We got our solar online this past March (2026) and we've had $0.00 dollar electric bills ever since. Up until 2 weeks ago, we enjoyed our net metering and banking hundreds of credit KWHs to use in the future. Well, we just got a letter from our electric company saying that we were going into net billing in 2 weeks. That means we won't get 1:1 credits anymore. Now we'll get a monetary credit worth a fraction of what a KWH is worth. In other words, they screwed us good. :(

Now we're thinking of getting a battery, maybe a Tesla Powerwall 3 so that we can store extra solar energy for when the sun goes down, we can run the house on the battery until the sun comes back up. I have a lot of decisions to make, like what size battery should we get, should I leave EV charger separate from the battery and leave it hooked to breaker panel? We have Tesla solar inverters, so a Tesla Powerwall 3 should hook up nicely.

We have 2 EVs and we are able to charge them during sunlight hours as my wife works from home and I leave for work around 2 pm. I'm thinking about Powerwall 3 holds 13.5 KWHs and should run the home and AC during non solar hours because except for the EVs, we don't use a ton of electricity during a 24 hour period. I just hate the thought of selling tons of KWHs of electricity to the grid everyday for pennies on the dollar, only to buy it back from them at full price when the sun goes down. They are literally thieves in the friggin night, ha ha!

What do you guys think about adding a single Tesla Powerwall 3 to run the house at night and just charge EVs during the day?

Thanks in advance for any feedback on this.

My original SunPower inverter went out recently. Looking to perform a DIY replacement as local solar companies want $2k+ to swap out for a new one .
The current inverter is ABB PVI-3.0-OUTD-S-US-A.
What would be a good option to replace it with?
Also have a separate SunPower system that has micro inverters and a PV55x box.
I will be getting a 10kW Tesla system added on soon with two Powerwall 3’s. The current systems will not feed directly into then Powerwalls as it’s going to be a lease, and rather they will be connected at the panel level. Thanks

Weighing options for a future system: an "off-grid" system (battery+solar) that uses grid support to charge when necessary or a zero-export system that monitors power and ensures none (or minimal) is sent to grid

For complicated reasons, Im unable to get an interconnect agreement. Im in rural California (balcony solar will be legal in January so a small amount of power incidentally sent to grid should not be an issue)

The goal is to generate the majority of my own power via solar and store in a large battery bank

Appreciate your insights

I was looking for a website where I can estimate what can go on my roof in terms of panels. I found several which use satelite photos but they don't get the roof size very accurate (under-sized). Is there one where I can enter the details like this:

The house is rectangular, 8.2m (in line with the apex) and 6.7m (at right angles to the apex). My roof is a symmetric pitched roof, one side facing 125° from North (i.e. approx SE), and the other facing 305° (i.e. approx NW). The roof has an additional overhang of 0.25m past all walls, making it 0.5m larger in both directions. The roof pitch is about 33°. Interlocking concrete roof tiles (if that matters), 1990 construction using premade A-frame roof trusses.

System details:

Inverter: Solis-S6-EH1P5K-L-PLUS

Battery: Dyness powerbox G2 10kw

Off grid setup, charging from a generator in the gen port.

No pv

I've installed the system myself (qualified electrician & electrical engineer) and it has been working perfect for the last month. I'm using it for a building site so the generator doesn't have to run consistent for small loads (work lights, charging power tools etc)

Had the generator running and I was using a 2.5kw tool for a few minutes. Power turned off so thought it might be a trip switch.

Checked the board, everything is OK. Checked the inverter and it's giving out about a BMS fault between the inverter & battery.

If checked the connections, powered it off (including the battery shut off) for 15 mins but no difference.

The battery is readying 52.8v so it should be about 80% charged.

Can't get support on a Sunday... Any suggestions on where to start? Or how to figure out if it's the inverter or battery that's at fault

This is r/SolarDIY’s step-by-step planning guide. It takes you from first numbers to a buildable plan: measure loads, find sun hours, choose system type, size the array and batteries, pick an inverter, design strings, and handle wiring, safety, permits, and commissioning. It covers grid-tied, hybrid, and off-grid systems.

