CFOs and finance directors have invested heavily in solar panels and commercial battery systems in recent years to combat energy price rises. However, in many cases, these assets don't deliver the savings expected. That’s because the software that controls them needs to coordinate how those assets work together in response to changing prices and demand, and it doesn't.
In this article, find out what building energy management systems (BEMS) are, how they generate savings and the questions CFOs need to ask installers and software providers before choosing a system and a provider.
BMS vs BEMS: why the difference matters
The terms BMS, BEMS and BACS are used loosely, and the definitions often overlap. For the purposes of this article, here's how to tell them apart:
- Building automation and control system (BACS): the umbrella term for all building automation and controls, including fire safety, access and security
- Building management system (BMS): the control layer that keeps building services like heating, cooling, lights and alarms running safely
- Building energy management system (BEMS): the energy-focused layer that manages when and how a building uses power to cut costs
The main differences between BMS and BEMS are:
| BMS | BEMS | |
|---|---|---|
| What it controls | Assets like heating, cooling, air con, lighting and access | Connection to solar panels, the grid, batteries, EV chargers, and major site loads such as production equipment |
| What it's trying to do | Keep the building running safely and comfortably | Reduce how much the building spends on energy |
| What it looks at | Temperatures, time-based schedules and fault alerts | Energy prices, solar output, available battery capacity, weather and demand patterns |
| How it makes decisions | Often fixed so it follows the same schedules every day | Bases decisions on forecasts (weather, electricity pricing, and expected demand on your site) |
| When something changes | Reacts after the fact meaning the issue has already cost you money | Can adjust ahead of time, for example, charging a battery before a spike in electricity rates |
| What you get back | Historical reports and fault alerts | Live data on what energy is costing you right now and likely to in the future |
| Multiple assets on one site | Often manages each one separately, with the battery unaware of what the solar is doing | Can coordinate everything together so the battery, solar and EV chargers work as one system |
Reactive BEMS vs proactive BEMS: why fixed schedule BEMS leave money on the table
There are two types of BEMS, reactive and proactive.
Most BEMS are reactive.
They are programmed with fixed schedules during installation, and very few are regularly updated afterwards. So, every day at the programmed times, batteries charge and discharge and the system exports solar power to the grid.
Research by Lawrence Berkeley National Laboratory found that most BEMS are rule-based. They don’t react to changing conditions like weather, electricity prices and site demand. So, on a day when cloud cover cuts solar output by half, the battery still discharges at the same time it always does instead of holding its charge for the afternoon peak when the site will need it most.
What difference does a proactive BEMS make?
By being able to respond to changes in pricing, weather and site demand, they can, for example, charge and discharge your batteries to reduce your electricity bills.
The evidence is consistent:
- Predictive control using weather forecasts saved 10 to 12% on energy compared with conventional control strategies
- Proactive energy management systems, using weather forecasting, sensors and real-time optimisation, achieved up to 30% HVAC energy savings
- Correctly implemented building automation and control systems can reduce energy use by around 30%
For finance leads and company boards, this matters. A 10% saving on a six-figure energy bill is significant, while a 30% saving with a fast payback period can justify a significant capex investment.
What this can look like for different sites
Energy usage varies widely by sector, and so does the potential saving. The examples below use different public benchmarks depending on what is available for each sector, but they all show with a 10% reduction in energy spend:
| Sector | Annual energy benchmark | What 10% better control is worth |
|---|---|---|
| Hotels | Invest NI puts total utility cost at £1,492 per bedroom per year. Knight Frank puts utilities at 5.6% of total hotel revenue. | For an 80-room hotel, Invest NI’s figures imply roughly £119,360 in annual utility spend. 10% of that is £11,900 a year, before any trading or export value from stored energy |
| Care homes | Knight Frank says utilities account for almost 36% of property costs. | Care England states the average annual energy cost of £1,233 per resident, with a range of £658 to £1,757. So, a 70-bed home spends roughly £86,310 a year on energy. 10% is about £8,630. |
| Manufacturing | A UK government survey found energy accounts for roughly 4% of total business costs on average across manufacturers. For energy-intensive manufacturers, that figure rises to around 15%. | For a manufacturer spending £500,000 a year on energy, 10% is £50,000. The exact figure depends on what you make, but the principle is the same: energy is a cost you can control. |
| Warehousing | Benchmark energy intensity of around 53 kWh/m² for electricity and 41 kWh/m² for gas, giving a total energy cost of roughly £13 to £19 per m² per year. | A 10,000m² warehouse spending roughly £130,000 to £190,000 a year on energy could save roughly £13,000 to £19,000. |
Some sectors spend even more on energy. Research shows that 60 to 70% of electricity in cold storage facilities goes on refrigeration alone, and CIBSE benchmarks put electricity intensity at 145 kWh/m², nearly three times the standard warehouse figure.
