Solar for Village Halls – Payback Scenario

Village halls are an interesting case with the following characteristics:

  • high level of community engagement
  • usually a low power usage during daytimes when peak generation occurs
  • often have a car park used for various purposes

The low power usage means these are not a typically advantageous case for solar. However, EV charging may be quite a critical element in the viability of an installation.

Not many villages are curently well provided with EV charge points and the confidence of publicly available charge points can help increase uptake of EVs. People without their own solar systems or economical source of electricity are likely to pay from 30p-60p per kwh for charging, which means or £30-60 to fully charge a high-range EV.

Lets look at a costs and benefits illustration for solar on a community building like a village hall:

  • 20kw installation requiring 120 m2 of suitably oriented roofspace (or car park canopy).
  • Expected capital cost around £20,000 and generating around 20,000kwh pa
  • Energy usage pattern (assumed) results in only 20% onsite usage when no storage or EC charging provided.
  • Payback time assuming power import (ie utility bill) price of 25p per kwh, export (sale back to grid) price of 5p per kwh and maintenance costs of 2% pa. 14 years (11 years for 8p per kwh export price)

(Note: throughout this article we are using simple cash payback measures to compare scenarios, not discounted cash flow or interest-adjusted cashflows that make an investment case.)

Suppose now we consider the economics of adding EV charging with a 22kw / 3 x 7kw charge points, at this stage with no battery storage. Capital costs of this addition are likely to come in at around £4000 including the relevant construction for a public facility. We have to make various assumptions about uptake and usage, but also remember that we can use variable pricing to encourage the village residents to get the best of the low cost power during peak solar generation times.

  • EV charger use modelled as 3-hour 7kW topup charges for simplicity: all three 7kw points used on average 1.5 x per day at weekends and 1 x per day on weekdays. Total power requirement is 26,400 kwh.
  • Based on seasonal and diurnal generation patterns we make the resaoned assumption of 30% of this being solar generated, which has a marginal opportunity cost of 5p per kwh (as the alternative is low-priced sale to the grid). Around 8000kwh of solar power would be used for charging and the remaining 18,400kwh is purchased from the local supplier at our import price of 25p per kwh.
  • Lets say that we set pricing of solar power at 20p per kwh and bought-in power at cost price of 25p (i.e. revenue-neutral for the puchased power.) The effect of selling some solar power is then a revenue increase of 8000 x 15p or £1200 pa. Assuming we can only now get 15% of our solar used in the village hall, this brings our payback time for the larger investment down to: £24,000 / (£750 hall savings + £450 grid sale + £1600 total EV sales) = 8.5 years. (Adding 10p to those selling prices, if viable, would add a further £2,640 of revenue and bring the payback time down to around 5 years.)

An 8.5 year payback for a community benefit investment is not a bad figure, and that is without adding in non-financial aspects such as facilitating EV uptake, the amenity value for guest parking and other things.

Adding battery storage is something else to be considered. While it does little for the winter scarcity of solar resource, if there is strong demand from the hall or EV chargers in the evening then might it be possible to achieve economic viability ?

Let’s make an estimation of how adding storage might change the scenario, based on a capital cost of £500 per kwh for the battery installation. As ever, we need to make a number of sensible assumptions, as there are a million possible usage patterns, so lets focus on the availability of evening power allowing more hall demand to be met due to evening light and cooking requirements, and some longer overnight EV charges during high-generation season.

  • 40kwh battery installation would cost £20,000 – a pretty large amount, but probably a good size to model as it makes a reasonable impact by allowing a single 40kwh EV overnight charge or power say 5 hours of hall usage at 5kw of light and cooking applicances with a residual 15kwh of overnight EV charging.
  • Note that this extra usage of solar only occurs under certain conditions: where there is excess solar generation not already consumed. This will be mainly during the season where solar generation peaks in the 3-4 brightest months. So if on 100 days where we have solar output at 20kw for more than 8 hours we manage to move a further 40kwh per day (2 hours full capacity generation) from grid sale to higher margin use (displacing purchases or EV charging) then at the best assumptions we gain £800 pa from this (4000 x 20p). That is a 25 year payback on the battery !
  • Of course there are many more possible scenarios. If we are displacing 2022/3 power at prices of 30 and 40p per kwh then the equation gets more favourable. If evening EV charging is the most important thing to people in the village and home charging installation is difficult, the value placed on a kwh of charge might be higher than 25p anyway.
  • Clearly though, at current prices, the batteries are the least atrractive investment of the options considered.

All figures in this calculation are rough estimates and ESD wll be grateful for any feedback if you think the figures can be refined, but hopefully this is a helpful guide to fast-forward thinking about a possible installation.

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