TL;DR

Plan in this order: Loads → Sun Hours → System Type → Array Size → Battery (if any) → Inverter → Strings → BOS and Permits → Commissioning. 

1) First Things First: Know Your Loads and Your goal

This part feels like homework, but I promise it's the most crucial step. You can't design a system if you don't know what you're powering. Grab a year's worth of power bills. We need to find your average daily kWh usage: just divide the annual total by 365.

Pull 12 months of bills.

• Avg kWh/day = (Annual kWh) / 365
• Note peak days and big hitters like HVAC, well pump, EV, shop tools.

Pick a goal:

• Grid-tied: lowest cost per kWh, no outage backup
• Hybrid: grid plus battery backup for critical loads
• Off-grid: full independence, design for worst-case winter

Tip: Trim waste first with LEDs and efficient appliances. Every kWh you do not use is a panel you do not buy.

Do not forget idle draws. Inverters and DC-DC devices consume standby watts. Include them in your daily Wh.

Example Appliance Load List:

Heads-up: The numbers below are a real-world example from a single home and should be used as a reference for the process only. Do not copy these values for your own plan. Your appliances may have different energy needs. Always do your own due diligence.

• Heat Pump (240V): ~15 kWh/day
• EV Charger (240V): ~20 kWh/day (for a typical daily commute)
• Home Workshop (240V): ~20 kWh/day (representing heavy use)
• Swimming Pool (240V): ~18 kWh/day (with pump and heater)
• Electric Stove (240V): ~7 kWh/day
• Heat Pump Water Heater (240V): ~3 kWh/day, plus ~2 kWh per additional person
• Washer & Heat Pump Dryer (240V): ~3 kWh/day
• Well Pump (240V): ~2 kWh/day
• Emergency Medical Equipment (120V): ~2 kWh/day
• Refrigerator (120V): ~2 kWh/day
• Upright Freezer (120V): ~2 kWh/day
• Dishwasher (120V): ~1 kWh/day (using eco mode)
• Miscellaneous Loads (120V): ~1 kWh/day (for lights, TV, computers, etc.)
• Microwave (120V): ~0.5 kWh/day
• Air Fryer (120V): ~0.5 kWh/day

2) Sun Hours and Site Reality Check

Before you even think about panel models or battery brands, you need to become a student of the sun and your own property. 

The key number you're looking for is:

Peak Sun Hours (PSH). This isn't just the number of hours the sun is in the sky. Think of it as the total solar energy delivered to your roof, concentrated into hours of 'perfect' sun. Five PSH could mean five hours of brilliant, direct sun, or a longer, hazy day with the same total energy.

Your best friend for this task is a free online tool called NREL PVWatts. Just plug in your address, and it will give you an estimate of the solar resources available to you, month by month.

Now, take a walk around your property and be brutally honest. That beautiful oak tree your grandfather planted? In the world of solar, it's a potential villain.

Shade is the enemy of production. Even partial shading on a simple string of panels can drastically reduce its output. If you have unavoidable shade, you'll want to seriously consider microinverters or optimizers, which let each panel work independently. Also, look at your roof. A south-facing roof is the gold standard in the northern hemisphere , but east or west-facing roofs are perfectly fine (you might just need an extra panel or two to hit your goals).

Quick Checklist:

• Check shade. If it is unavoidable, consider microinverters or optimizers.
• Roof orientation: south is best. East or west works with a few more watts.
• Flat or ground mount: pick a sensible tilt and keep airflow under modules.

Small roofs, vans, cabins: Measure your rectangles and pre-fit panel footprints. Mixing formats can squeeze out extra watts.

For resource and PSH data, see NREL NSRDB.

