# Pooled Energy’s Solar Optimiser Algorithm

**Background**

Any residential homeowner who is the proud owner of both solar PV and a swimming pool will likely have considered using their solar PV output to power their pool equipment. When electricity retailers are offering an average net-metered solar feed-in tariff of around 12c per kilowatt hour (kWh) exported from your home to the grid, but charging anywhere from 16c to 60c per kWh supplied to the house from the grid, depending on the time of day (average about 30c), it makes sense to purposefully use as much of your own generated electricity instead of exporting it. Simply changing the time-clocks for your pool equipment to run during the hours of peak solar output is a simple solution to get a positive financial outcome, right?

Yes.

… **but only for about 120 days of the year** when the sun is shining over the suburbs of Sydney, Australia. The real story for Sydneysiders requires a much smarter solution:

In a typical Sydney year, historical data projects there will be 109 clear days, 129 overcast rainy days, and 127 days where solar production is highly variable/intermittent. The clear Sydney days are ideal for solar electricity production, whereas the rainy days produce a minimum amount, and the variable days may product useful patches of solar electricity.

Here’s a chart which shows the drop in solar PV production on a couple of rainy days compared with some sunny days in Sydney in November 2017 (source: Australian Photovoltaic Institute http://pv-map.apvi.org.au/performance)

**Largely Sunny Period**

And again for the same solar PV system in June when it was largely rainy or overcast

Now, let’s have a quick look at the numbers for a house utilizing their solar PV to power their swimming pool every day of the year.

Take the above 5kW solar PV system as a baseline:

- On a sunny summer’s day, output may be around 30kWh, with more than 2.4kW available from 9am to 5pm.
- On a rainy/cloudy summer’s day, output may be around 16kWh, with an average of 1.5kW available from 9am to 5pm
- On a sunny winter’s day, output may be around 15kWh, with more than 2.4kW available from 11:30am to 3:30pm.
- On a rainy/cloudy winter’s day, output may be around 2kWh, with no more than 0.5kW available from 11:30am to 3:30pm

And assume an average base-load for the house of 1kW to account for basic household usage such as fridges and lighting but not including heaters/air-conditioners.

And assume a typical 1.4kW pool filtration and salt-water chlorination system conservatively running 8 hours in Summer and 4 hours in Winter, and operating in the above periods where the highest household solar PV output is expected.

And finally assume a time of use tariff with pricing off-peak/shoulder/peak of 16c/26c/59c respectively with off-peak 10pm-7am, shoulder pricing from 7am-2pm and 8pm-10pm and peak 2pm-8pm.

On a Summer’s day, the instantaneous power demand for house base-load plus pool between 9am and 5pm is 1.4kW + 1kW = 2.4kW and total consumption between 9am and 5pm is 2kW x 8h = 19.2kWh.

- If it’s a sunny day, the pool runs for free for the period that the sun is available AND 10.8kWh is exported to the grid so the net feed-in results in the homeowner being compensated $1.30 (10.8 x 12c) for the exported electricity.
- If it’s a cloudy/rainy day, the pool requires the 2.4kW – 1.5kW = 0.9kW instantaneous shortfall from the solar PV be obtained from the grid which results in a cost of 0.9kW x 5h x 26c + 0.9kW x 3h x 59c (5 hours of 0.9kW draw at shoulder price and 3 hours of 0.9kW draw at peak price) = – $2.76 charged to the homeowner for electricity usage with no net feed-in compensation as nothing exported to the grid.

On a Winter’s day, the instantaneous power demand for house base-load plus pool between 9am and 5pm is 1.4kW + 1kW = 2.4kW and total consumption between 11:30am and 3:30pm is 2kW x 4h = 9.6kWh.

- If it’s a sunny day, the pool requires the pool runs for free AND 6.4kWh is exported to the grid so the net feed-in results in the homeowner being compensated $0.76 (6.4 x 12c) for the exported electricity.
- If it’s a cloudy/rainy day, the pool requires the 2.4kW – 0.5kW = 1.9kW instantaneous shortfall from the solar PV be obtained from the grid which results in a cost of 1.9kW x 2.5h x 26c + 1.9kW x 1.5h x 59c (2.5 hours of 1.9kW draw at shoulder price and 1.5 hours of 1.9kW draw at peak price) = – $2.92 charged to the homeowner for electricity usage with no net feed-in compensation as nothing exported to the grid.

For simplicity’s sake in our modelling, let’s assume that the homeowner diligently updates their pool equipment time clock twice a year in Spring and again in Autumn and that Sydney experiences an even spread of inclement weather throughout the year, and the above solar output of for each 6 month period is reasonably represented by the above solar PV output examples. Let’s also conservatively assume that about half of the 127 days historically considered to have highly-variable solar have enough solar output on average to meet the 2.4kW required for pool + household base-load. With this measure, our example householder will

- Receive $1.30 x 55 + $0.76 x 54 = $112.54 for export on the 109 sunny Sydney days
- Pay – $2.76 x 65 – $2.92 x 64 = – $366.28 for usage on the 129 rainy/overcast Sydney days
- Receive $1.30 x 32 + $0.76 x 32 = $65.92 for export on the variable Sydney days that meet the solar capacity requirements
- Pay – $2.76 x 32 – $2.92 x 31 = – $178.84 for usage on the variable Sydney days without enough solar capacity to meet the pool + household demand

Which means that in an average year with our above assumptions, our homeowner with solar PV spends a net total of $366.66 per annum if they use their solar PV generation to maintain their pool and cover 1kW household base-load during pool-equipment runtime.

