What size 48V Grid-Tied with PV Panels ?

[michael8554]

I have the figures, but can’t work out what size of 48 Volt Grid-Tied battery would be best to build in the UK.

In the summer the PV panels supply peaks at about 13kWh per day.

But summer consumption is only about 3kWh per day.

In the winter the PV supply drops to a minimum of about 4 kWh per day.

But consumption goes up to an average of about 10kWh per day, over the period November to April.

The difference being the use of Storage Heaters in the winter, but not in the summer.

The house and Storage Heaters are on an Economy 10 Off-Peak tariff:

Cheap rate is between 13:00-16:00, 20:00-22:00, and 01:00-06:00.

The other large consumption is a 11kWh Plugin-Hybrid EV which accepts charging at 16 Amps max every couple of days, currently in the 1300-1600 period. I would use the overnight period but the car doesn’t have a Charge Timer, and I only like to charge to 80%. I should probably source a timer that will safely supply a continuous 20 Amps. A future BEV would probably be charged overnight at 30 Amps with it's own Charge Timer.

So do I install say 10kWh of batteries, and charge during the winter with Solar and Off-Peak ?

Or say 4kWh of batteries and “throw away” the extra summer kWh’s of Solar ?

Thanks for looking

Michael

 

[svetz]

Welcome to the forums!

I have the figures, but can’t work out what size of 48 Volt Grid-Tied battery would be best to build in the UK.

Grid-tied and battery are two totally different things.
You just need a grid-tied inverter that takes a 48V battery and outputs single-phase 230V (unless you're in someplace like BVI).

...In the summer the PV panels supply peaks at about 13kWh per day. But summer consumption is only about 3kWh per day.
...In the winter the PV supply drops to a minimum of about 4 kWh per day. But consumption goes up to an average of about 10kWh per day, over the period November to April.

Tell your representative to get net metering done already, it's BS they can't figure out how to bill it (California does it with a very complicated TOU).
But, failing that, tilt your panels to optimize for winter.

Cheap rate is between 13:00-16:00, 20:00-22:00, and 01:00-06:00.

You could also skip solar and get a battery/inverter and program it to charge during the cheap rates. As are 9 hours of "cheap" power at different times of the day you wouldn't need a full 10 kWh battery (depends on how steady the drain is). Another trick is to get a programable thermostat and set it to heat the house above normal just before the rate changes, then coast the temperature down during the rate hike.

So do I install say 10kWh of batteries, and charge during the winter with Solar and Off-Peak? Or say 4kWh of batteries and “throw away” the extra summer kWh’s of Solar ?

This is one of those things where you need to play with the numbers vs. costs to see what makes sense for you.

You can also cheat, if you go microinverters (e.g., Enphase) you can keep adding a bit of solar over time.

What size array would you need for 10 kWh/d ?
Let's assume you live in Bristol and lookup the insolation optimized for winter from a calculator: 1.05
So, the array size should be 10 kWh output / 1.05 / .9 round-trip conversion with LiFePO4 / .9 inverter eff ~= 12 kW array
(use actual location and efficiencies).

Of course, in summer the insolation is 3.6, so you'd be making 35 kWh and since you use 3 kWh/d throwing away 32 kWh/d.
(This is why net-metering is important, you could bank summer solar credits for winter grid costs).

I don't suppose winter the wind speeds averages > 12 mph where you could use a wind-turbine or have a stream where you could run a water turbine?

Failing that, about a 1 kW array would satisfy your summer needs. The battery size needed depends on if you're willing to charge it during the low rates and how effective banking home heat is.

 

[michael8554]

Thanks Svetz

48 Volt Grid-Tied battery - bad description by me, perhaps 48V battery size for a Grid-Tied system is better ?

Net metering sounds good and is available in the UK. Unfortunately it requires a Smart Meter from the supplier, they only make them for Full-Rate schemes and the Economy 7 Off-Peak scheme, not my Economy 10 scheme !!
Which I need for daytime top-ups to the heating. I neglected to say that the house has electric storage radiators, so it already "coasts" between the Off-Peak periods.

I have no space for a larger Solar array.

Much to digest, but first impression is I need a compromise capacity somewhere between 5kWh and 10kWh.

Many thanks

Michael

 

[svetz]

The problem is you consume the most power during winter when you have the worst insolation. Solar PV is roughly 20% efficient, so you need a large expensive system to cover winter needs electrically and end up throwing tons of power away in the summer. But, the thing is you really don't want electricity in the winter...you want heat.

So, instead of Solar PV panels that are 20% efficient, have you looked into solar thermal panels that are 70% efficient? Instead of making electricity, they capture heat. I've never looked into this, but possibly @upnorthandpersonal or @Steve_S have run some numbers?

Possibly a combination system? Some PV and some thermal?