3) Choose Your System Type

• Grid-tied: simple, no batteries. Utility permission and net-metering or net-billing rules matter. For example, California shifted to avoided-cost crediting under CPUC Net Billing
• Hybrid: battery plus hybrid inverter for backup and time-of-use shifting. Put critical loads on a backup subpanel
• Off-grid: batteries plus often a generator for long gray spells. More margin, more math, more satisfaction

Days of autonomy, practical view: Cover overnight and plan to recharge during the day. Local weather and load shape beat fixed three-day rules.

4) Array Sizing

Ready for a little math? Don't worry, it's simple. To get a rough idea of your array size, use this formula:

Array size formula

• Peak Sun Hours (PSH): This is the magic number you get from PVWatts for your location. It's not just how many hours the sun is up; it's the equivalent hours of perfect, peak sun.
• Efficiency Loss (η): No system is 100% efficient. Expect to lose some power to wiring, heat, and converting from DC to AC. A good starting guess is ~0.80 for a simple grid-tied system and ~0.70 if you have batteries
• Convert watts to panel count. Example: 5,200 W ÷ 400 W ≈ 13 modules

Validate with PVWatts and check monthly outputs before you spend.

Production sniff test, real world: about 10 kW in sunny SoCal often nets about 50 kWh per day, roughly five effective sun-hours after losses. PVWatts will confirm what is reasonable for your ZIP.

5) Battery Sizing (if Hybrid or Off-Grid)

If you're building a hybrid or off-grid system, your battery bank is your energy savings account.

Pick Days of Autonomy (DOA), Depth of Discharge (DoD), and assume round-trip efficiency around 92 to 95 percent for LiFePO₄.

Battery Size Formula

Let's break that down:

• Daily kWh Usage: You already figured this out in step one. It's how much energy you need to pull from your 'account' each day.
• Days of Autonomy (DOA): This is the big one. Ask yourself: 'How many dark, cloudy, or stormy days in a row do I want my system to survive without any help from the sun or a generator?' For a critical backup system, one day might be enough. For a true off-grid cabin in a snowy climate, you might plan for three or more.
• Depth of Discharge (DoD): You never want to drain your batteries completely. Modern Lithium Iron Phosphate (LiFePO₄) batteries are comfortable being discharged to 80% or even 90% regularly, which is one reason they're so popular. Older lead-acid batteries prefer shallower cycles, often around 50%.
• Efficiency: There are small losses when charging and discharging a battery. For LiFePO₄, a round-trip efficiency of 92-95% is a safe bet.

Answering these questions will tell you exactly how many kilowatt-hours of storage you need to buy.

Quick Take:

• LiFePO₄: deeper cycles, long life, higher upfront
• Lead-acid: cheaper upfront, shallower cycles, more maintenance

6) Inverter Selection

The inverter is the brain of your entire operation. Its main job is to take the DC power produced by your solar panels and stored in your batteries and convert it into the standard AC power that your appliances use. Picking the right one is about matching its capabilities to your needs.

First, you need to size it for your loads. Look at two numbers:

1. Continuous Power: This is the workhorse rating. It should be at least 25% higher than the total wattage of all the appliances you expect to run at the same time.
2. Surge Power: This is the inverter's momentary muscle. Big appliances with motors( like a well pump, refrigerator, or air conditioner) need a huge kick of energy to get started. Your inverter's surge rating must be high enough to handle this, often two to three times the motor's running watts.

Next, match the inverter to your system type. For a simple grid-tied system with no shade, a string inverter is the most cost-effective. 

If you have a complex roof or shading issues, microinverters or optimizers are a better choice because they manage each panel individually. For any system with batteries, you'll need a

hybrid or off-grid inverter-charger. These are smarter, more powerful units that can manage power from the grid, the sun, and the batteries all at once. When building a modern battery-based system, it's wise to choose components designed for a 48-volt battery bank, as this is the emerging standard.

