Solar/battery calculations

[Tim Howard]

Please be gentle - I don't normally venture into this area!

A good and long standing customer has a conference centre with a swimming pool.
The swimming pool has two 1700w filtration pumps that run 24/365.
(the same pump system also handles chemical dosing and water heating via a heat exchanger from bio-mass)

The question has been posed to me whether a nearby roof use could accommodate some solar panels with the specific goal of reducing the operating costs of these pumps.

I will share my attempt at mathematical reasoning and thinking, please feel free to fall about laughing, and maybe once vertical again give some advice....

2 x 1700w pumps = 3400w
In a 24 hour period, consumption is 81.6 kwh

I believe in the UK you can reckon on between 2 and 4 hours direct sunlight on PV panels. Advice seems to be work with a figure of 2.5 hours average for estimation purposes over a year?

I think we could fit (size wise) a 20kw system on a suitable nearby roof and this might be expected to generate 20 x 2.5 = 50kwh.
However during the direct sunlight hours, consumption from the pumps would be between 8.5kwh and 13.6kw depending on time of year.

Sticking the surplus in battery storage seems sensible, but this is where my ability to do calculations fail.

What I'm struggling to work out is how far the 'spare' 36kwh in the sunlight hours would go towards charging batteries, and therefore for how many hours a day the batteries could be the source of power for the pumps before it reverts to grid. I'm also wondering if battery systems are designed to be cycled to this degree.

The ultimate aim is working out if a battery system is feasible at all and eventually what the payback time would be.
Thanks a lot for any hints!

 

[mainline]

Please be gentle - I don't normally venture into this area!

A good and long standing customer has a conference centre with a swimming pool.
The swimming pool has two 1700w filtration pumps that run 24/365.
(the same pump system also handles chemical dosing and water heating via a heat exchanger from bio-mass)

The question has been posed to me whether a nearby roof use could accommodate some solar panels with the specific goal of reducing the operating costs of these pumps.

I will share my attempt at mathematical reasoning and thinking, please feel free to fall about laughing, and maybe once vertical again give some advice....

2 x 1700w pumps = 3400w
In a 24 hour period, consumption is 81.6 kwh

I believe in the UK you can reckon on between 2 and 4 hours direct sunlight on PV panels. Advice seems to be work with a figure of 2.5 hours average for estimation purposes over a year?

I think we could fit (size wise) a 20kw system on a suitable nearby roof and this might be expected to generate 20 x 2.5 = 50kwh.
However during the direct sunlight hours, consumption from the pumps would be between 8.5kwh and 13.6kw depending on time of year.

Sticking the surplus in battery storage seems sensible, but this is where my ability to do calculations fail.

What I'm struggling to work out is how far the 'spare' 36kwh in the sunlight hours would go towards charging batteries, and therefore for how many hours a day the batteries could be the source of power for the pumps before it reverts to grid. I'm also wondering if battery systems are designed to be cycled to this degree.

The ultimate aim is working out if a battery system is feasible at all and eventually what the payback time would be.
Thanks a lot for any hints!

The way they went with the holiday complex pool heating was to use solar tube instead of electric.

 

[Tim Howard]

The way they went with the holiday complex pool heating was to use solar tube instead of electric.

The heating of the water is sorted already, they have a huge biomass pellet system on site.
It's more the running costs of the filter pumps they are trying to reduce (long term)

 

[mainline]

The heating of the water is sorted already, they have a huge biomass pellet system on site.
It's more the running costs of the filter pumps they are trying to reduce (long term)

Is the pool open 24/7 then ? As this one, the pump is shut off overnight.

 

[binky]

Shutting down pumps for even just a few hours overnight will make a big difference.

With solar, it will spend more time working at say 60% of capacity than at full tilt. Less in winter, so I would install the pv array first, with hybrid inverters, monitor the system, then try to work out if batteries are worth the money. I suspect they will be, but try to avoid the mindset that the PV / batteries will do everything - that tends to get v expensive.

It may also be worth looking PV Gis, a free solar calculator.

 

[Tim Howard]

Thank you for the responses. My first question at the time was "Are you obliged to run the pumps 24/7" and was told "We are not obliged to, and there are certainly probably more times we could run only one, but they are filtering the water, heating and dosing the chemicals all at the same time, so it’s preferable one is always running. When the pool is used a lot it takes both filters to keep up."

I think they need to rethink the "always on" idea.
I'm not an expert on the dosing of chemicals and what is required.
I would imagine that stopping circulating hot water for between say 10pm and 4 am isn't going to make a material difference to the pool temperature at 9am.
I'd also imagine that by 10pm the pool with be as filtered as it's going to be if the water contents are unchanged since 5pm.

I like the idea of doing PV array first. Plenty to think about.
Thanks again