Real life solar performance (and lessons) 25 months after installation 1

Introduction

What is presented here is my experience with solar over the past 2+ years.  I hope this write up will be of value to readers and assist with their journey, its become a hobby.  Feel free to comment.

The section on Payback represents a situation faced by most homeowners and reflects an approach which I thought appropriate.  Our unit cost is relatively low, and the same applies to savings.  Data on the number of hours without power, cost of generating power using a generator is not readily available. There is recognition of increased cost of power during an outage, but the approach is debateable.  I’ve steered away from opportunity costs.

 

Objective

1.       To provide power during load shedding and frequent extended outages experienced due to unreliable and worsening municipal electrical infrastructure (also not keen on using a generator, bit of a closet greenie).

2.       Provide power to keep lights, fridge freezer, router, office, (desk top PC, screen, printers) as well as DSTV decoders and TV’s going.

3.       Eliminate (or reduce) frustration experienced every time power goes off.

4.       Recoup investment in solar in as short a time frame as possible and reduce reliance on ESKOM.

 

The system

·         Goodwe 5048D-ES 4.6 (current DOD while on grid 5%, off grid 90%)

·         17 x 365w Canadian solar panels = 6205w (8 facing North, 9 facing North West) at 11 degrees from horizontal

·         2 x 3.5kw Pylontech batteries current SOH 99% (changed from 100 to 99% shortly after 18Dec 2021 after 23.5 months of use).

·         Installed Jan 2020.

Photos of installation in separate post

General information on electrical set up

·         Household 4 adults, residential and home office.

·          750w heat pump, water is heated to 42 degrees, no cold water used when we shower.  1 degree increase in water temp takes 6 min. Starting water temperature in summer about 26 degrees, winter about 20 degrees.  Heat pump needs to be started a couple of hours before planned shower.

·         750w pool pump used for 2.5 hours per day from Oct to March.

·         Replaced electric hob with gas.

·         Replaced 50-amp municipal CB with 40-amp CB.

·         Due to extent of power failures all plugs, lights pumps are run through the inverter, only oven directly connected to municipal supply. 

·         The inverter capacity is 20 amps + 10 amps for 10 seconds before it trips.

·         Tripping of the inverter can be avoided by using 2 or less appliances at the same time, especially when the dishwasher or washing machine (max power use while heating water of 2400w) is on.  Training ongoing, it is easy to forget…

·         Normal background use of lights, fridge freezer, PC etc about 500 to 600w, this can be reduced to 350w in extreme cases if outside lights are turned off as well as PC and screen.

·         Power is sold and bought at the same rate (municipality under administration).

·         Only 40% of PV is used with current set up (self-use), rest provided to grid.

·         Electricity meter read at month end and provided to municipality.  They use the information!

Cost in December 2019 + fixes to DB later

 

Monthly power produced and consumed based on data from inverter and meter readings

Yellow = 5 months with lowest PV produced and highest meter reading.  Green = 5 months with best PV produced and lowest meter reading.

I suspect actual consumption is higher and saving would be higher than shown.  The Goodwe does not keep track of power supplied from the battery (both on and off grid).

Summary data (gradual improvement)

 

Payback

The variables used to calculate the original payback period changed.  The solar system produced less power than anticipated (635w vs 900w) and cost more.  Both would increase the payback period.

At the moment payback will be about 10 years based on the following assumptions.

·         Continue to sell to back power at same rate as purchased

·         Eskom increases for 2022 = 9.61% and from 2023 will be at least 6% per annum

·         No major breakages

·         At least 10 hours of monthly outages that equals 20 kWh at, at least 4 times the going rate per kW.  For March 2022, 10 hours x 2 kw per hour @ R1.51 x 4 per kW = R121/month.  I believe this assumption is conservative.  My calculations show kW cost from a generator is far greater than R10 per kW

·         No interest added to original investment of R150k.

Should increases be 8% per annum, power outages double and cost per kW increase from 4 to 8 times the going rate (see example above), payback will shorten to 7.5 years (so 5.5 years more to go).

SARS allows a proportional depreciation over 3 years for a home office, effectively reducing the original investment by about R25k.  This will reduce the payback period by at least another year from 7.5 years to 6.5 years.

Perhaps financially not the best investment decision (but better than Steinhoff) and to date happy with the outcome.

 

Lessons learnt, observations

·         Educate yourself about solar, speak to many people that have installed solar, join, read, and ask question on powerforum!

·         Understand what your objective is and what you want to achieve.

·         Get at least 3 quotes, make sure you deal with a reputable company and that the inverter has been “accepted” in the larger metropolitan areas of the country and that the batteries are compatible and supported by the inverter.

·         Give preference to systems that allow incremental additions e.g., adding extra battery capacity or extra inverter. I can’t do the latter.

·         The company should provide information on expected production, make sure they disclose the variables on which it is based and expected production throughout the year. If they don’t, move on.  Only one of the 3 companies that quoted provided this information.  Some also appear to be stuck on a single range of products.

·         Make sure to get a COC for the solar installation and the DB. Useful for insurance in case there is a problem (lightning, wind damage, surges)

·         I obtained theoretical production values from the website below for my location, and while the monthly values varied a lot, I’m at 96% of the predicted production of 16 513w for the 25 month period https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

·         Somehow everyone, forgot that parts of the country experience cloudy/rainy conditions and that the 30kwH per day or 900 kwh per month is probably only relevant in the desert.  Actual production of the “900 kw system” turned out to be 635kWh per month.  Don’t like me accept information at face value.  The screenprint below is an example of the type of information out there, ready to confuse the novice.…

·         Be aware that system losses can be between 14 to 25%.  Reasons include converting from DC to AC, temperature, inverter efficiency, etc.  For my system and location predicted losses were expected to be 25.6%. 

·         Bear in mind that your panel mounting areas largely dictate production.  In my location optimal angle = 35 degrees, however the roof angle is only 11 degrees.  Production in Gauteng will be better as solar radiation is higher.

·         Shop around, one supplier is seldom cheapest on all the major items (panels, inverter, mounting structures, batteries).

·         Include in the quote to fix, or have your DB checked beforehand to prevent surprises. I did not and probably paid R8+k extra.

·         Understand what items you want on the backup (battery) circuit.  In my case initially lights, fridge, freezer, TV, decoder, router.  Had it changed later to include all plugs, heat pump and pool pump as with frequent outages while the sun was shining, we were unable to consume the power being produced. Obviously cost extra.

·         Ensure there is good airflow between the roof and the panels, heat reduces production of power.

·         Plan to be able to clean the panels by leaving a walkway between sets, dust, grime, birds can reduce PV production by 5%.  At 11 degrees angle my panels don’t self-clean!  I use a soft broom with a plastic extension to reach 2 meters and a hose pipe.  There are small yellowish sticky deposits that even resist a high-pressure cleaner.

·         I can only communicate with the inverter via wifi. I installed an UPS to power the ONT box and router in case there is a need to change settings on the inverter.

·         Understand the limitations of your inverter, I am unable to use a generator with the Goodwe and hence unable to charge batteries in periods of ongoing power failure and consecutive cloudy/rainy days.

·         Specify that a bright LED be added where it is easily visible, (probably in the kitchen to indicate a power outage). This to prevent use/waste of battery power when there is no sun. Backup systems are so efficient you are often not aware that loadshedding or a power outage is occuring.

·         If in future unable to feed back into grid I will have to increase battery capacity and the payback period will increase.

·         Don’t wait, invest now.

22 March 2022