Quick Take:

• Continuous: at least 1.25 times expected simultaneous load
• Surge: two to three times for motors such as well pumps and compressors
• Grid-tie: string inverter for lower dollars per watt, microinverters or optimizers for shade tolerance and module-level data plus easier rapid shutdown
• Hybrid or off-grid: battery-capable inverter or inverter-charger. Match battery voltage. Modern builds favor 48 V
• Compare MPPT count, PV input limits, transfer time, generator support, and battery communications such as CAN or RS485

Heads-up: some inverters are re-badged under multiple brands. A living wiki map, brand to OEM, helps compare firmware, support, and warranty.

7) String Design

This is where you move from big-picture planning to the nitty-gritty details, and it's critical to get it right. Think of your inverter as having a very specific diet. You have to feed it the right voltage, or it will get sick (or just plain refuse to work).

Grab your panel's datasheet and your local temperature extremes. You're looking for two golden rules:

The Cold Weather Rule: On the coldest possible morning, the combined open-circuit voltage (Voc) of all panels in a series string must be less than your inverter's maximum DC input voltage. Voltage spikes in the cold, and exceeding the limit can permanently fry your inverter. This is a smoke-releasing, warranty-voiding mistake.

The Hot Weather Rule: On the hottest summer day, the combined maximum power point voltage (Vmp) of your string must be greater than your inverter's minimum MPPT voltage. Voltage sags in the heat. If it drops too low, your inverter will just go to sleep and stop producing power, right when you need it most.

String design checklist:

• Map strings so each MPPT sees similar orientation and IV curves
• Mixed modules: do not mix different panels in the same series string. If necessary, isolate by MPPT
• Partial shade: micros or optimizers often beat plain strings

Microinverter BOM reminder: budget Q-cables, combiner or Envoy, AC disconnect, correctly sized breakers and labels. These are easy to overlook until the last minute.

8) Wiring, Protection and BOS

Welcome to 'Balance of System,' or BOS. This is the industry term for all the essential gear that isn't a panel or an inverter: the wires, fuses, breakers, disconnects, and connectors that safely tie everything together. Getting the BOS right is the difference between a reliable system and a fire hazard

Think of your wires like pipes. If you use a wire that's too small for a long run of panels, you'll lose pressure along the way. That's called voltage drop, and you should aim to keep it below 2-3% to avoid wasting precious power.

The most important part of BOS is overcurrent protection (OCPD). These are your fuses and circuit breakers. Their job is simple: if something goes wrong and the current spikes, they sacrifice themselves by blowing or tripping, which cuts the circuit and protects your expensive inverter and batteries from damage. You need them in several key places, as shown in the system map

Finally, follow the code for safety requirements like grounding and Rapid Shutdown. Most modern rooftop systems are required to have a rapid shutdown function, which de-energizes the panels on the roof with the flip of a switch for firefighter safety. Always label everything clearly. Your future self (and any electrician who works on your system) will thank you.

• Voltage drop: aim at or below 2 to 3 percent on long PV runs, 1 to 2 percent on battery runs
• Overcurrent protection: fuses or breakers at array to combiner, combiner to controller or inverter, and battery to inverter
• Disconnects: DC and AC where required. Label everything
• SPDs: surge protection on array, DC bus, and AC side where appropriate
• Grounding and Rapid Shutdown: follow NEC and your AHJ. Rooftop systems need rapid shutdown

Don’t Forget: main-panel backfeed rules and hold-down kits, conduit size and fill, string fusing, labels, spare glands and strain reliefs, torque specs.

Mini-map, common order:

PV strings → Combiner or Fuses → DC Disconnect → MPPT or Hybrid Inverter → Battery OCPD → Battery → Inverter AC → AC Disconnect → Service or Critical-Loads Panel

9) Permits, Interconnection and Incentives in the U.S.

