A combined effort

Traditional renewable energy sources are oversubscribed, and many are turning to combined heat and power (chp) as a viable alternative. With the benefit of a high quality and secure energy source system on site, companies can reduce their dependency on the national grid for power.

Even the best quality chp system may not be as clean as renewable energies, but as it is usually a gas-fired product, its carbon footprint is far less than that of many other fossil fuels. In combining electricity and wasted heat, chp systems produce a 3:1 improvement over conventional set-ups with regards to CO2 emissions.

For an even greener solution, it’s possible to combine chp with the use of fuels such as digestor or landfill gases.

A chp system is a sizeable investment, which is why the specification process is so important. Mistakes at this stage can be costly, but there are a few golden rules that can help you along the way.

1 Know your annual heat and power requirement

CHP is ideal for buildings requiring both heat and power for more than 4000 hours a year. For example, a hospital, leisure centre or factory is likely to meet this criteria, whereas a school is not.

2 Know your electrical load profile

It’s more important to understand the base load profile than the mean or peak. Base load is the minimum continuous electrical demand over the entire period for which you are considering chp.

Getting this figure right and then making the correct selection will ensure the system runs efficiently by maximising utilisation and plant conversion efficiency. The best way to identify what’s going on is to plot load continually against time on a graph and to examine this over a year.

3 Know your heat demand in kW and °C

CHP configurations vary widely according to the amount of heat needed and the temperature required.

Some engine manufacturers will offer engines with much higher jacket heat recovery temperatures than others. It is important to know the temperature at which heat energy is required, as some low-grade heat cannot always be recovered.

Remember that a chp system can not only be used to keep facilities warm in the winter, but the waste heat can also be used to run absorption chillers in the summer to ensure buildings remain cool.

4 Know how much you pay for heat generation using gas or oil and electrical power without chp

If you know your current billing figures, you can produce a precise cost comparison showing the potential savings that can be made from each chp system.

There are many different tariff options and, in some cases, chp can add significant revenue in times of high external electrical demand on the supply network. Often, the potential savings that can be made are more wide-ranging than those from the more efficient combined generation of heat and power.

5 If in doubt, undersize

A chp unit that is too large for the application may not save money as it will not be able to run efficiently, or its utilisation will be low, whereas a system that is too small will save money, but slightly less than it would if correctly sized.

It’s a good idea to size the unit so that all heat and electricity can be used and the unit always runs at full capacity. Remember, neither heat nor electricity are easy to store.

6 Understand the lifecycle cost

The cheapest chp solution identified during the procurement process will not necessarily be the cheapest to run over a period of time.

CHP units have complex control systems, and the more expensive packages tend to have higher functionality and better quality components. These generally have reduced down time, greater savings and better long-term value.

Bundling chp with a main contractors’ build contract does not generally result in the best solution for the end user.

7 Track record

There are many existing chp systems that underperform, so look for a supplier with a good track record. Reliable suppliers will always allow you to view examples of their work, explain how and why it saves money and introduce you to long-term satisfied customers.

It is also worth checking that the supplier has experience of building systems in similar applications to your own.

8 Purchase an operations and maintenance contract

Buy an operations and maintenance (O&M) contract at the same time as the installation. This will guarantee the system’s performance, reduce risk and staffing costs, and can remove the need to budget for servicing, maintenance and overhauls.

Such contracts can be rolled up into a fixed monthly charge indexed to RPI for easy budgeting. Leasing schemes are also available, with the customer simply paying for heat and power.

9 Listen to the supplier

Reputable suppliers understand where money needs to be spent and where you can economise. While you may want a cost effective system it also needs to perform well.

Beware of specifications prepared by anyone who does not own, build, operate or maintain chp units. In addition, suppliers with experience of your industry may have suggestions that you didn’t know were possible.

Don’t start with a pre-engineered solution. A good chp system is nearly always custom built.

10 Know which renewable payments you can apply for

The viability of chp can vary greatly according to these payments. There are many incentives that make chp attractive. It is important to know which ones you can apply for at the time of purchase, as the energy metering of the project will need to be installed according to their qualifying guidelines.