Solar System Design (should I do it?)

[Y0rkie]

This is my first thread so I’d like to firstly thank everyone for all of the free knowledge you’ve put out there. I’v gained a lot through reading a collection of threads on this forum.

My background
I am a software developer and am very technically minded so I always want to know all the technical details of a system.

I am now considering my options for a solar install for my house in Hampshire UK. I started out getting quotes from various solar installers to get an idea of what the installers would recommend. What I got from this process was a wide variety of opinions and drastically different quotes with the top end at £46,000! This drove me down the rabbit hole of trying to understand the different components, brands and ultimately design a system for myself to get independently sourced prices for the hardware as I can’t justify anything near £46k given the long buy back period.

System Design (core solar components)
34x TrinaS+ 425W panels (14.45kW)
1x Victron Quattro 48/15000 (12kW inverter)
1x Victron SmartSolar MPPT RS 450/200 are
1x Victron SmartSolar MPPT 250/70 (with VE.Can)
Note: I decided on Victron because I am a software developer and they have very open APIs so I can integrate this with home automation easily.

Panel Layout (North Up)


Panel Strings
I would wire up the panels to the MPPT controllers like this:
- 18 (north facing) panels split into 3x 6S strings using 3 MPPT controllers in the RS.
- 10 (south facing) panels configured as 5S2P into the last MPPT controller in the RS.
- 3 (east) & 3 (west) panels configured as 3S2P into the MPPT 250/70 controller.

Battery Storage
For batteries I would probably go with either:
6x Fogstar ESR51.2V rack batteries (30kWh) or
7x Pylontech US5000 (31.5kWh) or
2x Seplos DIY (28.6kWh)

Rough Annual Consumption
6,600kW - General house electricity
2,400kW - Tesla charging

Estimated Solar Generation
Having averaged the quoted generation estimates and personally used a few online historical solar generation calculators to estimate generation taking into account the panel orientation for my house location I have arrived at 10,000kWh per year.

Solar Consumption
This is clearly a completely shot in the dark however looking at the estimated daily generation & sun hours for each month of the year I expect of the 10,000kWh generated I would only be able to consume & store 6,000kWh as the high production summer days I just won’t have the storage or loads to consume all of the solar energy so I expect 4,000kWh will be exported to the grid.

Electricity Tariff
I am currently with Octopus Energy on their Intelligent tariff; the standard daily rate is 30p a unit and also 6 hours of energy at 7.5p (11:30 - 5:30am) which is when the Tesla currently charges.

Considerations
I see that I have two options; either battery only or solar & battery storage. The average daily power consumption of my house is 15-18kW excluding the Tesla charging. So on my current energy tariff a 25kWh battery would give me the 80% DoD headroom to shift all of my daily usage to the 7.5p unit rate (night time charging) which we could increase to 8.25p to account for the conversion losses. This would drastically reduce my electricity cost for the lowest upfront costs.

The solar and battery option is considerably more expensive but would offset future electricity price increases & I could then investigate additional electrical loads to reduce the grid export (thermal batteries, immersion heater, AC, etc)

Questions
1) What’s your opinion on the above system?
2) Would you go battery only or with solar?
3) Is 30kWh too much/little battery?
4) Is installing the system in the loft a bad idea?
5) How would you consume the excess 4,000 excess units in summer?
6) What else haven’t I considered?

Thanks for your time.

 

[Dinobot248]

I'll try to provide some input. You provided a lot of information so please be patient. I just installed my system (6.5k inverter, 9kw solar, 30kw battery, and another 6.5k inverter not installed yet).

1. Don't let your "OCD" (obsessive compulsive disorder or simply nitpicking) drive or dictate your activities.

1a. Ignore the predicted 4kw spare solar for now. It is a solution looking for a problem. During colder / winter months, that 4kw likely will disappear.


2. Batteries are heavy. One 5kwh server rack battery weighs about 100 lbs or 45 kg. For DIY, that is manageable to carry and install. The giant energy wall batteries weigh 3 times as much. Personally if I cannot carry or easily move it, I won't buy it.

the ideal installation location is near your main electric panel and in a cool area. Easier to see wire and connect the system. That area should already be isolated. You will need to make compromises. Loft in the US implies living space and some where upstairs. That's not ideal but you can put anything where you want.


