over production near solar noon. Their data sheet looks good, but I can't seems to get the manual to download. They have an A/C coupled version which might work for me, but it does not look like they have a 120/240 split phase version for the US market. Oh well.

If you are convinced the inverter is not capable but the array is good, you can certainly swap out the inverter. If the battery is about 48 volts (which it does look like from the page I found), maybe an Outback Skybox would be a good fit as it is an all in one setup with the MPPT charge controller and a bidirectional inverter/charger for the batteries. It has about the same capabilities as the Growatt hybrid that I linked.

I am in the process of upgrading my solar to include batteries, and the Skybox is on my short list, but since I have micro inverters on the roof, I am leaning towards the Schneider XW-Pro inverter/charger. The Skybox can also do A/C coupling, but then I am buying charge controllers that I won't be using.
 
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