 

[upnorthandpersonal]

These things really depend on your local climate. For example, a nice cold clear day like today (-16C here) is great for solar, but I only have an hour or so of meaningful sunlight. It doesn't matter if it's solar PV or thermal: there just isn't enough energy. That's also why it's cold outside in the first place. You could use a heat pump since moving heat is more efficient that creating it, so with a CoP of 4 I could get 4kWh of heat for 1kWh I get from the sun. I'm not a big fan of solar thermal: expensive, piping requirements, fragile - but it's an option in some cases.

 

[Steve_S]

Pinged and read this, Thank Goodness it isn't 20 pages !

- Solar is maxed out per OP as they have no additional space for more.
- summer the PV panels supply peaks at about 13kWh per day.
- winter the PV supply drops to a minimum of about 4 kWh per day.
- Wants 48V Battery Bank base
- Grid FEED IN but no push out to grid at this time. Feed In Tariff possible but problematic (and comes with more expenses too, inspections etc.)
-?- NEED TO KNOW, Closest Urban Centre to work the numbers, most of us won't "guess" it won't help unless we know within 100km or so OK.
-?- Type of solar install... Roof Mount, Rack, or Ground Mount ???
-?- IF Ground Mounted or Accessibly Mounted are the panel racks adjustable ? Many Ground Mounts can be adjustable for 4 positions to optimize generation over seasons.

1st Conservation should be #1 priority as it is far cheaper than generation & storage. Worst offenders are Heating System, Hot Water Systems and Well Pumps if applicable then the electric appliances, Grannies fridge you inherited is likely a huge power pig, Electric coil stoves = Evil.

EV Charging Timers can be done in different ways or by using a different Smart-Charger it all depends on depth of wallet and/or capabilities.

Solar & Passive heating can be done, the further north you get the trickier it gets till you reach a point of pointless. We "deep northerners" have hyper insulated homes with radiant heating and such BUT in all honesty, both Myself & UpNorthand Personal built our homes and setups for our place on this rock and targetted for Solar etc... Some of our methods can be retrofit to "regular" structures but not all. You won't lift a house to install a Frost Protected Slab Foundation with radiant heating PEX embedded into it. But doing a Rainscreen Insulated Shell or a Passive Cool Roof system is doable and even those two can knock 25-45% off your Heating AND Cooling costs off the top.

Have a peak at this site, there are Solar Heating projects (DIY) and a lot more that do work, I used some of this knowledge when designing my home. I also know for FACT that many do work in our climate and the UK does not get winter like for me or upnorth.

BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution

Build It Solar will help people with Do It Yourself skills build solar projects that save money and reduce pollution. It is a "hands-on" site with detailed plans for solar projects including solar space heating, water heating, passive solar home design, solar pool heating, solar cooking...

www.builditsolar.com

Given what info has been provided, it seems to me that this installation could make use of Peak Shaving / Load Shifting methods.
Install a suitable battery bank with an Inverter/Charger system that can take from Genset and/or Grid INPUT to charge batteries during Off Peak Rate times if the batteries are in need of charge. Almost all can be programmed for when that is to occur. This would NOT require the hassle of Feed In Tariff deals as that only pulls from grid and is seen as another appliance drawing power.

Hope this helps and makes some sense. (still working on Mugga #1)
Steve

 

[michael8554]

Thanks Steve.

A good summation of my situation.

Location is UK, 51 north.

Somebody please take a stab at what size battery ?

Michael

 

[michael8554]

I forgot to mention that the PVs are 11 years old and are still on the highest rate of Feed In Tariff.

After a lot of googling these are my thoughts:

Summer load is about 3kWh per day, I'm calling that my "background" useage - lights, cooking, washing, hot water etc, which will be similar in the winter.

We have a surfeit of hot water for our monthly bath :-> from the immersion heater on Economy 10, so there's about 10kWh per day of PV "wasted" in the summer.

Wintertime load is 10kWh per day average versus 3.7kWh per day average PV output. The house storage heater's 3 hour afternoon Off-Peak period grabs all the available PV output, and a chunk of Off-Peak grid power too. Evenings and overnight the storage heaters are on Off-Peak.

So the case for batteries in my topsy-turvy situation is tricky - not enough winter PV output to charge more than about 3kWh of battery, but that will cover the summertime "background" load.

But 3kWh is 3kWh less "wasted" in the summer, so I'm going ahead.

Does a PYLONTECH US3000C 3.5KWH server rack battery, and add a 5kWh Hybrid Inverter and CT's to the PV inverter sound about right ?

I would have gone DIY with EVE 280mAh 48V cells, but seems more expensive than an off-the-shelf Pylontech.

 

[MisterB1959]

which way did you go in the end, which inverter did you install? i am just about to start a similar journey in the UK