3. Use the grid or electric company as your second battery bank for at least 1 year. A 30kwh battery bank is good to start with based on your initial estimate and design. After 1 year going through the seasons, you will really find out the ups and downs of relying on a solar and battery combination. Charge up your 30kwh battery bank as needed during the lower months of solar collection.

yes the 30kwh battery is good.

4. Can you provide more detail on your daily usage of 15-18kw. Sometimes it's easier to reduce usage than try to design for the usage.

With that said, get something like emporia vue to view your detail consumption.

5. This should have been number 1. You always pay. Meaning you pay with money to have someone do the work / installation or you pay with your own personal time / effort.

if this exercise is not tied to a hobby or recreational activity that you enjoy, just pay for someone to install it. You will be much better off.

Now, if you enjoy this, then proceed. All the effort and frustration will make it worth it since you will enjoy the journey.


6. By default I would go with battery and solar. You can easily go with battery, see how it works, then add solar later. Roof mount solar should be installed in a relatively newer roof to minimize uninstalling the solar to fix the roof.

7. Are there government subsidies. In the US, there is a one time 30% tax credit that drives my decision to buy and build most of what I can within one calendar year. If there was no subsidy or incentive, I would have built it smaller than add on later.

 

[Y0rkie]

Thanks for your reply.

Straight off the bat, you hit the nail on the head regarding my "OCD". However, I think its also worth noting that as much as Solar isn't a hobby of mine, I generally take on technical side projects to try out new technologies so knowing myself, I don't fall into the category of just wanting a closed system that I turn on and forget about. I like to analyse the data and geek out to the point where I suspect I will be spending a great amount of time monitoring and automating the house to make the most of the system which will inevitably result in extending the system in the future once I have actual data to work off.

The 4kWh spare generation is predicted in the summer when the solar panels have a few good hours a day and my storage & loads are too small but as you say, wait and see what the actual numbers are.

Given my background of IT; the server rack batteries formfactor is great and as you mention each 5kWh module is a manageable weight for one person, where typically the DIY batteries are considerably heavier given their 14/15kWh capacity which you aren't safely lifting as a single person.

Loft / Attic
Loft in the UK is the non living space inside the roof accessed via a ceiling hatch & ladder; perhaps attic is the correct term? The reason for locating the batteries in the loft is because my garage (where my main consumer board is) is not insulated so the temperature can drop to -5C, where the loft will not drop below 5C given the constant heat from below. I have seen that some batteries (Fogstar/DIY) have built in heaters and suggest they work well in sub zero temperatures however I haven't seen any reviews of this feature.

A colleague of mine who installed solar panels a couple years ago on his roof has been tracking the temperature of his loft and has found that the solar panels have insulated his roof from the sun which has resulted in his loft never exceeding 26C even with outside air temps are 30C+. This made me think that it might be quite a good place to store the batteries instead of taking up space in an already cramped garage.

Battery Size
I think you're right, 30kWh is a good starting capacity; other people I know who installed systems have all ended up adding additional batteries. Unfortunately, they all took the installers recommendation to keep costs down and installed 5 or 10kWh.

Grid as second battery is exactly my thoughts; I was going to automate the charging by looking at the weather forecast to estimate the solar generation the following day and charge the battery appropriately to take advantage of the cheaper night time energy while still having battery capacity to fully utilise the solar energy.

Daily Usage
My wife and I work from home 80%+, so the average 600-700W hourly draw is mostly the IT equipment in our respective offices and the background draw of the house (hot tap, fridge, freezer, lights, etc and then cooking with the electric oven, microwave, etc. I have briefly looked at Emporia Vue; seems like a great idea but doesn't look like a popular product in the UK (sold on Amazon but no reviews). So need to look into it some more. If you have any other brands/systems that are popular please recommend as I can take a look to see if any of those are a better alternative in the UK.

Tax Incentives
There is a UK green TAX incentive where Solar panels (usually 5% VAT) are 0% when installed. Batteries are usually 20% VAT when purchased or installed however if the batteries are installed as part of the solar system, they too are 0% VAT. So there are some savings to doing both at the same time.