If your annual energy spend runs into six figures, a 10% reduction in bills changes the question from whether you can afford to do it to the cost of not doing it.
EV charging: a different kind of saving
GRIDSERVE told a UK parliamentary committee that in 2025, about one third of the chargers it built were ready but couldn't be switched on because the grid couldn't supply them with power.
Upgrading the grid to fix this can cost between £60,000 and £2 million per site, according to a DNO estimate cited by Deloitte.
For EV charging firms, a BEMS can reduce or remove the need for a grid upgrade by storing cheaper electricity and releasing it when the chargers need it, so the site draws less power from the grid at peak times.
What the board needs to see before approving BEMS spend
If you’ve invested in renewable energy generation and commercial battery storage and not got the returns you want so far, the problem is fixable.
Systems rarely fail because of a hardware problem but because the control logic that operates them was never updated to reflect how your site actually uses energy. In many cases, you can recover those savings by switching software provider.
Here are five questions to ask a potential supplier:
| Question to ask | Green flag answer | Red flag warning |
|---|---|---|
| What site data have you used to build this case? | The model uses your site's actual tariff, usage patterns, operating hours and asset mix (panels, batteries, EV chargers, etc) | The numbers are based on generic tariffs or standard assumptions rather than your site in particular. |
| What works with what we already have, and what has to change? | They have reviewed your current equipment and you know for certain what you can use and what you need to add or replace | The clearest answer you’ve had is it "should work" but that’s not been confirmed and guaranteed in writing |
| What does the weaker case look like? | You have details on what would happen if site demands rise, tariffs change, solar output differs, and you use the battery less than planned | There is only one attractive base case and you have no view on what happens when conditions change. |
| Who measures performance after go-live, and against what baseline? | There is a named owner, a reporting rhythm and a clear way of checking live results against the original case | Once the system is live, no one at the firm is responsible for the system or proving the promised savings have been delivered |
| What proof do you have that this has worked on a site like ours? | They can show you a real deployment in a similar sector with measurable results, and you may get the chance to speak with the client | The evidence is limited to generic projections or unnamed references |
The picture in the UK and Ireland
Electricity is expensive in both markets, enough for a BEMS to make a material difference, but what you can do with it depends on where you are:
- Great Britain: Distribution charges mean a site that avoids importing at the wrong time saves more than just its unit rate. Since November 2024, a rule change known as P415 has made it easier for commercial battery owners to earn revenue from wholesale and balancing markets without switching suppliers. This means battery storage can generate income as well as cut bills.
- Ireland: Irish businesses face the highest non-household electricity prices in the EU at €0.2726 per kWh, against an EU average of €0.1902. Buildings where combined heating, air-conditioning and ventilation systems exceed 290 kW were required to comply with BACS regulations by 31 December 2024. The regulations mean many buildings need a modern control system anyway. The question is whether the one you install only meets compliance, or whether it also cuts your energy bill.
Where GridVolt fits in
GridVolt is the proactive BEMS software layer that controls your solar, batteries, EV chargers and more, minimising the cost of every energy asset.
It forecasts site load and PV generation 48 hours ahead, updates those forecasts 96 times a day, and replans every 15 minutes using the site’s actual tariff inputs. It delivers results, with one live deployment improving battery savings by 41% in the first 70 days.
The same software powers GridVolt's simulator. That means you can stress test the model in real time to reflect changing tariff inputs, site demand levels and more to see how it affects your return.
Our software connects to compatible third-party batteries, solar and EV chargers without replacing what is already there and without requiring a supplier switch.
Get in touch for a compatibility check and a site-specific review of your tariff, load profile and existing setup. If the savings case still stands up after your review, take it to your board.
Contact us now for more information.
Note: Article image courtesy of Nova.lv