I suspect it may come down to a cost/benefit analysis of options.  Storing enough power to last one evening and night may be viable.  Enough to last through a week of grey winter days may be totally unaffordable.

Thanks for the reply Simon. The client we are working with like to see visual representations of power and costs. We have as much said that it is not a viable option currently given the battery technology but we have to prove it to them


We are looking at a maximum generation of around 5MW on the roof and they want to know how many batteries and what kind of footprint it would take up


The facility would pull around 2.2MW at peak

Chris

I agree with Simon you need to build an economic analysis model (spreadsheet) incorporating all relevant information including capital costs, operating and maintenance costs, load factor, electricity demand, generation and battery supply profile (cost/value)and any decommissioning and disposal liabilities. 

The project cashflow (based on electricity price and generation profile), Net Present Value (at various discount rates),  breakeven time can be established (with and without a battery system), and various economic indicators and sensitivity to key factors on the project can be established. Normally run as a +/- % of key variables to establish a sensitivity spider diagram. 

There are several more pieces of information required:


1) What is the likely output profile of the solar panels where you are located? If you are in the UK for a 5MW peak system you may only average 1MW. If you are further south the average will be somewhat better.


2) What is the load profile? What is the expected average load? if it is more than the average output above where will you get the additional from?


3) The difference between peak output and minimum load will give a maximum charging rate for the batteries. The time this will last will give the required capacity.


4) Will the maximum discharge rate be higher than the maximum charge rate. If so this will also affect the costs.


Given the required capacity and maximum charge/discharge rates you can then contact battery system suppliers for cost estimates.

The other factor is how a long run of rainy days will be handled - is there a need for back up power, or is it the load of a form where it is OK for the load to be shed ?

A 5 MW system cannot run a 2.2.MW load 24/7 even with the best possible storage,  as more than half the time it is not unobscured midday sun, on which the output figures are predicated. Advice varies, but to see  10-20% of full sun output on an overcast day is typical, less with darker clouds of course.


There is a lot of difference between a system that is the sole means of generation, where over capacity by a factor of five or even ten and storage for several days is needed,  and one that is just used to shave a bit off the bill in summer, but is not essential. which may not need storage at all.

It is important to clarify this distinction  to a non technical customer.

regards Mike

I only have customer with domestic scale battery storage, they are quite happy with it seeing them through from sunset to around ten o’clock at night, rather than being completely off grid and the batteries maintaining a supply until sunrise.


Most of the year they export in the afternoons after the batteries are charged, but cannot justify installing extra batteries to go off grid, despite having spare generation capacity.


If they want grid backup they have to pay the standing charge for the connection, the balance payment for import minus export isn’t significant.

There cannot be a national electricity distribution network that people can connect to just in case their off grid setup lets them down without paying a high standing charge to cover the periods they are not using it.


The economy of scale is only available if everyone uses the grid.

EV chargers with buffer batteries may be the next step towards evening out the load noon the grid and offering fast charging without grid upgrades.


Rather than one set of centralised batteries there could soon be an option to have multiple batteries located with EV chargers in the car park area.
https://www.greencarreports.com/news/1130618_freewire-and-bp-unit-ally-for-more-uk-fast-chargers-without-grid-upgrades