I am now certain that going with Solar and Batteries is the correct option. I am pretty happy with the specific hardware choice:

Still uncertain about:
1) whether or not the Fogstar rack batteries are reliable or potentially better than the popular branded batteries (PylonTech)?
2) whether or not going down the DIY route for batteries (Grade A cells) is any more risky or less reliable than off the shelf
3) is installing the system something that's easily achieved DIY (apart from the final grid hook up where an electrician is required) or is DIY not recommended and its paying someone to install the system is recommended

I guess the reason I am wondering about 1) and 2) is because I have seen a number of threads where people are selling PylonTech batteries and opting to go DIY / Fogstar instead.

 

[MaikaiLifeDIY]

Regarding your questions:

1) I've spent a little time with multiple types of batteries, raw cells, car battery form factor, and rack mount batteries. IMO, rack mount batteries are the best choice, they cost nearly the same as building your own batteries and because of their standard form factor are easy to expand and stack for future adjustments.

I'm not sure if this brand is available in the UK, but here in the US this brand is outselling nearly every other battery and I can attest they are very well made batteries if you can get ahold of them.

EG4 LifePower4 Lithium Battery | 48V 100AH | Server Rack Battery | UL1973, UL9540A

EG4 (48V/100AH) LifePower4 Battery EG4 Lithium battery 51.2V (48V) 5.12kWh with 100AH internal BMS. Made of UL Listed Battery Cells. Off Grid Solar Batteries - Off Grid System - Solar Batteries for Home - Lithium Solar Batteries - Deep Cycle Solar Batteries - Power Reserve - Solar Panels Plus...

signaturesolar.com

Here is a teardown by a pretty sharp YouTube person, (who coincidently runs this site)

2) As mentioned in #1, why mess with all the complexities and safety concerns for nearly the same price without any warranty or support for he completed battery.

3) I feel extremely confident in installing and creating systems, I did my first system with Victron, then Enphase and now I'm all Sol-Ark. My only concern with Victron is you have to learn the catalog of devices they sell, they have devices that do nearly the same thing but are slightly different so there is a lot of shopping research you need to do to understand what you need. However, they are top-notch quality and very expansive, I even have Victron components in my Sol-Ark system for specific measurements, so you don't have to use all Victron, you can use them interchangeably with other equipment if desired.

You'll want to model our your system using a diagram or some sort so you can start to visualize all the components you'll need.

Here is an example of my system layout design. I made this with Google Draw, there are many other tools you could also use.

 

[Dinobot248]

For the same or very similar price, go with server rack batteries. First priority is to get the system to work. Once you get into work and it is stable, then feel free to go diy on certain upgrades.

I chose not to go diy batteries since the price is virtually the same and I loose the warranty. I don't know how much you will save going diy batteries. Some say 50%. If you look at the whole system, my diy current system cost around 27k. 30kwh batteries cost 9k or 33%. If I save 4k for diy batteries that puts the system cost at 23k. In my opinion, not much to save in the entire system. Another way to put it, I won't let 4k dictate my 20k+ project.

Buy cells from a reputable store and pay as much or more for the diy battery build. Buy direct from China and take the risk.


Now for the installation, if you chose to pay someone, then more than likely you are forced to buy their equipment. I would expect a project would cost at least $20k+ (I don't really know for the UK). Installers will likely not want to deal with a $5k project since it's too much hassle and not enough money. I would say ask around or get quotes.

Connecting a system together is fairly easy if you have some basic knowledge. I like to think electricity is invisible so double and triple check that things are off. 50v DC can hurt and may kill you. 400v DC from your PV array is worse. Be very careful and don't touch the metal parts unless you are absolutely sure and check with a volt / mulitmeter

DIY is a big hassle since little things can trip you up like needing a wire crimper for your MC4 connectors, drilling into your roof, missing the caulk gun, etc

I think that you will find setting up the system to be very easy to do. My guess is the roof installation may be quite a challenge. Solar panels are heavy eg 400w panel weighs 50lbs+ or 22kg. Try carrying that on your roof. I chose ground mount arrays since I have the yard space and while I am capable, prefer to not fall off the roof to install a roof array. BUT now that my system is operational, I can afford to tweak and add a roof mount and not jeopardize my system (e.g. it will continue to collect solar until I am ready to connect the roof solar panels).

 

[Dinobot248]

Almost forgot, I wish I had an inverter that I can program "gid assist". Don't know the actual name but want the grid to supplement the battery at a programmable threshold like battery powers tthe house from 0 to 3000w and the grid helps out beyond that.

Right now my EG4 6500EX inverter cant do that.