Now let’s take a look at the cost if our homeowner had instead run their filter pump and chlorinator off-peak every night from 10pm.

- Independent of the amount of solar generation the following day, the cost per kWh during off-peak is 16c kWh.
- Using our assumptions above, the pool equipment will run for 4 hours a day for the 6 months of the year containing Winter, and will run for 8 hours a day for the other half of the year containing Summer.
- Using our assumptions above, the pool equipment uses 1.4kW
- To compare apples to apples, there is still considered to be a household baseload of 1kW for 4 hours of the day in winter (11:30am – 3:30pm) and 8 hours of the day in summer (9am – 5pm)
- On a sunny Summer’s day the export to the grid beyond the household baseload for 8 hours is 22kWh = $2.64 (22kWh x 12c)
- On a rainy Summer’s day the export to the grid beyond the household baseload for 8 hours is 4kWh = $0.48 (4kWh x 12c)
- On a sunny Winter’s day, the export to the grid beyond the household baseload for 4 hours is 9.6kWh = $1.15 (9.6kWh x 12c)
- On a rainy Winter’s day, the import from the grid for the instantaneous shortfall for the solar PV is 2kWh = – $0.76 (2.5 x 26c x 0.5kWh + 1.5 x 59 x 0.5kWh i.e. half a kilowatt hour for 2.5 hours of shoulder and for 1.5 hours of peak)

So using the same assumptions as above our householder will:

- Receive $2.64 x 55 + $1.15 x 54 = $207.30 for export on the 109 sunny Sydney days
- Pay $0.48 x 65 – $0.76 x 64 = – $17.44 for household baseload usage on the 129 rainy/overcast Sydney days
- Receive $2.64 x 32 + $1.15 x 32 = $121.28 for export on the variable Sydney days that meet the solar capacity requirements
- Pay $0.48 x 32 – $0.76 x 31 = – $8.20 for usage on the variable Sydney days without enough solar capacity to meet the household demand
- Pay – 1.4kWh x 4h x 182 x 0.16c – 1.4kWh x 8h x 183 x 0.16c = $491 to run the pool equipment for 8 hours in Summer and 4 hours in Winter each night using off-peak power.

Which means that in an average year with our above assumptions, our homeowner with solar PV spends a net total of $153.20 per annum to cover both the household baseload and pool maintenance if they use their solar PV generation only for household baseload and only maintains the pool overnight in the off-peak period using no solar PV.

And so, in our modelled homeowner, they would actually be $213.46 better off if they only ran their pool equipment during off-peak, than if they use their solar PV to run the pool equipment.

## Things are very different with Pooled Energy’s Adaptive Solar Control…

The Pooled Energy Network Operating Centre checks the forecast each night ahead of the following day’s pool equipment run and makes a conservative judgement on whether to run the pool equipment on off-peak power during that night, or the following day using the solar PV if the weather forecast indicates a clear day with high solar PV output.

Using all the same assumptions as above, the numbers now look like this:

- Receive $1.30 x 55 + $0.76 x 54 = $112.54 for export on the 109 sunny Sydney days when the pool equipment runs during the daytime using the solar PV output
- Pay $0.48 x 65 – $0.76 x 64 = – $17.44 for household baseload usage on the 129 rainy/overcast Sydney days (running the pool equipment during the evening on off-peak power)
- Receive $2.64 x 32 + $1.15 x 32 = $121.28 for export on the variable Sydney days that meet the solar capacity requirements (running the pool equipment during the evening on off-peak power)
- Pay $0.48 x 32 – $0.76 x 31 = – $8.20 for usage on the variable Sydney days without enough solar capacity to meet the household demand (running the pool equipment during the evening on off-peak power)
- Pay – 1.4kWh x 4h x 128 x 0.16c – 1.4kWh x 8h x 128 x 0.16c = $344.06 to run the pool equipment for 8 hours in Summer and 4 hours in Winter each night using off-peak power on the days where we don’t run the equipment using solar PV.

Which means that in an average year with our above assumptions, our homeowner with solar PV spends a net total of $127.68 per annum to cover both the household baseload and pool maintenance. It’s also important to consider that this number is before the Pooled Energy Intelligent Pool Controller uses our variable speed pump control technology and advanced water chemistry to further reduce power consumption of the pool equipment by up to 70%. When this reduction is factored into the equation the homeowner actually pays nothing for the electricity required to maintain the pool and household baseload in our model and in fact **receives a net positive annual compensation of around $200** for their export to the grid inclusive of all pool equipment electricity consumption and 8 hours of 1kW household baseload in Summer and 4 hours of 1kW household baseload in Winter.

Pooled Energy’s Adaptive Solar Control also has significant benefits for homeowners with solar pool heating and without solar PV… but that’s for another blog.