• Most jurisdictions require permits, even off-grid. Submit plan set, one-line, spec sheets. Pass final inspection before flipping the switch
• Interconnection for grid-tie or hybrid: apply early. Utilities can take time on bi-directional meters
• Net-metering and net-billing rules vary and can change payback in a big way
• See our Tax Credit and Incentives Guide for the 30 percent federal ITC and state programs. For California policy context, seeCPUC Net Energy Metering and Net BillingCPUC Net Energy Metering and Net Billing

Tip: many save by buying a kit, handling permits and interconnection, and hiring labor-only for install.

10) Commissioning Checklist

• Polarity verified and open-circuit string voltages as expected
• Breakers and fuses sized correctly and labels applied
• Inverter app set up: grid profile, CT direction, time
• Battery BMS happy and cold-weather charge limits set
• First sunny day: see if production matches your PVWatts ballpark

Special Variants and Real-World Lessons

A) Cost anatomy for about 9 to 10 kW with microinverters and DIY

Panels roughly 32 percent of cost, microinverters roughly 31 percent. Racking, BOS, permits, equipment rental and small parts make up the rest.

B) Carports and Bifacial

• Design the steel to the module grid so rails or purlins land on factory holes. Hide wiring and optimizers inside purlins for a clean underside
• Cantilever means bigger footers and more permitting time. Some utilities require a visible-blade disconnect by the meter. Multi-inverter builds can need a four-pole unit. Ask early
• Chasing bifacial gains: rear-side output depends on ground albedo, module height, and spacing.

Handy Links

• Production calculator: NREL PVWatts
• Solar resource and PSH: NREL NSRDB
• Policy, California example: CPUC Net Energy Metering and Net Billing
• U.S. incentives: DSIRE
• Tax Credit and Incentives Guide: Link to wiki

You now have a clear path from first numbers to a buildable plan. Start with loads and sun hours, choose your system type, then size the array, batteries, and inverter. Finish with strings, wiring, and the paperwork that makes inspectors comfortable.

I'm looking at installing an EcoFlow STREAM 5000 in the UK and I'm trying to understand the electrical side properly before doing anything.

My cabin is supplied from the house via 3-core 6mm² SWA protected by a B32. The cabin has its own consumer unit, but with no spare ways.

This is the proposed circuit from the cabin cu.

B20 RCBO → 2.5mm² T&E radial → outside socket → double socket → proposed 13A switched FCU → EcoFlow STREAM 5000

The 2.5mm² cable run is only a few metres. Around 600mm currently passes under/alongside 20mm Kingspan, although I can reroute that section out of the insulation if necessary.

The existing loads are:

Weber Smoker on the outside socket occasionally

Samsung heat-pump tumble dryer

800W microwave occasionally

Nothing else

The STREAM would be hardwired through the FCU and I'd limit maximum AC discharge to 2.5kW (~10.9A).

It will also be using the EcoFlow Smart Meter/CT system to dynamically control charge/discharge according to household demand.

What I'm specifically trying to establish is:

1. Would you connect a STREAM 5000 to the end of this existing B20 radial through a 13A FCU, or would you insist on a dedicated circuit?

2. If not, what specific requirement prevents it?

3. Does the potential combined supply of B20 + ~10.9A generation mean the 2.5mm² conductors have to be rated for ~30.9A, even though the STREAM dynamically follows household demand?

4. Would upgrading the radial to 4mm²/6mm² and keeping it clear of insulation change anything?

5. Is a BS 1363 13A FCU appropriate for sustained bidirectional operation at up to 10.9A?

6. Most importantly: has anyone here actually installed a STREAM 5000 (or equivalent 2.5kW AC battery) onto an existing socket radial/ring through an FCU rather than running a dedicated circuit? If so, what protection/cable arrangement did you use?

I'm particularly interested in answers from electricians/installers familiar with this, because I've seen conflicting advice about the revised generation/battery requirements.

I'm not asking whether plugging it into a normal 13A socket is okay. I'm specifically asking about a fixed, fused connection to an existing final circuit.

Thanks in advanced — interested to see how people are actually designing these in the UK.